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EP-4214772-B1 - ORGANIC ELECTROLUMINESCENT DEVICE

EP4214772B1EP 4214772 B1EP4214772 B1EP 4214772B1EP-4214772-B1

Inventors

  • SHARIFIDEHSARI, Hamed
  • LIAPTSIS, Georgios
  • CARBALLO, Jaime Leganés
  • JOLY, Damien

Dates

Publication Date
20260506
Application Date
20210917

Claims (15)

  1. An organic electroluminescent device comprising at least one light-emitting layer B which is composed of one or more sublayers, wherein the one or more sublayers are adjacent to each other and as a whole contain: (i) at least one host material H B , which has a lowermost excited singlet state energy level E(S1 H ) and a lowermost excited triplet state energy level E(T1 H ); (ii) at least one phosphorescence material P B , which has a lowermost excited singlet state energy level E(S1 P ) and a lowermost excited triplet state energy level E(T1 P ); and (iii) at least one small full width at half maximum (FWHM) emitter S B , which has a lowermost excited singlet state energy level E(S1 S ) and a lowermost excited triplet state energy level E(T1 S ); and optionally (iv) at least one thermally activated delayed fluorescence (TADF) material E B , which has a lowermost excited singlet state energy level E(S1 E ) and a lowermost excited triplet state energy level E(T1 E ), wherein the one or more sublayers which are located at the outer surface of the light-emitting layer B contain at least one material selected from the group consisting of phosphorescence material P B , small FWHM emitter S B , and TADF material E B , wherein the at least one host material H B has a highest occupied molecular orbital HOMO(H B ) having an energy E HOMO (H B ) as determinable by cyclic voltammetry measurements, which is smaller than -5.60 eV, preferably wherein each host material H B has a highest occupied molecular orbital HOMO(H B ) having an energy E HOMO (H B ), which is smaller than -5.60 eV, wherein the energy E HOMO (H B ) is determined via density functional theory calculations using the Turbomole software package, or via cyclic voltammetry of solutions having concentration of 10 -3 mol/l of the organic molecules in dichloromethane, wherein 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 2 /FeCp 2 + as internal standard, wherein the HOMO data was corrected using ferrocene as internal standard against SCE, characterized in that S B emits light with a full width at half maximum (FWHM) of less than or equal to 0.25 eV as determinable at approximately 20°C measured from a film of 2% by weight of the small FWHM emitter in poly(methyl methacrylate) (PMMA).
  2. The organic electroluminescent device according to claim 1, wherein at least one of the one or more sublayers of the at least one light-emitting layer B, preferably each light-emitting layer B, comprises: (iv) at least one thermally activated delayed fluorescence (TADF) material E B , which has a lowermost excited singlet state energy level E(S1 E ) and a lowermost excited triplet state energy level E(T1 E ).
  3. The organic electroluminescent device according to one or both of claims 1 and 2, wherein the at least one TADF material E B , preferably each TADF material E B (i) is characterized by exhibiting a ΔE ST value, which corresponds to the energy difference between the lowermost excited singlet state energy level E(S1 E ) and the lowermost excited triplet state energy level E(T1 E ), of less than 0.4 eV; and (ii) displays a photoluminescence quantum yield (PLQY) of more than 30%.
  4. The organic electroluminescent device according to one or more of claims 1 to 3, wherein the relations expressed by the following formulas (1), (2) and (3) apply: E T 1 H > E T 1 P E T 1 P > E S 1 S E T 1 H > E T 1 E
  5. The organic electroluminescent device according to one or more of claims 1 to 4, wherein at least one sublayer comprises exactly one TADF material E B and exactly one phosphorescence material P B .
  6. The organic electroluminescent device according to one or more of claims 1 to 5, wherein a sublayer comprises exactly one TADF material E B and a sublayer comprises exactly one phosphorescence material P B and exactly one small FWHM emitter S B .
