Luminescence Principle of OLED Devices
The luminescence process of OLED devices can be divided into: electron and hole injection, electron and hole transport, electron and hole recombination, and exciton deexcitation light, specifically:
(1) Injection of electrons and holes. Driven by an external drive voltage, electrons in the cathode and holes in the anode move to the light-emitting layer of the device. During the movement towards the light-emitting layer of the device, if the device contains an electron injection layer and a hole injection layer, the electrons and holes must first overcome the energy barrier between the cathode and electron injection layer and between the anode and the hole. The hole injection layer is then moved to the electron transport layer and hole transport layer of the device through the electron injection layer and the hole injection layer. The electron injection layer and hole injection layer can improve the efficiency and lifetime of the device, and the mechanism of electron injection in OLED devices is still under continuous study, and the most commonly used mechanism is the tunneling and interface dipole mechanism.
(2) Transport of electrons and holes. Driven by the external driving voltage, the electrons from the cathode and the holes from the anode will move to the electron traansport layer and hole transport layer of the device, respectively, and the electron transport layer and hole transport layer will transmit electrons and holes to the device, and the OLED device is located at the interface of the light-emitting layer, respectively; At the same time, the electron transport layer and hole transport layer will block the holes from the anode and the electrons from the cathode at the interface of the light-emitting layer of the device, so that the electrons and holes are blocked at the interface. Hole accumulation in the light-emitting layer of the device.
(3) Recombination of electrons and holes. When the number of electrons and holes at the interface of the light-emitting layer of the OLED device reaches a certain number, the electrons and holes will recombine in the light-emitting layer and produce excitons.
(4) Excitation light of excitons. The excitons produced in the light-emitting layer activate the organic molecules in the light-emitting layer of the device, which in turn causes the outermost electrons of the organic molecules to transition from the ground state to the excited state. Since electrons in the excited state are very unstable, they move to the ground state. During the transition, energy will be released in the form of light, and then the device will emit light.