KR100928236B1 - White light-emitting organic light emitting device in which radiation from monomers and aggregates is mixed - Google Patents

Abstract

The present invention relates to an effective organic light emitting device (OLED). More particularly, the present invention relates to white light emitting OLEDs or WOLEDs. The device of the present invention fully covers the visible light spectrum using two emitters in a single emission region. White light radiation is achieved through the formation of an aggregate by one of the radiation centers from two emitters in a single radiation region. This makes it possible to construct a WOLED that exhibits a simple, bright and efficient high color rendering index.

Description

WHITE LIGHT EMITTING OLEDS FROM COMBINED MONOMER AND AGGREGATE EMISSION}

The present invention relates to an efficient organic light emitting device (OLED). More specifically, the present invention relates to white light emitting OLEDs or WOLEDs. The device of the present invention uses two emitters in a single emissive region to cover the visible light region sufficiently. White radiation is obtained from two emitters in a single radiation region through the formation of an aggregate by one of the radiation centers. This makes it possible to construct a simple, bright and efficient WOLED that exhibits a high rendering index.

Organic light emitting devices (OLEDs) use thin film materials that emit light when excited by electrical current, and are expected to be a popular type of flat panel display technology. This is because OLEDs can be applied to various fields including mobile phones, PDAs, computer displays, vehicle information displays, television monitors, and general lighting sources. Due to its bright color, wide viewing angle, compatibility with full-motion video, wide temperature range, thin and conformable molding factors, low power, and low cost manufacturing processes, OLED leads the $ 40 billion annually electronic display market. Existing cathode ray tube (CRT) and liquid crystal display (LCD) are expected to be replaced in the future. Because of the high brightness efficiency, it seems that field phosphor OLEDs can replace incandescent and even fluorescent lamps.

Devices having structures based on the use of organic optoelectronic layers generally rely on conventional mechanisms for causing optical radiation. Typically, this mechanism is based on the radioactive recombination of the captured charge.

Specifically, the OLED is composed of at least two thin film organic layers between an anode and a cathode. One of these layers, the material of the "hole transport layer" (HTL), is selected based on the ability of the material to transport holes, and the other layer, the material of the "electron transport layer" (ETL), of the material that transports electrons. It is chosen according to the ability. With such a configuration, the device can be considered as a diode having a forward bias when a voltage higher than the voltage applied to the cathode is applied to the anode. Under these bias conditions, the anode injects holes (positive charge carriers) into the HTL, while the cathode injects electrons into the ETL. The portion of the light emitting medium adjacent to the anode thus forms a hole injection and transport region, while the portion of the light emitting medium adjacent to the cathode forms an electron injection and transport region. The injected holes and electrons move to oppositely charged electrodes. Frenkel excitons are formed when electrons and holes are placed on the same molecule. These excitons are trapped in the material with the lowest HOMO-LUMO energy gap. Recombination of short-lived excitons can be developed as electrons falling from the lowest occupied molecular orbital (LUMO) to the highest occupied molecular orbital (HOMO) under certain conditions, preferably by a photoelectron emission mechanism.

Materials that function as the ETL or HTL of OLEDs also act as a medium in which exciton formation and electroluminescent emission occur. Such OLEDs are referred to as having "single heterostructure" (SH). Optionally, the electroluminescent material may be present as a separate emissive layer between the HTL and the ETL in what is referred to as the "dual heterostructure" (DH).

In a single heterostructure OLED, holes are injected from the HTL into the ETL that combines with the electrons to form the excitons, or electrons are injected from the ETL into the HTL that combines with the holes to form the excitons. The exciton is trapped in the material with the lowest energy gap, and since the commonly used ETL material generally has less energy than the commonly used HTL material, the emission layer of a single heterostructure device is typically an ETL. In such OLEDs, the materials used for the ETL and HTL should be chosen so that holes can be efficiently injected from the HTL to the ETL. It is also believed that the best OLEDs have a good energy level alignment between the HOMO levels of the HTL material and the ETL material.

In dual heterostructure OLEDs, holes are injected from the HTL and electrons are injected from the ETL into separate emitting layers where holes and electrons combine to form excitons.

Light emission from OLEDs is typically by fluorescence, but OLED light emission by phosphorescence has recently been demonstrated. The term "phosphorescence" as used herein denotes emission from triplet excited states of organic molecules, and the term "fluorescence" refers to emission from singlet excited states of organic molecules. The term luminescence refers to either or both of fluorescent and phosphorescent radiation.

Successful use of phosphorescent light has enormous prospects for organic electroluminescent devices. For example, the advantage of phosphorescence is that all potential excitons formed by recombination of holes and electrons can participate in luminescence as singlet or triplet excited states. This is because the lowest singlet excited state of the organic molecules is typically slightly higher in energy than the lowest triplet excited state. For example, in a typical phosphorescent organometallic compound, the lowest singlet excited state can collapse rapidly to the lowest triplet excited state, so that phosphorescence is produced. In contrast, in a fluorescent device only a small percentage (about 25%) of excitons can produce fluorescence resulting from a singlet excited state. The remaining excitons in the fluorescent apparatus are produced at the lowest triplet excited state and typically do not convert to the higher singlet excited state where fluorescence is produced. This energy is thus lost to the decay process of heating the device rather than emitting visible light.

Typically, phosphorescence emission from organic molecules is less common than fluorescence emission. However, phosphorescence can be observed from organic molecules under an appropriate set of conditions. Organic molecules coordinated to the lanthanum element often emit from an excited state disposed on the lanthanum metal. Such radioactive emissions are not from triplet excited states. In addition, it is not expected that such emissions will yield efficiencies high enough to be practical in the expected OLED field. Europium diketonate composites show one group of this type.

Organophosphorescence can be observed in molecules containing heteroatoms with lone pairs of electrons, but typically only at very low temperatures. Benzophenone and 2,2'-bipyridine are such molecules. Phosphorescence can be enhanced beyond fluorescence at room temperature by confining organic molecules, preferably through bonding, in close proximity to atoms of high atomic number. This phenomenon, called the heavy atom effect, is caused by a mechanism known as spin-orbit coupling. A related phosphorescent transition is metal-to-ligand charge transfer (MLCT) observed in molecules such as tris (2-phenylpyridine) iridium (III).

The realization of highly efficient blue, green and red field phosphors is required in the field of full color displays with low power consumption. Recently, high-efficiency green and red organic field phosphors, which acquire both single- and triplet excitons and have an internal quantum efficiency (η _inside ) close to 100%, have been demonstrated. Baldo, MA, O'Brien, DF, You, Y., Shoustikov, A., Sibley, S., Thompson, ME, and Forrest, SR, Nature (London), 395, 151-154 (1998); Baldo, MA, Lamansky, S., Burrows, PE, Thompson, ME, and Forrest, SR, Appl. Phys. Lett., 75, 4-6 (1999); Adachi, C., Baldo, MA, and Forrest, SR, App. Phys. Lett. , 77,904-906, (2000); Adachi, C., Lamansky, S., Baldo, MA, Kwong, RC, Thompson, ME, and Forrest, SR, App. Phys. Lett. , 78, 1622-1624 (2001); Adachi, C., Baldo, MA, Thompson, ME, and Forrest, SR, Bull. Am. Phys. Soc. , 46,863 (2001). Using the green phosphor, fac tris (2-phenylpyridine) iridium (Ir (ppy) ₃ ), an external quantum efficiency (η _external ) of (17.6 ± 0.5)%, in particular, corresponds to an internal quantum efficiency of> 85%. It was realized using a wide energy gap host material, 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole (TAZ). Adachi, C., Baldo, MA, Thompson, ME, and Forrest, SR, Bull. Am. Phys. Soc. , 46,863 (2001). More recently, high efficiency (η _outside = (7.0 ± 0.5)%) red field phosphor bis (2- (2'-benzo [4,5-a] trienyl) pyridinato-N, C ³ ) It was demonstrated using iridium (acetylacetone) [Btp ₂ Ir (acac)]. Adachi, C., Lamansky, S., Baldo, MA, Kwong, RC, Thompson, ME, and Forrest, SR, App. Phys. Lett. , 78,1622-1624 (2001).

In each of these latter cases, high efficiency is obtained by energy transfer from both host singlet and triplet states to phosphor triplet states or by direct capture of charge on the phosphor, thereby resulting in 100% excited state. Is obtained until. This is a significant improvement over what can be expected using fluorescence in small molecule or polymeric organic light emitting devices. Baldo, M. A., O'Brien, D. F., Thompson, M. E., and Forrest, S. R., Phys. Rev., B 60, 14422-14428 (1999); Friend, RH, GYMER, RW, Holmes, AB, Burroughes, JH, Marks, RN, Taliani, C., Bradley, DDC, Dos Santos, DA, Bredas, JL, Logdlund, M., Salaneck, WR, Nature (London ), 397, 121-128 (1999); See Cao, Y, Parker, I. D., Yu, G., Zhang, C., and Heeger, A. J., Nature (London), 397, 414-417 (1999). In either case, this transfer involves a resonance, exothermic process. As the triplet energy of the phosphor increases, it is less likely to find a suitable host with a moderately high energy triplet state. Baldo, M. A., and Forrest, S. R., Phys. Rev. See B 62, 10958-10966 (2000). The required very large exciton energy of the host suggests that the host material may not have the proper energy level alignment with other materials used in the OLED structure, thus leading to further efficiency reduction. In order to eliminate competition between the conductivity and energy transfer properties of the host, the route to efficient blue field phosphorescence can include transferring exothermic energy from the nearby resonance excited state of the host to the high triplet energy of the phosphor. Baldo, M. A., and Forrest, S. R., Phys. Rev. B 62, 10958-10966 (2000); Ford, W. E., Rodgers, M. A. J., J. Phys. Chem., 96,2917-2920 (1992); HARRIMAN, A., Hissler, M., Khatyr, A., Ziessel, R., Chem. See Commun., 735-736 (1999). This process can be very efficient if the energy required for delivery is not greater than thermal energy.

