Organic Electroluminescent Device Emitting Blue Light

Abstract

The present invention relates to organic electroluminescent devices comprising a light-emitting layer B comprising a host material H.sup.B, a first thermally activated delayed fluorescence (TADF) material E.sup.B, and a depopulation agent S.sup.B.

Claims

1. An organic electroluminescent device comprising a light-emitting layer B comprising: (i) a first material H.sup.B, which has a lowest unoccupied molecular orbital LUMO(H.sup.B) having an energy E.sup.LUMO(H.sup.B) and a highest occupied molecular orbital HOMO(H.sup.B) having an energy E.sup.HOMO(H.sup.B); (ii) a second material E.sup.B, which has a lowermost excited singlet state energy level S1.sup.E, a lowermost excited triplet state energy level T1.sup.E, a lowest unoccupied molecular orbital LUMO(E.sup.B) having an energy E.sup.LUMO(E.sup.B) and a highest occupied molecular orbital HOMO(E.sup.B) having an energy E.sup.HOMO(E.sup.B); and (iii) a third material S.sup.B, which has a lowermost excited singlet state energy level S1.sup.S, a lowermost excited triplet state energy level T1.sup.S, a lowest unoccupied molecular orbital LUMO(S.sup.B) having an energy E.sup.LUMO(S.sup.B) and a highest occupied molecular orbital HOMO(S.sup.B) having an energy E.sup.HOMO(S.sup.B), wherein the relations expressed by the following formulas (1) to (2) and either (3a) and (5a) or (4a) and (5b) apply:
S1.sup.S?S.sup.1E (1)
T1.sup.S?2.5 eV (2)
E.sup.LUMO(E.sup.B)<E.sup.LUMO(H.sup.B) (3a)
E.sup.HOMO(E.sup.B)>E.sup.HOMO(H.sup.B) (5a)
E.sup.LUMO(E.sup.B)>E.sup.LUMO(H.sup.B) (4a)
E.sup.HOMO(E.sup.B)<E.sup.HOMO(H.sup.B) (5b), and wherein the mass ratio of second material E.sup.B to a third material S.sup.B(E.sup.B:S.sup.B) is>1.

2. The organic electroluminescent device according to claim 1, the second material E.sup.B is characterized in that it has a ?E.sub.ST value, which corresponds to the energy difference between S1.sup.E and T1.sup.E, of less than 0.4 eV, and/or the third material S.sup.B is characterized in that it has a ?E.sub.ST value, which corresponds to the energy difference between S1.sup.S and T1.sup.S, of less than 0.4 eV.

3. The organic electroluminescent device according to claim 1, the light-emitting layer B emits light with CIEx color coordinate of between 0.02 and 0.30.

4. The organic electroluminescent device according to claim 1, the light-emitting layer B emits light with CIEy color coordinate of between 0.01 and 0.30.

5. The organic electroluminescent device according to claim 1, wherein at least one of the first material H.sup.B, the second material E.sup.B and the third material S.sup.B comprises a carbazole moiety.

6. The organic electroluminescent device according to claim 1, wherein each of the first material H.sup.B, the second material E.sup.B and the third material S.sup.Bcomprises a carbazole moiety.

7. The organic electroluminescent device according to claim 1, wherein the device exhibits an emission maximum ?.sub.max(D) of 440 to 480 nm.

8. The organic electroluminescent device according to claim 1, the light-emitting layer B further comprises a fourth material H.sup.B2 differing from the first material H.sup.B.

9. The organic electroluminescent device according to claim 1, wherein the relation expressed by the following formula (6) applies:
E.sup.HOMO(S.sup.B)<E.sup.HOMO(H.sup.B) (6).

10. The organic electroluminescent device according to claim 1, wherein said organic electroluminescent device is a device selected from the group consisting of an organic light emitting diode, a light emitting electrochemical cell, and a light-emitting transistor.

