Highly efficient red light-emitting devices using copolymer containing charged iridium complex in the side chain

Red emission was achieved in electroluminescent devices by using a novel charged Ir-copolymer. The electroluminescent device, with the configuration of ITO/PEDOT:PSS/Ir-copolymer/Au, exhibited the characteristics of light-emitting electrochemical cell (LEC), in which the redistribution of ions resulted in the ionic junction. The maximum external quantum efficiency (EQE) of 0.19 % and the maximum luminance of 352 cd/m2 were obtained after the device was driven to the maximum luminance at 7V. When aluminum (Al) was used as cathode, the maximum EQE of 0.15 % and the maximum luminance of 340cd/m2 were achieved, which were comparable with the results from the Au cathode device. After a 30nm thick TPBI (1,3,5-tris(2-N-phenylbenzimidazolyl)-benzene layer was inserted between light emitting layer and the Al cathode, the device performances were significantly enhanced. The maximum EQE and the maximum luminance reached 10.7 % and 2170 cd/m2, respectively, a more than 10 fold increase compared to the devices without TPBI layer. The TPBI layer not only functioned as hole blocking layer which made holes and electrons more balanced inside the device, but also moved the recombination zone away from the cathode, thereby enhancing the device performances.