The quality of the white light source can be fully explained by a simple set of parameters. The color of the light source is given by its CIE chromaticity coordinates x and y. CIE coordinates are typically represented by this dimensional plot. The monochromatic color corresponds to the perimeter boundary of the horseshoe type starting from blue on the lower left side and proceeding through the color spectrum clockwise to the red on the lower right side. The CIE coordinates and spectral shape of the light source of a given energy fall within the area of the curve. The sum of the light at all wavelengths gives a uniform white or neutral point and is found at the center of the diagram (CIE x, y-coordinate, 0.33, 0.33). Mixing light from two or more light sources provides light with color represented by the intensity weighted average of the CIE coordinates of the independent light sources. Thus mixing of light from two or more light sources can be used to generate white light. Although two-component and three-component white light sources look the same to the viewer (CIE x, y coordinates, 0.32, 0.32), they are not the same light source. When these white light sources are used for illumination, the CIE color rendering index (CRI) needs to be considered along with the CIE coordinates of the light sources. CRI provides an index indicating how well the light source will represent the color of the illuminated object. The perfect match of a given light source to a standard illuminator is CRI 100. Although a CRI value of at least 70 is acceptable in some applications, more preferred white light sources will have a CRI of about 80 or more.

The most successful approach used to generate the previously described white OLEDs is to separate three different emitters (luminescent dopants) into separate layers. Three emission centers need to achieve good color rendering index (CRI) values because the lines are not enough to cover the entire visible spectrum with fewer than three emitters. One approach to designing WOLEDs is to separate individual dopants into separate layers. In such a device the emission zone thus consists of a separate emitting layer. Kido, J. et. al. Science, 267, 1332-1334 (1995). The design of such a device can be complicated because careful control of the thickness and composition of each layer is essential to achieving good color balance. Separating the emitter into separate layers is essential to prevent energy transfer between the red, blue, and green emitters. The problem is that the highest energy emitters (blues) efficiently deliver their excitons to the red and green emitters. The efficiency of this energy transfer process is described by the Forster energy transfer equation. If the blue emitter has good spectral overlap with the spectral absorption of the red or green emitter, and the oscillator intensity is high for all transitions, the energy transfer process will be efficient. These energy transfers can occur at distances greater than 30 mW. Green emitters will also readily transfer their excitons to red emitters. As a result, the red emitter dominates the spectral composition if these three are doped into the film at the same concentration. The exciton migration distance of the fluorescent dye is relatively short, and the balance between the three emission colors can be controlled by varying the dopant ratio (more blue is needed than green, and more green is red to achieve the same intensity in all three colors). More needed). If the concentration of the dopant is kept low, the average length between the dopants can be kept lower than the Forster energy transfer length, and the influence of the energy transfer can be minimized. Having all three dyes in a single layer comprises a four component film, with each dopant present in less than 1%. The production of such films is very difficult to carry out in practice. Any shift in dopant ratio will seriously affect the color quality of the device.

The situation for phosphorescent emitters is quite different. The Forster radius of the phosphorescent dopant may be lower than the fluorescent dopant, and the exciton diffusion distance may be greater than 1000 kHz. In order to obtain a high efficiency field phosphor device, the phosphorescent material generally needs to be present at a higher concentration than the fluorescent dopant (typically 6% or more). The end result is that when the phosphorescent materials are mixed together in a single layer, serious energy transfer problems are observed as in fluorescent emitters. Conventional approaches to successfully separating separate fluorescent materials into separate layers are used to eliminate energy transfer problems.

Summary of the Invention

The present invention relates to an efficient organic light emitting device (OLED). More specifically, the present invention relates to white light emitting OLEDs or WOLEDs. The device of the present invention uses two luminescent emitters or lumophores in a single emission region to cover the visible light spectrum sufficiently. Lumopores emit either by fluorescence (from a singlet excited state) or by phosphorescence (from a triplet excited state). White radiation is obtained from two luminescent emitters in a single radiation region through the formation of an aggregate by one of the lipomores. Two radiation centers (aggregate emitter and monomer emitter) are doped in a single emitting layer. This makes it possible to construct a simple, bright and efficient WOLED exhibiting a high color rendering index.

It is therefore an object of the present invention to produce white light emitting OLEDs that exhibit high external emissivity (η _external ) and luminance.

Another object of the present invention is to produce a white light emitting OLED exhibiting a high color rendering index.

Another object of the invention is to produce a white light emitting organic light emitting device which produces white light having a CIE x, y-chromatic coordinate approaching (0.33, 0.33).

Still another object of the present invention is to provide an OLED that can be widely used as an efficient light source in the field of diffuse lighting, which is currently ubiquitous with a conventional fluorescent lamp.

For example, an object of the present invention is to produce a white light emitting OLED comprising a radiation region, the radiation region comprising an aggregate emitter and a monomer emitter, the radiation energy from the aggregate emitter being lower than that from the monomer emitter, The mixed emission spectrum of the aggregate emitter and the monomer emitter spans the visible light spectrum to provide white light.

To illustrate the invention, representative embodiments are shown in the accompanying drawings, which should not be construed as limited to the precise arrangements and apparatuses shown.

FIG. 1 shows the electroluminescence spectra of FIrpic and the sum of the two spectra in FPt and CBP (dopant alone) in TAZ (exiplex). The combined spectrum is not a single device, but combines two device output forms showing the potential for using monomers and exciplex emitters to achieve true white luminescence.

2 shows the photoluminescence spectra of CBP films doped with <1% and> 6% FPt. At 1% filling, the spectrum is dominated by monomer spinning. At 6% filling, the monomer signal is still present, but yellow, which is a relatively small component compared to excimer radiation.

3 shows the EL spectra at several different current levels, the device being ITO / PEODT (400) / NPD (300) / CBP: FIrpic 6%: FPt 6% (300) / FIrpic (500) / LiF (5) / Al (1000). CIE coordinates are given in the legend for each spectrum. The device is white at all current densities and has a CRI value of around 70.

4 shows quantum efficiencies (circles) related to ITO / PEODT (400) / NPD (300) / CBP: FIrpic 6%: FPt 6% (300) / FIrpic (500) / LiF (5) / Al (1000). Power efficiency (square) plots are shown. The current density-voltage plot is shown in the inset. This device demonstrates that excimer radiation can be combined with monomer radiation in a single OLED to achieve white light emission.

 5 shows photoluminescent emission (solid line) and excitation spectrum (white circle) of films 1-4. The film has a thickness of 1000 mm 3, and is grown in the quartz member. Film 1 shows a CBP PL spectrum with a peak at λ = 390 nm and a corresponding PLE between λ = 220− and 370 nm. The PLE of CBP shows the shoulder at λ = 300 nm and the main peak at λ = 350 nm. The CBP PLE peak corresponds to the absorption peak at λ = 300-350 nm (arrow, insert in Figure 6). These two CBP shapes appear in the PLE spectrum of all films where CBP is used as a host, and therefore, it is the main absorption spectrum in all films, and the energy is effectively FPt (acac) and FIr () in the CBP during the emission from these molecules. pic) must be delivered to both.

6 is a normalized electroluminescence spectrum at several current densities of device ITO / PEDOT-PSS / NPD (30 nm) / CBP: FIrpic 6%: FPt 6% (30 nm) / BCP (50 nm) / LiF. The upper left inset shows the absorption versus wavelength of a 1000 kHz thick CBP film on quartz. The lower left inset shows the structure of the device.

7 shows a plot of external quantum and power efficiency versus current density of device ITO / PEDOT-PSS / NPD (30 nm) / CBP: FIrpic 6%: FPt 6% (30 nm) / BCP (50 nm) / LiF. . The emission layer consists of 6% FIr (pic) and 6% FPt (acac) doped with CBP. The left inset shows the current density versus voltage characteristics of the device. The right inset shows the energy level of the CBP represented by the solid line, doped with FIr (pic) and FPt (acac) (dashed line). Where HOMO represents the position of the highest occupied molecular orbit and LUMO represents the position of the lowest occupied molecular orbit.

8 shows the photoluminescence spectra of CBP films doped with various levels of FPt.

9 shows the photoluminescence spectra of CBP films doped with various levels of FPt2.

10 shows photoluminescence spectra of CBP films doped with various levels of FPt3.

11 shows the photoluminescence spectra of CBP films doped with various levels of FPt4.

Figure 12 shows ITO / NPD (400 Hz) / IR (ppz) 3 (200 Hz) / CBP-FPt3 (300 Hz) / BCP (150 Hz) / Alq3 (200 Hz) / Mg-Ag OLED with FPt3 doped, various concentrations of FPt3. A plot of the current density versus voltage for.

FIG. 13 shows the electroluminescence spectra of the FPt3 doped OLED of FIG. 12 at various concentrations of FPt3.

FIG. 14 shows the CIE coordinates of the FPt3 doped OLED of FIG. 12 at various concentrations of FPt3.

FIG. 15 shows a plot of luminance versus voltage for the FPt3 doped OLED of FIG. 12 at various concentrations of FPt3.

FIG. 16 shows the quantum efficiency versus current density for the FPt3 doped OLED of FIG. 12 at various concentrations of FPt3.

