Highly efficient orange and green solid-state light-emitting electrochemical cells based on cationic Ir^III 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)₂sb]PF₆ and [Ir(dFppy) ₂sb]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)₂sb]PF₆ 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)₂sb]PF₆ and [Ir(dFppy)₂sb]PF ₆ achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 1m W^-1) at 2.5 V, and 7.1 % and 26.2 1m 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.