11. An organic electroluminescent device comprising a light-emitting layer B comprising: (i) a first material H.sup.B, which has a lowest unoccupied molecular orbital LUMO(H.sup.B) having an energy E.sup.LUMO(H.sup.B) and a highest occupied molecular orbital HOMO(H.sup.B) having an energy E.sup.HOMO(H.sup.B); (ii) a second material E.sup.B, which has a lowermost excited singlet state energy level S1.sup.E, a lowermost excited triplet state energy level T1.sup.E, a lowest unoccupied molecular orbital LUMO(E.sup.B) having an energy E.sup.LUMO(E.sup.B) and a highest occupied molecular orbital HOMO(E.sup.B) having an energy E.sup.HOMO(E.sup.B); (iii) a third material S.sup.B, which has a lowermost excited singlet state energy level S1.sup.S, a lowermost excited triplet state energy level T1.sup.S a lowest unoccupied molecular orbital LUMO(S.sup.B) having an energy E.sup.LUMO(S.sup.B) and a highest occupied molecular orbital HOMO(S.sup.B) having an energy E.sup.HOMO(S.sup.B); and (iv) a fourth material H.sup.B2 differing from the first material H.sup.B, which has a lowest unoccupied molecular orbital LUMO(H.sup.B2) having an energy E.sup.LUMO(H.sup.B2) and a highest occupied molecular orbital HOMO(H.sup.B2) having an energy E.sup.HOMO(H.sup.B2); wherein the relations expressed by the following formulas (1), (2), (7a) and (7b) apply:
S1.sup.S?S.sup.1E (1)
T1.sup.S?2.5 eV (2)
E.sup.HOMO(E.sup.B)?E.sup.HOMO(H.sup.B)?0.3 eV and E.sup.HOMO(E.sup.B)?E.sup.HOMO(H.sup.B)??0.3 eV (7a)
E.sup.LUMO(E.sup.B)?E.sup.LUMO(H.sup.B2)?0.4 eV and E.sup.LUMO(E.sup.B)?E.sup.LUMO(H.sup.B2)??0.4 eV (7b).

12. The organic electroluminescent device according to claim 11, wherein the first material H.sup.B comprises a carbazole moiety.

13. The organic electroluminescent device according to claim 11, wherein the first material H.sup.B is a hole-dominant host and the fourth material H.sup.B2 is an electron-dominant host.

14. The organic electroluminescent device according to claim 11, wherein the device exhibits an external quantum efficiency at 1000 cd/m.sup.2 of more than 10% and/or exhibits an emission maximum ?.sub.max(D) of 440 to 480 nm.

15. The organic electroluminescent device according to claim 11, wherein the relation expressed by the following formulas (3a) and (3b) or (4a) and (4b) apply:
E.sup.LUMO(E.sup.B)<E.sup.LUMO(H.sup.B) (3a)
0.2 eV<E.sup.LUMO(E.sup.B)?E.sup.LUMO(S.sup.B)<0.5 eV (3b)
E.sup.LUMO(E.sup.B)>E.sup.LUMO(H.sup.B) (4a)
0.2 eV<E.sup.LUMO(H.sup.B)?E.sup.LUMO(S.sup.B)<0.5 eV (4b).

16. The organic electroluminescent device according to claim 11, the second material E.sup.B is characterized in that it has a ?E.sub.ST value, which corresponds to the energy difference between S1.sup.E and T1.sup.E, of less than 0.4 eV, and/or the third material S.sup.B is characterized in that it has a ?E.sub.ST value, which corresponds to the energy difference between S1.sup.S and T1.sup.S, of less than 0.4 eV.

17. The organic electroluminescent device according to claim 11, wherein the relation expressed by the following formula (6) applies:
E.sup.HOMO(S.sup.B)<E.sup.HOMO(H.sup.B) (6).

18. The organic electroluminescent device according to claim 11, the device further comprises one or more protective layers.

19. The organic electroluminescent device according to claim 11, the device emits light with a FWHM of the main emission peak of below 0.50 eV.

20. The organic electroluminescent device according to claim 11, wherein said organic electroluminescent device is a device selected from the group consisting of an organic light emitting diode, a light emitting electrochemical cell, and a light-emitting transistor.

