Deep HOMO (highest occupied molecular orbital) emitter device structures

Abstract

Embodiments of the disclosed subject matter provide an organic light emitting diode (OLED) having an anode, a cathode, an emissive layer disposed between the anode and the cathode, and a hole blocking layer disposed between the emissive and the cathode. The emissive layer may include a phosphorescent dopant, where the phosphorescent dopant has an emission in 0.5% doped PMMA (Poly(methyl methacrylate)) thin film with a peak maximum wavelength that is greater than or equal to 600 nm at room temperature. The energy of a highest occupied molecular orbital (HOMO) of the phosphorescent dopant may be lower than or equal to −5.1 eV, and the energy of the HOMO of the hole blocking layer is at least 0.1 eV lower than the energy of the HOMO of the phosphorescent dopant.

Claims

1. An organic light emitting diode (OLED) comprising: an anode; a cathode; an emissive layer disposed between the anode and the cathode; and a hole blocking layer disposed between the emissive layer and the cathode, wherein the emissive layer comprises a phosphorescent dopant, wherein the phosphorescent dopant has an emission with a peak maximum wavelength greater than or equal to 600 nm when measured at room temperature in 0.5% doped PMMA (Poly(methyl methacrylate)) thin film, wherein the energy of a highest occupied molecular orbital (HOMO) of the phosphorescent dopant is lower than or equal to −5.1 eV, and wherein the energy of the HOMO of the hole blocking layer is at least 0.1 eV lower than the energy of the HOMO of the phosphorescent dopant.

2. The OLED of claim 1, wherein the peak maximum wavelength of the phosphorescent dopant is selected from the group consisting of: greater than or equal to 610 nm, greater than or equal to 620 nm, greater than or equal to 630 nm, greater than or equal to 650 nm, greater than or equal to 700 nm, greater than or equal to 750 nm, and greater than or equal to 800 nm.

3. The OLED of claim 1, wherein the energy of the HOMO of the phosphorescent dopant is selected from the group consisting of: lower than or equal to −5.2 eV, lower than or equal to −5.3 eV, and lower than or equal to −5.4 eV.

4. The OLED of claim 1, wherein the energy of the HOMO of the hole blocking layer is selected from the group consisting of: at least 0.2 eV lower than the energy of the HOMO of the phosphorescent dopant, at least 0.3 eV lower than the energy of the HOMO of the phosphorescent dopant, and at least 0.4 eV lower than the energy of the HOMO of the phosphorescent dopant.

5. The OLED of claim 1, wherein the hole blocking layer comprises a compound of Formula I, which is at least one selected from the group consisting of: ##STR00106## wherein R.sup.1 and R.sup.2 each independently represent mono to the maximum allowable substitution, or no substitution, wherein each R.sup.1 and R.sup.2 is independently a hydrogen or a substituent selected from the group consisting of: deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, wherein Y is selected from the group consisting of: O, S, Se, NAr.sup.4, CAr.sup.4Ar.sup.5, SiAr.sup.4Ar.sup.5, Fluorene (C-Ar.sup.1Ar.sup.2), and Silicon (Si-Ar.sup.1Ar.sup.2), and wherein Ar.sup.1 and Ar.sup.2 are the same or different aryl groups, wherein each Ar.sup.1-Ar.sup.5 is independently selected from the group consisting of: aryl, heteroaryl, and a combination thereof, and wherein L is a direct bond or a linker comprising at least one aromatic ring.

6. The OLED of claim 5, wherein each R.sup.1 and R.sup.2 is independently a hydrogen or a substituent selected from the group consisting of: aryl, heteroaryl, and combinations thereof.

7. The OLED of claim 5, wherein Y is selected from the group consisting of O, S, and NAr.sup.4.

8. The OLED of claim 5, wherein the compound of Formula I is at least one selected from the group consisting of: ##STR00107## ##STR00108## ##STR00109## ##STR00110## ##STR00111## ##STR00112## ##STR00113## ##STR00114## ##STR00115## ##STR00116## ##STR00117## ##STR00118## ##STR00119## ##STR00120## ##STR00121## ##STR00122## ##STR00123## ##STR00124## ##STR00125## ##STR00126## ##STR00127## ##STR00128## ##STR00129## ##STR00130## ##STR00131## ##STR00132## ##STR00133## ##STR00134## ##STR00135## ##STR00136## ##STR00137## ##STR00138## ##STR00139## ##STR00140##

9. The OLED of claim 1, wherein the phosphorescent dopant is a metal coordination complex having a metal-carbon bond.

10. The OLED of claim 9, wherein the metal is selected from the group consisting of: Ir, Os, Pt, Pd, Ag, Au, and Cu.

11. The OLED of claim 9, wherein the metal coordination complex comprises a ligand comprising a chemical moiety selected from the group consisting of: pyridazine, pyrimidine, pyrazine, and triazine.

