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]PF6 and [Ir(dFppy)(2)sb]PF6 (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]PF6 and [Ir(dFppy)(2)sb]PF6 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]PF6 and [Ir(dFppy)(2)sb]PF6 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.