ORGANIC ELECTROLUMINESCENT DEVICES

[0001] This application is a Continuation-In-Part of U.S. patent application Ser. No. 19/275,169 filed Jul. 21, 2025, which claims priority to U.S. provisional application No. 63/677,573 filed Jul. 31, 2024, and to U.S. provisional application No. 63/780,690 filed Mar. 31, 2025, each of which is incorporated herein by reference in its entirety. Furthermore, this application claims priority to U.S. Provisional Patent Application No. 63/804,573 filed May 12, 2025, which is also incorporated herein by reference in its entirety.

[0002] This invention was made with government support under DE-EE0009688 awarded by the U.S. Department of Energy. The government has certain right in the invention.

[0003] The present invention relates to emissive devices including organic emissive devices including nanoparticles in one or more transport layers.

[0004] Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting diodes/devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

[0005] OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

[0006] One application for phosphorescent molecules capable of phosphorescent emission is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Alternatively, the OLED can be designed to emit white light. In conventional liquid crystal displays emission from a white backlight is filtered using absorption filters to produce red, green and blue emission. The same technique can also be used with OLEDs. The white OLED can be either a single EML device or a stack structure. Color may be measured using CIE coordinates, which are well known to the art.

[0007] As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which comprises a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

[0008] As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

[0009] As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

[0010] A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

[0011] As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

[0012] As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

[0013] Layers, materials, regions, and devices may be described herein in reference to the color of light they emit. In general, as used herein, an emissive region that is described as producing a specific color of light may include one or more emissive layers disposed over each other in a stack.

[0014] As used herein, a “red” layer, material, region, or device refers to one that emits light in the range of about 570-700 nm or having a highest peak in its emission spectrum in that region. Similarly, a “green” layer, material, region, or device refers to one that emits or has an emission spectrum with a peak wavelength in the range of about 500-600 nm; a “blue” layer, material, or device refers to one that emits or has an emission spectrum with a peak wavelength in the range of about 400-500 nm; a “yellow” layer, material, region, or device refers to one that has an emission spectrum with a peak wavelength in the range of about 540-600 nm; a “cyan” layer, material, or device refers to one that emits or has an emission spectrum with a peak wavelength in the range of about 490-520 nm; and an “orange” layer, material, or device refers to one that emits or has an emission spectrum with a peak wavelength in the range of about 570-620 nm. In some arrangements, separate regions, layers, materials, regions, or devices may provide separate “deep blue” and a “light blue” light. As used herein, in arrangements that provide separate “light blue” and “deep blue”, the “deep blue” component refers to one having a peak emission wavelength that is at least about 4 nm less than the peak emission wavelength of the “light blue” component. Typically, a “light blue” component has a peak emission wavelength in the range of about 465-500 nm, and a “deep blue” or “dark blue” component has a peak emission wavelength in the range of about 400-470 nm, though these ranges may vary for some configurations. A “light green” component has a peak emission wavelength in the range of about 520-560 nm, and a “deep green” or “dark green” component has a peak emission wavelength in the range of about 500-520 nm, though these ranges may vary for some configurations. A near infrared (“NIR”) component has a peak emission wavelength in the range of about 700-1800 nm. Similarly, a color altering layer refers to a layer that converts or modifies another color of light to light having a wavelength as specified for that color. For example, a “red” color filter refers to a filter that results in light having a wavelength in the range of about 580-700 nm. In general, there are two classes of color altering layers: color filters that modify a spectrum by removing unwanted wavelengths of light, and color changing layers that convert photons of higher energy to lower energy. A component “of a color” refers to a component that, when activated or used, produces or otherwise emits light having a particular color as previously described. For example, a “first emissive region of a first color” and a “second emissive region of a second color different than the first color” describes two emissive regions that, when activated within a device, emit two different colors as previously described.

[0015] As used herein, emissive materials, layers, and regions may be distinguished from one another and from other structures based upon the spectrum of light initially generated by the material, layer or region, as opposed to light eventually emitted by the same or a different structure. The initial light generation typically is the result of an energy level change resulting in emission of a photon. For example, an organic emissive material may initially generate blue light, which may be converted by a color filter, quantum dot or other structure to red, green, or yellow light, such that a complete emissive stack or sub-pixel emits the red, green, or yellow light. In this case the initial emissive material or layer may be referred to as a “blue” component, even though the sub-pixel is a “red”, “green”, or “yellow” component.

[0016] In some cases, it may be preferable to describe the color of a component such as an emissive region, sub-pixel, color altering layer, or the like, in terms of 1931 CIE coordinates. For example, a yellow emissive material may have multiple peak emission wavelengths, one in or near an edge of the “green” region, and one within or near an edge of the “red” region as previously described. Accordingly, as used herein, each color term also corresponds to a shape in the 1931 CIE coordinate color space. The shape in 1931 CIE color space is constructed by following the locus between two color points and any additional interior points. For example, interior shape parameters for red, green, blue, and yellow may be defined as shown below:

	Color	CIE Shape Parameters
	Central	Locus: [0.6270, 0.3725]; [0.7347, 0.2653];
	Red	Interior: [0.5086, 0.2657]
	Central	Locus: [0.0326, 0.3530]; [0.3731, 0.6245];
	Green	Interior: [0.2268, 0.3321
	Central	Locus: [0.1746, 0.0052]; [0.0326, 0.3530];
	Blue	Interior: [0.2268, 0.3321]
	Central	Locus: [0.373 I, 0.6245]; [0.6270, 0.3725];
	Yellow	Interior: [0.3 700, 0.4087]; [0.2886, 0.4572]

[0017] More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

[0018] Some embodiments of the invention disclosed herein are set forth below, and any combination of these embodiments (or portions thereof) may be made to define another embodiment.

[0019] In one aspect, a light emitting device comprises a first electrode, a first transport layer above the first electrode, a first emissive layer above the first transport layer, a second transport layer above the first emissive layer, and a second electrode above the second transport layer, wherein at least one of the first transport layer and the second transport layer comprises nanoparticles.

[0020] In some embodiments, the nanoparticles comprise metal nanoparticles.

[0021] In some embodiments, the metal comprises Ag, Al, Au, Pt, or Ti.

[0022] In some embodiments, the nanoparticles are dispersed randomly throughout the layer.

[0023] In some embodiments, the nanoparticles are dispersed periodically throughout the layer.

[0024] In some embodiments, the nanoparticles have a spacing of 1 nm to 1000 nm in at least one direction.

[0025] In some embodiments, the nanoparticles are dispersed quasi-periodically throughout the layer.

[0026] In some embodiments, the device further comprises at least one second emitter stack between the first electrode and the first transport layer.

[0027] In some embodiments, the at least one second emitter stack comprises a third transport layer, a second emissive layer over the third transport layer, a fourth transport layer over the second emissive layer, and a charge generating layer over the fourth transport layer.

[0028] In some embodiments, at least one of the third transport layer and the fourth transport layer comprises nanoparticles.

[0029] In some embodiments, an absorption edge of the nanoparticles is tuned so the nanoparticles are strongly coupled to a singlet exciton emission of the first transport layer or second transport layer.

[0030] In some embodiments, the nanoparticles have a size of 10 nm to 1000 nm.

[0031] In some embodiments, a cubed root of the concentration (C) of the nanoparticles is within a wavelength (λ) of the light emitted from the device, as defined by

$\lambda =\sqrt[3]{\left(1/C\right)}.$

[0032] In some embodiments, at least one of the first and second transport layers comprising nanoparticles is positioned at an interface of at least one of the first and second electrodes. In some embodiments, the device comprises a series stacked device.

[0033] In some embodiments, each of the first and second emissive layers is associated with one or more of the first, second, third, and fourth transport layers comprising nanoparticles.

[0034] In some embodiments, each of the first and second emissive layers is adjacent to one or more of the first, second, third, and fourth transport layers comprising nanoparticles.

[0035] In some embodiments, a spacing of the nanoparticles is in the range of 1 nm to 1000 nm.

[0036] In some embodiments, at least one of the first and second transport layers comprises an organic transport layer.

[0037] In another aspect, a light emitting device comprises a first electrode, a polaritonic hole transport layer (HTL) over the first electrode, an organic phosphor-sensitized fluorescent emissive layer (EML) over the polaritonic HTL, a polaritonic electron transport layer (ETL) over the EML; and a second electrode over the polaritonic ETL.

[0038] In some embodiments, the device comprises a full cavity type device.

[0039] In some embodiments, the EML comprises a blue EML.

[0040] In some embodiments, the polaritonic ETL comprises at least one of BPyTP2 and SiTrzCz2.

[0041] In some embodiments, the polaritonic HTL comprises at least one of, SiCzCz, BCFN and HATCN.

[0042] In some embodiments, the EML comprises SiCzCz:SiTrzCz2:PtON-TBBI:v-DABNA.

[0043] In some embodiments, the v-DABNA is 0.5 volume percent.

[0044] In some embodiments, the first electrode comprises an anode comprising ITO/Ag/ITO.

[0045] In some embodiments, the first electrode further comprises ITO 10 nm/TiN 3 nm/Ti 3 nm/Ag 16 nm/Ti 3 nm/ITO 40 nm.

[0046] In some embodiments, the second electrode comprises a cathode comprising Ag.

[0047] In some embodiments, the second electrode further comprises Ag 120 nm/Al 3 nm/Liq 1.5 nm.

[0048] In some embodiments, the EML is 30 nm thick.