12. The OLED of claim 9, wherein the metal coordination complex has the formula of M(L.sup.1).sub.x(L.sup.2).sub.y(L.sup.3).sub.z, wherein L.sup.1, L.sup.2 and L.sup.3 can be the same or different, wherein x is 1, 2, or 3, wherein y is 0, 1, or 2, wherein z is 0, 1, or 2, wherein x+y+z is the oxidation state of the metal M, wherein L.sup.1, L.sup.2 and L.sup.3 are each independently selected from the group consisting of: ##STR00141## ##STR00142## wherein L.sup.2 and L.sup.3 can also be ##STR00143## wherein each Y.sup.1 to Y.sup.13 are independently selected from the group consisting of carbon and nitrogen, wherein Y′ is selected from the group consisting of BR.sub.e, NR.sub.e, PR.sub.e, O, S, Se, C═O, S═O, SO.sub.2, CR.sub.eR.sub.f, SiR.sub.eR.sub.f, and GeR.sub.eR.sub.f; wherein R.sub.e and R.sub.f are optionally fused or joined to form a ring, wherein each R.sub.a, R.sub.b, R.sub.c, and R.sub.d may independently represent from mono substitution to the maximum possible number of substitution, or no substitution, wherein each R.sub.a, R.sub.b, R.sub.c, R.sub.d, R.sub.e and R.sub.f is independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, and wherein any two adjacent substituents of R.sub.a, R.sub.b, R.sub.c, and R.sub.d are optionally fused or joined to form a ring or form a multidentate ligand.

13. The OLED of claim 12, wherein the metal coordination complex has a formula selected from the group consisting of: Ir(L.sub.A).sub.3, Ir(L.sub.A)(L.sub.B).sub.2, Ir(L.sub.A).sub.2(L.sub.B), Ir(L.sub.A).sub.2(L.sub.C), and Ir(L.sub.A)(L.sub.B)(L.sub.C); wherein L.sub.A, L.sub.B, and L.sub.C are different from each other.

14. The OLED of claim 12, wherein the metal coordination complex has a formula of Pt(L.sub.A)(L.sub.B), wherein L.sub.A, and L.sub.B can be same or different, and wherein L.sub.A, and L.sub.B are optionally connected to form a tetradentate ligand.

15. The OLED of claim 13, wherein the metal coordination complex has a formula of Ir(L.sub.A).sub.2(L.sub.C), wherein L.sub.A is selected from the group consisting of: ##STR00144## wherein L.sub.C is ##STR00145## and wherein each R.sup.A, and R.sup.B may independently represent from mono substitution to the maximum possible number of substitution, or no substitution, wherein each R.sup.A, and R.sup.B is independently selected from the group consisting of: hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, and wherein any two adjacent substituents of R.sup.A, and R.sup.B are optionally fused or joined to form a ring or form a multidentate ligand.

16. The OLED of claim 15, wherein the metal coordination complex is at least one selected from the group consisting of: ##STR00146## ##STR00147## ##STR00148## ##STR00149## ##STR00150## ##STR00151## ##STR00152## ##STR00153##

17. The OLED of claim 14, wherein the metal coordination complex is a Pt complex having a tetradentate ligand.

18. The OLED of claim 17, wherein the tetradentate ligand has four coordination atoms selected from the group consisting of: (two anionic C, two neutral N); (one anionic C, one carbene C, one neutral N, and one anionic N); (two anionic C, one carbene C, one neutral N); (one anionic C, one anionic N, two neutral N); (one anionic C, one anionic O, two neutral N); and (two carbene C, two anionic N).

19. The OLED of claim 1, wherein the electron blocking layer comprises a compound of Formula II: ##STR00154## wherein R.sup.3, R.sup.4, and R.sup.5 each independently represent mono to the maximum allowable substitution, or no substitution, wherein each R.sup.3, R.sup.4, and R.sup.5 is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, and wherein each Ar.sup.5 and Ar.sup.6 is independently selected from the group consisting of aryl, heteroaryl, and combination thereof.

20. A consumer product including an organic light emitting device (OLED) comprising: an anode; a cathode; an emissive layer disposed between the anode and the cathode; and a hole blocking layer disposed between the emissive layer and the cathode, wherein the emissive layer comprises a phosphorescent dopant, wherein the phosphorescent dopant has an emission with a peak maximum wavelength greater than or equal to 600 nm when measured at room temperature in 0.5% doped PMMA (Poly(methyl methacrylate)) thin film, wherein the energy of a highest occupied molecular orbital (HOMO) of the phosphorescent dopant is lower than or equal to −5.1 eV, and wherein the energy of the HOMO of the hole blocking layer is at least 0.1 eV lower than the energy of the HOMO of the phosphorescent dopant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an organic light emitting device.

(2) FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

(3) FIG. 3 shows an example device structure according to an embodiment of the disclosed subject matter.

(4) FIG. 4 shows example materials used in OLED (organic light emitting diode) devices according to embodiments of the disclosed subject matter.