FIG. 17 shows power efficiency versus current density as a function of current density for the FPt3 doped OLED of FIG. 12 at various concentrations of FPt3.

18 shows platinum (II) (2- (4 ', 6'-difluorophenyl) pyridinato-N, C ^2' ) (2,4-pentanedinato) (FPt, FPt (acac)), Platinum (II) (2- (4 ', 6'-difluorophenyl) (pyridinato-N, C ^2' ) (2,2,6,6-tetramethyl-3,5-heptanedionato) (FPt2), platinum (II) (2- (4 ', 6'-difluorophenyl) pyridinato-N, C ^2' ) (6-methyl-2,4-heptanedionato) (FPt3), Platinum (II) (2- (4 ', 6'-difluorophenyl) pyridinato-N, C ^2' ) (3-ethyl-2,4-heptanedionato) (FPt4), iridium-bis ( 4,6, -F ₂ -phenyl-pyridinato-N, C ^{2 ′} ) picolinate (FIrpic), fac -iridium (III) tris (1-phenylpyrazolato-N, C ^{2 ′} ) (Irppz ) And N, N'- meta -dicarbazolobenzene (mCP) compounds.

FIG. 19 shows the photoluminescence spectra of CBP films individually doped with 8% FPt (denoted "Me") and 20% FPt2 (denoted "iPr").

20 shows photoluminescence spectra for concentration changes of FPt doped into mCP thin film. The spectrum was measured by exciting the film at the maximum excitation of the matrix material (300 nm in mCP).

21 shows energy minimization structures of CBP and mCP host molecules. Molecular modeling and energy minimization were performed at the PM3 level using the MacSpartan Pro v 1.02 software package from Wavefunction Inc. (Irvine, CA 92612).

22 shows an energy level diagram showing HOMO and LUMO levels for the selected material. The energy for each orbit is listed by the appropriate rod below (HOMOs) or above (LUMOs). HOMO and LUMO levels for the radioactive dopant FPt are shown in dashed lines in each plot. The doped light emitting layer (CBP or mCP) is enclosed in parentheses. Each device has either a CBP or mCP layer or neither. The top plot shows a diagram for a four layer OLED (no electron blocking layer), and the bottom plot shows a similar OLED with Irppz EBL.

Fig. 23 shows device characteristics of mCP-based WOLEDs (ITO / NPD (400 Hz) / Irppz (200 Hz) / mCP: FPt (doping level 16%, 300 Hz) / BCP (150 Hz) / Alq3 (200 Hz) / LiF-Al). Indicates. A schematic illustration of the device with Irppz EBL is shown in the inset of the upper plot. Spectrum and CIE coordinates (inset) are shown in the upper plot.

FIG. 24 shows the quantum efficiency versus current density and current-voltage characteristics (inset) for the device shown in FIG.

FIG. 25 shows lumens per W and luminance versus current density plot for the associated structure without the WOLED and Irppz EBL shown in FIG. 23.

Detailed description of the invention

The invention will be described in detail with respect to preferred embodiments of the invention. These embodiments are used only as exemplary embodiments, and the invention is not limited thereto.

The present invention is to produce an efficient white light emitting OLED. The device of the present invention utilizes two emitters in a single radiation region to sufficiently cover the visible light spectrum. White radiation is obtained from two luminescent emitters in a single radiation region through the formation of aggregates by one of the lumopores. The aggregate emitter comprises two or more radioactive molecules or moieties defined in the ground state and / or in the excited state. In general, aggregate emitters consist of two radioactive molecules (ie, dimers) that can be the same or different. Lumopores can emit through fluorescence (from a singlet excited state) or through phosphorescence (from a triplet excited state). Two radiation centers (aggregate emitter and monomer emitter) may be doped in a single emitting layer. This enables the construction of WOLEDs that are simple, bright, efficient and exhibit high color rendering index. Of the methods for producing white light, field phosphorescence is preferred as the most efficient OLED light emitting mechanism because of the demonstrated possibility of achieving 100% internal quantum efficiency. Surprisingly, the phosphorescence emission from the excited state aggregate was found to be much larger than expected and provided the possibility to achieve 100% internal quantum efficiency. Field phosphorescence, typically achieved by doping an organometallic phosphor to a conductive host, has been successfully used to generate the essential colors necessary in the display area, while the efficient generation of the broad spectral emission required for white light sources has been difficult to date. .

Separating the radiation material into separate layers is a color tuning of three dopant electroluminescent devices, as disclosed in co-pending application No. 60 / 291,496, filed "High Efficiency Multicolor Electroluminescent OLEDs." While color tuning can be made a relatively simple process, the multilayer approach complicates the device. If the device could be made of two emitters and both emitters could be in the same emission area, it would be much simpler. In such a case, the device may be manufactured with the same high efficiency as demonstrated for monochrome electroluminescent OLEDs. To use only two dopants and obtain an acceptable CRI value, one of the dopants must have a very wide emission line. Unfortunately, wide emission lines have typically been observed only in inefficient devices.

A promising approach to reduce the number of dopants and the inherent structural heterogeneity in multicolor-band structures is to use lumopores to form broadly radiating exciplexes (ie, wave functions overlap with neighboring molecules) in an excited state. will be. Recently, it has a CIE (Commissiion International de l'Eclairage) coordinate close to the ideal white light source (0.33, 0.33), the external efficiency (η _external ) is 0.3%, the luminous efficiency (η _p ) is 0.58㏐ / W and the maximum luminance. A fluorescent exciplex OLED having a value of 2000 cd / m 2 was demonstrated. Berggren, M. et al. J. Appl. Phys. 76, 7530-7534 (1994) and Feng, J. et al, Appl. Phys. Lett. See 78, 3947-3949. This figure is considerably lower than what is needed in the real world of lighting. Emissions from such OLEDs have been reported to be produced only by exciplex.

The solution for obtaining efficient white light emitting OLEDs has been found to include obtaining radiation from two luminescent emitters (one of the centers of radiation and one of the aggregates) in a single emission region. The aggregate emitter comprises two or more lumopores bound to the ground and / or excited states. In general, aggregate emitters may consist of two molecules (ie, dimers) which may be different or identical.

An excimer or exciplex is formed when a lumophor containing the aggregate emitter is bound in an excited state but not in a ground state. Excimers are dimers with excited state wavefunctions extending across two identical molecules. Exiplexes are dimers with excited state wavefunctions extending across two dissimilar molecules. In excimers and exciplexes, the constituent molecules are bound in an excited (exciton) state, but after relaxation they rapidly separate into two separate molecules. The end result is that the excitons do not have any absorption in the ground state. Excimer and exciplex formation are preferred where there is a significant overlap between the LUMOs of the constituent species. The excimer and exciplex energy are lower than the energy of the exciton localized in either of the two molecules that make up it, and its emission is typically a wide line. Since both the excimer and the exciplex have no bounded ground state, they provide the only solution to achieving efficient energy transfer from the charge-carrying host matrix to the emission center. In both light emitting centers, the use of excimers or exciplexes prevents energy transfer between the light emitting centers and eliminates complex intermolecular interactions, causing color balance problems using multiple dopants. For a review of the properties of excimers and excitons, Andrew Gilbert and Jim Baggott, Essentials of Molecular Photochemistry , 1991, CRC Press, Boston, pp. See 145-167.

In another embodiment of the invention, molecules comprising aggregate emitters are bound in both ground and excited states. For example, dimers of phosphorescent organometallic compounds can have a metal-metal bond in the ground state. In practice, it can be difficult to determine whether or not Lupomore containing aggregate emitters are bound to the ground state when doped into a molecular thin film of the type used in the manufacture of OLEDs. It may be true that for some aggregate emitters it is somewhere between the extremes. For example, the dimer of the phosphorescent organometallic compound may have a weak metal-metal bond in the ground state, but in the excited state the bond is shortened and the dimer is strongly bonded. In this case, the dimer is not an excimer or exciplex because it is bound to the ground. Phosphorescent dopants may be involved in both π-π stacking and metal-metal interactions, leading to excimer or MMLCT excited states in the doped film. Thus, radiation from such films can have contributions from both excimer and oligomeric excited states. In either case, the emission spectrum observed from the aggregate is typically wide, unstructured and occurs at a lower energy than that of the monomer, whether or not bound to the ground state. Thus, the term "excimer" or "exiplex" as used herein may, in some cases, refer to an aggregate having a strongly bounded excited state and a weakly bound excited state. Also, as used herein, the term “aggregate” includes excimers and exciplexes.

In one embodiment of the invention, monomer or aggregate spinning is all achieved from the same dopant. These dopant molecules in relatively close contact with other dopant molecules may form aggregate states. Isolated dopant molecules provide monomers but do not provide aggregate spinning. White OLEDs can be achieved if the relative contribution from each radiation center can be properly adjusted, for example by adjusting the concentration of each emitter in the emitting layer. In order to obtain well-balanced monomer and aggregate emissions from the emissive layer with a single luminescent dopant and to obtain high efficiency, the ratio of monomer-aggregate must be achieved at an appropriate concentration of dopant. Different approaches affecting the nature of the intermolecular interactions in the film and thus the degree of monomer-aggregate spinning can be used to control the monomer-aggregate emissivity. One such approach is to change the amount of steric bulk in the dopant molecule. The second is to change the host matrix. Both approaches are believed to affect the degree of association of dopant material in the emissive layer and thus the ratio of monomer and aggregate states.