  7. The organic electroluminescent device according to one or more of claims 1 to 6, wherein the at least one H B , preferably each H B , is a p-host H P , comprising or consisting of: - one first chemical moiety, comprising or consisting of a structure according to any of the formulas H P -I, H P -II, H P -III, H P -IV, H P -V, H P -VI, H P -VII, H P -VIII, H P -IX, and H P -X: and - one or more second chemical moiety, each comprising or consisting of a structure according to any of formulas H P -XI, H P -XII, H P -XIII, H P -XIV, H P -XV, H P -XVI, H P -XVII, H P -XVIII, and H P -XIX: wherein each of the at least one second chemical moieties which is present in the p-host material H P is linked to the first chemical moiety via a single bond which is represented in the formulas above by a dashed line; wherein Z 1 is at each occurrence independently of each other selected from the group consisting of a direct bond, C(R II ) 2 , C=C(R II ) 2 , C=O, C=NR II , NR II , O, Si(R II ) 2 , S, S(O) and S(O) 2 ; R I is at each occurrence independently of each other a binding site of a single bond linking the first chemical moiety to a second chemical moiety or is selected from the group consisting of: hydrogen, deuterium, Me, i Pr, and t Bu, and Ph, which is optionally substituted with one or more substituents independently of each other selected from the group consisting of: Me, i Pr, t Bu, and Ph; wherein at least one R I is a binding site of a single bond linking the first chemical moiety to a second chemical moiety; R II is at each occurrence independently of each other selected from the group consisting of: hydrogen, deuterium, Me, i Pr, t Bu, and Ph, which is optionally substituted with one or more substituents independently of each other selected from the group consisting of: Me, i Pr, t Bu, and Ph; wherein two or more adjacent substituents R II may optionally form an aliphatic or aromatic, carbo- or heterocyclic ring system so that the fused ring system consisting of a structure according to any of formulas H P -XI, H P -XII, H P -XIII, H P -XIV, H P -XV, H P -XVI, H P -XVII, H P -XVIII, and H P -XIX as well as the additional rings optionally formed by adjacent substituents R II comprises in total 3-60 carbon atoms.
  8. The organic electroluminescent device according to one or more of claims 1 to 7, wherein the relations expressed by the following formulas (3) and (4) apply: E T 1 H > E T 1 E E T 1 E > E T 1 P
  9. The organic electroluminescent device according to one or more of claims 1 to 8, wherein: (i) the at least one host material H B , preferably each host material H B , has a highest occupied molecular orbital HOMO(H B ) having an energy E HOMO (H B ); (iii) the at least one phosphorescence material P B , preferably each phosphorescence material P B , has a highest occupied molecular orbital HOMO(P B ) having an energy E HOMO (P B ); (iv) the at least one each small full width at half maximum (FWHM) emitter S B , preferably each small full width at half maximum (FWHM) emitter S B , has a highest occupied molecular orbital HOMO(S B ) having an energy E HOMO (S B ); wherein the relations expressed by the following formulas (10) and (11) apply: E HOMO P B > E HOMO H B E HOMO P B > E HOMO S B
  10. The organic electroluminescent device according to one or more of claims 1 to 9, wherein the relation expressed by formulas (4) applies: E T 1 E > E T 1 P
  11. The organic electroluminescent device according to one or more of claims 1 to 10, wherein the at least one small FWHM emitter S B fulfills at least one of the following requirements, preferably each small FWHM emitter S B , fulfills at least one of the following requirements: (i) it is a boron (B)-containing emitter, which means that at least one atom within each small FWHM emitter S B is boron (B); (ii) it comprises a polycyclic aromatic or heteroaromatic core structure, wherein at least two aromatic rings are fused together such as, e.g., anthracene, pyrene or aza-derivatives thereof.
  12. The organic electroluminescent device according to one or more of claims 1 to 11, wherein the one or more sublayers as a whole comprise or consist of: (i) 30-99.8 % by weight of one or more host compound H B ; (ii) 0.1-30 % by weight of one or more phosphorescence material P B and (iii) 0.1-10 % by weight of one or more small FWHM emitter S B ; and optionally (iv) 0-69.8 % by weight of one or more TADF material E B ; and optionally (v) 0-69.8 % by weight of one or more solvents.
  13. The organic electroluminescent device according to one or more of claims 1 to 12, wherein the at least one light-emitting layer B, preferably each light-emitting layer B, is composed of exactly one (sub)layer.
  14. A method for generating light, comprising the steps of: (i) providing an organic electroluminescent device according to any of claims 1 to 13; and (ii) applying an electrical current to said organic electroluminescent device.
  15. The method according to claim 14, wherein the method is for generating light at a wavelength range selected from one of the following wavelength ranges: (i) from 510 nm to 550 nm, or (ii) from 440 nm to 470 nm, or (iii) from 610 nm to 665 nm.

Description

The present invention relates to organic electroluminescent devices comprising one or more light-emitting layers B, each of which is composed of one or more sublayers, wherein the one or more sublayers of each light-emitting layer B as a whole comprise at least one host material HB, at least one phosphorescence material PB, at least one small FWHM emitter SB, and optionally at least one TADF material EB, wherein the at least one, preferably each, SB emits light with a full width at half maximum (FWHM) of less than or equal to 0.25 eV. Furthermore, the present invention relates to a method for generating light by means of an organic electroluminescent device according to the present invention. Description Organic electroluminescent devices containing one or more light-emitting layers based on organics such as, e.g. organic light-emitting diodes (OLEDs), light-emitting electrochemical cells (LECs) and light-emitting transistors gain increasing importance. In particular, OLEDs are promising devices for electronic products such as e.g. screens, displays and illumination devices. In contrast to most electroluminescent devices essentially based on inorganics, organic electroluminescent devices based on organics are often rather flexible and producible in particularly thin layers. The OLED-based screens and displays already available today bear either good efficiencies and long lifetimes or good color purity and long lifetimes, but do not combine all three properties, i.e. good efficiency, long lifetime, and good color purity. The color purity or color point of an OLED is typically provided by CIEx and CIEy coordinates, whereas the color gamut for the next display generation is provided by so-called BT-2020 and DCPI3 values. Generally, in order to achieve these color coordinates, top emitting devices are needed to adjust the color coordinate by changing the cavity. In order to achieve high efficiency in top emitting devices while targeting these color gamut, a narrow emission spectrum in bottom emitting devices is needed. State-of-the-art phosphorescence emitters exhibit a rather broad emission, which is reflected in a broad emission of phosphorescence-based OLEDs (PHOLEDs) with a full-width-half-maximum (FWHM) of the emission spectrum, which is typically larger than 0.25 eV. The broad emission spectrum of PHOLEDs in bottom devices, leads to high losses in out-coupling efficiency for top emitting device structure while targeting BT-2020 and DCPI3 color gamut. Additionally, phosphorescence materials are typically based on transition metals, e.g. iridium, which are quite expensive materials within the OLED stack due to their typically low abundance. Thus, transition metal based materials have the most potential for cost reduction of OLEDs. Lowering of the content of transition metals within the OLED stack thus is a key performance indicator for pricing of OLED applications. Recently, some fluorescence or thermally-activated-delayed-fluorescence (TADF) emitters have been developed that display a rather narrow emission spectrum, which exhibits an FWHM of the emission spectrum, which is typically smaller than or equal to 0.25 eV, and therefore more suitable to achieve BT-2020 and DCPI3 color gamut. However, such fluorescence and TADF emitters typically suffer from low efficiency due to decreasing efficiencies at higher luminance (i.e. the roll-off behaviour of an OLED) as well as low lifetimes due to for example the excitonpolaron annihilation or exciton-exciton annihilation. These disadvantages may be overcome to some extend by applying so-called hyper approaches. The latter rely on the use of an energy pump which transfers energy to a fluorescent emitter preferably displaying a narrow emission spectrum as stated above. The energy pump may for example be a TADF material displaying reversedintersystem crossing (RISC) or a transition metal complex displaying efficient intersystem crossing (ISC). However, these approaches still do not provide organic electroluminescent devices combining all of the aforementioned desirable features, namely: good efficiency, long lifetime, and good color purity. A central element of an organic electroluminescent device for generating light typically is the at least one light-emitting layer placed between an anode and a cathode. When a voltage (and electrical current) is applied to an organic electroluminescent device, holes and electrons are injected from an anode and a cathode, respectively. Typically, a hole transport layer is(typically) located between a light-emitting layer and an anode, and an electron transport layer is typically located between a light-emitting layer and a cathode. The different layers are sequentially disposed. Excitons of high energy are then generated by recombination of the holes and the electrons in a light-emitting layer. The decay of such excited states (e.g., singlet states such as S1 and/or triplet states such as T1 to the ground state (S0) desirably leads