KR20040075043A - White light emitting oleds from combined monomer and aggregate emission - Google Patents

Abstract

The present invention relates to effective organic light emitting devices (OLEDs). More particularly, the present invention relates to white emitting OLEDs or WOLEDs. The device of the present invention covers the visible spectrum sufficiently by using two emitters in a single radiation area. White radiation is achieved through the formation of an aggregate by one of the radiation centers from two radiators in a single radiation region. This enables the construction of WOLEDs that exhibit a simple, bright and efficient high color rendering index.

Description

WHITE LIGHT EMITTING OLEDS FROM COMBINED MONOMER AND AGGREGATE EMISSION

Organic light emitting devices (OLEDs) use thin film materials that emit light when excited by electrical current, and are becoming an increasingly popular model of flat panel display technology. This is because OLEDs have a variety of potential applications such as mobile phones, personal digital assistants (PDAs), computer displays, vehicle information displays, television monitors and general lighting sources. Due to their bright color, wide viewing angle, compatibility with full video video, wide temperature range, thin and conformable molding factors, low power, and inexpensive manufacturing processes, OLEDs are characterized by cathode ray tubes (CRTs) and liquid crystal displays ( It is seen as a future replacement for LCDs, which are currently leading the growing $ 40 billion annual electronic display market. They appear to have the potential to replace incandescent light, due to their high brightness efficiency, possibly replacing fluorescent, any type of lamps.

Devices whose structure is based on the use of an organic optoelectronic layer are in accordance with the usual conventional mechanisms leading to luminescence. Typically, this mechanism is based on the radial recombination of trapped charges.

Specifically, OLEDs consist of at least two thin film organic layers between an anode and a cathode. One material of these layers is specifically selected based on the ability to transmit holes, the "hole transport layer" (HTL), and the other layer of material is selected based on the ability to specifically transfer electrons. An "electron transport layer" (ETL). With such a structure, the device can be viewed as a diode with a forward bias when a voltage higher than that applied to the cathode is applied to the anode. Under these bias conditions, the anode fires holes into the HTL (positive charge carriers), and the cathode fires electrons into the ETLs. The light emitting medium portion adjacent to the anode thus forms a hole launching and transmitting region, while the light emitting medium portion adjacent to the cathode forms an electron emitting and transmitting region. The emitted holes and electrons move to oppositely charged electrodes. When electrons and holes are localized in the same molecule, Frenkel excitons are formed. These excitons are trapped in the material with the lowest HOMO-LUMO energy gap. Recombination of short-lived excitons, with relaxation occurring, can be developed with electrons dropping from the lowest unoccupied molecular orbital to the highest occupied molecular orbital, under certain conditions, preferably via a luminescent device.

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

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

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

Light emission from OLEDs is typically via fluorescence, but OLED light emission through phosphorescence has recently been exemplified. As used herein, the term "phosphorescence" refers to emission from a triple excited state of an organic molecule, and the term "fluorescence" refers to emission from a single excited state of an organic molecule. The term luminescence means fluorescence and phosphorescence emission.

Successful use of phosphorescence promises many promises 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 in single or triple excited states. This is because the lowest single excited state of the organic molecule is typically in a slightly higher energy state than the lowest triple excited state. For example, in a typical phosphorescent organometallic compound, the lowest single excited state rapidly collapses into the final triple excited state, from which phosphorescence is produced. Conversely, only a few percent (about 25%) of excitons can produce fluorescent luminescence resulting from a single excited state in a fluorescent device. The remaining excitons are produced in the lowest triple excited state in the fluorescent device and typically do not convert to the higher single excited state where fluorescence is produced. This energy is thus lost to a decay process that heats the device rather than emitting visible light.

Typically, phosphorescence emission from organic molecules is less common than fluorescent emission. However, phosphorescence can be observed under an appropriate set of conditions from organic molecules. Organic molecules arranged with lanthanum elements typically radiate from excited states localized in the lanthanum metal. Such radiation emission is not from triple excited state. In addition, such emission is not seen to be able to produce efficiencies high enough to be practical in anticipated OLED applications. Europium diketonate complexes show a group of this type of species.

Organic phosphorescence can be observed in molecules containing heteroatoms with lone pairs of electrons, but typically at very low temperatures. Benzophenone and 2,2'-bipyridine are such molecules. Phosphorescence can be improved over fluorescence at room temperature, preferably by bending, by limiting organic molecules close to atoms of high atomic number. Such a phenomenon is referred to herein as the atomic effect, which is created by a mechanism known as spin-orbital coupling. A related phosphorescent transition is gold-to-ligand charge transfer (MLCT) observed in molecules such as tris (2-phenylpyridine) iridium (III).

The realization of high efficiency blue, green and red field phosphor is a demand for all color display applications with low power loss. Recently, high efficiency green, red electrophosphorescent devices have been exemplified for harvesting single and triple excitons, with an internal quantum efficiency ( _inside η) approaching 100%. 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); and Adachi, C., Baldo, MA, Thompson, ME, and Forrest, SR, Bull. Am. Phys. See SOC., 46,863 (2001). In the use of green phosphors, factris (2-phenylpyridine) iridium (Ir (ppy) ₃ ), in particular having a large external quantum efficiency (η _external ) (17.6 ± 0.5%), corresponding to an internal quantum efficiency of at least 85% It was reproduced using an 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, red field phosphorescence of high efficiency (η _outside = (7.0 ± 0.5)%) has been illustrated, with bis (2- (2'-benzo [4,5-a] trienyl) pyridinato-N , C ³ ) iridium (acetylacetone) [Btp ₂ Ir (acac)] is used. Adachi, C., Lamansky, S., Baldo, MA, Kwong, RC, Thompson, ME, and Forrest, SR, App. Phys. See Lett., 78,1622-1624 (2001).