(5) FIG. 5 shows an example PHOLED (phosphorescent organic light emitting diode) structure energy levels according to an embodiment of the disclosed subject matter.

(6) FIG. 6 shows a graph of external quantum efficiency (EQE) vs. current density for devices with RD1 and RD2 emitters according to embodiments of the disclosed subject matter.

(7) FIG. 7 shows device materials according to embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

(8) 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.

(9) The initial OLEDs used emissive molecules that emitted light from their singlet states (“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.

(10) 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.

(11) 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.

(12) 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 F.sub.4-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. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

(13) 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.

(14) 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.

(15) 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.

(16) 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. 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. 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, which 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 initial light emitted by the emissive layer.

(17) Unless otherwise specified, any of the layers of the various embodiments may be 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 processability 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.

(18) 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 consists essentially of polymeric silicon and inorganic silicon.

(19) 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 flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, laser printers, telephones, mobile phones, tablets, phablets, personal digital assistants (PDAs), wearable devices, laptop computers, digital cameras, camcorders, viewfinders, micro-displays (displays that are less than 2 inches diagonal), 3-D displays, virtual reality or augmented reality displays, vehicles, video walls comprising multiple displays tiled together, 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.

(20) 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.

(21) Embodiments of the disclosed subject matter may provide an organic light emitting diode (OLED) having an anode, a cathode, an emissive layer disposed between the anode and the cathode, and a hole blocking layer disposed between the emissive and the cathode. The emissive layer may include a phosphorescent dopant. The phosphorescent dopant may have an emission in 0.5% doped PMMA (Poly(methyl methacrylate)) thin film with a peak maximum wavelength that is greater than or equal to 600 nm at room temperature. The energy of a highest occupied molecular orbital (HOMO) of the phosphorescent dopant may be lower than or equal to −5.1 eV, and the energy of the HOMO of the hole blocking layer may be at least 0.1 eV lower than the energy of the HOMO of the phosphorescent dopant. In some embodiments, the OLED may have the hole blocking layer disposed on the emissive layer.

(22) The peak maximum wavelength of the phosphorescent dopant may be greater than or equal to 610 nm, greater than or equal to 620 nm, greater than or equal to 630 nm, greater than or equal to 650 nm, greater than or equal to 700 nm, greater than or equal to 750 nm, or greater than or equal to 800 nm.

(23) The energy of the HOMO of the phosphorescent dopant may be lower than or equal to −5.2 eV, lower than or equal to −5.3 eV, or lower than or equal to −5.4 eV. The energy of the HOMO of the hole blocking layer may be at least 0.2 eV lower than the energy of the HOMO of the phosphorescent dopant, at least 0.3 eV lower than the energy of the HOMO of the phosphorescent dopant, or at least 0.4 eV lower than the energy of the HOMO of the phosphorescent dopant.

(24) The hole blocking layer may include the compound of Formula I, which may be one or more of:

(25) ##STR00020##
R.sup.1 and R.sup.2 each may independently represent mono to the maximum allowable substitution, or no substitution. Each R.sup.1 and R.sup.2 may be independently a hydrogen or deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and/or combinations thereof. Y may be O, S, Se, NAr.sup.4, CAr.sup.4Ar.sup.5, SiAr.sup.4Ar.sup.5, Fluorene (C—Ar.sup.1Ar.sup.2), and/or Silicon (Si—Ar.sup.1Ar.sup.2), where Ar.sup.1 and Ar.sup.2 may be the same or different aryl groups. Each Ar.sup.1-Ar.sup.5 may be independently selected from aryl, heteroaryl, and/or a combination thereof, and L may be a direct bond or a linker comprising at least one aromatic ring. Each R.sup.1 and R.sup.2 may be independently a hydrogen or a substituent such as aryl, heteroaryl, and/or combinations thereof. Y may be O, S, and/or NAr.sup.4. In some embodiments, the compound of Formula I may be the only compound in the hole blocking layer.

(26) The compound of Formula I may be one or more of:

(27) ##STR00021##

(28) In some embodiments, the compound of Formula I may be one or more of:

(29) ##STR00022## ##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028## ##STR00029## ##STR00030## ##STR00031## ##STR00032## ##STR00033## ##STR00034## ##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045## ##STR00046## ##STR00047## ##STR00048## ##STR00049## ##STR00050## ##STR00051## ##STR00052## ##STR00053## ##STR00054## ##STR00055## ##STR00056## ##STR00057## ##STR00058## ##STR00059## ##STR00060## ##STR00061## ##STR00062## ##STR00063## ##STR00064## ##STR00065## ##STR00066##