[0049] In some embodiments, the polaritonic HTL has a thickness of 5-20 nm.

[0050] In some embodiments, the polaritonic ETL has a thickness of 5-20 nm.

[0051] In another aspect, a method to produce a light emitting device comprises depositing a polaritonic hole transport layer (HTL) over a first electrode, depositing an organic phosphor-sensitized fluorescent emissive layer (EML) over the polaritonic HTL, depositing a polaritonic electron transport layer (ETL) over the EML, and depositing a second electrode over the polaritonic ETL.

[0052] In some embodiments, the polaritonic ETL comprises at least one of BPyTP2 and SiTrzCz2, and the polaritonic HTL comprises at least one of, SiCzCz, BCFN and HATCN.

[0053] In some embodiments, the first electrode comprises an anode comprising ITO/Ag/ITO, and the second electrode comprises a cathode comprising Ag.

[0054] In some embodiments, the EML comprises SiCzCz:SiTrzCz2:PtON-TBBI:v-DABNA.

[0055] In some embodiments, the v-DABNA is 0.5 volume percent.

[0056] In some embodiments, the light emitting device achieves improved operational lifetime and efficiency by engineering the metal electrode configuration to form a strong optical cavity that modifies the electromagnetic environment of a phosphor sensitized fluorescent (PSF) system. Contrary to conventional expectations that optical cavity effects primarily influence radiative light emission, tailoring the optical cavity can alter the behavior of the sensitizer in a PSF device, even where energy transfer from the sensitizer to the fluorescent chromophore occurs predominantly through non radiative mechanisms. By modifying the photonic density of states and the excitonic decay pathways of the sensitizer, the engineered cavity increases the fraction of excitonic energy that successfully reaches the chromophore, thereby improving device lifetime and performance.

[0057] In embodiments employing phosphor sensitized fluorescent (PSF) materials, incorporating such PSF systems into a device having a strong optical cavity formed by engineered metal electrodes is not conventional practice. In PSF OLEDs, energy generated in the sensitizer does not primarily propagate as emitted light, but instead is transferred to the fluorescent chromophore through non radiative or diffusive processes. Such energy spreading or diffusion is generally not expected to be influenced by polaritonic, plasmonic, or Purcell type optical effects. Contrary to this expectation, engineering the metal electrodes to form a strong optical cavity alters the behavior of the sensitizer, increasing the fraction of excitonic energy that successfully reaches the chromophore. This effect enables significant improvements in operational lifetime and device performance, even though the energy transfer pathway is not based on direct light emission.

[0058] In some embodiments, a consumer electronic device incorporates one or more of the devices as described above, wherein the consumer electronic device is at least one type selected from the group consisting of: a flat panel display, a curved display, a computer monitor, a medical monitor, a television, a billboard, a light for interior or exterior illumination and/or signaling, a heads-up display, a fully or partially transparent display, a flexible display, a rollable display, a foldable display, a stretchable display, a laser printer, a telephone, a cell phone, tablet, a phablet, a personal digital assistant (PDA), a wearable device, a laptop computer, a digital camera, a camcorder, a viewfinder, a micro-display that is less than 2 inches diagonal, a 3-D display, a virtual reality or augmented reality display, a vehicle, an automotive display, a video walls comprising multiple displays tiled together, a theater or stadium screen, and a sign.

[0070] Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

[0071] The initial OLEDs used emissive molecules that emitted light from their singlet states

[0072] (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

[0073] More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

[0074] FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

[0075] More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. Barrier layer 170 may be a single- or multi-layer barrier and may cover or surround the other layers of the device. The barrier layer 170 may also surround the substrate 110, and/or it may be arranged between the substrate and the other layers of the device. The barrier also may be referred to as an encapsulant, encapsulation layer, protective layer, or permeation barrier, and typically provides protection against permeation by moisture, ambient air, and other similar materials through to the other layers of the device. Examples of barrier layer materials and structures are provided in U.S. Pat. Nos. 6,537,688, 6,597,111, 6,664,137, 6,835,950, 6,888,305, 6,888,307, 6,897,474, 7,187,119, and 7,683,534, each of which is incorporated by reference in its entirety.

[0076] FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

[0077] The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

[0078] Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

[0079] In some embodiments disclosed herein, emissive layers or materials, such as emissive layer 135 and emissive layer 220 shown in FIGS. 1-2, respectively, may include quantum dots. The emissive layer may use different emissive display technologies. Such technologies may include inorganic and/or organic devices, such as LEDs, mini LEDs, microLEDs, thin electroluminescent films, organic light emitting devices, and the like. An “emissive layer” or “emissive material” as disclosed herein may include an organic emissive material and/or an emissive material that contains quantum dots or equivalent structures, unless indicated to the contrary explicitly or by context according to the understanding of one of skill in the art. In general, an emissive layer includes emissive material within a host matrix. Such an emissive layer may include only a quantum dot material which converts light emitted by a separate emissive material or other emitter, or it may also include the separate emissive material or other emitter, or it may emit light itself directly from the application of an electric current. Similarly, a color altering layer, color filter, upconversion, or downconversion layer or structure may include a material containing quantum dots, though such layer may not be considered an “emissive layer” as disclosed herein. In general, an “emissive layer” or material is one that emits an initial light based on an injected electrical charge, where the initial light may be altered by another layer such as a color filter or other color altering layer that does not itself emit an initial light within the device, but may re-emit altered light of a different spectra content based upon absorption of the initial light emitted by the emissive layer and downconversion to a lower energy light emission. In some embodiments disclosed herein, the color altering layer, color filter, upconversion, and/or downconversion layer may be disposed outside of an OLED device, such as above or below an electrode of the OLED device.

[0080] Unless otherwise specified, any of the layers of the various embodiments may be placed, disposed, or deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

[0081] Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material comprises essentially polymeric silicon and inorganic silicon.

[0082] In some embodiments, at least one of the anode, the cathode, or a new layer disposed over the organic emissive layer functions as an enhancement layer. The enhancement layer comprises a plasmonic material exhibiting surface plasmon resonance that non-radiatively couples to the emitter material and transfers excited state energy from the emitter material to non-radiative mode of surface plasmon polariton. The enhancement layer is provided no more than a threshold distance away from the organic emissive layer, where the emitter material has a total non-radiative decay rate constant and a total radiative decay rate constant due to the presence of the enhancement layer and the threshold distance is where the total non-radiative decay rate constant is equal to the total radiative decay rate constant. In some embodiments, the OLED further comprises an outcoupling layer. In some embodiments, the outcoupling layer is disposed over the enhancement layer on the opposite side of the organic emissive layer. In some embodiments, the outcoupling layer is disposed on opposite side of the emissive layer from the enhancement layer but still outcouples energy from the surface plasmon mode of the enhancement layer. The outcoupling layer scatters the energy from the surface plasmon polaritons. In some embodiments this energy is scattered as photons to free space. In other embodiments, the energy is scattered from the surface plasmon mode into other modes of the device such as but not limited to the organic waveguide mode, the substrate mode, or another waveguiding mode. If energy is scattered to the non-free space mode of the OLED other outcoupling schemes could be incorporated to extract that energy to free space. In some embodiments, one or more intervening layer can be disposed between the enhancement layer and the outcoupling layer. The examples for intervening layer(s) can be dielectric materials, including organic, inorganic, perovskites, oxides, and may include stacks and/or mixtures of these materials.

[0083] The enhancement layer modifies the effective properties of the medium in which the emitter material resides resulting in any or all of the following: a decreased rate of emission, a modification of emission line-shape, a change in emission intensity with angle, a change in the stability of the emitter material, a change in the efficiency of the OLED, and reduced efficiency roll-off of the OLED device. Placement of the enhancement layer on the cathode side, anode side, or on both sides results in OLED devices which take advantage of any of the above-mentioned effects. In addition to the specific functional layers mentioned herein and illustrated in the various OLED examples shown in the figures, the OLEDs according to the present disclosure may include any of the other functional layers often found in OLEDs.

[0084] The enhancement layer can be comprised of plasmonic materials, optically active metamaterials, or hyperbolic metamaterials. As used herein, a plasmonic material is a material in which the real part of the dielectric constant crosses zero in the visible or ultraviolet region of the electromagnetic spectrum. In some embodiments, the plasmonic material includes at least one metal. In such embodiments the metal may include at least one of Ag, Al, Au, Ir, Pt, Ni, Cu, W, Ta, Fe, Cr, Mg, Ga, Rh, Ti, Ru, Pd, In, Bi, Ca alloys or mixtures of these materials, and stacks of these materials. In general, a metamaterial is a medium composed of different materials where the medium as a whole acts differently than the sum of its material parts. In particular, we define optically active metamaterials as materials which have both negative permittivity and negative permeability. Hyperbolic metamaterials, on the other hand, are anisotropic media in which the permittivity or permeability are of different sign for different spatial directions. Optically active metamaterials and hyperbolic metamaterials are strictly distinguished from many other photonic structures such as Distributed Bragg Reflectors (“DBRs”) in that the medium should appear uniform in the direction of propagation on the length scale of the wavelength of light. Using terminology that one skilled in the art can understand: the dielectric constant of the metamaterials in the direction of propagation can be described with the effective medium approximation. Plasmonic materials and metamaterials provide methods for controlling the propagation of light that can enhance OLED performance in a number of ways.