Using such a method, a feature of the present invention is that WOLEDs can be produced with very high efficiency and very high CRI by adjusting the concentration of dopant to be substantially the same across the emissive layer. Naturally occurring changes in the distance between neighboring molecules determine the degree of aggregate formation for a given host-dopant bond, resulting in the desired balance of monomer and aggregate spinning. The emission spectrum obtained by the device of the present invention is sufficiently over the visible light spectrum to exhibit substantially white (eg, CIE x-coordinates from about 0.30 to 0.40 and CIE y-coordinates from about 0.30 to about 0.45). Preferably the CIE x, y-coordinate is approximately (0.33, 0.33). In addition, the apparatus of the present invention can preferably produce white light having a CIE color rendering index (CRI) of at least 70 or more. More preferably, the CRI is higher than about 80. Alternatively, instead of finding a very high CRI, the method of the present invention can be used to produce a selected color with defined CIE coordinates.

The device of the present invention consists of an anode, an HTL, an ETL and a cathode. In addition, the device may include, but is not limited to, additional layers such as an exciton barrier layer (EBL), a separate emissive layer, or a hole injection layer (HIL). In one embodiment, the HTL also functions as a region where excitons are formed and electroluminescent radiation occurs. In another embodiment, the device may include a separate emissive layer in which excitons are formed and electroluminescent radiation occurs. The radiation area includes two types of radiation centers. One of the radiation centers forms an aggregate that provides a broad emission spectrum. Other emitters emit as monomers. In one embodiment of the invention, a single luminescent material can emit as both aggregate emitter and monomer emitter. Color optimization up to a high color rendering index can be achieved by selecting aggregate forming and monomeric emitters and changing the concentration of emitters such that the radiation covers the visible light spectrum.

In a preferred embodiment, two luminescent materials are doped into the matrix material. Matrix materials are typically charge transport materials. In a particularly preferred embodiment, the luminescent material will be a phosphorescent emitter (ie, a emitter that emits from triplet excited states). Materials present as charge transport hosts and dopants are selected to have a high level of energy transfer from the host to the dopant material. High efficiency can be obtained by energy transfer from both singlet and triplet states to phosphorus triplet states or by direct capture of charge in the phosphorescent material, thereby obtaining up to 100% of the excited state. In addition, these materials need to be able to produce acceptable electrical properties for OLEDs. In addition, such host and dopant materials can be readily introduced into the OLED by using starting materials that can be introduced into the OLED, preferably using conventional manufacturing techniques. For example, small molecule nonpolymeric materials, such as those disclosed in US Application No. 08 / 972,156 filed November 17, 1997, "Low Pressure Vapor Deposition Of Organic Thin Films", are incorporated herein by reference. -of-sight) can be deposited using vacuum deposition or organic vapor deposition (OVPD). Optionally, polymeric materials may be deposited using spin coating.

In a preferred embodiment of the invention, the radiation zone of the device may consist of excimer and monomer emitters. Luminescent materials including monomers and excimers can emit by fluorescence and phosphorescence. The monomer emitter will preferably emit a high energy (eg blue or green) portion. Since there is no absorption in this excimer state, there will be a minimum energy transfer from the monomer emitter to the excimer.

In order to obtain efficient excimer emission from the doped layer, control of the dopant concentration is an important consideration. Excimers will typically form when the planar molecules are very close to each other. For example, square planar metal complexes, such as certain complexes of Pt, are known to form excimers in concentrated solutions and thin films. For example, FPt (acac) represents monomer spinning in a ^10-6 M solution of dichloromethane and excimer spinning in a concentrated ^10-3 M solution.

At appropriate concentrations, both monomer and excimer spinning can be obtained from the same dopant. Only dopant molecules that are in relatively close contact with other dopant molecules may form excimer states. The isolated dopant molecule provides monomer emission but will not give excimer emission. If the monomer emits blue and the excimer emits yellow, and if the relative contribution from each emitter can be controlled appropriately, for example by adjusting the concentration of each emitter in the emitting layer, it may be a white OLED.

Forming an excimer state requires the radioactive molecules to be in close proximity to one another so that when one of the two radioactive molecules goes into an excited state. This suggests that there may be very strong concentration dependence on excimer formation. For example, at 1%, when FPt is doped with a host matrix such as CBL, only monomer emission is observed in the photoluminescence spectrum of the thin film. At this low doping level, the molecules are sequestered. As the doping concentration rises, the amount of excimer radiation increases as the monomer line decreases. When the FPt doping level is 2-3%, the ratio of monomer to excimer spinning is close to 1: 1. At this level of doping, some FPt molecules are sequestered and others are in close proximity to other FPt molecules, leading to effective excimer formation. Nearly complete excimer emission is observed at the 6% doping level.

If the OLED is made of FPt film doped with about 2-3%, it is possible to produce white OLEDs. The device has only a single dopant present evenly doped in the thin film. Unfortunately, the doping level of about 2-3% is too low to effectively restrain host excitons, resulting in significant host emission in the electroluminescent spectrum. In order to produce efficient photoluminescent OLEDs, the doping level is preferably about 6% or more and has the highest efficiency at higher doping levels. At high doping levels to produce efficient OLEDs, only excimer emission is observed at the FPt. In order to obtain more efficient white emission (by simultaneous monomer and excimer emission) from a single dopant, the doping level leading to balanced emission must be increased.

When the steric bulk of the emitter increases, the likelihood that the excimer can form in the solid state is reduced. The added bulk prevents the molecules from associating closely. This is easily found in the spectrum of FPt2 (FIG. 9). The t- Bu group of the complex interferes with the intimate face-to-face packing of these molecules in the doped film. As a result, only monomer emission is observed in the photoluminescence spectrum of the doped thin film of FPt2 at a high doping level of 25%. FPt forms the excimer too easily and FPt 2 does not form the excimer. When molecules with medium levels of steric bulk are used, it is possible to achieve mixed monomer / excimer spinning at the appropriate doping level. The role of the added steric bulk is clearly seen in the photoluminescence spectra of FPt3 (FIG. 10) and FPt4 (FIG. 11). Monomer spinning is found at low doping levels, and excimer spinning dominates at high doping levels. Near 10% doping, almost balanced monomer-eximer emission for all of these complexes is observed. At low doping levels, many contributions from the host can be observed. As the doping level increases, the host contribution decreases as expected for more efficient exciton transfer at higher doping levels.

In another embodiment of this experiment, the monomer / aggregate spinning ratio is optimized by changing the host matrix material. For example, in a single dopant system (both monomer spinning and collective spinning from the same dopant), the degree of association of dopants in the emissive layer and the ratio of the states of radiation can be changed by changing the host matrix material. Without wishing to be bound by theory, there is a competition process between aggregation and dispersion of dopants in the host matrix during the growth of the doped film. If the host matrix acts as a good solvent, the dopant will be more uniformly dispersed in the film. Insufficient soluble host matrices will not effectively disperse monomer dopants and thus lead to dopant aggregation. A good soluble host thus supports monomeric species over aggregate species at a given dopant concentration. Various properties of the host material may be important in determining solvent properties for a particular dopant, which include other physical properties such as dipole moment, association energy, and crystallinity.

In another exemplary embodiment, the device is made from two dopant emissive materials to emit blue light from the monomer excited state. The other dopant emits from the excimer state, leading to broad yellow radiation. For example, the device fabricated to demonstrate this concept used a blue emitting octahedral Ir composite, FIrpic, which did not form an excimer state at any doping level. Another dopant used in the device is the planar Pt composite, FPt, which effectively forms excimer states even at very low doping levels. When each dopant is present at 6%, the resulting electroluminescent emission consists of approximately equal contributions from FIrpic (monomer) and FPt excimer.

Whenever an exciplex emitter is used to provide wide radiation over the low energy portion of the visible light spectrum, the radiation region of the device will consist of the exciplex and the monomer emitter. Luminescent materials comprising monomers and excimers emit by phosphorescence or fluorescence. The monomer emitter is preferably one that emits high energy portions of the visible light spectrum (eg blue or green). Exiplex emitters provide broad radiation that spans the low energy portion of the visible light spectrum. Since there is no absorption in this exciplex state, there will be minimal energy transfer from the monomer emitter to the exciplex. Thus, for example, if a device is made of two blue emitting phosphors, one forming an exciplex with a matrix material and one not, a white device can be manufactured. The exciplex can emit yellow and will not capture energy from the non-exiplex forming dopants, since the exciplex does not have any ground state absorption (the oscillator strength for absorption is zero and therefore Forster Radius = 0). The ratio of blue to yellow radiation can thus be easily adjusted by varying the ratio of the two emitters, without the complexity of energy transfer from the blue emitter to the yellow emitter. Examples of such two materials are FIrpic and FPt. The Ir complex does not form an exciplex and the Pt complex forms a yellow exciplex in the TAZ matrix. The electroluminescence spectra of the two devices and their sum are shown in FIG. 1. Ir-based devices have a peak external efficiency of 6% and Pt-based devices (exiplex radiation) have an external efficiency of 4%. The combined two light sources provide a white light source with CRI 82, comparable to some of the best light sources.

Monomer emitters that are not involved in aggregate emission can be selected from high energy (eg blue) luminescent materials. Monomer emitters are luminescent compounds that typically have sufficient steric bulk to interfere with the proximity required in the solid state for aggregate formation at certain concentrations. Preferred monomer emitters include organometallic transition metal complexes that have an octahedal coordinate form or have three-dimensional bulk ligands sufficient to prevent aggregate formation and have a square flat form.

The phosphor for use in the device is typically an organometallic compound. The phosphor may be selected from organometallic compounds such as those disclosed in the ongoing application US Serial No. 08 / 980,986, filed June 8, 2001, and 09/978455, filed October 16, 2001. Are hereby incorporated by reference in their entirety.