(30) The phosphorescent dopant may emit light from a triplet excited state to a ground singlet state in the device at room temperature. The phosphorescent dopant may be a metal coordination complex having a metal-carbon bond. The metal may be Ir, Os, Pt, Pd, Ag, Au, or Cu. The metal coordination complex may include a ligand having a chemical moiety of pyridazine, pyrimidine, pyrazine, and/or triazine. The metal coordination complex may have the formula of M(L.sup.1).sub.x(L.sup.2).sub.y(L.sup.3).sub.z, where L.sup.1, L.sup.2 and L.sup.3 may be the same or different, where x is 1, 2, or 3, where y is 0, 1, or 2, where z is 0, 1, or 2, where x+y+z is the oxidation state of the metal M, where L.sup.1, L.sup.2 and L.sup.3 may each independently selected from:

(31) ##STR00067## ##STR00068## ##STR00069## ##STR00070##
where L.sup.2 and L.sup.3 can also be

(32) ##STR00071##
where each Y.sup.1 to Y.sup.13 are independently selected from carbon and nitrogen, where Y′ may be at least one of BR.sub.e, NR.sub.e, PR.sub.e, O, S, Se, C═O, S═O, SO.sub.2, CR.sub.eR.sub.f, SiR.sub.eR.sub.f, and GeR.sub.eR.sub.f, where R.sub.e and R.sub.f may be optionally fused or joined to form a ring, where each R.sub.a, R.sub.b, R.sub.c, and R.sub.d may independently represent from mono substitution to the maximum possible number of substitution, or no substitution, where each R.sub.a, R.sub.b, R.sub.c, R.sub.d, R.sub.e and R.sub.f is independently selected from hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, and where any two adjacent substituents of R.sub.a, R.sub.b, R.sub.c, and R.sub.d are optionally fused or joined to form a ring or form a multidentate ligand.

(33) The metal coordination complex may have the formula of Ir(L.sub.A).sub.3, Ir(L.sub.A)(L.sub.B).sub.2, Ir(L.sub.A).sub.2(L.sub.B), Ir(L.sub.A).sub.2(L.sub.C), or Ir(L.sub.A)(L.sub.B)(L.sub.C), where L.sub.A, L.sub.B, and L.sub.C are different from each other. The metal coordination complex may have a formula of Pt(L.sub.A)(L.sub.B), where L.sub.A, and L.sub.B can be same or different, and where L.sub.A, and L.sub.B may be optionally connected to form a tetradentate ligand.

(34) The metal coordination complex may have a formula of Ir(L.sub.A).sub.2(L.sub.C), where L.sub.A is selected from:

(35) ##STR00072## ##STR00073##
where L.sub.C is

(36) ##STR00074##
and where each R.sup.A, and R.sup.B may independently represent from mono substitution to the maximum possible number of substitution, or no substitution. Each R.sup.A, and R.sup.B may be independently selected from: hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. Any two adjacent substituents of R.sup.A, and R.sup.B may be optionally fused or joined to form a ring or form a multidentate ligand.

(37) In some embodiments, the metal coordination complex may be selected from:

(38) ##STR00075## ##STR00076## ##STR00077## ##STR00078## ##STR00079## ##STR00080## ##STR00081## ##STR00082## ##STR00083##

(39) The metal coordination complex may be a Pt complex having a tetradentate ligand. The tetradentate ligand may have four coordination atoms selected from: (two anionic C, two neutral N); (one anionic C, one carbene C, one neutral N, and one anionic N); (two anionic C, one carbene C, one neutral N); (one anionic C, one anionic N, two neutral N); (one anionic C, one anionic O, two neutral N); (two carbene C, two anionic N.

(40) The electron blocking layer may include the compound of Formula II:

(41) ##STR00084##
where R.sup.3, R.sup.4, and R.sup.5 may each independently represent mono to the maximum allowable substitution, or no substitution, where each R.sup.3, R.sup.4, and R.sup.5 may be independently a hydrogen or a substituent selected from deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and/or combinations thereof, and where each Ar.sup.5 and Ar.sup.6 may be independently selected from aryl, heteroaryl, and/or combination thereof. Each R.sup.3, R.sup.4, and R.sup.5 may independently be a hydrogen or a substituent selected from aryl, heteroaryl, and/or combination thereof.

(42) The electron blocking layer may include a compound selected from:

(43) ##STR00085## ##STR00086## ##STR00087## ##STR00088## ##STR00089##

(44) In some embodiments, the OLED has one or more characteristics selected from the group consisting of 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 comprising carbon nanotubes.

(45) In some embodiments, the OLED further comprises a layer comprising 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.

(46) In some embodiments of the emissive region, the emissive region further comprises a host.

(47) In some embodiments, the compound 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.

(48) 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.

(49) 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.

(50) Combination with Other Materials

(51) 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.

(52) 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.

(53) Conductivity Dopants:

(54) 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.

(55) HIL/HTL:

(56) 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.

(57) EBL:

(58) 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.

(59) Host:

(60) 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.

(61) HBL:

(62) 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.

(63) ETL:

(64) 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.

(65) Charge Generation Layer (CGL)

(66) 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.

EXPERIMENTAL

(67) Deep HOMO emitters may be PHOLED (phosphorescent organic light emitting diode) emitters with narrow spectrum, high LE/EQE (luminous efficacy/external quantum efficiency) ratio, long lifetime, and an EQE value above a predetermined amount. For example, the narrow spectrum of the deep HOMO emitters may have full width at half maximum (FHWM) values of less than 50 nm, less than 45 nm, less than 40 nm, or the like. Due to narrow electroluminescent (EL) spectrum, the amount of photon emitting in invisible range over 670 nm may be minimized compared to conventional broad red emitters, and thus less photons losses may occur. Most of the emitted photons may be in the visible range, which may provide for higher luminance efficiency at the same EQE for the narrow EL emitters.

(68) Many narrow EL emitters may have deeper HOMO levels (e.g., ˜−5.3 eV) when compared to the HOMO levels for broad emitters (e.g., ˜−5.1 eV). This may cause different behavior of the emitter in the device. Embodiments of the disclosed subject matter may provide a different approach for the efficient device structure architecture for deep HOMO emitters, such as for deep HOMO red emitters.

(69) Many families of deep HOMO emitters may have desirable PHOLED performance with narrow spectrum, high LE/EQE ratio, long lifetime, and potentially very high EQE. Due to narrow EL spectrum, the amount of photon emitting in invisible range over 670 nm may be minimized, compared to conventional broad red emitters and thus less photons losses occur. Most of the emitted photons may be in the visible range, so as to provide higher luminance efficiency at the same EQE for the narrow EL emitters.

(70) Many narrow EL emitters may have deeper HOMO level (e.g., ˜5.3 eV) when compared to the HOMO level for broad emitters (e.g., ˜5.1 eV). This may cause different behavior of the emitter in the device, and different device structure architecture for deep HOMO emitters may be used.

(71) In addition to narrow red emitters, there may be families of green emitters with desired performance and deep HOMO (e.g., >5.2 eV), and similar device structure architectures may be used.

(72) Embodiments of the disclosed subject matter provide designs for an efficient device structure for deep HOMO emitters. There may be differences in the device properties between the emitters RD1 and RD2 in the same device structure (e.g., as shown in FIG. 6 and Table 2). The differences may be attributed to a recombination zone (RZ) location in the EML. A hole blocking layer (HBL) may affect the efficiency of deep HOMO RD1 emitter device, whereas an electron blocking layer (EBL) may not affect efficiency (e.g., as shown in examples 1, 2, 3, 4 of Table 2). For the emitter RD2, there may be no difference in device efficiency due to HBL, but there may be differences due to EBL (see, e.g., examples 5, 6, 7, 8 of Table 2).

(73) The RD1 device may have a recombination zone close to the HBL side of EML (emissive layer). The HBL may improve RD1 device efficiency by preventing exciton quenching and electron leakage to the ETL (electron transport layer). For the same reason, the RD2 device may have a recombination zone (RZ) close to the EBL, and the EBL may improve device efficiency by prevention of exciton quenching and hole leakage to the HTL (hole transport layer). Deep HOMO RD1 may provide improved hole transport to the HBL side of EML, as there may be less hole trapping. In contrast, the reference shallow HOMO RD2 may not provide enough hole transport through the EML, as there may be more hole trapping. The RZ may be localized so as to be in the proximity of EBL.

(74) Embodiments of the disclosed subject matter may provide for the combination of the deep HOMO emitter and HBL to provide improved device efficiency. Efficiency roll off with luminance increase may be a problem for phosphorescent devices, and reduction of efficiency roll-off may be important in order to provide increased device efficiency at higher luminances. EQE roll off may be calculated as ratio of EQE at 10 mA/cm.sup.2 to EQE of 1 ma/cm.sup.2 for the same device (see, e.g., last column in Table 2). Data in Table 2 and FIG. 6 shows that HBL may provide efficiency roll-off reduction for the RD1 deep HOMO emitter (see, e.g., Example 1 vs. Example 2 and Example 3 vs. Example 4 in Table 2) and may have no or minimal roll off effect on a device with an RD2 emitter (see, e.g., Example 6 vs. Example 5 and Example 7 vs. Example 8 in Table 2).

(75) All example devices were fabricated by high vacuum (<10.sup.−7 Torr) thermal evaporation. The anode electrode was 1,150 Å of indium tin oxide (ITO). The cathode was comprised of 10 Å of Liq (8-hydroxyquinoline lithium) followed by 1,000 Å of A1. All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H.sub.2O and O.sub.2) immediately after fabrication, and a moisture getter was incorporated inside the package. The organic stack of the device examples sequentially included, from the ITO surface, 100 Å of HAT-CN (Hexaazatriphenylenehexacarbonitrile) as the hole injection layer (HIL); 400 or 450 Å of HTM (hole transport material) as a hole transporting layer (HTL); 50 Å of EBM (electron blocking material) (if any) as an electron blocking layer (EBL); 400 Å of an emissive layer (EML) containing from red host H1 and 3% of RD1 or RD2 red emitters, 50 Å of HBM as hole blocking layer (HBL) (if any) and 300 (with HBL) or 350 Å (no HBL) of Liq (8-hydroxyquinoline lithium) doped with 35% of ETM as the ETL.

(76) FIG. 3 shows a device structure according to an embodiments of the disclosed subject matter. The device may include a cathode, an electron ejection layer (EIL), an electron transport layer (ETL), an optional a hole blocking layer (HBL), an emissive layer (EML), an optional electron blocking layer (EBL), a hole transport layer (HTL) a hole injection layer (HIL), and an anode.

(77) When not including the using EBL, the HTL thickness was 50 Å thicker, and when the HBL is not includes, the ETL thickness was 50 Å thicker, so total device thickness remained the same to prevent possible device performance distortion due to different layer thicknesses.

(78) Table 1 shows the device layer thickness and materials. The chemical structures of the device materials are shown in FIG. 4.

(79) TABLE-US-00001 TABLE 1 Device layer materials and thicknesses Layer Material Thickness [Å] Anode ITO 1,150 HIL HAT-CN 100 HTL HTM 400-450 EBL EBM 50 (if any) EML Host: RD 3% 400 HBL HBM 50 (if any) ETL Liq: ETM 35% 300-350 EIL Liq 10 Cathode Al 1000

(80) Upon fabrication, the devices have been EL and JVL (current density, voltage, luminance) tested. The device performance data are summarized in Table 2.

(81) TABLE-US-00002 TABLE 2 Device structures and performance of the device examples with various red emitters and blocking layers. At 1 mA/cm.sup.2 At 10 mA/cm.sup.2 EQE roll-off Device Emitter 1931 CIE Voltage LE EQE Voltage LE EQE 10/1 Example EBL Host 3% HBL x y [v] [cd/A] [%] [v] [cd/A] [%] mA/cm.sup.2 Example 1 EBM Host 1 RD1 HBM 0.686 0.313 2.9 23.5 24.7 3.8 20.8 21.8 0.89 Example 2 EBM Host 1 RD1 0.686 0.313 2.8 21.6 22.7 3.7 18.0 18.9 0.83 Example 3 Host 1 RD1 HBM 0.686 0.313 2.9 23.4 24.6 3.8 20.7 21.7 0.88 Example 4 Host 1 RD1 0.686 0.313 2.8 21.7 22.7 3.7 17.9 18.8 0.83 Example 5 EBM Host 1 RD2 HBM 0.683 0.316 3.1 23.2 27.1 4.3 21.0 24.5 0.90 Example 6 EBM Host 1 RD2 0.683 0.316 3.0 23.2 27.0 4.1 21.0 24.4 0.90 Example 7 Host 1 RD2 HBM 0.683 0.317 3.0 22.5 26.1 4.2 20.0 23.2 0.89 Example 8 Host 1 RD2 0.682 0.317 2.9 22.7 26.3 4.1 20.1 23.2 0.88

(82) To understand the device performance, HOMO-LUMO and T1 energy levels of the materials have been used. Energy Levels were determined by solution cyclic voltammetry and differential pulsed voltammetry. Measurements were performed using a CH Instruments model 6201B potentiostat using anhydrous dimethylformamide solvent and tetrabutylammonium hexafluorophosphate as the supporting electrolyte. Glassy carbon, and platinum and silver wires were used as the working, counter and reference electrodes, respectively. Electrochemical potentials were referenced to an internal ferrocene-ferroceniumredox couple (Fc/Fc+) by measuring the peak potential differences from differential pulsed voltammetry. The corresponding highest occupied molecular orbital (HOMO) energy and the lowest unoccupied molecular orbital (LUMO) energy were determined by referencing the cationic and anionic redox potentials to ferrocene (4.8 eV vs. vacuum). That is:
HOMO=−(CV ox)−4.8 (eV)
LUMO=−(CV red)−4.8 (eV)

(83) To determine the T1 level, less than 1 mg of material was dissolved by ultrasonication in 2 mL of 2-methyltetrahydrofuran solvent. The solution was filtered through a 2 micron filter into a quartz tube. The tube was sealed with a rubber septum and bubble degassed with nitrogen in order to prevent oxygen quenching. The phosphorescence spectrum was carried out on a Horiba Jobin Yvon Fluorolog-3 system equipped with a xenon lamp at low temperature close to 77 K. The T1 is determined using PL at 77K. That is:
T1 (eV)=1240/triplet wavelength [nm]

(84) HOMO-LUMO and T1 levels are listed in Table 3 below, and FIG. 5 shows the HOMO-LUMO levels of a device materials according to embodiments of the disclosed subject matter.