In these latter cases, high efficiency is obtained through energy transfer from both host singlet and triplet states to phosphorus triplets or direct capture of charge on the phosphor, thereby harvesting up to 100% excited state. This is a significant improvement over what can be expected with fluorescence in low molecular or polymer organic light emitting devices (OLEDs). 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); and Cao, Y, Parker, 1. D., Yu, G., Zhang, C., and Heeger, A. J., Nature (London), 397,414-417 (1999). In both cases, these transfers involve a resonance, exothermic process. Like the triplet energy of a phosphor, it is less likely to find a suitable host with a moderately high, 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 also suggests that the host material may not have the proper energy level order with other materials used in the OLED structure, resulting in further efficiency reduction. In order to eliminate the competition between the conductivity and energy transfer properties of the host, the route to efficient blue field phosphorescence can include exothermic energy transfer from the host in a near resonance excited state to a higher triplet energy 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); and HARRIMAN, A .; Hissler, M .; Khatyr, A .; Ziessel, R. Chem. See Commun., 735-736 (1999). This process can be efficient if the energy required for transfer is not greater than thermal energy.

The quality of the white light source can be described completely by a simple set of factors. The color of the light source is given by its CIE chromaticity coordinates x and y. CIE coordinates are typically represented by two-dimensional plots. The monochromatic color corresponds to the perimeter boundary of the horseshoe shape starting from blue on the lower left and proceeds through the color spectrum clockwise to the red on the lower right. 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 provides a uniform white or neutral point and is found at the center of the diagram (CIE x, y coordinates, 0.33, 0.33). Mixing light from two or more light sources provides light whose color is 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 that indicates 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 100 CRI. Although a CRI value of at least 70 is acceptable for some applications, more preferred white light sources will have about 80 or higher CRI.

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 efficient organic light emitting devices (OLEDs). More specifically, the present invention relates to white emitting OLEDs or WOLEDs. The device of the present invention is to use two light emitting emitters or lumophores in a single emission region sufficient to cover the visible spectrum. Lumopores emit either through fluorescence (from a singlet excited state) or through phosphorescence (from a triplet excited state). White emission is achieved from two luminescent emitters in a single emission region through the formation of an aggregate by one lumopore. Two emission centers (aggregate emitter and monomer emitter) are doped in a single emission layer. This allows for simple construction, high efficiency WOLEDs showing high color rendering index.

Thus, it is an object of the present invention to produce white light emitting OLEDs that exhibit high external emissivity (η _external ) and brightness.

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

Another object of the invention is to produce a white luminescent organic device that produces a white emission with a CIE x, y-chromatic coordinate approaching (0.33, 0.33).

Yet another object of the invention is to provide OLEDs that can be used as large area efficient light sources in diffusion-emitting applications, such as are now ubiquitously filled with conventional fluorescent lamps.

For example, it is an object of the present invention to produce white light emitting OLEDs comprising emitting regions, wherein the emitting regions comprise aggregate emitters and monomer emitters, wherein emission from the aggregate emitters is lower in energy than monomer emitters, and Wherein the combined spectrum of the aggregate emitter and the monomer emitter extends sufficiently in the visible spectrum to provide white emission.

The present invention relates to efficient organic light emitting devices (OLEDs). More particularly, the present invention relates to white light emitting OLEDs, or WOLEDs. The device of the present invention retains two emitters in a single emissive region to sufficiently cover the visible region. White radiation is achieved from two emitters in a single radiation region through the formation of an aggregate by one of the radiation centers. This allows the construction of a simple, bright and efficient WOLED with a high color rendering index.

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 efficiency (empty) and power efficiency (empty square) plots for devices ITO / PEODT (400) / NPD (300) / CBP: FIrpic 6%: FPt 6% (300) / FIrpic (500) / LiF ( 5) / Al (1000). Current density-voltage plots are shown as interpolations. This device shows that excimer radiation can be paired with monomer radiation in a single OLED that achieves white 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 ( pic) must be delivered to both.

FIG. 6 shows devices ITO / PEDOT-PSS / NPD (30 nm) / CBP: FIrpic 6%: FPt 6% (30 nm) / BCP (50 nm) / LiF stacked vertically to appear transparent at some current densities Is the normalized spectrum of. The figure in the upper left shows the wavelength versus absorption of 1000 Å thickness CBP in quartz. The lower left figure shows the structure of the device.

FIG. 7 shows the current quantum versus power efficiency and external quantum of device ITO / PEDOT-PSS / NPD (30 nm) / CBP: FIrpic 6%: FPt 6% (30 nm) / BCP (50 nm) / LiF. The stratification layer consists of 6% FIr (pic) and 6% FPt (acac) doped with CBP. The left interpolation shows the current density versus voltage characteristics for this device. The right interpolation shows the energy level diagram of CBP doped with FIr (pic) and FPt (acac) (dotted lines) shown in solid lines. HOMO teaches the position of the highest occupied molecular orbital, and LUMO teaches the position of the lowest occupied molecular orbital.

8 shows 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 the 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.

FIG. 12 shows ITO / NPD (400 μs) / IR (ppz) 3 (200 μs) / CBP-FPt3 (300 μs) / BCP (150 μs) / Alq3 (200 μs) with various concentrations of FPt3 doped Plot between current density and voltage for / Mg-Ag OLEDs.

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

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

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

FIG. 16 shows a plot of power efficiency versus brightness for the OLEDs of FIG. 12 doped with FPt3 at various concentrations of FPt3.

