Enhancing carrier injection efficiency of light-emitting electrochemical cells based on Cationic Ir(III) complexes by interface modification

Abstract

Light-emitting electrochemical cells (LECs) have the advantages of simple structure, low driving voltage, and low packaging requirements. However, due to the different mobility of electrons and holes in emission layer, exciton quenching is inevitable caused by carrier imbalance. In this work, a red light cationic Ir(Ⅲ) complexes [Ir(tBuPBI)2(qibi)]PF6 (R) was used as the luminescent materials for the LECs, and we use the doping of MoOx into poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) layer to lower the energy barrier between complexes R and anode. In combination with the introduction of Al/LiF composite cathode, the carrier injection efficiency of the LECs is significantly improved, leading to the enhanced balance of carrier injection. In particular, high electron injection efficiency would significantly contribute to the device improvement based on the complexes with hole-preferred transporting characteristic. With enhanced carrier injection, the recombination region of the carrier is located near the center of emission layer, and the exciton quenching near the electrode will be significantly alleviated. The maximum external quantum efficiency of the LEC device is as high as 11.77%, which is 1.3 time that of the standard device. The half-lifetime of the device is 690 min, which is about 1.37 times of that of the standard device.