In OLED materials, voltage-driven electrons and holes are respectively injected from the cathode and anode into the organic functional thin film layer between the electrodes. Electrons and holes enter the light-emitting layer through the electron transport layer and the hole transport layer respectively. When they meet, they recombine to form excitons. The excitons undergo radiative transition to generate visible light. Phosphors can use singlet and triplet excitons at the same time, which can make the internal quantum efficiency reach 100% and the external quantum efficiency reach 20%. Therefore, phosphors have broader application prospects in OLEDs. Currently, the main applications of phosphors include rare metal complexes, pure organic molecules, polymers, metal organic framework materials and carbon quantum dots. The corresponding raw materials such as platinum, iridium, rhenium and other heavy metal complexes, carbazole, thiophene, furan and other compounds have been widely used and researched. In the field of optoelectronic applications, due to the development of electro-phosphorescent devices, the quantum efficiency and luminous brightness of the devices have been greatly improved, and green and red phosphorescent devices have been commercialized.
Figure 1. Some organometallic phosphorescent complexes
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