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
- Organic phosphorescent materials: The group VIII heavy metal as the central atom of the complex can be used as an organic electrophosphorescent material in OLED devices, and has the advantages of easy synthesis, easy purification, strong structural modification, and good light and heat stability. Among them, heavy metals can produce a strong spin-orbit coupling effect, which allows the original forbidden triplet transition to be allowed, and significantly improves the internal quantum efficiency of the device, and the luminous efficiency is significantly improved.
- Gas sensor: OLED gas sensors have the advantages of high sensitivity, diverse modes, and small size. Phosphors have high quantum efficiency, can emit strong visible light, can also achieve light color conversion through molecular design, and have high reaction sensitivity. On this basis, phosphors are used as the main light-emitting body in OLED sensors, which can detect oxygen and hydrazine, so that it can distinguish lactic acid, ethanol and glucose waiting to be measured.
- Hsin-Hung Kuo, Ling-Yang Hsu, Jen-Yung Tso, Wen-Yi Hung, Shih-Hung Liu, Pi-Tai Chou, Ken-Tsung Wong, Ze-Lin Zhu, Chun-Sing Lee, Alex K.-Y. Jen,Yun Chi. Blue-emitting bis-tridentate Ir(iii) phosphors: OLED performances vs. substituent effects [J]. J. Mater. Chem. C, 2018,6, 10486-10496.