ORGANIC ELECTROLUMINESCENT MATERIALS AND DEVICES

The present disclosure provides for an organic electroluminescent device (OLED) including an anode; a cathode; and an emissive layer, disposed between the anode and the cathode. The emissive layer includes a phosphorescent dopant, a first host, and a second host, wherein the first host transports holes, the second host transports electrons, and the first host is fully or partially deuterated. Consumer products that include the OLED are also provided.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for various 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.

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.

SUMMARY

In one aspect, the present disclosure provides an OLED comprising an anode; a cathode; and an emissive layer, disposed between the anode and the cathode. The emissive layer comprises a phosphorescent dopant, a first host, and a second host, wherein the first host transports holes, the second host transports electrons, and the first host is fully or partially deuterated.

In yet another aspect, the present disclosure provides a consumer product comprising an OLED as described herein.

DETAILED DESCRIPTION

The term “ester” refers to a substituted oxycarbonyl (—O—C(O)—Rsor —C(O)—O—Rs) radical.

The term “ether” refers to an —ORsradical.

The term “selenyl” refers to a —SeRsradical.

The term “sulfinyl” refers to a —S(O)—Rsradical.

The term “sulfonyl” refers to a —SO2—Rsradical.

The term “phosphino” refers to a —P(Rs)3radical, wherein each Rscan be same or different.

The term “silyl” refers to a —Si(Rs)3radical, wherein each Rscan be same or different.

The term “germyl” refers to a —Ge(Rs)3radical, wherein each Rscan be same or different.

The term “boryl” refers to a —B(Rs)2radical or its Lewis adduct —B(Rs)3radical, wherein Rscan be same or different.

The term “alkenyl” refers to and includes both straight and branched chain alkene radicals. Alkenyl groups are essentially alkyl groups that include at least one carbon-carbon double bond in the alkyl chain. Cycloalkenyl groups are essentially cycloalkyl groups that include at least one carbon-carbon double bond in the cycloalkyl ring. The term “heteroalkenyl” as used herein refers to an alkenyl radical having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si, and Se, preferably, O, S, or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl, cycloalkenyl, or heteroalkenyl group may be optionally substituted.

The term “alkynyl” refers to and includes both straight and branched chain alkyne radicals. Alkynyl groups are essentially alkyl groups that include at least one carbon-carbon triple bond in the alkyl chain. Preferred alkynyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group may be optionally substituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer to an alkyl group that is substituted with an aryl group. Additionally, the aralkyl group may be optionally substituted.

The term “heterocyclic group” refers to and includes aromatic and non-aromatic cyclic radicals containing at least one heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si, and Se, preferably, O, S, or N. Hetero-aromatic cyclic radicals may be used interchangeably with heteroaryl. Preferred hetero-non-aromatic cyclic groups are those containing 3 to 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers, such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and the like. Additionally, the heterocyclic group may be optionally substituted.

In some instances, the more preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy, aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinations thereof.

In yet other instances, the most preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, aryl, heteroaryl, and combinations thereof.

The terms “substituted” and “substitution” refer to a substituent other than H that is bonded to the relevant position, e.g., a carbon or nitrogen. For example, when R1represents mono-substitution, then one R1must be other than H (i.e., a substitution). Similarly, when R1represents di-substitution, then two of R1must be other than H. Similarly, when R1represents zero or no substitution, R1, for example, can be a hydrogen for available valencies of ring atoms, as in carbon atoms for benzene and the nitrogen atom in pyrrole, or simply represents nothing for ring atoms with fully filled valencies, e.g., the nitrogen atom in pyridine. The maximum number of substitutions possible in a ring structure will depend on the total number of available valencies in the ring atoms.

In some instance, a pair of adjacent substituents can be optionally joined or fused into a ring. The preferred ring is a five, six, or seven-membered carbocyclic or heterocyclic ring, includes both instances where the portion of the ring formed by the pair of substituents is saturated and where the portion of the ring formed by the pair of substituents is unsaturated. As used herein, “adjacent” means that the two substituents involved can be on the same ring next to each other, or on two neighboring rings having the two closest available substitutable positions, such as 2, 2′ positions in a biphenyl, or 1, 8 position in a naphthalene, as long as they can form a stable fused ring system.

B. The OLEDs and the Devices of the Present Disclosure

In one aspect, the present disclosure is drawn to an OLED that comprises an anode; a cathode; and an emissive layer, disposed between the anode and the cathode where the emissive layer comprises a phosphorescent dopant, a first host, and a second host, wherein the first host transports holes, the second host transports electrons, and the first host is fully or partially deuterated.