[0085] In some embodiments, the enhancement layer is provided as a planar layer. In other embodiments, the enhancement layer has wavelength-sized features that are arranged periodically, quasi-periodically, or randomly, or sub-wavelength-sized features that are arranged periodically, quasi-periodically, or randomly. In some embodiments, the wavelength-sized features and the sub-wavelength-sized features have sharp edges.

[0086] In some embodiments, the outcoupling layer has wavelength-sized features that are arranged periodically, quasi-periodically, or randomly, or sub-wavelength-sized features that are arranged periodically, quasi-periodically, or randomly. In some embodiments, the outcoupling layer may be composed of a plurality of nanoparticles and in other embodiments the outcoupling layer is composed of a plurality of nanoparticles disposed over a material. In these embodiments the outcoupling may be tunable by at least one of varying a size of the plurality of nanoparticles, varying a shape of the plurality of nanoparticles, changing a material of the plurality of nanoparticles, adjusting a thickness of the material, changing the refractive index of the material or an additional layer disposed on the plurality of nanoparticles, varying a thickness of the enhancement layer, and/or varying the material of the enhancement layer. The plurality of nanoparticles of the device may be formed from at least one of metal, dielectric material, semiconductor materials, an alloy of metal, a mixture of dielectric materials, a stack or layering of one or more materials, and/or a core of one type of material and that is coated with a shell of a different type of material. In some embodiments, the outcoupling layer is composed of at least metal nanoparticles where the metal comprises Ag, Al, Au, Ir, Pt, Ni, Cu, W, Ta, Fe, Cr, Mg, Ga, Rh, Ti, Ru, Pd, In, Bi, Ca, alloys or mixtures of these materials, and stacks of these materials. The plurality of nanoparticles may have additional layer disposed over them. In some embodiments, the polarization of the emission can be tuned using the outcoupling layer. Varying the dimensionality and periodicity of the outcoupling layer can select a type of polarization that is preferentially outcoupled to air. In some embodiments the outcoupling layer also acts as an electrode of the device.

[0087] In embodiments of the disclosed subject matter, a device may include an enhancement layer that is disposed over an emissive area of at least one sub-pixel that is configured to have a Lambertian emission and/or at least one sub-pixel having a microcavity configured for direct emission, as described in detail below. In at least some of such embodiments, the enhancement layer may include a plasmonic structure that is disposed a predetermined threshold distance from the emissive area. The predetermined threshold distance may be a distance at which a total non-radiative decay rate constant is equal to a total radiative decay rate constant. In some of such embodiments, device may include an outcoupling layer is disposed over the enhancement layer on the opposite side of the emissive area.

[0088] It is believed that the internal quantum efficiency (IQE) of fluorescent OLEDs can exceed the 25% spin statistics limit through delayed fluorescence. As used herein, there are two types of delayed fluorescence, i.e., P-type delayed fluorescence and E-type delayed fluorescence. P-type delayed fluorescence is generated from triplet-triplet annihilation (TTA).

[0089] In some embodiments, a compound in an emissive material and/or layer in an OLED may be used as a phosphorescent sensitizer, where one or multiple layers in the OLED may include an acceptor in the form of one or more fluorescent and/or delayed fluorescence emitters. In some embodiments, the compound can be used as one component of an exciplex to be used as a sensitizer. As a phosphorescent sensitizer, the compound may be capable of energy transfer to the acceptor, and the acceptor may emit the energy or further transfer energy to a final emitter. The acceptor concentrations may range from 0.001% to 100%. The acceptor may be in either the same layer as the phosphorescent sensitizer or in one or more different layers. In some embodiments, the acceptor may be a TADF emitter. In some embodiments, the acceptor may be a fluorescent emitter. In some embodiments, the emission may arise from any or all of the sensitizer, acceptor, and/or final emitter.

[0090] On the other hand, E-type delayed fluorescence described above does not rely on the collision of two triplets, but rather on the thermal population between the triplet states and the singlet excited states. Compounds that are capable of generating E-type delayed fluorescence are required to have very small singlet-triplet gaps. Thermal energy can activate the transition from the triplet state back to the singlet state. This type of delayed fluorescence is also known as thermally activated delayed fluorescence (TADF). A distinctive feature of TADF is that the delayed component increases as temperature rises due to the increased thermal energy. If the reverse intersystem crossing rate is fast enough to minimize the non-radiative decay from the triplet state, the fraction of back populated singlet excited states can potentially reach 75%. The total singlet fraction can be 100%, far exceeding the spin statistics limit for electrically generated excitons.

[0091] E-type delayed fluorescence characteristics can be found in an exciplex system or in a single compound. Without being bound by theory, it is believed that E-type delayed fluorescence requires the luminescent material to have a small singlet-triplet energy gap (AES-T). Organic, non-metal containing, donor-acceptor luminescent materials may be able to achieve this. The emission in these materials is often characterized as a donor-acceptor charge-transfer (CT) type emission. The spatial separation of the HOMO and LUMO in these donor-acceptor type compounds often results in small AES-T. These states may involve CT states. Often, donor-acceptor luminescent materials are constructed by connecting an electron donor moiety such as amino- or carbazole-derivatives and an electron acceptor moiety such as N-containing six-membered aromatic ring.

[0092] Additionally, in some embodiments, an emissive region may have one or more emissive layer. In an embodiment, the number of layers in each emissive region of each device may be the same. In alternative embodiment, the number of layers in each emissive region of each device may be different. In yet another alternative embodiment, the number of layers in some emissive regions of each device may be the same and some emissive regions of each device may be different. In some embodiments, an emissive layer of the one or more emissive layers of any emissive region may comprise a phosphorescent material, a fluorescent material or any combination thereof. In some embodiments, the emissive regions in the device may comprise a sensitizer and an acceptor with various sensitizing device characteristics disclosed in this application.

[0093] Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of electronic component modules (or units) that can be incorporated into a variety of electronic products or intermediate components. Examples of such electronic products or intermediate components include display screens, lighting devices such as discrete light source devices or lighting panels, etc. that can be utilized by the end-user product manufacturers. Such electronic component modules can optionally include the driving electronics and/or power source(s). Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. A consumer product comprising an OLED that includes the compound of the present disclosure in the organic layer in the OLED is disclosed. Such consumer products would include any kind of products that include one or more light source(s) and/or one or more of some type of visual displays. Some examples of such consumer products include a flat panel display, a curved display, a computer monitor, a medical monitor, a television, a billboard, a light for interior or exterior illumination and/or signaling, a heads-up display, a fully or partially transparent display, a flexible display, a rollable display, a foldable display, a stretchable display, a laser printer, a telephone, a cell phone, tablet, a phablet, a personal digital assistant (PDA), a wearable device, a laptop computer, a digital camera, a camcorder, a viewfinder, a micro-display that is less than 2 inches diagonal, a 3-D display, a virtual reality or augmented reality display, a vehicle, an automotive display, a video walls comprising multiple displays tiled together, a theater or stadium screen, and a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 C to 30 C, and more preferably at room temperature (20-25 C), but could be used outside this temperature range, for example, from-40 C to 80 C.

[0094] The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

[0095] In some embodiments, the OLED has one or more characteristics comprising being flexible, being rollable, being foldable, being stretchable, and being curved. In some embodiments, the OLED is transparent or semi-transparent. In some embodiments, the OLED further comprises a layer having carbon nanotubes.

[0096] In some embodiments, the OLED further comprises a layer having a delayed fluorescent emitter. In some embodiments, the OLED comprises a RGB pixel arrangement or white plus color filter pixel arrangement. In some embodiments, the OLED is a mobile device, a hand held device, or a wearable device. In some embodiments, the OLED is a display panel having less than 10 inch diagonal or 50 square inch area. In some embodiments, the OLED is a display panel having at least 10 inch diagonal or 50 square inch area. In some embodiments, the OLED is a lighting panel.

[0097] In some embodiments of the emissive region, the emissive region further comprises a host.

[0098] In some embodiments, the compound causing light to be generated can be an emissive dopant. In some embodiments, the compound can produce emissions via phosphorescence, fluorescence, thermally activated delayed fluorescence, i.e., TADF (also referred to as E-type delayed fluorescence), triplet-triplet annihilation, or combinations of these processes, including phosphor sensitized fluorescence.

[0099] The OLED disclosed herein can be incorporated into one or more of a consumer product, an electronic component module, and a lighting panel. The organic layer can be an emissive layer and the compound can be an emissive dopant in some embodiments, while the compound can be a non-emissive dopant in other embodiments.

[0100] The organic layer can also include a host. In some embodiments, two or more hosts are preferred. In some embodiments, the hosts used maybe a) bipolar, b) electron transporting, c) hole transporting or d) wide band gap materials that play little role in charge transport. In some embodiments, the host can include a metal complex. The host can be an inorganic compound.

Combination with Other Materials

[0101] The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

[0102] Various materials may be used for the various emissive and non-emissive layers and arrangements disclosed herein. Examples of suitable materials are disclosed in U.S. Patent Application Publication No. 2017/0229663, which is incorporated by reference in its entirety.

[0103] A charge transport layer can be doped with conductivity dopants to substantially alter its density of charge carriers, which will in turn alter its conductivity. The conductivity is increased by generating charge carriers in the matrix material, and depending on the type of dopant, a change in the Fermi level of the semiconductor may also be achieved. Hole-transporting layer can be doped by p-type conductivity dopants and n-type conductivity dopants are used in the electron-transporting layer.

[0104] A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material.