FIG. 17 shows a plot of luminance as a function of power efficiency versus current density for the OLEDs of FIG. 12 doped with FPt3 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'-meth-dicarbazolobenzene (mCP).

19 shows the photoluminescence spectra of CBP films doped separately with 8% FPt (labeled "Me") and 20% FPt2 (labeled "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, Wavefunction Inc, Irvine, CA 92612.

22 shows an energy level diagram depicting HOMO and LUMO levels for the selected material. The energy for each orbital is listed as an appropriate bar below (HOMO) or above (LUMOs). HOMO and LUMO levels for the emission dopant FPt are represented by dotted lines in each plot. The doped light emitting layer (CBP or mCP) is enclosed in parentheses. Each device has 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 for 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). Shows. A schematic of the device with Irppz EBL is shown as an interpolation of the upper plot. Spectrum and CIE coordinates (interpolation) are shown in the upper plot.

FIG. 24 shows the quantum efficiency, current density and current-voltage characteristics (interpolates) for the device described in FIG.

FIG. 25 shows plots for lumens per W and brightness and current density for the associated structures without the WOLED and Irppz EBL described 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 efficient white emitting OLEDs. The device of the present invention utilizes two emitters in a single emission area that sufficiently covers the visible spectrum. White emission is achieved from two luminescent emitters in a single emission region through the formation of aggregates by one of the lumopores. The aggregate emitter includes two or more radioactive jets or portions defined in a ground state and / or in an excited state. In general, aggregate emitters are composed of two release molecules (ie, dimers), which can be different or similar. Lumopores can emit via fluorescence (from a singlet excited state) or through phosphorescence (from a triplet excited state). Two spinning centers (aggregate emitter and monomer emitter) may be doped in a single emitting layer. This allows for simple, bright, and efficient WOLEDs structure and shows high color rendering index. Among the methods of producing white light, electrophosphorescence is preferred as the most efficient OLED light emitting mechanism, because of its illustrated potential for achieving 100% internal quantum efficiency. Surprisingly, it was found that phosphorescence emission from the set of excitation states is much larger than expected, providing the potential to achieve 100% internal quantum efficiency. Field phosphorescence, typically achieved by doping an organometallic phosphorescent material into 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 is to date understood. Difficult to do

Separating the radioactive material into separate layers is a relatively simple process, e.g., co-pending application No. 60 / 291,496, titled “High Efficiency Multicolor Electroluminescent OLEDs” While the process described in the May 16, 2001 application can be made, the multilayer approach adds complexity to the device. If the device can be made of two emitters, and if both emitters can be present in the same emission area, this can be much simpler. In such a case, the device can be manufactured with the same high efficiency, and can be manufactured with the long lifetime exemplified in monochromatic electrophosphorescent OLEDs. Using only two dopants, and in order to obtain acceptable CRI values, one of the dopants must have a very wide emission line. Unfortunately, wide emission lines can typically only be observed in inefficient devices.

A good approach to reduce the number of dopants and the structural heterogeneity resulting from multiple color-band constructions is to use lumopores that form broad radiant excited complexes in their excited states (i.e., adjacent to wavefunctions, overlapping different molecules). ). Recently, fluorescent excited composite OLEDs have a Commissiion International de l'Eclairage (CIE) coordinate close to an ideal white light source (0.33, 0.33), external efficiency η _external = 0.3%, luminous efficiency η _p = 0.58 lm / W And the maximum brightness is known to be 2000 cd / m ^2. 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 field of practical lighting. It has been reported that radiation from such OLEDs can be produced alone by excitable composites.

We find that the solution to achieving efficient white light emitting OLEDs involves obtaining radiation from two light emitting emitters in a single emission region, where one emission center is a monomer and the other emission center is an aggregate. The aggregate emitter comprises two or more lumopores that are confined to the ground state and / or the excited state. In general, aggregate emitters may be composed of two molecules (ie, dimers) which may be different or identical.

An excimer or exciplex is formed when a lumopore containing an 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, structural molecules are bound to an excited (excitonic) 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 sufficient overlap between the LUMOs of the constituent species. The excimer and exciplex energy make up it, and the emission is lower than the energy of the exciton localized in one of the two molecules, typically a wide line. Since both excimer and exciplex are tied to ground state deficiency, they provide the same solution for the achievement of efficient energy transfer from the charge transfer host matrix to the light emission center. In fact, in the case of two emission centers, the use of excimers or exciplexes eliminates energy transfer between the emission centers and eliminates complex intermolecular interactions, which allows color to be adjusted using problematic complex dopants. For a review of the properties of excimers and excitons, see 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 immobilized in both ground and excited states. For example, dimers of phosphorescent organometallic compounds may have a metal-metal bond in the ground state. In practice, this makes it difficult to determine whether, when doped into a molecular thin film, a lumopore containing aggregate emitters is anchored to the ground state of the type used in the manufacture of OLEDs. The truth may be the case between extremes of any collective radiator. For example, dimers of phosphorescent organometallic compounds may have weak metal-metal bonds in the ground state, but in the excited state the bonds are shortened and the dimers bond strongly. In this case, the dimer is not an excimer or an exciplex because the dimer is fixed in the ground state. Phosphorescent dopants are involved in π-π stacking and metal-metal interactions in doped films, leading to excimer or MMLCT excited states. Thus, radiation from these films can have contributions from both excimeric or oligomeric excited states. In either case, the emission spectrum observed from the set is typically wide and unstructured, whether fixed in the ground state, and generates lower energy than the monomers. Thus, the term "eximer" or "exiplex", as used herein, refers to a set having a strong fixed excited state and a weak fixed excited state in some cases. In addition, the term “set” includes excimers and exciplexes that are commonly understood, as used herein.