In some embodiments of the inventive OLED, at least one of the following conditions is true:

(i) the second host does not comprise a carbazole or an indolocarbazole;

(ii) the second host has a HOMO level <−5.75 eV;

(iii) the second host has a HOMO level >−5.5 eV and is at least 25% deuterated;

(iv) the second host comprises biscarbazole or indolocarbazole moiety that is at least 60% deuterated;

(v) the first host comprises a hole transporting moiety that is at least 50% deuterated and the second host comprises an electron transporting moiety that is at least 50% deuterated; and

(vi) the lifetime (measured as LT95) of the inventive OLED is at least 75% higher than the lifetime (LT95) of a comparative OLED where the only difference between the inventive OLED and the comparative OLED is that the first host in the comparative OLED is not deuterated.

The HOMO levels referenced herein can be measured by solution cyclic voltammetry and differential pulsed voltammetry performed using a potentiostat (e.g., CH Instruments model 6201B) using anhydrous dimethylformamide solvent and tetrabutylammonium hexafluorophosphate as the supporting electrolyte. Glassy carbon, platinum, and silver wires can be used as the working, counter, and reference electrodes, respectively. Electrochemical potentials can be referenced to an internal ferrocene-ferroconium redox couple (Fc/Fc+) by measuring the peak potential differences from differential pulsed voltammetry. The corresponding HOMO and LUMO energies can be determined by referencing the cationic and anionic redox potentials to ferrocene (4.8 eV vs. vacuum) according to literature ((a) Fink, R.; Heischkel, Y.; Thelakkat, M.; Schmidt, H.-W.Chem. Mater.1998, 10, 3620-3625. (b) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler, H.; Porsch, M.; Daub,J. Adv. Mater.1995, 7, 551.

The lifetime measurements (LT95) of OLEDs referenced herein are the time to reduction of luminance of the OLEDs to 95% of the initial luminance at a constant current density of 80 mA/cm2.

In some embodiments, the first host comprises a carbazole or indolocarbazole moiety.

In some embodiments, the first host comprises at least one moiety selected from the group consisting of naphthalene, biphenyl, triphenylene, dibenzothiophene, dibenzofuran, silyl, boryl, phenanthrene, phenanthridine, arylamine, and fluorene.

In some embodiments, the first host is at least 10% deuterated. In some embodiments, the first host is at least 25% deuterated. In some embodiments, the first host is at least 50% deuterated. In some embodiments, the first host is >75% deuterated. In some embodiments, the first host is >90% deuterated.

In some embodiments, the second host does not comprise a carbazole or an indolocarbazole.

In some embodiments, the second host has a HOMO level <−5.75 eV.

In some embodiments, the second host has a HOMO level >−5.5 eV and is at least 25% deuterated.

In some embodiments, the second host comprises a biscarbazole or indolocarbazole moiety that is at least 60% deuterated.

In some embodiments, the first host comprises a hole transporting moiety that is at least 50% deuterated and the second host comprises an electron transporting moiety that is at least 50% deuterated.

In some embodiments, the hole transporting moiety of the first host is selected from the group consisting of the structures of the following LIST 1:

each of RAto RWrepresents mono, up to the maximum number of allowable substitutions, or no substitution;

any two adjacent of R, R′, and RAto RWcan be joined or fused to form a ring; and

In some embodiments, the electron transporting moiety of the second host is selected from the group consisting of the structures of the following LIST 2:

each of X1to X22is independently C or N;

at least one of X1to X3is N;

at least one of X4to X11is N;

each of RR′to RZ′and RAAto RAKrepresents mono, up to the maximum number of allowable substitutions, or no substitution;

any two adjacent R, R′, RR′to RZ′, or RAAto RAKcan be joined or fused to form a ring; and

In some embodiments, the second host is not deuterated.

In some embodiments, the first host comprises at least one deuterated fused moiety selected from the group consisting of carbazole, biscarbazole, and indolocarbazole, and the at least one deuterated fused moiety is at least 50% deuterated. In some embodiments, the at least one deuterated fused moiety is at least 70% deuterated. In some embodiments, the at least one deuterated fused moiety is at least 90% deuterated.

In some embodiments, the device has an EQE at 10 mA/cm2greater than 25%.

In some embodiments, the device has a voltage at 10 mA/cm2less than 4.5V.

In some embodiments, the device has a LT95 at 1000 nits that is greater than 30,000 hours.