[0105] An electron blocking layer (EBL) may be used to reduce the number of electrons and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies, and or longer lifetime, as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and/or higher triplet energy than the emitter closest to the EBL interface. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and/or higher triplet energy than one or more of the hosts closest to the EBL interface. In one aspect, the compound used in EBL contains the same molecule or the same functional groups used as one of the hosts described below.

[0106] The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. Any host material may be used with any dopant so long as the triplet criteria is satisfied.

[0107] A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies and/or longer lifetime as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. In some embodiments, the HBL material has a lower HOMO (further from the vacuum level) and or higher triplet energy than the emitter closest to the HBL interface. In some embodiments, the HBL material has a lower HOMO (further from the vacuum level) and/or higher triplet energy than one or more of the hosts closest to the HBL interface.

[0108] An electron transport layer (ETL) may include a material capable of transporting electrons. The electron transport layer may be intrinsic (undoped) or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

[0109] In tandem or stacked OLEDs, the CGL plays an essential role in the performance, which is composed of an n-doped layer and a p-doped layer for injection of electrons and holes, respectively. Electrons and holes are supplied from the CGL and electrodes. The consumed electrons and holes in the CGL are refilled by the electrons and holes injected from the cathode and anode, respectively; then, the bipolar currents reach a steady state gradually. Typical CGL materials include n and p conductivity dopants used in the transport layers.

[0110] Previous work has demonstrated that the operational lifetime of blue organic light-emitting diodes (OLEDs) can be improved by increasing the Purcell factor of the cavity and further by coupling excitons to plasmon-exciton-polaritons (PEPs), formed at metal/organic interfaces via strong coupling. In the existing technology, the OLED structure is designed such that the PEPs form at the planar interfaces between the organic transporting layers and metal electrodes. Further details can be found in U.S. patent application Ser. No. 17/666,664, U.S. patent application Ser. No. 17/932,475, U.S. patent application Ser. No. 18/157,308, U.S. patent application Ser. No. 18/413,235, and U.S. patent application Ser. No. 18/951,352, each incorporated herein by reference in its entirety. This design is limited to, at most, two interfaces within the device and dictates the choice of electrode material. Disclosed herein is a design for increasing the local Purcell factor and generating plasmon-exciton-polaritons in a nanoparticle-enhanced organic transporting layer.

[0111] In some embodiments, the nanoparticle-enhanced transporting layer comprises an electron transport material and/or a hole transporting material that is doped with nanoparticles. In some embodiments, the nanoparticles comprise metal nanoparticles. In some embodiments, the nanoparticle material (e.g. Ag, Al, Au, Pt, Ti, etc.), size, and concentration can be varied to achieve the appropriate absorption edge of the metal nanoparticle such that the nanoparticle can strongly couple to the transporting layer singlet exciton emission. In some embodiments, the nanoparticles have a size in the range of 10 nm to 1000 nm and the nanoparticles can have any suitable shape. In some embodiments, the nanoparticles are dispersed randomly throughout the layer. In some embodiments, the nanoparticles are dispersed periodically or quasi-periodically throughout the layer, having a spacing of 1 nm to 1000 nm in at least one direction. In some embodiments, the cubed root of the concentration (C) of the nanoparticles is within a wavelength (λ) of the light emitted from the device, as defined by

$\lambda =\sqrt[3]{\left(1/C\right)}.$

In some embodiments, the nanoparticle-enhanced transporting layer can be included at any point throughout the device. For example, in a single emissive layer (EML) device structure, the transporting layer(s) would be included at the electrode (anode and/or cathode) interfaces. In a series-stacked, multiple EML device structure, the nanoparticle-enhanced transport layers can be included throughout the device, for each EML, such as depicted in FIG. 3. This structure is applicable with both top and bottom emitting structures.

[0112] In some embodiments, a light emitting device 300 comprises a substrate 301, a first (bottom) electrode 302 above the substrate 301, a first transport layer 307 above the first electrode 302, a first emissive layer 308 above the first transport layer 307, a second transport layer 309 above the first emissive layer 308, and a second (top) electrode 310 above the second transport layer 309. In some embodiments, the first transport layer 307 and/or the second transport layer 309 is a nanoparticle-enhanced transport layer comprising nanoparticles. In some embodiments, either of the first and/or second transport layers can comprise a hole transport layer (HTL) and/or an electron transport layer (ETL). In some embodiments, either of the first and/or second electrodes can comprise an anode and/or cathode. In some embodiments, at least one of the first and/or second transport layers (307, 309, respectively) comprising nanoparticles is positioned at an interface of at least one of the first and/or second electrodes (302, 310, respectively). In some embodiments, at least one of the first and/or second transport layers (307, 309, respectively) comprises an organic transport layer.

[0113] In some embodiments, the device 300 further includes at least one second emitter stack 350 between the first electrode 302 and the first transport layer 307. In some embodiments, the second emitter stack(s) 350 comprises a third transport layer 303 over the first electrode 302, a second emissive layer 304 over the third transport layer 303, a fourth transport layer 305 over the second emissive layer 304, and a charge generating layer 306 over the fourth transport layer 305. In some embodiments, the third transport layer 303 and/or the fourth transport layer 305 is a nanoparticle-enhanced transport layer comprising nanoparticles. In some embodiments, the device 300 comprises a series stacked device. In some embodiments, each of the first and second emissive layers (308, 304, respectively) is associated with one or more of the first, second, third, and fourth transport layers comprising nanoparticles (307, 309, 303, 305, respectively). In some embodiments, one or more of the first and/or second emissive layers (308, 304, respectively) is adjacent to one or more of the first, second, third, and/or fourth transport layers comprising nanoparticles (307, 309, 303, 305, respectively). In some embodiments, each of the first and second emissive layers (308, 304, respectively) is adjacent to one or more of the first, second, third, and/or fourth transport layers comprising nanoparticles (307, 309, 303, 305, respectively). In some embodiments, at least one of the first, second, third, and/or fourth transport layers (307, 309, 303, 305, respectively) comprises an organic transport layer.

[0114] In some embodiments, the nanoparticle comprise metal nanoparticles, such as, for example, Ag, Al, Au, Pt, Ti, or any other suitable metal, combinations, or oxides thereof. In some embodiments, an absorption edge of the nanoparticles is tuned so the nanoparticles are strongly coupled to a singlet exciton emission of the first transport layer 307, second transport layer 309, third transport layer 303, and/or fourth transport layer 305. In some embodiments, the nanoparticles have a size of 10 nm to 1000 nm. In some embodiments, a concentration of the nanoparticles is within a wavelength of light emitted from the device. In some embodiments, a spacing of the nanoparticles is in the range of 1 nm to 1000 nm.

[0115] In some embodiments, a consumer electronic device incorporates the device 300 as described above, wherein the consumer electronic device is a flat panel display, a curved display, a computer monitor, a medical monitor, a television, a billboard, a light for interior or exterior illumination and/or signaling, a heads-up display, a fully or partially transparent display, a flexible display, a rollable display, a foldable display, a stretchable display, a laser printer, a telephone, a cell phone, tablet, a phablet, a personal digital assistant (PDA), a wearable device, a laptop computer, a digital camera, a camcorder, a viewfinder, a micro-display that is less than 2 inches diagonal, a 3-D display, a virtual reality or augmented reality display, a vehicle, an automotive display, a video walls comprising multiple displays tiled together, a theater or stadium screen, and/or a sign.

[0116] Using COMSOL, the electric field distribution was simulated surrounding an Ag nanoparticle in a square lattice with background medium with n=1.7, which is approximately the index of refraction for organic materials, see FIG. 4. By varying the size and spacing of this nanoparticle, one can tune the absorbance of the nanoparticle, as shown in FIGS. 5A-5B. For this example, Ag was chosen for the nanoparticle material, since its absorbance is aligned well for coupling to blue emission. Other materials, such as gold, can be useful for longer wavelength applications for emission in the red and green.

[0117] One can estimate the localized Purcell factor by computing the ratio of the Poynting vector calculated with a 20 nm diameter Ag nanoparticle in a 60 nm unit cell to the Poynting vector calculated for a unit cell of the same size with index n=1.7. The localized Purcell factor as a function of wavelength is shown in FIG. 6. While the localized Purcell factor will only affect excitons within the unit cell boundaries, one can calculate the Purcell factor throughout the device using Green's function methods by using the calculated absorbance of the nanoparticle-enhanced transporting layer for one of the transporting layers. In this example the device structure comprised: 700 μm glass/70 nm ITO/50 nm nanoparticle-enhanced transport layer/50 mCBP/30 nm transport layer with n=1.7/120 nm Al. The Purcell factor for this device, which employs the nanoparticle-enhanced transport layer for the bottom transport layer, was compared to the Purcell factor for the same structure, with the nanoparticle-enhanced layer replaced by a n=1.7 transport layer, see FIG. 7. The nanoparticle-enhanced layer increases the Purcell factor around its absorption peak without any modification to the cathode/anode cavity structure.

[0118] In some embodiments, the device may include more than one emissive stack including at least one nanoparticle-enhanced a transport layer. Additionally, a charge generation layer is located between each emissive stack of the more than one emissive stack.

