High-efficiency near-infrared organic light-emitting devices based on an iridium complex with negligible efficiency roll-off NRan TaoDKey Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China.Mqjuan@mail.tsinghua.edu.cn

摘要

For NIR-emitting organic light-emitting devices (OLEDs), platinum complexes have the record maximum external quantum efficiency (EQE), although such devices generally suffer from severe efficiency roll-off with increasing current densities. Here, we report on iridium complexes as a competent alternative for NIR dyes with high EQEs and negligible efficiency roll-off. A simple, charge-neutral iridium complex, iridium(III) bis(2-methyl-3-phenylbenzo[g]quinoxaline-N,C) acetylacetonate (lr(mpbqx-g)2acac, 1), has been synthesized and characterized by a strong NIR emission with λ_(max,peak) at 777 nm and λ_(max,shoulder) shouider at 850 nm in CH2CI2 solutions. The single-crystal and electronic structure as well as photophysical and electrochemical properties were systematically studied in comparison with its cationic counterpart [lr(mpbqx-g)2(Bphen)]~+PF6~-(2, Bphen = 4,7-diphenyl-1,10-phenanthroline). Complex 1 has seven times the quantum efficiency of complex 2 because of its much stronger spin-orbit coupling. NIR-emitting OLEDs based on complex 1 have been fabricated with a bipolar gallium complex as the host. The devices achieved a maximum EQE of up to 2.2% (J = 13 mA cm~(-2)) and a maximum radiant emittance (R_(max)) of 1-8 mW cm~(-2). In particular, the EQEs remained around 2% over a wide range of current densities from 3 to 100 mA cm~(-2).