(85) TABLE-US-00003 Energy levels and T1 for the materials used in the device examples HOMO LUMO Material [eV] [eV] T1 [nm] ITO 4.70 HAT-CN 9.70 4.20 HTM 5.16 1.85 523 EBM 5.38 1.84 452 Host 1 5.43 2.88 516 RD1 5.32 2.81 614 RD2 5.05 2.49 606 HBM 5.96 2.74 484 ETM 5.64 2.71 706 Host 2 5.96 2.74 484 Host 3 5.11 2.37 536 HBL 1 5.90 2.90 569 HBL 2 5.64 2.73 454 HBL 3 5.70 2.47 420

(86) The calculated energy levels for HBM are shown below, and may have similarities to compound H:

(87) ##STR00090##

(88) TABLE-US-00004 DFT (Density Functional Theory) Ti 421 S1 370 Gap 3.804 HOMO −5.795 LUMO −1.991

(89) There may be differences in the device properties between emitter RD1 and RD2 in the same device structure (see, e.g., FIG. 6 and Table 2), and may be based on the recombination zone (RZ) location in the EML. The HBL may affect the efficiency of deep HOMO RD1 emitter device, whereas the EBL may not affect efficiency (see, e.g., Examples 1, 2, 3, 4 in Table 2).

(90) In contrast, with reference emitter RD2, there may be no difference in device efficiency due to HBL, but there may be a difference due to EBL (see, e.g., examples 5, 6, 7, 8 shown in Table 2). The RD1 device may have a recombination zone close to the HBL side of EML, and the HBL may improve RD1 device efficiency by preventing exciton quenching and electron leakage to the ETL. When the RD2 device may have recombination zone RZ close to EBL, and the EBL may improve device efficiency by prevention of exciton quenching and hole leakage to the HTL.

(91) Deep HOMO RD1 may exhibit less hole trapping and/or improved hole transport, which may provide a higher exciton population near the cathode side of the EML. In contrast, reference shallow HOMO RD2 may hole trap more strongly and/or hole transport less through the EML, which may provide a RZ localized in the proximity of EBL. In embodiments of the disclosed subject matter, the combination of deep HOMO emitter and HBL may provide the desired device efficiency.

(92) Efficiency roll off with luminance increase may be a problem for phosphorescent devices. Reduction of efficiency roll-off may provide a higher device efficiency at a higher luminance. EQE roll off was calculated as ratio of EQE at 10 mA/cm.sup.2 to EQE of 1 mA/cm.sup.2 for the same device (see, e.g., the last column in the Table 2). Data in Table 2 and FIG. 6 show that HBL provides efficiency roll-off reduction for the RD1 deep HOMO emitter (see, e.g., Example 1 vs. Example 2 and Example 3 vs. Example 4 in Table 2) and has no or minimal roll off effect on device with RD2 emitter (see, e.g., Example 6 vs. Example 5 and Example 7 vs. Example 8 shown in Table 2).

(93) The hole transporting layer (HTM) may have good hole transporting properties (e.g., HOMO 5.16 eV). The electron blocking layer (EBL) may have a shallow LUMO level (e.g., 1.84 eV) to prevent electron leakage to HTL and high T1 energy (e.g., 452 nm) enough to prevent any exciton leakage from EML into HTL and reasonable hole transporting properties (e.g., HOMO 5.38 eV).

(94) In embodiments of the disclosed subject matter, EBL T1 may be higher than T1 of the emitter. Host (Host 1) may provide electron transport through the EML (e.g., LUMO 2.88 eV), as well as hole transport (e.g., HOMO 5.43 eV), in the absence of emitters with shallower HOMO levels. Embodiments of the disclosed subject matter may include one or more hosts (e.g., single host dual host, or the like).

(95) Shallow HOMO emitters e.g., RD2-(HOMO 5.05 eV), may provide more hole trap and deep HOMO emitters e.g. RD1 (HOMO 5.32 eV) may provide more hole transport through the EML. This may shift the recombination zone in the EML depending on the emitter. In case with deep HOMO emitters, the recombination zone may be shifted toward HBL. The HBL effect on the device efficiency may be more pronounced with RD1 deep HOMO emitter. RD2 may provide more hole trapping, resulting in less hole transport through the EML, so RZ may be shifted toward the EBL interface. The EBL may affect the efficiency of the RD2 emitter device.

(96) The HOMO for deep HOMO emitters may be in the range of 5.1-5.6 eV, more preferable 5.15-5.55 eV, even more preferable 5.2-5.5 eV.

(97) Hole trapping may be a function of the emitter-host HOMO energy gap. The HBL for emitter-host energy gap may be less than 0.15 eV. The hole blocking material (HBM) may have a deep HOMO (5.96 eV), which may block holes from leaking into ETL, and may have high T1 energy (e.g., 484 nm) to prevent exciton leakage into ETL. In embodiments of the disclosed subject matter, the HBL may have a HOMO level deeper than 5.5 eV.

(98) The ETM may provide electron transport through the ETL toward the EML (e.g., LUMO 2.71 eV).