[0119] FIGS. 8A-8E show details on enhancing the stability of deep blue phosphor-sensitized-fluorescent OLEDs using polariton-enhanced Purcell effects. Polariton-enhanced Purcell effects can increase the PHOLED stability via reduction of the density of triplet emitters (see Zhao 2024). Phosphor-sensitized fluorescent (PSF) OLEDs enable highly efficient OLED with saturated colors. However, long-lived, efficient, deep blue PSF-OLEDs are still rare to find. The Purcell effect increase the PSF-OELD stability for its enhancement on all radiative processes resonant to the cavity, reducing intrinsic degradation. FIG. 8A depicts energy transfer processes in PDF-OLEDs.

[0120] The Purcell effect increases the radiative decay rates of both triplets and singlets in phosphor and fluorophores. Low exciton density residing on the triplet states of both phosphors and fluorophores result in low triplet annihilation and device degradation rates. Organic plasmon-exciton-polaritons between Ag and transporting layers (ETL/HTL) greatly increase Purcell factor (PF), which equates to the ratio of radiative decay rates with and without cavities (see Zhao 2025). FIG. 8B depicts energy transfer rates modified by the Purcell effect in PSF-OLEDs. FIGS. 8C-8D depict simulated device structures and components thereof. The device structures had three optical cavities: Al-ITO control C (weak), Ag-ITO half cavity H (medium), Ag-ITO/Ag/ITO full cavity F (strong).

[0121] FIGS. 9A-9F depict simulated experimental results for the control (C), half cavity (H), and full cavity (F) device structures detailed in FIGS. 8A-8E. FIG. 9A shows intensity vs. wavelength. FIG. 9B shows EQE vs. current density. FIG. 9C shows luminance vs. time. FIG. 9D shows EL intensity vs. time. FIG. 9E shows Purcell factor vs distance to cathode. FIG. 9F shows luminance vs. time. The full cavity device had the greatest device lifetime (3.1× direct increase under J=10 mA/cm²), followed by the half cavity device, followed by the control device. The full cavity device had the greatest color saturation, followed by the control device, followed by the half cavity device. The cavity reduces vibronic peaks and lead to a CIExy=[0.13, 0.09] from PH-only [0.15, 0.21]. The full cavity device had the greatest EQE roll-off, followed by the half cavity device, followed by the control device. The full cavity reduced EQE roll-off from 35% to 17%, achieving higher EQE at high luminances. The spatial dependent Purcell factor was scanned by thin exciton blocked emissive layers in the half cavity device. Faster EL transients lead to longer device lifetime.

[0122] In conclusion, the disclosed devices demonstrate that polariton-enhanced Purcell effects accelerate all radiative decay process and increase the PSF-OLED lifetime. By using the strong full polaritonic cavity (Ag electrodes and polaritonic ETL/HTL), PSF-OLED has achieved 3.1× direct lifetime increase, saturated color at CIExy=[0.13, 0.09], low EQE roll-off and high EQE. Device lifetime increase and accelerated TrEL quantitatively follow the increased PF.

[0123] The stability of efficient, deep blue organic light-emitting diodes (OLEDs) remains a major challenge in the field of organic electronics. Poor device stability originates from the high probability for destructive non-radiative triplet exciton annihilation events. Phosphor-sensitized fluorescence (PSF) has been proposed to achieve efficient, deep blue color by energy transfer from phosphors to fluorophores. Recently, the polariton-enhanced Purcell (PEP) effect was introduced to decrease the triplet radiative lifetime and density, resulting in an increase in blue phosphorescent OLED lifetime. Described herein is the PEP effect to enhance the stability of the PSF-OLEDs. As detailed below the PEP effect increases all radiative decay rates of the phosphors and fluorophores, leading to a reduction in the triplet annihilation events. Using a Pt-complex phosphor sensitizer and a so-called multiresonance fluorescent emitter in a PEP cavity, a 3.1-fold lifetime increase was observed at a current density of J=10 mA/cm², and reduced EQE roll-off and deep blue color with Commission Internationale de l'Eclairage coordinates of (0.13, 0.09) was measured. The PEP effect maximally extends PSF-OLED lifetimes in devices with the highest triplet-to-singlet energy transfer rates. Moreover, this work suggests that the benefits of PEPs apply to all triplet-based OLEDs.

[0124] Phosphorescent organic light-emitting devices (PHOLEDs) have revolutionized display and lighting technologies, yet stable PHOLEDs with near-unity quantum efficiency in the deep blue remain unavailable. A unity internal quantum efficiency (IQE) requires harvesting triplet exciton radiation, such as by using heavy-metal phosphors or thermally activated delayed fluorescence (TADF). However, due to the long lifetimes of triplets, the increased probability for destructive high energy triplet annihilation (e.g. triplet-triplet and triplet-polaron annihilation, TTA and TPA) reactions result in intrinsic blue-emitting device instability. Promising solutions include triplet-sensitized OLEDs, including phosphor-sensitized fluorescence (PSF) and TADF-sensitized fluorescence (TSF). In these systems, efficient Förster resonant energy transfer (FRET) and Dexter energy transfer (DET) enable triplet harvesting via a fast fluorescent emitter, reducing the probability for triplet annihilation. Heimel et al. have reported a linear relationship between the PSF-OLED lifetimes and the sensitized radiative decay rates. Nevertheless, intrinsically stable, deep blue OLEDs with high quantum efficiencies remain a rarity.

[0125] Recently, the polariton-enhanced Purcell (PEP) effect has been used to increase PHOLED stability by reducing triplet radiative decay lifetime and density. The large optical density of states (ODoS) of plasmon-exciton-polaritons (plexcitons) and surface plasmon polaritons (SPPs) can increase the radiative rates of nearby emitters. Particularly, plexcitons formed within the metal electrode and the adjacent organic charge transporting layers enable a larger Purcell factor (PF) deeper in the emissive layer (EML) than by the direct excitation of surface plasmons. An analytical model based on Marcus theory describes the nonlinear enhancement observed in PHOLED lifetimes by the PEP effect, with a power exponent m ranging from 1.5 to 2.5 depending on the relative strength of TPA and TTA. That is, the aging time of PHOLEDs to reach x % of their initial luminance, L₀, is given by LTx∝PF^m.

[0126] PSF-OLED stability can also be enhanced by the PEP effect as detailed below. Three PtON-TBBI-sensitized PSF-OLED structures were investigated with increasing Purcell effects containing the so-called multi-resonance-type (MR) deep blue fluorophore emitter, v-DABNA. A 3.1-fold device lifetime increase was demonstrated, from LT70=63+1 h to 197+3 h at a current density of J=10 mA/cm² for the weakest Al-ITO control optical cavity to the strongest Ag-ITO/Ag/ITO (IAI) full cavity, respectively. The IAI cavity PSF-OLED has a deep blue emission with 1931 Commission Internationale de l'Eclairage coordinates of CIExy=(0.13,0.09) at an initial luminance of L₀=1590+30 cd/m², whereas the conventional Al-ITO PSF-OLED emits in a lighter blue color at (0.14,0.15) for L₀=1920+10 cd/m², based on the phosphor-only (PH-only) device whose native CIExy=(0.15, 0.20). Furthermore, the EQE roll-off is reduced from 35% to 17% at a current density of J=100 mA/cm² due to a decreased triplet annihilation rate. The transient electroluminescence (TrEL) is measured for thin-EML, Ag-ITO half cavity devices to understand the Purcell effect enhancement of the PSF-OLED operational lifetime.

[0127] In PSF OLEDs, energy generated in the sensitizer does not necessarily propagate as emitted light prior to reaching the fluorescent chromophore. Instead, energy transfer may occur through other pathways. Despite this, engineering the metal electrodes to form a strong optical cavity can substantially influence sensitizer behavior. In particular, the cavity modifies the local electromagnetic environment of the sensitizer, affecting exciton lifetime, decay probabilities, and the balance between competing radiative and non-radiative processes. As a result, a greater portion of the energy generated in the sensitizer is transferred to the fluorescent chromophore, leading to enhanced operational lifetime and overall device stability.

[0128] Additionally, in PSF systems, a portion of the excitonic energy is distributed or diffuses through the sensitizer and host materials prior to reaching the fluorescent chromophore, and such diffusive energy transfer mechanisms are not typically considered responsive to optical cavity, plasmonic, or polaritonic effects. Nonetheless, configuring the metal electrodes to form a strong optical cavity modifies the local electromagnetic environment of the sensitizer, thereby affecting its excitonic decay behavior and transfer efficiency. As a result, a greater proportion of the energy generated in the sensitizer is delivered to the chromophore, leading to improved operational lifetime and stability of the OLED device.

[0129] As depicted in FIG. 8A, the energy transfer and radiative dissipation of a Frenkel exciton in the EML is governed by three processes that depend on the physical separation, r, between the donor and acceptor, and their characteristic interaction distance, R₀. DET is the exchange transfer between contacting molecules with rate k_DET∝exp(−2r/R₀), where R₀≅1 nm. FRET is the resonant near-field coupling at rate k_FRET∝(R₀/r)⁶, where R0≤10 nm. Spontaneous radiative decay rate in the intermediate (<100 nm) to far-field range (>100 nm) depends on the ODOS of the optical microcavity according to the Fermi's golden rule. Chance et al. give the ODOS of a planar optical microcavity determined by its dispersion relations with respect to the in-plane wavevector, k_∥/k₀, where k₀ is the vacuum wavevector. Particularly, the Purcell effect for a chromophore near a metal surface yields an enhanced radiative decay rate PF·k_r∝(R₀/r)⁴, with an SPP excitation range of R₀≈15 nm. Previous work showed that PEPs strongly couple the exciton in the adjacent charge transporting layers and the metal electrode, thereby extending the Purcell effect to distances of 50 nm into the EML. With the double-sided polariton-enhanced Purcell effect used in a tandem blue emitting PHOLED, a radiatively enhanced region of 100 nm was achieved, covering almost the entire active organic layers in the PHOLED stack.