In one embodiment of the invention, monomer or aggregate spinning is achieved from the same dopant. These dopant molecules that are in close contact with relatively other dopant molecules may form aggregates. Isolated dopant molecules provide monomers but do not provide aggregate spinning. White OLEDs would be possible if the relative contributions from each emission center could be adjusted appropriately, for example by adjusting the concentration of each emitter in the emitting layer. In order to achieve well matched monomer and aggregate spinning from the emissive layer with a single emissive dopant, and to achieve high efficiency, the monomer-set ratio 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. Such an 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 degradation of the dopant material in the emissive layer, and thus the ratio of monomer and aggregate state.

In using such a method, features of the present invention can be made by adjusting the concentration of dopants substantially equally across the emissive layer such that WOLEDs have both very low efficiency and very high CRI. Naturally occurring changes in the distance between adjacent molecules determine the degree of aggregate formation for a given host-dopant combination, so that a certain balance between monomer and aggregate emission can be achieved. The emission spectrum produced by the device of the invention covers the visible spectrum sufficiently, so that it is substantially white, for example the CIE x coordinate is approximately 0.3 to 0.4 and the CIE y coordinate is approximately 0.3 to 0.45. Preferably, the CIE x, y coordinates are approximately (0.33, 0.33). In addition, the device of the present invention may produce white radiation, preferably 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, it can be used to produce a selected color with the described CIE coordinates.

The device of the present invention consists of an anode, an HTL, an ETL, and a cathode. The device may also include additional layers, such as but not limited to, an exciton blocking layer (EBL), a separate emitting layer, or a hole firing layer (HIL). In one embodiment, the HTL also serves as a region where excitons are formed and electroluminescent radiation occurs. Optionally, the ETL may serve as a region in which excitons are formed and electroluminescent emission 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 a collection that provides a broad emission spectrum. The other emitter emits as monomer. In one embodiment of the invention, the single luminescent material may emit as aggregate emitter and monomer emitter. Color optimization up to a high color rendering index can be achieved by selecting aggregated and monomeric emitters so that their emissions cover the visible spectrum and varying the concentration of the emitters.

In a preferred embodiment, two light emitting materials are doped into the matrix material. The matrix material is typically a charge transfer material. In a particularly preferred embodiment, the luminescent material will be phosphorescent emitters (ie they emit from triplet excited states). Materials present as charge transfer 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 the singlet and triplet states to the phosphorus triplet state or by direct capture of charge from the phosphorescent material, retrieving up to 100% of the excited state. In addition, these materials need to be able to produce acceptable electronic properties for OLEDs. In addition, such host and dopant materials can be readily introduced into the OLED using starting materials that can be introduced into the OLED, preferably by using conventional manufacturing techniques. For example, small molecular, nonpolymeric materials can be deposited using line-of-sight vacuum-deposition or can be deposited using organic vapor deposition (OVPD). The technique uses an application entitled “Low Pressure Vapor Deposition Of Organic Thin Films” filed Nov. 17, 1997, filed 08 / 972,156, incorporated herein by reference. Optionally, the polymeric materials can 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 through fluorescence and phosphorescence. The monomer emitter is preferably one that emits a high energy (eg blue or green) portion. There is no absorption in this excimer state, so there will be minimal energy transfer from the monomer emitter to the excimer.

In order to obtain effective excimer emission from the doped layer, control of the dopant concentration is an important consideration. Excimers will typically form when planar molecules are in close proximity to one another. For example, square planar metal composites, such as some Pt composites, are known to form excimers in thin films and highly concentrated solutions. For example, FPt (acac) shows monomer spinning in a ^10-6 M solution of dichloromethane and excimer deflation in a ^10-3 M concentrated solution.

At appropriate concentrations, it is possible to obtain both monomeric and excimer spinning from the same dopant. Only those dopant molecules that are in relatively close contact with other dopant molecules will be able to form excimer states. The isolated dopant molecules provide monomer spinning but do not excimer spinning. If the monomer is blue emission and the excimer is yellow emission, and if the relative contribution from each emitter can be controlled, for example by adjusting the concentration of each emitter in the emitting layer, it may be a white OLED. .

Forming an excimer state requires two emitting molecules that are in close proximity to each other, so they can be dimers when one of them is enhanced to its excited state. This shows that there can be very strong concentration dependence on excimer formation. For example, when FPt at 1% is doped with a host matrix, for example 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 monomer and excimer emission ratios are 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. This 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 block host excitons, resulting in significant host emission in the electroluminescent spectrum. To produce an effective photoluminescent OLED, the doping level is preferably about 6% or more, with the highest efficiency at higher doping levels. At a doping level high enough to produce an effective OLED, only excimer emission is observed at the FPt. In order to achieve a more effective white emission form single dopant (through simultaneous monomer and excimer emission), the doping level leading to harmonized emission must be increased.

As the emitter of steric bulk increases, the tendency for the excimer to form in the solid state is increased. The added bulk prevents the molecules from close together. This is easily found in the spectrum of FPt2 (FIG. 9). The t-Bu group of the complex interferes with the near face-to-face filling 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 FPt2 does not form the excimer. When molecules with moderate levels of steric bulk are used, it is possible to achieve mixed monomer / excimer spinning at the appropriate doping level. The role of the steric bulk administered is clearly seen in the photoluminescence spectra of FPt3 (FIG. 10) and FPt4 (FIG. 11). At low doping levels monomer emission is found and at high doping levels excimer spinning is overwhelming. Near 10% doping, closely matched monomer-excimer emission is observed for these complexes of both. At low doping levels, many contributions can be observed from the host. As the level of doping increases, the host contribution decreases as expected for more effective exciton transfer at higher emission levels.

