Highly Efficient Orange and Green Solid‐State Light‐Emitting Electrochemical Cells Based on Cationic IrIII Complexes with Enhanced Steric Hindrance

Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy) 2 sb]PF 6 and [Ir(dFppy) 2 sb]PF 6 (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy) 2 sb]PF 6 and [Ir(dFppy) 2 sb]PF 6 in neat films (compared with quantum yields of these complexes dispersed in m ‐bis( N ‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy) 2 sb]PF 6 and [Ir(dFppy) 2 sb]PF 6 achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W –1 ) at 2.5 V, and 7.1 % and 26.2 lm W –1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.