[0130] For conventional PSF-OLEDs, the slow phosphor radiative decay (10⁶-10⁷ s⁻¹) limits FRET rates to 10⁵-10⁷ s⁻¹, which often competes with DET to inefficient fluorophore triplets. To suppress this lossy transfer, the spectral overlap between donor emission and acceptor absorption can be increased to favor FRET. Also, the fluorophore concentration, sensitization via multi-step transfer, and molecular design can be optimized to suppress DET. Further, nonradiative loss can be reduced using TADF molecules as the fluorescent emitter. In this case, the limiting factor is the small ratio of the endothermic intersystem crossing (ISC) rate of triplets (k_ISC,T~10³-10⁷ s⁻¹) to the exothermic ISC rate (k_ISC,S~10⁹ s⁻¹). For example, the commonly used efficient deep blue MR-type molecule, t-DABNA, has k_ISC,T/k_ISC,S=0.008% at room temperature due to a large singlet-triplet splitting energy, ΔE_ST=170 meV.

[0131] The Purcell effect applies to the spontaneous radiation from all emitting molecules that are resonant with the cavity optical modes. FIG. 8B shows the PEP effect reducing the triplet density via enhancing the radiative decay of the phosphor donor triplets, and the fluorophore singlet and triplets. Here, TADF emitters are considered as a special case of fluorescent molecules that have intersystem crossing rates comparable to the spontaneous radiative decay rates. Therefore, the Purcell-enhanced PSF-OLED can reduce triplet annihilation and intrinsic device degradation caused by exciton annihilation, analogous to a conventional PHOLED.

[0132] The time dependent concentrations of singlets and triplets are given by three coupled equations:

$\begin{array}{cc}\frac{\partial S_A}{\partial t}=\frac{1}{4}{f}_A\frac{J}{q}-P{F}_A{k}_{f,A}{S}_A+k_{FRET}{T}_D-k_{\mathrm{isc},S}{S}_A+k_{\mathrm{isc},T}{T}_A& \left(1\right)\end{array}$ $\begin{array}{cc}\frac{\partial T_A}{\partial t}=\frac{3}{4}{f}_A\frac{J}{q}-P{F}_A{k}_{\mathrm{ph},A}{T}_A+k_{DET}{T}_D+k_{\mathrm{isc}.S}{S}_A-k_{\mathrm{isc},T}{T}_A& \left(2\right)\end{array}$ $\begin{array}{cc}\frac{\partial T_D}{\partial t}=f_D\frac{J}{q}-\left(P{F}_D{k}_{ph,D}+k_{FRET}+k_{DET}\right)T_D& \left(3\right)\end{array}$

[0133] Here, S_A, T_A and T_D are the acceptor singlet, acceptor triplet and phosphor donor triplet densities, respectively. When the device is turned on at a current density, J, a fraction of excitons is generated on the three species S_A, T_A and T_D, depending on donor (acceptor) concentrations f_D (f_A=1 f_D) and spin statistics (¾ for triplets, ¼ for singlets). The natural spontaneous radiative decay rates are k_f,A, k_ph,A, and k_ph,D for acceptor fluorescence, acceptor phosphorescence and donor phosphorescence, respectively. The acceptor and donor molecules have independent Purcell factors, PF_A and PF_D, depending on their emission spectra and dipole orientations. For fluorescent emitters whose radiation is only from singlets, terms involving triplets T_A contribute only to non-radiative decay, and hence are not coupled to the cavity (i.e. PF_A=1).

[0134] In some embodiments, a light emitting device 800 comprises a first electrode 801, a polaritonic hole transport layer (HTL) 802 over the first electrode 801, an organic phosphor-sensitized fluorescent emissive layer (EML) 803 over the polaritonic HTL 802, a polaritonic electron transport layer (ETL) 804 over the EML 803, and a second electrode 805 over the polaritonic ET 804. In some embodiments, the device 800 comprises a full cavity type device.

[0135] In some embodiments, the first electrode 801 comprises an anode comprising ITO/Ag/ITO. In some embodiments, the first electrode 801 comprises ITO 10 nm/TIN 3 nm/Ti 3 nm/Ag 16 nm/Ti 3 nm/ITO 40 nm. In some embodiments, the first electrode 801 comprises any suitable materials, such as ITO, IZO, AZO, PEDOT: PSS, graphene, silver nanowires (AgNWs), carbon nanotubes, thin metal films (e.g., Ag, Au), NiO, Al, Mg: Ag, Ca, Ba, LiF/AI, CsF/Al, Ca/Al, Ba/Al, Ag, Au, and/or LiF/Al. In some embodiments, the first electrode 801 has a thickness of 0.1-100 nm, 1-50 nm, 50-100 nm, 5-25 nm, 25-50 nm, 50-75 nm, 75-100 nm, 1-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, 40-50 nm, 50-60 nm, 60-70 nm, 70-80 nm, 80-90 nm, 90-100 nm, or any other suitable thickness.

[0136] In some embodiments, the polaritonic HTL 802 comprises at least one of, SiCzCz, BCFN and HATCN. In some embodiments, the polaritonic HTL 802 has a thickness of 5-20 nm. In some embodiments, the polaritonic HTL 802 comprises any suitable material, such as NPB (N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine), TPD (N,N′-Diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine), TAPC (1,1-Bis [(di-4-tolylamino)phenyl] cyclohexane), TCTA (4,4′,4″-Tris (carbazol-9-yl)triphenylamine), Spiro-OMeTAD (2,2′, 7,7′-Tetrakis [N,N-di (4-methoxyphenyl)amino]-9,9′-spirobifluorene), CBP (4,4′-Bis (carbazol-9-yl) biphenyl), m-MTDATA (4,4′,4″-Tris [phenyl (m-tolyl)amino] triphenylamine), a-NPD, TFB (Poly (9,9-dioctylfluorene-alt-N-(4-butylphenyl)diphenylamine)), PVK (Poly (N-vinylcarbazole)), and/or PTAA (Poly [bis(4-phenyl) (2,4,6-trimethylphenyl) amine]). In some embodiments, the polaritonic HTL 802 has a thickness of 0.1-100 nm, 1-50 nm, 50-100 nm, 5-25 nm, 25-50 nm, 50-75 nm, 75-100 nm, 1-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, 40-50 nm, 50-60 nm, 60-70 nm, 70-80 nm, 80-90 nm, 90-100 nm, or any other suitable thickness.

[0137] In some embodiments, the EML 803 comprises a blue EML. In some embodiments, the EML 803 comprises SiCzCz:SiTrzCz2:PtON-TBBI:v-DABNA. In some embodiments, the v-DABNA is 0.5 volume percent. In some embodiments, the EML 803 is 30 nm thick. In some embodiments, the EML 803 comprises a stack of light emitting layers. In some embodiments, the EML 803 comprises a red, blue, green, white, UV, and/or IR emitter, or combinations thereof. In some embodiments, the EML 803 comprises any suitable material, such as Alq3, Ir(ppy)3, Flrpic, Ir(MDQ)2(acac), PtOEP, Rubrene, DPVBi, DCM, DCJTB, DMQA, Coumarin 545T, 4CzIPN, 4CzTPN, DMAC-DPS, PXZ-DPS, CBP, mCP, 2CzPN, BODIPY derivatives, quinacridone, perylene, anthracene derivatives, poly (phenylene vinylene) (PPV), polyfluorene (PFO), fluorescent, phosphorescent (Ir/Pt complexes), and/or TADF emitters. In some embodiments, the EML 803 has a thickness of 0.1-100 nm, 1-50 nm, 50-100 nm, 5-25 nm, 25-50 nm, 50-75 nm, 75-100 nm, 1-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, 40-50 nm, 50-60 nm, 60-70 nm, 70-80 nm, 80-90 nm, 90-100 nm, or any other suitable thickness.

[0138] In some embodiments, the polaritonic ETL 804 comprises at least one of BPyTP2 and SiTrzCz2. In some embodiments, the polaritonic ETL has a thickness of 5-20 nm. In some embodiments, the polaritonic ETL 804 comprises any suitable material, such asAlq3 (tris (8-hydroxyquinoline) aluminum), TPBi (2,2′,2″-(1,3,5-Benzinetriyl)-tris (1-phenyl-1-H-benzimidazole)), BCP (Bathocuproine or 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline), BPhen (Bathophenanthroline), TmPyPB (1,3,5-Tri (m-pyridin-3-ylphenyl)benzene), TAZ (3-(4-Biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole), PBD (2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), Bebq2 (Bis (10-hydroxybenzo[h]quinolinato) beryllium), BAlq (Aluminum (III) bis(2-methyl-8-quinolinato)-4-phenylphenolate), Liq (Lithium 8-hydroxyquinolinate), and/or Bepp2 (Bis (2-(2-hydroxyphenyl)pyridine) beryllium). In some embodiments, the polaritonic ETL 804 has a thickness of 0.1-100 nm, 1-50 nm, 50-100 nm, 5-25 nm, 25-50 nm, 50-75 nm, 75-100 nm, 1-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, 40-50 nm, 50-60 nm, 60-70 nm, 70-80 nm, 80-90 nm, 90-100 nm, or any other suitable thickness.