In another embodiment of this experiment, the monomer / aggregate emission ratio is optimized by the change of host matrix material. For example, in a single dopant system (both monomer and aggregate spinning from the same dopant), the degree of binding of the dopant in the emissive layer, and so the ratio of the spinning state, can be varied by changing the host matrix material. Without wishing to be bound by theory, there is a competitive process between the aggregation of dopants in the host matrix and their dispersion during the growth of the doped film. While the host matrix serves as a good solvent, the dopant will be more uniformly dispersed in the film, favoring monomeric species. Poor soluble host matrices will not effectively disperse monomer dopants and lead to dopant aggregation. Thus, more soluble hosts will prefer monomer species over aggregate species at a given dopant concentration. Various properties of the host material may be important in determining its solvent properties for a particular dopant, including dipole moment, binding energy, and other physical properties, such as 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 spectrum. The emission region of the device consists of exciplex and monomer emitter. Luminescent materials, including monomers and excimers, emit through phosphorescence or fluorescence. The monomer emitter is preferably one that emits high energy portions of the visible spectrum (eg blue or green). Exiplex emitters provide broad radiation that spans the low energy portion of the visible spectrum. There is no absorption into this exciplex state, so there will be minimal energy transfer from the monomer emitter to the Xplex. So, 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 because the exciplex does not have any ground state absorption (the oscillator strength for absorption is zero, so the Forster radius = 0). Thus, the ratio of blue to yellow emission can be easily adjusted by changing the ratio of the two emitters, without completing the energy transfer from the blue emitter to the yellow emitter. Examples of such two materials are FIrpic and FPt. Ir complex does not form an exciplex and 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 two light sources combined provide a white light source with CRI 82 and can be 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 may include, in particular, aryl substituted oxadiazoles, aryl-substituted triazoles, aryl-substituted phenanthrolines, benzoxazoles, or benzthiazol compounds, for example 1,3-bis ( N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7); 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) -benziazolate) zinc; See, eg, C. Adachi et al., Appl. Phys. Lett., Vol. 77, 904 (2000). 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 transfer holes from the anode to the radiation area of the device. HTL materials consist of almost various forms of triaryl amines and show 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 hole flowability of about 5 x 10 ^-4 cm ² / V sce. to be. 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-toryl) amino) -3,3'-dimethylbiphenyl (M14), 4,4', 4 "-tris (30methylphenylphenyl Amino) triphenylamine (MTDATA), 4,4'-bis [N, N '-(3-toryl) 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). Additionally 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 its entirety.

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

Preferred host matrix materials for the emissive layer are carbazole biphenyl (CBP), and derivatives thereof, N, N'-dicarbazoleolibenzene and derivatives thereof, and N, N ', N "-1,3,5 Tricarbazoleolibenzenes 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 the above compounds substituted with halo. Particularly preferred host matrix materials in the emissive layer are silver 4,4 ', N, N'-dicarbazole-biphenyl (CBP), N, N'- Metadicarbozololibenzene (mCP), and N, N ', N "-1,3,5-tricarbazoleolibenzene (tCP). CBP has a number of important properties as a matrix material, for example, a high triplet energy of 2.56 eV (484 nm) and bipolar charge transfer properties, making it an excellent host in phosphorescent dopants.

Pure CBP thin film is easily crystallized. Doping small molecules into small molecules into CBP (such as a radioactive dopant) stabilizes the film in amorphous or glass form, which is stable for long periods of time. MCP, on the other hand, forms stable glass, even when it is not doped. Crystallization during device operation can lead to device failure, so this is avoided. Even when undoped, it is advantageous to have a material capable of forming stable glass, since the crystallization process tends to occur. The metering used to quantify the glass forming capacity of a given material is its glass transition temperature, T _g . This temperature characterizes the thermal stability of the glass material, so high T _g is desirable for OLED materials. At Tg, sufficient thermal expansion typically occurs and leads to device failure. mCP has a Tg of 65 ° C. While this value is acceptable for device fabrication, higher Tg is desirable for making devices with the longest possible lifetime. Increasing Tg can be readily accomplished by introducing large, rigid groups into the molecule, for example phenyl and poly-phenyl groups, and similar aryl groups. This phenyl addition / substitution must be done in a way that does not lower the triplet energy further, however, or 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, compound 1 to 4 ′ position) generally lowers the triplet energy and makes the mCP derivative less suitable for blue or white devices.

Substitution at the 2, 4, 5 or 6 position of the phenyl or polyphenyl group in the compound tends to lead to significant shifts in the 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 and derivatives thereof.

Suitable electrode (ie, anode and cathode) materials include conductive materials, such as gold, metal alloys, or electrically conductive oxides, such as ITO, which are connected to electrical contacts. Deposition of electrical contact can be accomplished by vapor deposition or other suitable metal deposition techniques. These electrical contacts can be made from 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, a cathode or an anode, typically a cathode), ie when depositing an electrode on one side of the OLED furthest from the member, 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 typically deposited from a direction that is substantially perpendicular to the member.

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

In a preferred embodiment, the cathode is preferably a low work function, electron launch material, for example a metal layer. Preferably, the cathode material has a work function of less than about 4 electron volts. The metal cathode layer may consist of a substantially thicker metal layer if the cathode is opaque. If the cathode must be transparent, a thin low work function metal can be used in combination with a transparent and electrically conductive oxide, for example ITO. Such transparent cathodes may have a metal layer having a thickness of 50-400 mm 3, preferably a metal layer having a thickness of about 100 mm 3. Transparent cathodes, for example LiF / Al may be used.

In the top-spinning apparatus, transparent cathodes can be used, for example those disclosed in U.S. Patent Nos. 5,703,436, each of which is hereby incorporated by reference, or in patent applications U.S. Ser.Nos. 08 / 964,863 and 09 / 054,707, which are pending together. Since the transparent cathode has the light transmission property, the OLED has the optical transmission property of at least about 50%. Preferably, the transparent cathode has a light transmission characteristic such that the OLED has a light transmission characteristic of at least about 70%, preferably at least about 85%.

The device of the present invention may comprise additional layers, for example an exciton blocking layer (EBL), a hole blocking layer (HBL), or a hole firing layer (HIL). One embodiment of the invention utilizes an exciton barrier layer that prevents exciton diffusion to improve overall device efficiency, and is disclosed, for example, in US Pat. No. 6,097,147, which is incorporated herein by reference in its entirety.

Particularly in devices with high energy (blue) phosphorescent emitters, an electron / exciton blocking layer can be introduced into the light emitting layer and the HTL company to prevent exciton electron leakage from the light emitting layer to the hole transport layer. High energy phosphorescent dopants tend to have high energy LUMO levels in proximity to the transport and host materials. If 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. An efficient electron / exciton barrier layer has a wide energy gap, preventing exciton leakage to HTL, high LUMO for electron blocking, and HOMO levels above HTL. Preferred materials for use in electron / exciton blocking layers are fac-tris (1-phenylpyrazolato-N, C ² ) iridium (III) (Irppz).

In another embodiment of the invention, the hole firing layer may be present between the anode layer and the hole transport layer. The hole firing layer material of the present invention may be defined as a material that wets or planarizes the anode surface to prevent effective hole transfer from the anode to the hole transport material. The hole transport materials of the present invention favorably match the HOMO energy levels, which are contiguous with the emitter-coated electron transport layer on the adjacent anode layer on one side of the HIL layer and on the other side of the HIL layer, as defined by their relative IP energy. It is defined as having The highest occupied molecular orbital (HOMO) obtained for each material corresponds to its ionization potential (IP). The highest unoccupied molecular orbital (LUMO) is equal to the sum of the optical energy gap and IP and is measured from the absorption spectrum. The relative alignment of the energy in the fully assembled device may be slightly different from that predicted, for example, from the absorption spectrum.

HIL materials, which may be hole transport materials, are distinguished from conventional hole transport materials typically used in the hole transport layer of OLEDs, and HIL materials have fluidity that may be substantially less than the hole flowability of conventional hole transport materials. . For example, m-MTDATA has been defined as effective in enhancing the firing of holes from the ITO with, for example, HTL consisting of α-NPD or TPD. If possible, the HIL effectively fires a hole due to a decrease in HTL HOMO level / ITO offset energy or wetting of the ITO surface. Compared with α-NPD and TPD having hole flow of about 5 x 10 ^-4 cm ² / V sec and 9 x 10 ^-4 cm ² / V sec, respectively, the HIL material m-MTDATA is about 3 x 10 ^-5 It is believed to have hole flowability in cm ² / V sec. Thus, the m-MTDATA material has less than one order of hole flowability than the commonly used HTL materials α-NPD and TPD.

Other HIL materials include phthalocyanine compounds, for example copper phthalocyanine, or poly-3,4-ethylenedioxythiophene (PEDOT) or poly (ethene), which are effective for promoting the firing of holes from the anode to the HIL material and then to the HTL. Deoxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS) and other materials including polymeric materials.

The HIL thickening of the present invention needs to be thick enough to help wet or planarize the anode layer. For example, HIL thicknesses on the order of 10 nm are 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 to mimic the light emitted, for example, 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.

There may be substantial variations in the type, number, thickness, and order of the layers, depending on whether there is an inverse order of the OLED layers, or other design changes may be used. Those skilled in the art will recognize various modifications to the embodiments of the invention described and reported herein. Such modifications are intended to be covered by the spirit and scope of the invention. That is, although the invention is described in detail with reference to certain specific embodiments, those skilled in the art will recognize that there may be other embodiments of the invention 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 2,4-difluorophenylboronic acid and 2-bromopyridine (Aldrich) Suzuki coupling. 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). The dimers were treated with _three equivalent chelating diketone ligands and ten equivalent Na ₂ CO ₃ . 2,6-dimethyl 3,5-heptanedione, and 6-methyl-2,2-heptanedione were granulated 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 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 coupling of aryl halides and arylamines (T. Yamamoto, M. Nishiyama, Y. Koie Tet. Lett., 1998, 39, 2367-2370).

Example 1

Field phosphor excimer WOLEDs were grown on glass members previously coated with an iridium-tin-oxide (ITO) layer having a sheet resistance of 20-W / sq. Before lamination of the organic layer, the member was degreased in an ultrasonic solvent bath and then treated with oxygen plasma at 20 W alc 150 mTorr for 8 minutes. Poly (ethylene-deoxythiophene): poly (styrene sulfonic acid) (PEDOT: PSS) used to reduce OLED leakage and improve production yield is spun on 4000 rpm ITO for 40 s, and 120 It was baked in vacuo at 15 ° C. for about 40 nm in thickness. Hole transfer and host materials, and both dopants, were prepared by standard procedures (Lamansky, S. et al., Inorg. Chem. 40, 1704-1711, 2001). The molecular organic layer was subsequently deposited without vacuum rupture by thermal evaporation at a base pressure of <8 x 10 ^-7 Torr.

Deposition begins with 30 nm-thick 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl (α-NPD) hole transport layer (HTL), both 6% by weight Followed by a 30 nm thick radiation region consisting of FIr (pic) and FPt (acac), blue emission doped on a 4,4'-N, N'-dicarbazole-biphenyl (CBP) host. The final left organic layer deposited was 50 nm of vasocuproin (BCP). This layer serves as a hole and exciton blocking layer and an electron transport medium.

After the organic layer is deposited, the sample is transferred to a N ₂ filled glove box containing ≦ 1 ppm H ₂ O and O ₂ in a vacuum chamber. After fixing the masks with 1 mm diameter openings to the sample, they are transferred into a second vacuum chamber (<10 ⁻⁷ Torr) where a cathode metal (comprising 5 μL LiF followed by 70 nm Al) is deposited through the mask. It became. 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 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 a double doped system by mentioning the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the three organic compounds (right bottom interpolator). Adachi, C. et al., Appl. Phys. Lett. The endothermic process described by 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), similar endothermic triplet energy transfer pathways lead to CBP and FPt Can be expected for (acac). The resonance energy transfer between the triplet levels of the two dopants is also similar because they are also present in high concentrations in the CBP matrix. However, direct energy transfer from FIr (pic) to the excimer cannot occur because the excimer has zero ground state absorption and interferes with the energy cascade from blue to yellow emission centers. This inevitably unpairs these molecules in an excited state and allows a simple optimization of doping to achieve the desired color harmonization.

Light output from the WOLED is measured through a Newport Power Meter and a calibrated silicon photodiode, and then calculated using η _ext using the current density-voltage characteristics shown in the left interpolation of FIG. The Ramada intensity profile is assumed to calculate η _p (FIG. 7) and luminous intensity. Here, η _ext ≧ 3.0% is between J = 1 × 10 ⁻³ mA / cm ² to 10 mA / cm ² . Roll-off at J> 300 mA / cm ² contributes to sample heating and triple-triple extinction. WOLEDs have a maximum η _ext = (4.0 ± 0.4)%, which means 16.6 V, η _p = (4.0 ± 0.4) lm / W and CRI 78 (9.2 ± 0.9) cd / A, luminous intensity (31 000 ± 3000) corresponds to cd / m ² .

Pure films of FPt (acac) have lifetimes of t = 4.8 ms and 5.2 ms at λ = 470 nm and λ = 600 nm, respectively. As the current density increases, the FPt (acac) excimer state may be saturated compared to the monomer and FIr (pic), leading 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 prepared at 8,10 and 12% doping levels with FPt ₃ . The device structure consists 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 are similar, and as the doping level increases, less leakage occurs at low voltages. CBP host radiation was not found at any doping level, indicating that the FPt ₃ dopant effectively captured all excimers formed in the CBP matrix. While excimer formation in CBP is a possible result of hole-electron recombination, it is possible that holes or electrons are captured in FPt ₃ molecules, and direct recombination can occur in the dopant. The latter process leads to excitons formed in the dopant and does not require energy transfer from the matrix material, in this case CBP. It is essential for the Ir (ppz) ₃ electron blocking layer to prevent leakage to the NPD layer, which leads to NPD radiation in addition to the dopant monomer-eximer radiation. All three devices show turn-on voltages between 3 and 4 volts, and maximum luminous intensity between 4000 and 10,000 Cd / m ² . The spectrum of the device shows very little change as the voltage rises, ie the ratio of monomer to excimer is not significantly affected by voltage or current density. 10 to 12% doped devices provide peak efficiencies of 4 and 3.5%, respectively. The 10 and 12% doped devices also provide very good output efficiencies of 8 and 6.5 lm / W (at 1 Cd / m ² ), respectively.

Example 4

A thin film of mCP doped with varying weight% FPt was prepared through simultaneous deposition of the two materials on the glass member. The FPt spectrum doped with mCP is shown in FIG. 20 in the concentration range. The maximum emission wavelength for the aggregate state of monomers and FPt doped into mCP is the same as that of FPt in CBP. Harmonized monomer / aggregate spinning was found at the doping level of about 15% by weight, which is almost three times required to achieve an equivalent monomer / aggregate spinning ratio. This means that mCP is a better solvent for FPt, leading to fewer FPt ... FPt interactions at the mCP doped at a given concentration.

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 than CBP to FPt. Point. Despite the high triplet energy of CBP (phosphorescence lambda _max = 460 nm), the energy transfer from CBP to the blue phosphorescent dopant, for example the Pt composites used here, is an endothermic process. On the other hand, mCP has a peak phosphorescence spectrum at 410 nm and makes a more efficient exothermic process 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% by weight give the CIE coordinates closest to white (0.33, 0.33) and maximum CRI is observed in the concentration range of about 15-20% by weight. 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

NPD (400 mV) / Irppz (200 mV) / mCP: FPt (16% 300 mV) / BCP (150 mV) / Alq3 (200 mV) / LiF (10 mV) / (Al 1000 mV) structure. The use of mCP hosts in CBP locations significantly improves device performance. The efficiency, current-voltage characteristics and spectrum of the device are shown in FIGS. 23, 24, and 25. Higher doping concentrations and improved energy transfer from the mCP to the dopant resulted in maximum quantum efficiency of 6.4 ± 0.6% (12.2 1.4 lum / W, 17.0 cd / A) at low brightness levels (1 CD / m ² ) and 4.3 ± 0. 5% (8.1 ± 0.6 lum / W, 11.3 cd / A) is provided at 500 cd / m ² . The quantum efficiency exemplified by these mCP / FPt WOLEDs is the maximum efficiency reported for WOLEDs. Quantum efficiency decreases with increasing current density, as reported by other devices, but the decrease is less severe than most other field phosphor 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.

Energy level diagrams for mCP and CBP devices are shown in FIG. 22, showing that the impediment to electron migration from the dopant / CBP LUMO level to the NPD LUMO can be comparable to the impaired hole firing from the NPD to the emitting layer. Elimination of electron / exciton leaks into the HTL results in improved WOLED efficiency and color stability. Irppz complexes emit exclusively from phosphorescent excited states (λ _max = 414 nm 77K, τ = 15 μs). The optical gap of this composite was taken as the low energy edge of the absorption spectrum at 370 nm (3.4 eV). This measurement 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 / ferrocenium), but no reduction occurs -3.0 V in DMF, consistent with> 3.4 eV carrier gap. The HOMO energy of Irppz was measured by extreme ultraviolet photoelectron spectroscopy (UPS) and found to be 5.5 eV. Using the Irppz optical gap to predict the carrier gap, the Irppz LUMO is 2.1 eV and predicts that it 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 (45)

An organic light emitting device comprising an emission layer, The emitting layer is an aggregate emitter, and A monomer emissive layer, Wherein the radiation from the aggregate emitter is lower in energy than the radiation from the monomer emitter, and wherein the mixed emission of the aggregate emitter and the monomer emitter is sufficiently over the visible spectrum to provide white emission. The device of claim 1, wherein the aggregate emitter is an excimer. The device of claim 1, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 4. The device of claim 3, wherein the excimer emitter and the monomer emitter are comprised of the same chemical compound. 4. The device of claim 3, wherein the monomer emitter and aggregate emitter are phosphorescent organometallic compounds. 6. The device of claim 5, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). The device of claim 1, wherein the blended radiation has a color rendering index of at least about 80. The device of claim 1, wherein the blended radiation has a CIE x-coordinate of about 0.30 to about 0.40 and a CIE y-coordinate of about 0.30 to about 0.45. The device of claim 1, wherein the emissive layer comprises an exciplex emitter and a monomer emitter. 10. The device of claim 9, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. The device of claim 10, wherein the monomer emitter and exciplex emitter are phosphorescent organometallic compounds. The device of claim 1, wherein the emissive layer further comprises a polymer matrix. The apparatus of claim 12, wherein the polymer matrix is PVK. Enod, Hall transport floor, An electron transport layer, and Including a cathode, Wherein the hole transport layer or electron transport layer is an emissive layer, the emissive layer comprising an aggregate emitter and a monomer emitter layer, wherein radiation from the aggregate emitter is lower in energy than radiation from the monomer emitter, and wherein the aggregate emitter and monomer emitter An organic light-emitting device in which the mixed radiation of s is sufficiently spanning the visible spectrum to provide white emission. 15. The apparatus of claim 14, wherein the hole transport layer is an emissive layer. 15. The device of claim 14, wherein the electron transport layer is an emissive layer. 15. The apparatus of claim 14, wherein the aggregate emitter is an excimer. 15. The apparatus of claim 14, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 19. The device of claim 18, wherein the aggregate emitter and the monomer emitter are comprised of the same chemical compound. 19. The device of claim 18, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 21. The apparatus of claim 20, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). 15. The apparatus of claim 14, wherein the mixed radiation has a color rendering index of at least about 80. The apparatus of claim 14, wherein the blended radiation has a CIE x-coordinate of about 0.30 to about 0.40 and a CIE y-coordinate of about 0.30 to about 0.45. 15. The device of claim 14, wherein the emissive layer comprises an exciplex emitter and a monomer emitter. The apparatus of claim 24 wherein the exciplex emitter and the monomer emitter emit by phosphorescence. The device of claim 24, wherein the monomer emitter and exciplex emitter are phosphorescent organometallic compounds. 15. The apparatus of claim 14, wherein the emissive layer further comprises a polymer matrix. The apparatus of claim 27, wherein the polymer matrix is PVK. 15. The device of claim 14, further comprising an exciton blocking layer. 15. The apparatus of claim 14, further comprising a hole transport layer. An anode; Hole transport layer; Emission layer; Electron transport layer; And Including a cathode, Wherein the emitting layer comprises an aggregate emitter and a monomer emitter, wherein radiation from the aggregate emitter is lower in energy than radiation from the monomer emitter, and wherein the mixed emission of the aggregate emitter and the monomer emitter is in the visible spectrum providing white emission. Fully spread organic light emitting device. 32. The device of claim 31, wherein the emissive layer comprises an excimer emitter and a monomer emitter. 32. The apparatus of claim 31, wherein the aggregate emitter and the monomer emitter emit by phosphorescence. 34. The device of claim 33, wherein the aggregate emitter and the monomer emitter are comprised of the same chemical compound. 34. The device of claim 33, wherein the aggregate emitter and the monomer emitter are phosphorescent organometallic compounds. 36. The apparatus of claim 35, wherein the aggregate emitter comprises FPt (acac) and the monomer emitter comprises FIr (pic). 32. The apparatus of claim 31, wherein the blended radiation has a color rendering index of at least about 80. The apparatus of claim 31, wherein the blended radiation has a CIE x-coordinate of about 0.30 to about 0.40 and a CIE y-coordinate of about 0.30 to about 0.45. 32. The device of claim 31, wherein the emissive layer comprises an exciplex emitter and a monomer emitter. 40. The device of claim 39, wherein the exciplex emitter and the monomer emitter emit by phosphorescence. 41. The device of claim 40, wherein the monomer emitter and exciplex emitter are phosphorescent organometallic compounds. 32. The device of claim 31, wherein the emissive layer further comprises a polymer matrix. 43. The apparatus of claim 42, wherein the polymer matrix is PVK. 32. The device of claim 31, further comprising an exciton barrier layer. A light source incorporating the claim 1 or a device.