Description

EXAMPLES

[0501] Cyclic Voltammetry

[0502] Cyclic voltammograms of solutions having concentration of 10?3 mol/l of the organic molecules in dichloromethane or a suitable solvent and a suitable supporting electrolyte (e.g. 0.1 mol/l of tetrabutylammonium hexafluorophosphate) are measured. The measurements are conducted at room temperature and under nitrogen atmosphere with a three-electrode assembly (Working and counter electrodes: Pt wire, reference electrode: Pt wire) and calibrated using FeCp.sub.2/FeCp.sub.2.sup.+ as internal standard. HOMO data was corrected using ferrocene as internal standard against SCE.

[0503] Density Functional Theory Calculation

[0504] Molecular structures are optimized employing the BP86 functional and the resolution of identity approach (RI). Excitation energies are calculated using the (BP86) optimized structures employing Time-Dependent DFT (TD-DFT) methods. Orbital and excited state energies are calculated with the B3LYP functional. Def2-SVP basis sets (and a m4-grid for numerical integration were used. The Turbomole program package was used for all calculations.

[0505] Photophysical Measurements

[0506] Sample pretreatment: Spin-coating

[0507] Apparatus: Spin150, SPS euro.

[0508] The sample concentration is 10 mg/ml, dissolved in a suitable solvent.

[0509] Program: 1) 3 s at 400 U/min; 20 s at 1000 U/min at 1000 Upm/s. 3) 10 s at 4000 U/min at 1000 Upm/s. After coating, the films are tried at 70? C. for 1 min.

[0510] Photoluminescence spectroscopy and TCSPC (Time-correlated single-photon counting)

[0511] Steady-state emission spectroscopy is recorded using a Horiba Scientific, Modell FluoroMax-4 equipped with a 150 W Xenon-Arc lamp, excitation- and emissions monochromators and a Hamamatsu R.sup.928 photomultiplier and a time-correlated single-photon counting option. Emissions and excitation spectra are corrected using standard correction fits.

[0512] Excited state lifetimes are determined employing the same system using the TCSPC method with FM-2013 equipment and a Horiba Yvon TCSPC hub.

[0513] Excitation Sources: [0514] NanoLED 370 (wavelength: 371 nm, puls duration: 1,1 ns) [0515] NanoLED 290 (wavelength: 294 nm, puls duration: <1 ns) [0516] SpectraLED 310 (wavelength: 314 nm) [0517] SpectraLED 355 (wavelength: 355 nm).

[0518] Data analysis (exponential fit) was done using the software suite DataStation and DAS6 analysis software. The fit is specified using the chi-squared-test.

[0519] Photoluminescence Quantum Yield Measurements

[0520] For photoluminescence quantum yield (PLAY) measurements an Absolute PL Quantum Yield Measurement C.sub.9920-03G system (Hamamatsu Photonics) is used. Quantum yields and CIE coordinates were determined using the software U6039-05 version 3.6.0.

[0521] Emission maxima are given in nm, quantum yields ? in % and CIE coordinates as x,y values.

[0522] PLQY was determined using the following protocol: [0523] 1) Quality assurance: Anthracene in ethanol (known concentration) is used as reference [0524] 2) Excitation wavelength: the absorption maximum of the organic molecule is determined and the molecule is excited using this wavelength [0525] 3) Measurement

[0526] Quantum yields are measured for sample of solutions or films under nitrogen atmosphere. The yield is calculated using the equation:

[00001]${?}_{PL}=\frac{n_{\mathrm{photon}},\mathrm{emited}}{n_{\mathrm{photon}},\mathrm{absorbed}}=\frac{?\frac{?}{hc}\left[{\mathrm{Int}}_{\mathrm{emitted}}^{\mathrm{sample}}\left(?\right)-{\mathrm{Int}}_{a\mathrm{bsorbed}}^{\mathrm{sample}}\left(?\right)\right]d?}{?\frac{?}{hc}\left[{\mathrm{Int}}_{\mathrm{emitted}}^{\mathrm{reference}}\left(?\right)-{\mathrm{Int}}_{a\mathrm{bsorbed}}^{\mathrm{reference}}\left(?\right)\right]d?}$

wherein n.sub.photon denotes the photon count and Int. is the intensity.

[0527] Production and Characterization of Organic Electroluminescence Devices

[0528] Via vacuum-deposition methods OLED devices comprising organic molecules according to the invention can be produced. If a layer contains more than one compound, the weight-percentage of one or more compounds is given in %. The total weight-percentage values amount to 100%, thus if a value is not given, the fraction of this compound equals to the difference between the given values and 100%.

[0529] The not fully optimized OLEDs are characterized using standard methods and measuring electroluminescence spectra, the external quantum efficiency (in %) in dependency on the intensity, calculated using the light detected by the photodiode, and the current. The OLED device lifetime is extracted from the change of the luminance during operation at constant current density. The LT50 value corresponds to the time, where the measured luminance decreased to 50% of the initial luminance, analogously LT80 corresponds to the time point, at which the measured luminance decreased to 80% of the initial luminance, LT97 to the time point, at which the measured luminance decreased to 97% of the initial luminance etc.

[0530] Accelerated lifetime measurements are performed (e.g. applying increased current densities). Exemplarily LT80 values at 500 cd/m.sup.2 are determined using the following equation:

[00002]$\mathrm{LT}80\left(500\frac{c{d}^2}{m^2}\right)=\mathrm{LT}80\left(L_0\right){\left(\frac{L}{500\frac{{\mathrm{cd}}^2}{m^2}}\right)}^{1.6}$

wherein L.sub.0 denotes the initial luminance at the applied current density.

[0531] The values correspond to the average of several pixels (typically two to eight), the standard deviation between these pixels is given. Figures show the data series for one OLED pixel.

Examples D1 and D2 and Comparative Examples C.SUB.1

[0532] ##STR00083## ##STR00084##

TABLE-US-00001 ?.sub.max.sup.PMMA [nm] HOMO [eV] LUMO [eV] S1 [eV] T1 [eV] mCBP ?6.02 ?2.34 3.60 2.95 TADF1 469 ?5.81 ?2.86 2.94 MAT1 450 ?6.14 ?3.11 3.03 2.75 MAT2 465 ?6.16 ?3.16 2.94 2.83

TABLE-US-00002 Layer Thickness D1 D2 C2 10 100 nm Al Al Al 9 2 nm Liq Liq Liq 8 20 nm NBPhen NBPhen NBPhen 7 10 nm HBL1 HBL1 HBL1 6 50 nm TADF1 (20%): TADF1 (20%): TADF1 (20%): MAT1 (5%): MAT2 (5%): mCBP (80%) mCBP (75%) mCBP (75%) 5 10 nm mCBP mCBP mCBP 4 10 nm TCTA TCTA TCTA 3 40 nm NPB NPB NPB 2 5 nm HAT-CN HAT-CN HAT-CN 1 50 nm ITO ITO ITO substrate glass glass glass

[0533] Device D1 yielded an external quantum efficiency (EQE) at 1000 cd/m.sup.2 of 15.4?0.5%. The LT80 value at 500 cd/m.sup.2 was determined to be 81 h from accelerated lifetime measurements. The emission maximum is at 472 nm with a FWHM of 67 nm at 10 mA/cm.sup.2. The corresponding CIEy value is 0.24.

[0534] Device D2 yielded an external quantum efficiency (EQE) at 1000 cd/m.sup.2 of 12.6?0.2%. The LT80 value at 500 cd/m.sup.2 was determined to be 57 h from accelerated lifetime measurements. The emission maximum is at 471 nm with a FWHM of 67 nm at 10 mA/cm.sup.2. The corresponding CIEy value is 0.25.

[0535] Comparative device C.sub.1 comprises an emitting layer containing only TADF1 as emitter and mCBP as host material. The EQE at 1000 cd/m.sup.2 is at 9.5?0.1%, thus lower than for D1 and D2 and the lifetime is significantly shorter (LT80 at 500 cd/m.sup.2=29 h). The emission maximum appears at 475 nm with a FWHM of 68 nm at 10 mA/cm.sup.2. The corresponding CIEy value is 0.24.