[0139] In some embodiments, the second electrode 805 comprises a cathode comprising Ag. In some embodiments, the second electrode 805 comprises Ag 120 nm/Al 3 nm/Liq 1.5 nm. In some embodiments, the second electrode 805 comprises any suitable materials, such as ITO, IZO, AZO, PEDOT: PSS, graphene, silver nanowires (AgNWs), carbon nanotubes, thin metal films (e.g., Ag, Au), NiO, Al, Mg: Ag, Ca, Ba, LiF/Al, CsF/AI, Ca/Al, Ba/Al, Ag, Au, and LiF/Al. In some embodiments, the second electrode 805 has a thickness of 0.1-100 nm, 1-50 nm, 50-100 nm, 5-25 nm, 25-50 nm, 50-75 nm, 75-100 nm, 1-10 nm, 10-20 nm, 20-30 nm, 30-40 nm, 40-50 nm, 50-60 nm, 60-70 nm, 70-80 nm, 80-90 nm, 90-100 nm, or any other suitable thickness.

[0140] In some embodiments, a method to produce a light emitting device 800 comprises depositing a polaritonic hole transport layer (HTL) 802 over a first electrode 801, depositing an organic phosphor-sensitized fluorescent emissive layer (EML) 803 over the polaritonic HTL 802, depositing a polaritonic electron transport layer (ETL) 804 over the EML 803, and depositing a second electrode 805 over the polaritonic ETL 804.

[0141] The blue phosphor, PtON-TBBI, was used as the donor, and the deep blue MR-type emitter, v-DABNA as the acceptor in a SiTrzCz2 and SiCzCz cohost EML matrix with a volume ratio of SiCzCz:SiTrzCz2:PtON-TBBi:vDABNA=42.8:49.7:7.0:0.5. The MR-molecule, v-DABNA, has a ΔE_ST=70 meV, a singlet lifetime of 4 ns and a TADF lifetime of τ_TADF=4.1 us. See FIG. 8C for the organic layer energy levels, and device structures, and FIG. 8D for molecular structural formulas and their International Union of Pure and Applied Chemistry names. The optical cavities shown in FIG. 8E are: (i) C, a conventional weak Al-ITO cavity whose Purcell effect is provided by the Al/BPyTP2 SPPs; (ii) H, Ag-ITO half cavity that has a single-sided Purcell effect induced by the Ag/BPyTP2 plexcitons, and (iii) F, full Ag-ITO/Ag/ITO cavity that has the double-sided Purcell effect, from both Ag/BPyTP2 cathode and Ag/BCFN anode plexcitons.

[0142] As shown in FIG. 9B, the PSF-OLED has an peak forward-viewing EQE=23.0±0.1%, increased from 15.3±0.3% of the PH-only device owing to the greater than 90% horizontal alignment of the v-DABNA exciton transition dipole moments. Half cavity H has a reduced outcoupling efficiency due to coupling to the polariton modes, leading to a lower peak EQE=16.2±0.1%. Although F has an enhanced double-sided coupling to the polaritons in both electrodes, it nevertheless recovers EQE=18.7±0.3% because of the balanced Fabry-Perot and the plexciton modes. Note that the metal/dielectric mirror full cavity

[0143] As reported in Zhao et al. (Nature 2024, 626, 300) a single-sided PEP-enhancement allowed for the full recovery of EQE due to balance between the far-field outcoupling (k_x/k₀<1) and the high-k_x/k₀ plexciton modes. Furthermore, in FIG. 9B inset shows a reduced EQE roll-off for H and F with a higher PF due to the reduced exciton density, and hence reduced probability for exciton annihilation. Comparing the EQE at 100 mA/cm² and 1 mA/cm², device C has a 35±2% reduction in EQE, while the PEP-enhanced cavities reduce the roll-off from 26±2% for H to 17±2% for F.

[0144] Aging of all devices is carried out at J=10 mA/cm², resulting in a 1.4- and 3.1-fold increase in device operational lifetime for PSF-OLEDs H and F, compared to C, as shown in FIG. 9C. In FIG. 9G, device F features a deep blue color with CIE_xy=(0.13, 0.09) due to both the increased PSF and stronger cavity. The sensitized emission of v-DABNA shifts CIE_xy to (0.14, 0.15) from (0.15, 0.20) of the PH-only device C with a conventional Al-ITO cavity. However, color saturation via sensitization alone is limited by the slow phosphor FRET process in device C, leading to residual PtON-TBBI, as shown in FIG. 9G inset. At an initial luminance of L₀=1590±30 cd/m², F has LT90=56.1±0.5 h compared to 17.8±0.3 h, and LT70=198±3 h to 63+1 h for C. Further, the voltage rise during aging shown in FIG. 9H is a function of the EML defect generation rate, following F<H<C. The power law, ΔV=At^k, is fit to the voltage rise to show the asymptotic behavior, where larger A and k indicate a steeper voltage rise, and hence an increased defect generation rate. From C to H, the constant A decreases from (2.0±0.1)×10⁻³ V to (1.5±0.1)×10⁻³ V. From C to F, k decreases from 1.02±0.01 to 0.90±0.01. Note that the PH-only device C has a slightly longer lifetime compared to the PSF-OLED C, indicating that there may exist additional degradation routes brought on by v-DABNA doping.

[0145] To understand the PEP effect on the transient energy transfer in the PSF-OLED, the TrEL response was measured for four, exciton-blocked 10 nm-thick EMLs placed at 10 nm intervals in half cavity devices, H1-H4, shown in FIG. 9E. A thin EML minimizes the delays due to exciton diffusion in thicker EMLs, which is also driven by energy transfer. The PEP-enhanced PF varies from 2.2 for horizontally aligned transition dipole moments (TDMs), to 7.0 for vertically aligned dipoles 20 nm from the cathode since vertically aligned dipoles efficiently couple Ag/BPyTP2 plexcitons to transverse magnetic modes. For v-DABNA that shows horizontal alignment in the host matrix, the PF is closer to its value for complete horizontal alignment, indicated by the dark-shaded histograms in FIG. 9E. For phosphors such as pseudo-octahedral Ir(III)-complexes and tetradentate Pt (II)-complexes, the average TDM falls between isotropic (⅔ horizontal+⅓ vertical) and the horizontal alignment, indicated by the light-shaded histograms. FIG. 9F shows the device operational lifetime for H1-H3 at J=10 mA/cm² (corresponding to L₀=1820+20 cd/m² for H1, H2, and 1500±30 cd/m² for H3). Again, the enhancement of the PSF-OLED stability at the same current density is consistent with the simulated PF in FIG. 9E.

[0146] FIG. 9D shows the TrEL for H1-H4 at J=20 mA/cm². Fits to a biexponential yield a decay lifetime that decreases from 1.12±0.01 μs to 0.61±0.01 μs for H1 and H4, respectively. However, after the initial decay, the time increases to 3 μs for all four devices. Fitting Eq. (1-3) to the transient data gives transfer rates of k_FRET=(1.0±0.1)×10⁵ s⁻¹ and k_DET=(0.8±0.1)×10⁵ s⁻¹.

[0147] The model fit in FIG. 91 (see Table 2 in FIG. 11B for parameters used) shows that the transient response is limited by the slow energy transfer and the decay of the v-DABNA triplets due a small k_isc,T/K_isc,S=0.2 μs⁻¹/23.2 μs⁻¹=8.7×10⁻³ from Kondo et al. (Nat. Photonics 2019, 13, 678). Because of its small ΔE_ST=70 meV, the slow ISC and energy transfer lead to a cross-over between PtON-TBBI and v-DABNA triplet densities after approximately 0.5-1.2 μs in both high- and low-PF devices, H4 and H1, leading to a deviation from the single exponential EL transient. The v-DABNA triplet decay is responsible for the long transient tails, even though the v-DABNA triplet density is lower than PtON-TBBI triplet density in steady state. The triplet density cross-over behavior limits the lifetime enhancement compared to the analogous PH-only OLED since the PEP effect only applies to radiative states. Nevertheless, the analysis shows the efficacy of the Purcell effect for reducing the triplet densities on both PtON-TBBI and v-DABNA in steady state.

[0148] Similar to the PH-only OLEDs, the PSF-OLED operational stability is closely tied to the steady-state triplet density, which is a result of slow energy transfer and incomplete triplet harvesting. To address these challenges, common strategies involve increasing the Förster transfer rate, k_FRET, suppressing Dexter transfer rate, k_DET and increasing k_isc,T/k_isc,S by reducing ΔE_ST. The triplet density in steady state depends on the rate of triplet-to-singlet energy transfer, which differs from pure phosphorescent or TADF systems where the triplet decay rate is the determining factor.