In some embodiments, the first host has a HOMO level greater than −5.75 eV.

In some embodiments, the second host has a HOMO level less than −5.75 eV, and the first host has a HOMO greater than −5.6 eV. In some embodiments, the second host has a HOMO level less than −5.45 eV, and the first host has a HOMO greater than −5.3 eV.

In some embodiments, the second host has a HOMO level less than −5.75 eV, and the first host has a HOMO less than −5.8 eV but greater than −5.75 eV. In some embodiments, the second host has a HOMO level less than −5.9 eV, and the first host has a HOMO less than −5.95 eV but greater than −5.9 eV.

In some embodiments, the first host is selected from the group consisting of the structures in the following LIST 3:

each of X1to X11is independently C or N;

L′ is a direct bond or an organic linker;

each of RA′, RB′, RC′, RD′, RE′, RF′, and RG′independently represents mono, up to the maximum substitutions, or no substitutions;

two adjacent of RA′, RB′, RC′, RD′, RE′, RF′, and RG′are optionally joined or fused to form a ring; and

In some embodiments, the first host is selected from the group consisting of the structures of the following LIST 4:

YZis selected from the group consisting of O, S, and N-phenyl; and

the first host is at least partially deuterated.

In some embodiments where the first host is one of the structures of LIST 4, at least 50% of the hydrogen atoms are replaced with deuterium. In some embodiments where the first host is one of the structures of LIST 4, at least 70% of the hydrogen atoms are replaced with deuterium. In some embodiments where the first host is one of the structures of LIST 4, at least 90% of the hydrogen atoms are replaced with deuterium.

In some embodiments, the first host is selected from the group consisting of the structures of the following LIST 5:

In some embodiments, the second host is selected from the group consisting of the structures of the following LIST 6:

each of X1to X11is independently C or N;

L′ is a direct bond or an organic linker;

each of RA′, RB′, RC′, RD′, RE′, RF′, and RG′independently represents mono-, up to the maximum number of allowable substitutions, or no substitution;

any two adjacent of RA′, RB′, RC′, RD′, RE′, RF′, and RG′can be joined or fused to form a ring.

In some embodiments, the second host is selected from the group consisting of the structures of the following LIST 7:

In some embodiments, the phosphorescent dopant has a formula of M(LA)p(LB)q(LC)rwherein LBand LCare each a bidentate ligand; and wherein p is 1, 2, or 3; q is 0, 1, or 2; r is 0, 1, or 2; and p+q+r is the oxidation state of the metal M.

In some embodiments, the phosphorescent dopant has a formula selected from the group consisting of Ir(LA)3, Ir(LA)(LB)2, Ir(LA)2(LB), Ir(LA)2(LC), and Ir(LA)(LB)(LC); and wherein LA, LB, and LCare different from each other.

In some embodiments, LBis a substituted or unsubstituted phenylpyridine, and LCis a substituted or unsubstituted acetylacetonate.

In some embodiments, the phosphorescent dopant has a formula of Pt(LA)(LB); and LAand LBcan be same or different. In some such embodiments, LAand LBare connected to form a tetradentate ligand.

In some embodiments, the phosphorescent dopant is a transition metal complex having at least one ligand or part of the ligand, if the ligand is more than bidentate, selected from the group consisting of the structures of following LIST 8:

two adjacent substituents of Ra, Rb, Rc, and Rdcan be fused or joined to form a ring or form a multidentate ligand.

In some embodiments, the phosphorescent dopant is selected from the group consisting of the structures of the following LIST 9:

wherein

each of X96to X99is independently C or N;

each Y is independently selected from the group consisting of a NR, O, S, and Se;

each of R10, R20, R30, R40, and R50independently represents mono, up to the maximum number of allowed substitutions, or no substitution;

In some embodiments, the phosphorescent dopant is selected from the group consisting of the structures of the following LIST 10:

In some embodiments, the phosphorescent dopant is selected from the group consisting of the structures of the following LIST 11:

each Y is independently selected from the group consisting of a NR, O, S, and Se;

each X and X′ is independently selected from the group consisting of O, S, Se, NR″, and CR″R′″;

each R, R′, R″, R′″, RA″, RB″, RC″, RD″, RE″, and RF″independently represents mono, up to the maximum number of allowed substitutions, or no substitution;

In some embodiments, the phosphorescent dopant is selected from the group consisting of the structures of the following LIST 12:

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, wherein 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.

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.

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.

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.

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 wherein the metal is selected from the group consisting 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. 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.