Various compounds have been used as HTL materials or ETL materials. ETL materials can include, in particular, aryl-substituted oxadiazoles, aryl-substituted triazoles, aryl-substituted phenanthrolines, benzoxazoles, or benzthiazole compounds, such as C. Adachi et al., Appl . Phys. Lett. , Vol. 3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7) as disclosed in 77, 904 (2000); 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole (TAZ); 2,9-dimethyl-4,7-diphenyl-phenanthroline (vasocuproin or BCP); Bis (2- (2-hydroxyphenyl) -benzoxazolate) zinc; Or bis (2- (2-hydroxyphenyl) -benzthiazolate) zinc. Other electron transport materials include (4-biphenyl) (4-t-butylphenyl) oxydiazole (PDB) and aluminum tris (8-hydroxyquinolate) (Alq3).

The material of the hole transport layer is selected to transport holes from the anode to the radiation region of the device. HTL materials are almost composed of several types of triaryl amines that exhibit high hole flow (~ 10 ^-3 cm 2 / Vs). Suitable materials for the hole transport layer are 4,4'-bis [N- (naphthyl) -N-phenyl-amino] biphenol (α-NPD) with a hole flowability of about 5x10 ^-4 cm 2 / Vs. Other examples include N, N'-bis (3-methylphenyl) -N, N'-diamine (TPD), 4,4'-bis [N- (2-naphthyl) -N-phenyl-amino] biphenol ( β-NPD), 4,4'-bis [N, N '-(3-tolyl) amino) -3,3'-dimethylbiphenyl (M14), 4,4', 4 "-tris (30methylphenylphenyl Amino) triphenylamine (MTDATA), 4,4'-bis [N, N '-(3-tolyl) amino] -3,3'-dimethylphenyl (HMTPD), 3,3'-dimethyl-N ⁴ , N ⁴ , N ^{4 '} , N ^4' -tetra- p -tolyl-biphenyl-4,4'-diamine (R854), N, N ', N "-1,3,5-tricarbazoloylbenzene ( tCP) and 4,4'-N, N'-dicarbazole-biphenyl (CBP). Additional suitable hole transport materials are known and examples of materials that may be suitable for the hole transport layer can be found in US Pat. No. 5,707,745, which is incorporated herein by reference.

In addition to the small molecules described above, the matrix may comprise a polymer or polymer blend. In one embodiment, the emissive material is added as a free molecule, i.e., in a form that is not bound to the polymer but dissolved in the polymer "solvent". Preferred polymers used as matrix materials are poly (9-vinylcarbazole) (PVK). In an alternative embodiment, the emitter is part of a repeating unit of the polymer, such as Dow's polyfluorene material. Both fluorescent and phosphorescent emitters can be attached to polymer chains and used to make OLEDs. In devices comprising a polymer matrix, the layers are typically deposited by spin coating.

Preferred host matrix materials for the emissive layer include carbazole biphenyl (CBP), and derivatives thereof, N, N'-dicarbazoleolibenzenes and derivatives thereof, and N, N ', N "-1,3,5-tri Carbazoleolibenzenes and derivatives thereof Derivatives include one or more alkyl, alkylene, aryl, CN, CF ₃ , CO ₂ alkyl, C (O) alkyl, N (alkyl) ₂ , NO ₂ , O-alkyl and Particularly preferred host matrix materials in the emissive layer are 4,4 ', N, N'-dicarbazole-biphenyl (CBP), N, N'- meta -dicarbozololi. Benzene (mCP) and N, N ', N "-1,3,5-tricarbazoleolibenzene (tCP). CBP has a number of important properties as a matrix material. For example, the high triplet energy and bipolar charge transport characteristics of 2.56 eV (484 nm) make this an excellent host for phosphorescent dopants.

Pure thin films of CBP are easily crystallized. Doping small molecules with CBP (such as a radioactive dopant) stabilizes the thin film in amorphous or glass form, which is stable for a long time. MCP, on the other hand, forms stable glass, even in the undoped state. Crystallization during device operation can lead to device failure and is avoided. It is advantageous to have a material that can form a stable glass even when it is not doped, because less crystallization can occur. The measurement used to evaluate the glass forming ability of a given material is the glass transition temperature (Tg). This temperature characterizes the thermal stability of the glass material, so high Tg is preferred for OLED materials. At Tg, significant thermal expansion typically occurs and causes device failure. mCP has a Tg of 65 ° C. This value is acceptable for device fabrication, but higher Tg is desirable for making devices with the longest possible lifetime. Increasing Tg can be easily accomplished by adding large, hard groups such as phenyl, polyphenyl groups and similar aryl groups to the molecule. This phenyl addition / substitution must be done in a manner that does not lower triplet energy, but the host material may not be suitable for use in blue or white emitting devices. For example, adding a phenyl group to the carbazole unit itself (eg, the 4 ′ position in compound I) will generally lower triplet energy and make the mCP derivative less suitable for blue or white devices.

Substitution of phenyl or polyphenyl groups at the 2, 4, 5 or 6 positions of compound I will not result in significant shifts in triplet energy. These substitutions generally increase the Tg of the materials and make them better materials for long life OLEDs. Examples of such compounds include, but are not limited to the following compounds:

Suitable electrode (ie, anode and cathode) materials include conductive materials such as metals, metal alloys, or electrically conductive oxides such as ITO that are connected to the electrical contacts. Deposition of electrical contacts can be accomplished by vapor deposition or other suitable metal deposition techniques. Such electrical contacts can be made from, for example, indium, magnesium, platinum, gold, silver, or a combination such as Ti / Pt / Au, Cr / Au or Mg / Ag.

When depositing an upper electrode layer (ie, cathode or anode, typically a cathode), i.e., the electrode on the OLED side furthest from the substrate, damage to the organic layer should be avoided. For example, the organic layers should not be heated above their glass transition temperature. The upper electrode is preferably deposited from a direction substantially perpendicular to the substrate.

The electrode serving as the anode preferably comprises a high work function metal (≧ 4.5 eV), or a transparent electroconductive oxide such as indium tin oxide (ITO), zinc tin oxide or the like.

In a preferred embodiment, the cathode is preferably a low work function, electron injection material such as a metal layer. Preferably, the cathode material has a work function of less than about 4 eV. The metal cathode layer may consist of a substantially thicker metal layer if the cathode is opaque. If the cathode is to be transparent, a thin low work function metal can be used in combination with a transparent electrically conductive oxide such as ITO. Such transparent cathodes may have a metal layer of 50 to 400 microns thick, preferably about 100 microns thick. As an example, a transparent cathode such as LiF / Al may be used.

For the top radiator, transparent cathodes such as those disclosed in U. S. Patent No. 5,703, 436, co-pending U. S. Patent Application Nos. 08/964, 863 and 09/054, 707, incorporated herein by reference, can be used. The transparent cathode has light transmission properties such that the OLED has at least about 50% optical transmission. Preferably, the transparent cathode has light transmission properties that allow the OLED to have optical transmission of at least about 70%, preferably at least about 85%.

The device of the present invention may include additional layers such as an exciton blocking layer (EBL), a hole blocking layer (HBL) or a hole injection layer (HIL). As disclosed in US Pat. No. 6,097,147, incorporated herein by reference, one embodiment of the present invention employs an exciton blocking layer that blocks exciton diffusion to increase overall device efficiency.

Particularly in devices with high energy (blue) phosphorescent emitters, an electron / exciton blocking layer may be included between the emitting layer and the HTL to prevent exciton electron leakage from the emitting layer to the hole transport layer. High energy phosphorescent dopants have high energy LUMO levels in close proximity to the transport and host materials. When the dopant LUMO level approaches the LUMO energy of the HTL material, electrons can leak into the HTL.

Similarly, exciton leakage into the HTL layer can occur as the radiant energy of the dopant approaches the absorbed energy of the HTL material. Therefore, the introduction of the electron / exciton blocking layer between the HTL and the light emitting layer can improve the device characteristics. Efficient electron / exciton blocking layers will have a high energy gap to prevent exciton leakage into HTL, a high LUMO energy to block electrons, and a higher HOMO level than HTL. Preferred materials for use in the electron / exciton blocking layer are fac-tris (1-phenylpyrazolato-N, C ² ) iridium (III) (Irppz).

In another embodiment of the invention, a hole injection layer may be present between the anode layer and the hole transport layer. The hole injection layer material of the present invention may be characterized as a material that wets or planarizes the anode surface to provide efficient hole injection from the anode to the hole injection material. The hole injection materials of the present invention can be characterized as having HOMO energy levels defined by relative IP energy, which advantageously matches the adjacent anode layer on one side of the HIL and the emitter-doped electron transport layer on the opposite side of the HIL. The highest occupied molecular orbital (HOMO) obtained for each material corresponds to its ionization potential (IP). The lowest unoccupied molecular orbital (LUMO) is equal to the sum of the IP and the optical energy gap, and is measured from the absorption spectrum. In a fully assembled device, the relative alignment of the energies may be somewhat different from that expected for example from the absorption spectrum.

HIL materials are distinguished from conventional hole transport materials typically used in the hole transport layer of OLEDs in that HIL materials have hole flow properties that can be substantially lower than the hole flow properties of conventional hole transport materials. For example, m-MTDATA has been found to be effective in enhancing hole injection from ITO, such as HTL consisting of α-NPD or TPD. HIL will effectively inject holes due to a decrease in HTL HOMO level / ITO offset energy or wetting of the ITO surface. α-NPD and TPD have hole flowability of about 5 × 10 ⁻⁴ cm 2 / Vs and 9 × 10 ^-4 cm 2 / Vs, respectively, while HIL material m-MTDATA has holes of about 3 × 10 ^-5 cm 2 / Vs It is believed to have fluidity. The m-MTDATA material thus has a hole order of order size smaller than the commonly used HTL materials α-NPD and TPD.

Other HIL materials include phthalocyanine compounds such as copper phthalocyanine, or poly-3,4-ethylenedioxythiophene (PEDOT) or poly (ethene-dioxythiophene): poly effective to promote hole injection from anode to HIL material and then to HTL. Other materials including polymeric materials such as (styrenesulfonic acid) (PEDOT: PSS).

The HIL thickness of the present invention needs to be thick enough to help wet or planarize the anode layer. For example, a HIL thickness as thin as 10 nm is acceptable for very smooth anode surfaces. However, since the anode surface tends to be very rough, a HIL thickness of up to 50 nm may be desirable in some cases.

The member according to the invention may be opaque or substantially transparent, and may be rigid or soft, and / or plastic, metal or glass. Although not limited to the thickness range recited herein, the member may be as thin as 10 mm, or if present as a rigid, transparent or opaque member, or if the member is made of silicone, provided it is a flexible plastic or metal foil member If so, it can be thicker.

The OLEDs and OLED structures of the present invention may optionally have additional effects, such as a protective layer (for protecting any material during the processing process), an insulating layer, a reflective layer for guiding the wavelength in some direction, and a protective gap. Layers, which cover the electrodes and organic layers to protect these layers from the environment. Techniques for insulating layers and protective gaps are contained, for example, in US Pat. No. 6,013,538, which is incorporated herein by reference.

Although high CRO values are often mentioned, the device of the present invention can be used to produce light sources that also provide other colors as well. Incandescent bulbs are slightly yellow rather than substantially pure white. By varying the ratio of monomer emitter to aggregate emitter, as described herein, the color of the resulting device can be adjusted, for example, to mimic the light emitted from an incandescent bulb. By adjusting the dopant, the steric volume of the dopant, and the host material used in the emissive layer, the device can be configured to provide unsaturated (not monochromatic) color radiation.

Depending on whether the reverse order of the OLED layers is present, or whether another design variant is used, there may be substantial variations in the type, number, thickness and order of the layers. Those skilled in the art will recognize various modifications to the embodiments of the invention described and illustrated herein. Such modifications are intended to be protected by the spirit and scope of the invention. That is, although the invention will be described in detail with reference to certain specific embodiments, those skilled in the art will recognize that other embodiments of the invention exist within the spirit and scope of the claims.

Example

Solvents and reagents available were purchased from Aldrich Chemical Company. The reagents were used as the highest quality product was obtained.

Ligand 2- (2,4-difluorophenyl) pyridine (F ₂ ppy) was prepared by Suzuki binding 2,4-difluorophenylboronic acid and 2-bromopyridine (Aldrich). Pt (II) μ-dichloro-bridged dimer [(F ₂ ppy) ₂ Pt (μ-Cl) ₂ Pt (F ₂ ppy) ₂ ] was prepared by a modified Lewis method (Lohse, O et al. , Synlett. 1999, 1, 45-48). Dimers were treated with 3 equivalents of chelating diketone ligand and 10 equivalents of Na ₂ CO ₃ . 2,6-dimethyl-3,5-heptanedione and 6-methyl-2,2-heptanedione were purchased from TCI. 3-ethyl-2,4-pentanedione was purchased from Aldrich. The solvent was removed under reduced pressure and the compound was chromatographically purified. The product was recrystallized from dichloromethane / methanol and sublimed.

Irppz was prepared by dissolving Ir (acac) ₃ (3.0 g) and 1-phenylpyrazole (3.1 g) in 100 ml glycerol and refluxing in an inert atmosphere for 12 hours. After cooling the product was separated by filtration, washed with some portions of water, methanol, ethanol, and hexanes and dried in vacuo. The crude product was sublimed at a temperature gradient of 220-250 ° C. and the next pale yellow product was obtained (yield 58%).

mCP was prepared by palladium catalyzed crosslinking of aryl halides with arylamines (T. Yamamoto, M. Nishiyama, Y. Koie Tet. Lett. , 1998, 39, 2367-2370).

Example 1

Field phosphor excimer WOLEDs were grown on glass substrates precoated with an indium tin oxide (ITO) layer with a sheet resistance of 20-W / sq. Prior to organic layer deposition, the substrate was degreased in an ultrasonic solvent bath and treated with oxygen plasma at 20 W and 150 mTorr for 8 minutes. Poly (ethylene-deoxythiophene): poly (styrene sulfonic acid) (PEDOT: PSS) used to reduce OLED leakage and increase production yield was spun on 4000 rpm ITO for 40 seconds and vacuum at 120 ° C. for 15 minutes. After baking, the thickness of about 40 nm was obtained. Hole transport and host materials and two dopants were prepared by standard procedures (Lamansky, S. et al., Inorg. Chem. 40, 1704-1711, 2001). Molecular organic layers were deposited sequentially without vacuum breakdown by thermal evaporation at a base pressure of <8 × 10 ⁻⁷ Torr.

Depositions beginning with 30 nm thick 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl (α-NPD) hole transport layer (HTL) were all performed at 6 wt% to 4, This was followed by a 30 nm thick radiation region consisting of blue phosphors FIr (pic) and FPt (acac) doped with 4'-N, N'-dicarbazole-biphenyl (CBP) host. The final organic layer deposited was 50 nm of vasocuproin (BCP). This layer functions as a hole and exciton blocking layer and as an electron transport medium.

After deposition of the organic layers, the samples were transferred from the vacuum chamber to an N ₂ filled glove box containing ≦ ₁ ppm H ₂ O and O ₂ . After fixing the mask with 1 mm diameter openings to the samples, they were transferred to a second vacuum chamber (<10 ^-7 Torr), where a cathode metal (comprised of 5Å LiF followed by 70 nm Al) was deposited through the mask. . The samples were only exposed to air during the test. The cross-sectional structure of the device is shown in FIG.

It is easy to begin the design of WOLDE by examining the photoluminescent emission (PL) and excitation (PLE) spectra of the materials used in the device emission region. Three doped films and undoped "control" CBP films were grown by thermal evaporation on separate solvent washed quartz members, each 1000 mm thick. The PL and PLE spectra of the film were made using a Photo Technology International QuaataMaster fluorometer. 5 shows the composition of the films and their associated PL CIE coordinates.

5 shows the PL (solid line) and PLE (empty circle) spectra of films 1-4. Film 1 shows a CBP PL spectrum with peaks at λ = 390 nm and corresponding PLE between λ = 220 and 370 nm. PLE of CBP has a shoulder at λ = 300 nm, and the main peak is λ = 350 nm (arrow, interpolation in FIG. 6). These two CBP properties appear in the PLE spectrum of all films where CBP is used as a host: therefore, for all films, this is the main absorbing species, and the energy is derived from these molecules from CBP to FPt (acac) and FIr (pic). It must be delivered effectively to produce radiation.

The PL spectrum of film 2 shows bands consistent with CBP and only FPt (acac) monomer emission. CBP radiation has λ = 390 nm, and FPt (acac) monomer radiation has a peak at λ = 470 nm, and has a peak at λ = 500 nm (FIG. 5). The observed spectrum for FPt (acac) in CBP is very similar to the same molecule in dilute solution. At <1% by weight, randomly distributed FPt (acac) molecules are separated by 30 kV on average, precluding significant excimer formation in advance. The absence of wide, long wavelength peaks in film 2 suggests that no exciplex is formed between CBP and FPt (acac). That is, if an exciplex is formed between these moieties, exciplex radiation from the FPt (acac) -CBP complex will be present even in the lightest doped sample.

As the FPt (acac) doping concentration increases to ˜7 wt% (film 3), excimer emission is observed at λ = 570 nm with an orange-red peak with characteristic emission at λ = 470 nm and λ = 500 nm. Higher doping levels lead to complete disappearance of CBP fluorescence. For Film 3, the measured lifetime of t = 7.2 ms of FPt (acac) emission at λ = 570 nm is consistent with excimer formation of the FPt (acac) composite when compared to 8.3 ms at λ = 470 nm.

Doping of FPt (acac) between 1% and 7% by weight leads to a spectrum consistent with the simultaneous emission of monomer and excimer from the dopant. At doping levels of 3% to 4% by weight, the monomer and excimer lines are harmonized and lead to white emission. While this film composition can be used primarily to make white OLEDs, the doping level is too low for the device to have a reasonable efficiency and provide a spectrum free of CBP fluorescence.

Film 4 consists of CBP doped with 6 wt% FIr (pic) and 6 wt% FPt (acac). Here, CBP radiation is not in PL, but the PLE spectrum still indicates that it is the main absorbing species, and energy is effectively transferred to FIr (pic) and FPt (acac). The PL radiation of the double doped film is similar to the field phosphorescence (EL) of WOLED shown in FIG.

The energy transfer process can be understood in double doped systems by referring to the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of three organic components (lower right inset). Adachi, C. et al., Appl. Phys. Lett. The endothermic process described in 79, 2082-2084 (2001) results in the transfer of triplet energy from CBP to FIr (pic). Assuming that the same location of the HOMO energy level of (5.8 ± 0.1 eV) and the LUMO energy level of (3.2 ± 0.1 eV) of both FPt (acac) and FIr (pic), a similar endothermic triplet energy transfer pathway results in CBP and FPt Can be expected for (acac). The resonance energy transfer between triplet levels of the two dopants is also similar because they are present in high concentrations within the CBP matrix. However, direct energy transfer from FIr (pic) to the excimer cannot occur by interrupting the energy cascade from blue to yellow radiation centers because the excimer has zero ground state absorption. This essentially releases the excited state of these molecules, allowing a simple optimization of the doping to achieve the desired color matching.

Light output from WOLED was measured using a Newport Power Meter and a calibrated silicon photodiode, and η _ext was calculated using the current density-voltage characteristics shown in the left inset of FIG. A Lambertia intensity profile is used to calculate η _p (FIG. 7) and luminous intensity. Where η _ext ≧ 3.0% between J = 1 × 10 ⁻³ μs / cm 2 and 10 μs / cm 2. Roll-off at J > 300 kPa / cm 2 contributes to sample heating and triplet-triple extinction. WOLEDs have a maximum η _ext = (4.0 ± 0.4)%, corresponding to (9.2 ± 0.9) cd / A, luminous intensity of (31 000 ± 3000) cd / m2 at 16.6V, η _p = (4.0 ± 0.4) ㏐ / W And CRI of 78.

Pure film of FPt (acac) has a lifetime of t = 4.8 kPa and 5.2 kPa at lambda = 470 nm and lambda = 600 nm, respectively. As the current density increases, the FPt (acac) excimer state can be saturated compared to the monomer and FIr (pic) and lead to increased blue emission. The spectral change reflects a slight change in the CIE coordinates from (0.40, 0.44) to (0.35, 0.43).

Example 2

OLEDs were made with FPt ₃ at 8, 10 and 12% doping levels. The device structure consisted of ITO / NPD (400 Hz) / Ir (ppz) ₃ (200 Hz) / CBP-FPt ₃ (300 Hz) / BCP (150 Hz) / Alq ₃ (200 Hz) / Mg-Ag. The current-voltage characteristics of the three devices were similar, and as the doping level increased, the leakage current gradually decreased at low voltages. CBP host radiation was not observed at any doping level, indicating that the FPt ₃ dopant efficiently captures all excimers formed in the CBP matrix. While excimer formation in CBP is a possible result of electron-electron recombination, it is also possible that holes or electrons are trapped in the FPt ₃ molecule and direct recombination can occur in the dopant. The latter process will lead to excitons formed in the dopant and do not require energy transfer from the matrix material, ie CBP in this case. Ir (ppz) ₃ electron blocking layer was necessary to prevent electron leakage into NPD layer, which leads to NPD radiation in addition to dopant monomer-eximer radiation. All three devices exhibit turn-on voltages between 3 and 4 volts and achieve maximum luminous intensity between 4000 and 10,000 Cd / m 2. The spectrum of the device shows very small changes as the voltage rises. That is, the monomer to excimer ratio is not significantly affected by voltage or current density. 10% and 12% doped devices provide peak efficiencies of 4% and 3.5%, respectively. 10% and 12% doped devices provide very good output efficiencies of 8 kW / W and 6.5 kW / W, respectively (at 1 Cd / m 2).

Example 4

A thin film of mCP doped with varying weight percent FPt was prepared by co-depositing two materials on a glass substrate. The spectrum of FPt doped in mCP is shown in FIG. 20 at various concentration ranges. The wavelengths of maximum emission in terms of monomer and aggregate states of FPt doped with mCP are the same as those of FPt in CBP. Balanced monomer / aggregate spinning was observed at a doping level of about 15% by weight, which is approximately three times the concentration required to obtain equivalent monomer / aggregate spinning ratios from FPt doped CBP thin films. This indicates that mCP is a better solvent for FPt and, at a given concentration, less FPt... Leads to FPt interaction.

In contrast to the CBP doped film, no host emission was observed in the photoluminescence spectrum of the lightly doped mCP film (<1 wt% FPt), indicating that energy transfer from mCP to FPt is more efficient from CBP to FPt. . Despite the high triplet energy (phosphorescence λ _max = 460 nm) of CBP, the energy transfer from CBP to the blue phosphorescent dopant (eg, the Pt composite used here) is an endothermic process. On the other hand, mCP has a peak phosphorescence spectrum at 410 nm and makes a more efficient exotherm from mCP to Pt composite dopant. More efficient energy transfer from the host to the dopant will affect the amount of dopant required to dissipate radiation as observed.

Both CBP and mCP have a low dipole moment (ca. 0.5 D), so the electrostatic interaction between the dopant and the host material is expected to be similar. This is consistent with the observation that the spectrum of monomer and aggregate states for doped mCP and CBP films is the same. Without being limited by theory, the difference between CBP and mCP leads to different dopant solubility and is related to their molecular structure. Flat molecules tend to have high binding energies, which promote crystallization and hinder glass formation. CBP is expected to be a larger plane in the solid state. This is consistent with the observation that undoped CBP thin film is rapidly crystallized when directly deposited on glass or ITO member. High CBP binding energy may tend to exclude monomeric dopants, leading to the formation of aggregates at appropriate doping levels. When mCP is deposited on an inorganic or organic member, it suggests that it has a non-flat ground state structure, forming an easily stable glass. The glass transition temperature for mCP is 65 ° C. The steric interaction between adjacent carbazole groups and the phenyl ring leads to the prediction that CBP and mCP should have an unplanar ground state structure, as shown in the geometry of the minimum energy structure in FIG. 21. It is important to remember that the calculated energy difference between the structure shown and the planar conformer is only 18 kJ / mol, while the CBP minimum structure appears slightly uneven. In contrast, the energy for planarizing mCP is 35 kJ / mol. The main cause of the large barrier to flat mCP is the H… H is backlash. Based on the structural differences, it is expected that the solubility of the square planar Pt dopant by mCP is significantly different from that of CBP. This has a significant effect on the monomer / aggregate ratio at a given doping level in CBP to mCP.

The photoluminescence spectrum CIE coordinates and color rendering index (CRI) of 1 doped into mCP are given in Table 1.

Table 1

Concentrations between 4 and 10 weight percent gave the CIE coordinates closest to white (0.33, 0.33), while maximum CRI was observed in the concentration range of about 15 to 20 weight percent. At higher concentrations, the CIE coordinates are similar to those found in incandescent lamps (ca. 0.41, 0.41). Therefore, a concentration range of 10-20% by weight for 1 doped mCP was chosen to be optimal for use in WOLEDs.

Example 5

An apparatus having an NPD (400 mV) / Irppz (200 mV) / mCP: FPt (16% 300 mV) / BCP (150 mV) / Alq3 (200 mV) / LiF (10 mV) / Al (1000 mV) structure was produced. The use of mCP hosts instead of CBP significantly improves device performance. The efficiency, current-voltage characteristic and spectrum of the device are shown in FIGS. 23, 24 and 25. Higher doping concentration and improved energy transfer from mCP to dopant provide a maximum quantum efficiency of 6.4 ± 0.6% (12.2 ± 1.4 lum / W, 17.0cd / A) at low luminance levels (1cd / m2) and 500cd / m2 At 4.3 ± 0.5% (8.1 ± 0.6 lum / W, 11.3cd / A). The quantum efficiency demonstrated by these mCP / FPt WOLEDs is the maximum efficiency reported for WOLEDs. As observed for other devices, the quantum efficiency decreases with increasing current density, but the decrease is less severe than most other electrophosphorescent devices.

Example 6

OLEDs were prepared as in Example 3, except that Irppz EBL was omitted (ie NPD / mCP-FPt / BCP / Alq3). The EL spectrum receives a significant contribution from the NPD and the quantum efficiency of the device drops by almost two factors (see FIG. 24). Overall, the Irppz electron / exciton blocking layer increases OLED efficiency, eliminates NPD radiation in the spectrum, and makes the spectrum independent of voltage.

The energy level diagram for the mCP and CBP devices shown in FIG. 22 shows that the barrier to electron migration from the dopant / CBP LUMO level to the NPD LUMO can be comparable to the hole injection barrier from NPD to the emissive layer. Elimination of electron / exciton leaks into the HTL improves both WOLED efficiency and color stability. The Irppz complex emits only from the phosphorescent excited state (λ _max = 414 nm, τ = 15 μs at 77 K). The optical gap of this composite was taken as the low energy edge of the absorption spectrum at 370 nm (3.4 eV). This evaluation of the optical gap shows a lower lower limit for the carrier gap. Irppz shows reversible oxidation in fluid solution at 0.38 eV (vs. ferrocene / ferrocene), but no reducing wave occurs up to -3.0 V in DMF and is consistent with> 3.4 eV carrier gap. The HOMO energy of Irppz was measured by ultraviolet photoelectron spectroscopy (UPS) and was determined to be 5.5 eV. Using Irppz optical gaps to trap the carrier gap, one can estimate that the Irppz LUMO is 2.1 eV and is significantly above both CPB and dopant LUMO. The energy schematic of FIG. 22 suggests that Irppz makes an excellent electron / exciton blocking layer.

Although the present invention has been described with reference to specific embodiments and preferred embodiments, it is understood that the invention is not limited to these embodiments and embodiments. In particular, the present invention can be applied to a wide range of electronic devices. Therefore, as will be apparent to those skilled in the art, the claimed invention includes modifications from the specific and preferred embodiments described herein.

Claims (86)

In an organic light emitting device comprising an emission layer, The emitting layer comprises an aggregate emitter and a monomer emitter, The aggregate emitter, the monomer emitter, or both emit by phosphorescence, The radiation energy from the aggregate emitter is lower than the radiation energy from the monomer emitter, Mixed emission of the aggregate emitter and the monomer emitter spans the visible light spectrum to be white light. The organic light emitting device of claim 1, wherein the aggregate emitter is an excimer. The organic light emitting device of claim 1, wherein the aggregate emitter and the monomer emitter emit light by phosphorescence. The organic light emitting device of claim 3, wherein the aggregate emitter and the monomer emitter are made of the same chemical compound. The organic light emitting device of claim 3, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. The organic light emitting device of claim 5, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). The organic light emitting device of claim 1, wherein the mixed radiation has a color rendering index of 80 or more. The organic light emitting device of claim 1, wherein the mixed radiation has a CIE x-coordinate of 0.30 to 0.40 and a CIE y-coordinate of 0.30 to 0.45. The organic light emitting device of claim 1, wherein the emission layer comprises an exciplex emitter and a monomer emitter. The organic light emitting device of claim 9, wherein the exciplex emitter and the monomer emitter emit light by phosphorescence. The organic light emitting device of claim 10, wherein the exciplex emitter and the monomer emitter are phosphorescent organometallic compounds. The organic light emitting device of claim 1, wherein the emission layer further comprises a polymer matrix. The organic light emitting device of claim 12, wherein the polymer matrix is PVK. In the organic light emitting device comprising an anode, a hole transport layer, an electron transport layer and a cathode, The hole transport layer or the electron transport layer is an emission layer, The emitting layer comprises an aggregate emitter and a monomer emitting layer, The aggregate emitter, the monomer emitter, or both emit by phosphorescence, The radiation energy from the aggregate emitter is lower than the radiation energy from the monomer emitter, Mixed emission of the aggregate emitter and the monomer emitter spans the visible light spectrum to be white light. The organic light emitting device of claim 14, wherein the hole transport layer is an emission layer. The organic light emitting device of claim 14, wherein the electron transport layer is an emission layer. The organic light emitting device of claim 14, wherein the aggregate emitter is an excimer. The organic light emitting device of claim 14, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 19. The organic light emitting device of claim 18, wherein the aggregate emitter and the monomer emitter are composed of the same chemical compound. 19. The organic light emitting device of claim 18, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 21. The organic light emitting device of claim 20, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). 15. The organic light emitting device of claim 14, wherein the mixed radiation has a color rendering index of 80 or more. 15. The organic light emitting device of claim 14, wherein the mixed radiation has a CIE x-coordinate of 0.30 to 0.40 and a CIE y-coordinate of 0.30 to 0.45. The organic light emitting device of claim 14, wherein the emission layer comprises an exciplex emitter and a monomer emitter. The organic light emitting device of claim 24, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. The organic light emitting device of claim 24, wherein the exciplex emitter and the monomer emitter are phosphorescent organometallic compounds. The organic light emitting device of claim 14, wherein the emission layer further comprises a polymer matrix. The organic light emitting device of claim 27, wherein the polymer matrix is PVK. The organic light emitting device of claim 14, further comprising an exciton blocking layer. The organic light emitting device of claim 14, further comprising a hole injection layer. In an organic light emitting device comprising an anode, a hole transport layer, an emission layer, an electron transport layer and a cathode, The emitting layer comprises an aggregate emitter and a monomer emitter, The aggregate emitter, the monomer emitter, or both emit by phosphorescence, The radiation energy from the aggregate emitter is lower than the radiation energy from the monomer emitter, Mixed emission of the aggregate emitter and the monomer emitter spans the visible light spectrum to be white light. 32. The organic light emitting device of claim 31, wherein the emission layer comprises an excimer emitter and a monomer emitter. 32. The organic light emitting device of claim 31, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 34. The organic light emitting device of claim 33, wherein the aggregate emitter and the monomer emitter are composed of the same chemical compound. 34. The organic light emitting device of claim 33, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 36. The organic light emitting device of claim 35, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). 32. The organic light emitting device of claim 31, wherein the mixed radiation has a color rendering index of 80 or more. 32. The organic light emitting device of claim 31, wherein the mixed radiation has a CIE x-coordinate of 0.30 to 0.40 and a CIE y-coordinate of 0.30 to 0.45. 32. The organic light emitting device of claim 31, wherein the aggregate emitter is an exciplex. 40. The organic light emitting device of claim 39, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. 41. The organic light emitting device of claim 40, wherein the exciplex emitter and the monomer emitter are phosphorescent organometallic compounds. 32. The organic light emitting device of claim 31, wherein the emission layer further comprises a polymer matrix. 43. The organic light emitting device of claim 42, wherein the polymer matrix is PVK. 32. The organic light emitting device of claim 31, further comprising an exciton blocking layer. A light source comprising the organic light emitting device according to claim 1. In an organic light emitting device comprising an emission layer, The emitting layer comprises an aggregate emitter and a monomer emitter, The emission layer is composed of a single layer, The aggregate emitter, the monomer emitter, or both emit by phosphorescence, The radiation energy from the aggregate emitter is lower than the radiation energy from the monomer emitter, Mixed emission of the aggregate emitter and the monomer emitter spans the visible light spectrum to be white light. 47. The organic light emitting device of claim 46, wherein the aggregate emitter is an excimer. 47. The organic light emitting device of claim 46, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 49. The organic light emitting device of claim 48, wherein the aggregate emitter and the monomer emitter are made of the same chemical compound. 49. The organic light emitting device of claim 48, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 51. The organic light emitting device of claim 50, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). 47. The organic light emitting device of claim 46, wherein the mixed radiation has a color rendering index of 80 or more. 47. The organic light emitting device of claim 46, wherein the mixed radiation has a CIE x-coordinate of 0.30 to 0.40 and a CIE y-coordinate of 0.30 to 0.45. 47. The organic light emitting device of claim 46, wherein the emission layer comprises an exciplex emitter and a monomer emitter. 55. The organic light emitting device of claim 54, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. The organic light emitting device of claim 55, wherein the exciplex emitter and the monomer emitter are phosphorescent organometallic compounds. 47. The organic light emitting device of claim 46, wherein the emission layer further comprises a polymer matrix. 58. The organic light emitting device of claim 57, wherein the polymer matrix is PVK. In an organic light emitting device comprising an emission layer, The emission layer comprises an excimer emitter and a monomer emitter, The emission layer is composed of a single layer, The radiation energy from the excimer emitter is lower than the radiation energy from the monomer emitter, And the mixed emission of the excimer emitter and the monomer emitter spans the visible light spectrum to be white light. An organic light emitting device comprising an emission layer, The emitting layer comprises an aggregate emitter; Monomer emitters; And a matrix material comprising a compound of formula (I):

(Ⅰ) (Substituents at 2, 4, 5, 6 and each 4 'position are independently selected from hydrogen, phenyl, or polyphenyl), The radiation energy from the aggregate emitter is lower than the radiation energy from the monomer emitter, Mixed emission of the aggregate emitter and the monomer emitter spans the visible light spectrum to be white light. 61. The organic light emitting device of claim 60, wherein the aggregate emitter is an excimer. 61. The organic light emitting device of claim 60, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 63. The organic light emitting device of claim 62, wherein the aggregate emitter and the monomer emitter are made of the same chemical compound. 63. The organic light emitting device of claim 62, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 61. The organic light emitting device of claim 60, wherein the mixed radiation has a color rendering index of 80 or more. 61. The organic light emitting device of claim 60, wherein the mixed radiation has a CIE x-coordinate of 0.30 to 0.40 and a CIE y-coordinate of 0.30 to 0.45. 61. The organic light emitting device of claim 60, wherein the emission layer comprises an exciplex emitter and a monomer emitter. 68. The organic light emitting device of claim 67, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. 69. The organic light emitting device of claim 68, wherein the exciplex emitter and the monomer emitter are phosphorescent organometallic compounds. In an organic light emitting device comprising an anode, a hole transport layer, an emission layer, an electron transport layer and a cathode, The emitting layer comprises an aggregate emitter; Monomer emitters; And a matrix material comprising a compound of formula (I):

(Ⅰ) (Substituents at 2, 4, 5, 6 and each 4 'position are independently selected from hydrogen, phenyl, or polyphenyl), The radiation energy from the aggregate emitter is lower than the radiation energy from the monomer emitter, Mixed emission of the aggregate emitter and the monomer emitter spans the visible light spectrum to be white light. The organic light emitting device of claim 70, wherein the emission layer comprises an excimer emitter and a monomer emitter. 71. The organic light emitting device of claim 70, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 73. The organic light emitting device of claim 72, wherein the aggregate emitter and the monomer emitter are made of the same chemical compound. 73. The organic light emitting device of claim 72, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 71. The organic light emitting device of claim 70, wherein the mixed radiation has a color rendering index of 80 or more. 71. The organic light emitting device of claim 70, wherein the mixed radiation has a CIE x-coordinate of 0.30 to 0.40 and a CIE y-coordinate of 0.30 to 0.45. 71. The organic light emitting device of claim 70, wherein the aggregate emitter is an exciplex. 78. The organic light emitting device of claim 77, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. 79. The organic light emitting device of claim 78, wherein the exciplex emitter and the monomer emitter are phosphorescent organometallic compounds. The organic light emitting device of claim 70, further comprising an exciton blocking layer. 81. The organic light emitting device of claim 80, wherein the exciton blocking layer is positioned between the hole transport layer and the emission layer. The organic light emitting device of claim 81, wherein the exciton blocking layer comprises a fac-iridium (III) tris (1-phenylpyrazonato-N, C ^{2 '} ). 61. The organic light emitting device of claim 60, wherein the matrix material comprises a compound of the formula:

. 61. The organic light emitting device of claim 60, wherein the matrix material comprises mCP. 71. An organic light emitting device according to claim 70 wherein the matrix material comprises a compound of the formula

. 71. The organic light emitting device of claim 70, wherein the matrix material comprises mCP.

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