[0149] FIGS. 10A-10C show simulations of TrEL that illustrate the effect of reducing steady-state triplet density (i.e., the triplet density right before turn-off at t=0) by enhancing the PF, k_FRET, and k_ISC,T, assuming the natural exciton decay rates of PtON-TBBI and v-DABNA. FIG. 10A shows that increasing PF (cf. solid vs. dashed curves) is more efficient than increasing k_FRET (cf. red vs. green curves) in determining the steady-state triplet density and the transient response. This is because the triplet density reduction via increasing k_FRET saturates when the system is dominated by the non-radiative triplet lifetime on the fluorophore. Since FRET cannot shorten the fluorophore triplet lifetime, there is an asymptotic, lowest steady-state triplet density achievable by increasing FRET, comparable to applying an optical microcavity with a 5-fold increase in PF (cf. the green solid vs, the red dashed lines at t<0 in FIG. 10A). Similarly, in FIG. 10B, an asymptotic increase in the k_ISC,T (cf. red vs. green curves) eliminates the slow transient tail but fails to shorten the phosphor triplet lifetime that dominates the early EL transients. Therefore, the steady-state triplet density is scarcely reduced. Since increasing k_ISCc,T does not affect FRET, employing a fast TADF emitter is not as effective in reducing triplet density as increasing PF, as indicated by the green solid and red dashed lines. Only simultaneously increasing the k_FRET and k_isc,T alleviates constraints imposed by the slow phosphor decay and endothermic ISC of the fluorophore, reducing the triplet density via a five-fold increase in PF which is as effective as via a 10-fold increase in both k_FRET and k_isc,T. Moreover, increasing PF can be combined with an increase in k_FRET and k_isc,T to further minimize the triplet density, as shown by the green solid and red dashed curves in FIG. 10C.

[0150] For PSF-OLEDs, the slow FRET and phosphor emission rates limit both the device lifetime and quantum efficiency, where the former depends on the steady-state triplet density and the latter depends on the competition between FRET and DET. For TSF-OLEDs, the slow endothermic ISC rate, k_isc,T, of the donor TADF is the limiting factor. When using TADF emitters as sensitizer, the endothermic intersystem crossing k_ISC,T competes with the triplet non-radiative decay, enabling fluorescence from TADF singlet states. However, the maximum PEP enhancement of device stability is achieved when intermolecular and intramolecular triplet-to-singlet conversions are efficient in the sensitization process. Moreover, introducing narrow-emitting, horizontally aligned MR-type emitters improves the device color purity and EQE compared to the PH-only device, shown in FIGS. 9B and 9G. Therefore, the PSF-OLEDs with fast-mixed triplets and singlets can simultaneously enhance the device lifetime, EQE and color purity.

[0151] In conclusion, the enhanced lifetime of the phosphor-sensitized organic light-emitting devices (PSF-OLEDs) using the polariton-enhanced Purcell effect is shown. The studies are based on the PSF-OLED using the phosphor sensitizer, PtON-TBBI, and an MR-type fluorescent emitter, v-DABNA. From the weakest Al-ITO cavity to the strongest Ag-ITO/Ag/ITO full cavity that has double-sided PEP-enhanced Purcell effect, a 3.1-fold increase was observed in LT70 from 63+1 h to 197±3 h at J=10 mA cm⁻², or an initial luminance of 1590±30 cd/m² at a deep blue color of CIE_xy=(0.13, 0.09) for the full cavity device. This deep blue color is saturated by two steps: (i) sensitized v-DABNA emission that shifts the color of the PH-only device with CIE_xy=(0.15, 0.20) to CIE_xy=(0.14, 0.15), and (ii) use of a Fabry-Perot cavity to generate the plexcitons that further narrows the emission to CIE_xy=(0.13, 0.09). The transient electroluminescent (TrEL) behavior of the PSF-OLEDs that use thin EMLs was studied to map the spatially varying Purcell effect in half cavities, showing that the Purcell effect reduces the triplet densities residing on both sensitizing donor and acceptor molecules. The reduced triplet densities lead to decreasing the triplet annihilation probability, and thereby, the device degradation rate. Fitting to a rate equation model, the reduction of the total triplet density via the Purcell effect, Förster resonant energy transfer (FRET), Dexter energy transfer (DET) and intersystem crossing (ISC) processes were analyzed.

[0152] The results are general, in that PEPs benefit all devices (PHOLEDs, TADF emitters, PSF and TSF) whose emission is controlled by triplets. Moreover, the Purcell effect operates on both singlets and triplets, thereby affecting the equilibrium exciton populations in TADF emitters. This is the first demonstration of the Purcell effect enhancement on the PSF-OLED lifetime, paving for the intrinsically stable, efficient, deep blue devices for display and lighting technology.

[0153] The PH-only device organic structure for C, H and F is: BPyTP2 15 nm/SiTrzCz2 5 nm/SiCzCz: SiTrzCz2:PtON-TBBI (43:50:7 vol. %) 30 nm/SiCzCz 5 nm/BCFN 10 nm/HATCN 5 nm. PSF-OLEDs have the same device structure, but adding 0.5 vol. % v-DABNA to the EML comprising SiCzCz:SiTrzCz2: PtON-TBBI:v-DABNA (43:50:7:0.5 vol. %) 30 nm. The 10 nm-thin-EML devices have an organic structure of: BPyTP2 15+X nm/SiTrzCz2 5 nm/SiCzCz:SiTrzCz2:PtON-TBBI (43:50:7 vol. %) 0 nm/SiCzCz 5 nm/BCFN 20 nm/HATCN 10 nm, with X=0, 10, 20, 30 nm for H1-H4, respectively. The organic layers are deposited by thermal evaporation in a vacuum chamber with a base pressure less than 10⁻⁷ torr. Devices are grown on glass substrates with pre-patterned bottom electrodes that are solvent-cleaned, and ITO-only anodes are treated by UV-ozone plasma for 15 min prior to organic film deposition. For device C, the cathode is Al 120 nm/Liq (8-Hydroxyquinolinolato-lithium) 1.5 nm and the anode is 50 nm ITO. For device H, the cathode is Ag 120 nm/Al 3 nm/Liq 1.5 nm and the anode is 50 nm ITO. For device F, the cathode is Ag 120 nm/Al 3 nm/Liq 1.5 nm, and the anode is ITO 10 nm/TIN 3 nm/Ti 3 nm/Ag 16 nm/Ti 3 nm/ITO 40 nm. ITO-only anodes are wet-etched. ITO/Ag/ITO anodes are deposited via magnetron sputtering, with a N₂ partial pressure of 3 mTorr. Ag, Ti and TIN are deposited using a shadow mask and sandwiched between unpatterned ITO layers, followed by wet-etching in HCl:H2O 1:3 vol. ratio for 8 min to define the device area.

[0154] The cathodes are deposited by thermal evaporation at a base pressure less than 10⁻⁷ torr, using a thin metal shadow mask to define the 2.0±0.1 mm² device active area. Device active areas are measured using a microscope (Keyence VHX-S750E).

[0155] The EQE-J-V characteristics were measured using a parameter analyzer (B1500A, Keysight Technologies) and a calibrated large area photodiode (S3584-08, Hamamatsu Photonics) to collect emission in all forward-viewing angles and avoid angular dependence following standard procedures. The emission spectra were collected via an optical fiber (P400-5-UV-VIS, Ocean Optics, Inc.) positioned at the bottom surface of the substrate. The optical fiber was connected to a calibrated spectrometer (USB4000, Ocean Optics, Inc). For lifetime tests, PHOLEDs were operated at constant current (Agilent, U2722), and the luminance and voltage data were automatically collected (Agilent, 34972A). All devices were encapsulated using a glass cover slip sealed with UV-cured epoxy in the glovebox filled with an ultrapure N₂ atmosphere (<0.1 ppm O₂ and H₂O).

[0156] Devices were driven by a pulse generator (Agilent, 8114A) with response time of less than 5 ns and stabilized for at least 50 μs. The EL and TrPL signals were collected by a streak camera (C10910, Hamamatsu). The TrPL data were taken on fresh devices and bare EMLs on glass substrates. The pump laser (Thorlabs NPL41C) wavelength was 405 nm, with a repetition rate of 10 kHz and a pump energy less than 5nJ.

[0157] The ODOS and η_out and are simulated using the dyadic Green's function for planar structures. According to Fermi's golden rule, the triplet radiative decay rate is:

$\begin{array}{cc}{k}_r=\frac{2\pi }{\hslash }\sum _{h,\omega ,n}{❘{\hat{\mu }}_{\omega ,n}❘}^2{\rho }_n\left(x,\omega \right)& \left(4\right)\end{array}$

[0158] Here, {circumflex over (μ)}_ω,n is the triplet transition dipole moment matrix element at energy ω and dipole orientation n, is the reduced Planck's constant, and PF is the ratio of the local ODOS, ρ_n(x,ω) in the OLED cavity vs. ρ_0,n(x,ω) in EML medium that hosts the exciton. Then:

$\begin{array}{cc}PF\left(x,n,\omega \right)=\frac{{\rho }_n\left(x,\omega \right)}{{\rho }_{0,n}\left(x.\omega \right)}=\frac{n·\mathrm{IM}\left[G\left(x,x;\omega \right)\right]·n}{n·\mathrm{IM}\left[G_0\left(x,x;\omega \right)\right]·n}& \left(5\right)\end{array}$

[0159] where the dyadic Green's functions G (x, x; ω) in the planar OLED cavity and G₀(x, x; ω) in the medium vacuum are calculated from the multimode expansion G (k_x/k₀,ω) using the effective index k_x/k₀. η_out is the ODOS at forward-viewing angles normalized to the total ODOS, corresponding to 0<k_x/k₀<1. The PF_D is the average PF (x, n, w) over an isotropic distribution of n, while PF_A is the average PF (x, n, ω) over a 90% horizontal orientation based on the reported horizontal alignment of v-DABNA.

[0160] Further details can be found in Zhao et al. (Adv. Mater. 37, no. 35 (2025): 37), which is incorporated herein by reference in its entirety.

[0161] It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting.

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[0195] The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention.