Search

EP-3698417-B1 - LIGHTING DEVICE FOR MOTOR VEHICLES AND INCREASED OPERATING TEMPERATURES

EP3698417B1EP 3698417 B1EP3698417 B1EP 3698417B1EP-3698417-B1

Inventors

  • Volz, Daniel
  • FLÜGGE, Harald

Dates

Publication Date
20260513
Application Date
20181018

Claims (14)

  1. The use of a lighting device comprising at least one organic light-emitting diode (OLED) with an emission layer B, wherein the emission layer B comprises at least one emitter E that emits light by means of thermally activated delayed fluorescence (TADF), wherein the emitter E has a glass transition temperature of over 130 °C, and wherein the composition of the emission layer B comprises, in addition to the emitter E, an electron-dominant and a hole-dominant host material, wherein the HOMO (highest occupied molecular orbital) of the hole-dominant host material lies energetically below the HOMO of the emitter E, and the LUMO (lowest unoccupied molecular orbital) of the electron-dominant host material lies energetically above the LUMO of the emitter E, in or on a motor vehicle.
  2. The use according to claim 1, wherein the emitter E has an energy difference ΔE between the lowest excited singlet state S1 and the underlying triplet state T1 of no more than 0.3 eV.
  3. The use according to any one of claims 1 or 2, wherein the OLED has an emission maximum in the range from 420 nm to 800 nm.
  4. The use according to any one of claims 1 to 3, wherein the external quantum efficiency (EQE) of the OLED increases with rising temperature.
  5. The use according to any one of claims 1 to 4, wherein the lighting device is a signal light on the exterior of the motor vehicle, which may be selected from the group consisting of an alternating directional indicator, a tail light, a brake light, an optional raised brake light, and an exterior display.
  6. The use according to any one of claims 1 to 5, wherein the emitter E has a molecular weight of more than 1000 g/mol.
  7. The use according to any one of claims 1 to 6, wherein the emitter E is a purely organic TADF emitter.
  8. The use according to any one of claims 1 to 7, wherein the distance between the LUMO of the electron-dominant host material and the LUMO of the emitter E is less than 0.5 eV, preferably less than 0.3 eV, more preferably less than 0.2 eV.
  9. The use according to any one of claims 1 to 8, wherein the distance between the HOMO of the hole-dominant host material and the HOMO of the emitter E is less than 0.5 eV, preferably less than 0.3 eV, more preferably less than 0.2 eV.
  10. The use according to any one of claims 1 to 9, wherein the emission layer B consists of: (a) the emitter E; (b) one or more host materials H that are different from the emitter E; (c) one or more TADF emitters K, which are different from the emitter E, and (d) one or more further components selected from the list consisting of one or more emitters F that are not TADF emitters, one or more dyes C, one or more solvents L, and combinations of two or more thereof.
  11. The use according to any one of claims 1 to 10, wherein the lighting device is arranged on or in the motor vehicle such that, during long-term operation of the motor vehicle at an outside temperature of 20°C, it is subjected to an operating temperature that is at least 10°C higher than the outside temperature.
  12. A motor vehicle comprising at least one lighting device as defined in any one of claims 1 to 11.
  13. A method for generating light using an organic light-emitting diode (OLED) at an operating temperature of the OLED in the range of 30°C to 160°C, comprising the steps: (i) providing the OLED having characteristics as defined in any one of claims 1 to 11; and (ii) applying an electrical voltage to the OLED from step (i), wherein the OLED forms part of a lighting device, as defined in any one of claims 1 to 11, in or on a motor vehicle.
  14. The method according to claim 13, wherein light is generated in the wavelength range of 420 to 800 nm.

Description

The present invention relates to the use of a lighting device as defined in claim 1, a motor vehicle as defined in claim 12, and a method for generating light as defined in claim 13. Lighting systems based on organic light-emitting diodes (OLEDs) are characterized by their thin, lightweight, and flexible structure, which enables new design possibilities. For example, OLED-based lighting systems can be applied to the vehicle body or, due to the potential transparency of OLEDs, to the vehicle's windows, particularly by adhesive application. The OLED lighting system can also be integrated into the window or applied to the inside of the window. It is also possible to apply the OLED lighting system to an existing lighting system. DE-A 10217633 describes various application possibilities of OLED-based outdoor lighting systems. Also discussed in JP 2017 188399 A , DE-A 102009009087 , DE-A 102013217848 , DE-A 102014111119 and WO 2014/179824 OLED-based lighting in motor vehicles was taught. However, the OLEDs used here exhibit some suboptimal properties. It is known that such conventional OLEDs show increasingly poorer optical properties and reduced lifespans at elevated temperatures. For applications in automotive exterior lighting, OLEDs must maintain the legally required luminance over extended operating periods, even at high ambient temperatures. Even when not in use, external influences such as solar radiation can expose the lighting device to temperatures significantly above ambient. During operation, the component temperature is further increased by the OLED's own heating. Temperatures typically range from approximately 30°C to over 100°C, and sometimes up to 160°C, can be reached. Current automotive OLEDs do not regularly meet these requirements, particularly regarding temperature stability. Therefore, the use of OLEDs in vehicles has been considerably hampered to date. Therefore, there was a need for OLEDs for the automotive sector that offer high efficiency and a sufficient lifespan when used at elevated temperatures. Surprisingly, it was found that the use of OLEDs utilizing the principle of thermally activated delayed fluorescence (TADF) is particularly advantageous in automotive lighting systems. Specifically, the temperature stability and lifetime of the OLEDs could be significantly improved under conditions typical of the automotive industry. The external quantum efficiency (EQE) of such a TADF-based OLED can even increase with rising temperature. A first aspect of the disclosure therefore relates to a lighting device for a motor vehicle, comprising at least one organic light-emitting diode (OLED) with an emission layer B, wherein the emission layer B comprises at least one emitter E which emits light by means of thermally activated delayed fluorescence (TADF). In other words, the disclosure relates to a lighting device that is (or will be) arranged on or in the motor vehicle, comprising at least one organic light-emitting diode (OLED) with an emission layer B, wherein the emission layer B contains at least one emitter E which emits light by means of thermally activated delayed fluorescence (TADF). An OLED typically has the following structure: a substrate, an anode at least one emission layer B (light-emitting layer), and a cathode wherein the anode or the cathode is applied to the substrate, and the at least one emission layer is arranged between the anode and the cathode. Typically, one or more hole injection and/or hole transport and/or electron blocking layers are located between the anode and the light-emitting layer B, and one or more electron injection and/or electron transport and/or hole blocking layers are located between the cathode and the light-emitting layer B. The individual layers are deposited sequentially. The emission layer B is a central component of the OLED. When a voltage is applied to the OLED, holes and electrons are injected from the anode and cathode. Excitons are generated through recombination of the holes and electrons in the emission layer. Relaxation from excited states (e.g., from singlet states like S1 and/or triplet states like T1) to the ground state S0 should occur via light emission. The emission layer B contains a thermally activated delayed fluorescence (TADF) emitter E. TADF emitters have a first excited triplet state T1, which is sufficiently close in energy to the first excited singlet state S1 that up to 100% of the excitons generated by the recombination of holes and electrons can be used for light emission. This enables thermal repopulation of the S1 state from the T1 state. According to a preferred embodiment, the emitter E has an energy difference ΔE between the lowest excited singlet state S1 and the underlying triplet state T1 (E(S1-T1) value) of no more than 0.3 eV. According to a more preferred embodiment, the emitter E has an E(S1-T1) value of no more than 0.2 eV, in particular no more than 0.1 eV. Due to the thermal repopulation of the S1 state,