In another aspect, the inventive OLED of the present disclosure can include an emissive region containing an emissive layer that comprises a phosphorescent dopant, a first host, and a second host, wherein the first host transports holes, the second host transports electrons, and the first host is fully or partially deuterated.

In another aspect, the present disclosure also provides a consumer product that comprises an inventive OLED of the present disclosure, where the inventive OLED includes an emissive layer that comprises a phosphorescent dopant, a first host, and a second host, wherein the first host transports holes, the second host transports electrons, and the first host is fully or partially deuterated.

In some embodiments, the consumer product can be one of a flat panel 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 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, a video wall comprising multiple displays tiled together, a theater or stadium screen, a light therapy device, and a sign.

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.

In one aspect, (Y101—Y102) is a 2-phenylpyridine derivative. In another aspect, (Y101—Y102) is a carbene ligand. In another aspect, Met is selected from Ir, Pt, Os, and Zn. In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc*/Fc couple less than about 0.6 V.

wherein k is an integer from 1 to 20; L101is another ligand, k′ is an integer from 1 to 3.

Electron transport layer (ETHL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ET 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.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated. The minimum amount of hydrogen of the compound being deuterated is selected from the group consisting of 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, and 100%. Thus, any specifically listed substituent, such as, without limitation, methyl, phenyl, pyridyl, etc. may be undeuterated, partially deuterated, and fully deuterated versions thereof. Similarly, classes of substituents such as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. also may be undeuterated, partially deuterated, and fully deuterated versions thereof.

EXPERIMENTAL SECTION

All experimental devices tested were fabricated by high vacuum (<10-7 Torr) thermal evaporation (VTE). The anode electrode was 800 Å of indium tin oxide (ITO). The cathode consisted of 10 Å of LiQ followed by 1000 Å of Al. All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H2O and O2) immediately after fabrication, and a moisture getter was incorporated inside the package.

The organic stack of the device examples consisted of sequentially, from the ITO surface, 100 Å of HATCN as the hole injection layer (HIL), 400 Å of hole transport material HTM as the hole transport layer (HTL), 50 Å of EBL as an electron blocking layer (EBL), 400 Å of the first host doped with 30 wt % of a second host and 10 wt % emitter (see table) as the emissive layer (EML), 50 Å of the second host as a blocking layer (BL), and 300 Å of 35% ETM in LiQ as the electron transport layer (ETL). As used herein, HATCN, HTM, ETM, EBL, H1, H2, DH1, DH2, GD1, GD2, GD3, and GD4 have the following structures:

DH1 and DH2 were synthesized by subjecting H1 and H2, respectively, to H/D exchange conditions as described by WO2011053334A1. The inventive devices, Example 1 through Example 8, were fabricated with deuterated first host DH1 according to the present disclosure. The comparative devices, Comparison 1 through Comparison 8, were fabricated with the non-deuterated first host H1. The measured lifetime (LT95) for Example 1-8 and Comparison 1-8 are reported in Table 1 below where LT95is the time to reduction of brightness to 95% of the initial luminance at a constant current density of 80 mA/cm2. LT95reported for Comparison 1, Comparison 2, Example 1, and Example 2 are normalized relative to the LT95for Comparison 1. LT95reported for Comparison 3, Comparison 4, Example 3, and Example 4 are normalized relative to the LT95for Comparison 3. LT95reported for Comparison 5, Comparison 6, Example 5, and Example 6 are normalized relative to the LT95for Comparison 5. LT95reported for Comparison 7, Comparison 8, Example 7, and Example 8 are normalized relative to the LT95for Comparison 7.

The above data shows that the inventive device Examples 1-2 each exhibited a substantially higher lifetime than the comparative devices Comparison 1 and Comparison 2. The 100%-130% lifetime enhancement is beyond any value that could be attributed to experimental error and the observed improvement is statistically significant. Furthermore, enhancement from deuteration of the first host is greater than 90% larger than the enhancement from deuteration of the second host in Comparison 2. Based on the fact that the devices have the same structure with the only difference being the deuteration of the first host, the significant performance improvement observed in the above data was unexpected. Similarly, the inventive devices Examples 3-8 each exhibited 50-120% longer lifetimes than their respective comparative devices Comparison 3-8. This is in contrast to Comparison 4, Comparison 6, and Comparison 8 in which deuteration of the second host gave significantly smaller enhancement compared to the non-deuterated host system. Without being bound by any theories, this improvement may be attributed to the suppression of intermolecular decomposition reactions between deuterated hosts and dopants involving hosts in their cationic state.