(99) The combination of the deep HOMO emitter R1 and the HBL in the devices and/or structures of the disclosed subject matter may provide increased efficiency, minimal efficiency roll off, and increased power efficiency.

(100) Embodiments of the disclosed subject matter may provide the following types of red emitters with deep HOMO:

(101) ##STR00091##

(102) Embodiments of the disclosed subject matter may provide deep HOMO red ligand structures for emissive ligand:

(103) ##STR00092## ##STR00093##
CF3 containing ancillary ligand may provide deeper HOMO:

(104) ##STR00094##
The above may be combined with one or more other emissive ligands to shift the HOMO by 0.1 to 0.15 eV (or more, there are a plurality of CF3 groups).

(105) In some embodiments, the OLED may include at least one emitter selected from the group of emitters shown below.

(106) ##STR00095## ##STR00096## ##STR00097## ##STR00098## ##STR00099## ##STR00100## ##STR00101## ##STR00102## ##STR00103## ##STR00104## ##STR00105##

(107) Additional device data was obtained to show the blocking layer material and hosts classes of the compounds that may provide improvement of the performance of deep HOMO red emitter devices with a blocking layer. Two hosts, single Host 1 and dual Host 2:Host 3 (4:1), and three blocking layer materials (e.g., HBL1, HBL2, HBL3) were used in the devices with deep HOMO emitter RD1 and shallow HOMO emitter RD2. Both emitters have approximately same color saturation, but different type of energy levels.

(108) The device fabrication is the same as described above, and FIG. 7 shows device materials according to embodiments of the disclosed subject matter.

(109) Experimental data are summarized below in Table 4, which shows the correlation of the device EQE and the blocking layer in the device.

(110) TABLE-US-00005 TABLE 4 Device performance of additional experiments. HBL effect on EQE of deep HOMO red emitter structures. EQE at Device Emitter 1931 CIE 10 mA/cm.sup.2 Example EBL Host 3% HBL x y [%] Example 9 EBM Host 1 RD1 HBL1 0.685 0.315 20.1 Example 10 EBM Host 1 RD1 HBL2 0.685 0.315 20.1 Example 11 EBM Host 1 RD1 HBL3 0.684 0.315 19.5 Example 12 EBM Host 1 RD1 0.685 0.314 18.2 Example 13 EBM Host 2: Host 3 (4:1) RD1 HBL1 0.674 0.325 23.7 Example 14 EBM Host 2: Host 3 (4:1) RD1 HBL2 0.673 0.326 24.3 Example 15 EBM Host 2: Host 3 (4:1) RD1 HBL3 0.673 0.326 24.1 Example 16 EBM Host 2: Host 3 (4:1) RD1 0.674 0.325 22.2 Example 17 EBM Host 1 RD2 HBL1 0.683 0.316 24.0 Example 18 EBM Host 1 RD2 HBL2 0.683 0.316 23.5 Example 19 EBM Host 1 RD2 HBL3 0.683 0.316 24.1 Example 20 EBM Host 1 RD2 0.683 0.316 24.0 Example 21 EBM Host 2: Host 3 (4:1) RD2 HBL1 0.671 0.328 24.8 Example 22 EBM Host 2: Host 3 (4:1) RD2 HBL2 0.672 0.327 25.4 Example 23 EBM Host 2: Host 3 (4:1) RD2 HBL3 0.672 0.327 25.2 Example 24 EBM Host 2: Host 3 (4:1) RD2 0.669 0.330 24.9

(111) The EQE of the devices with deep HOMO RD1 emitter may be affected by a BL (blocking layer), which may be about 10% higher, versus the EQE of a device without a BL. For a single host, as shown in examples 9, 10, and 11, the EQE with the blocking layer structures may be about 20%. In contrast, Example 12 shows that reference structure without a BL may have an EQE about 18%.

(112) Dual host devices with the RD1 deep HOMO emitter may be similarly affected by the BL. In examples 13, 14, and 15, the BL structures have an EQE about 24%. In example 16, devices with no BL structures may have an EQE-22%.

(113) The EQE of the device with the RD2 shallow HOMO emitter may not be affected by HBL. In single host examples 17, 18, and 19, BL devices may have similar EQE to the EQE of devices without the BL (e.g., Example 20, where the EQE is about 24%). The EQE of the dual host devices including BL, such as in examples 21, 22, and 23, may be similar to the EQE of the devices without the BL of Example 24 (e.g., about 25%).

(114) Different classes of BL materials may be used with the HOMO emitters. Examples BL1, BL2, BL3, and/or HBM may belong to the following classes of the materials: Aluminum Quinoline complexes, Aza-dibenzothiopene derivatives, Indolo[2,3-a] carbazole derivatives, 4,6-disubstituted Dibenzothiophenes. These different classes may work as BL materials for deep HOMO red emitter PHOLED devices.

(115) The energy levels of additional hosts and blocking layers are shown above in Table 3. Table 3 shows the energy levels of all the materials used in the device examples.

(116) 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.