Efficient solid-state host-guest light-emitting electrochemical cells based on cationic transition metal complexes

The authors demonstrate highly efficient solid-state light-emitting electrochemical cells (LECs) consisting of green-emitting [Ir (dFppy)2 (SB)] + (P F6-) as the host and orange-emitting [Ir (ppy)2 (SB)] + (P F6-) as the guest [where dFppy is 2-(2,4-difluorophenyl)pyridine, SB is 4,5-diaza-9, 9′ -spirobifluorene, and ppy is 2-phenylpyridine]. Photophysical studies show that with the optimized host-guest compositions, the emission is mainly from the guest and photoluminescence quantum yields are largely enhanced over those of pure host and guest films due to suppressed intermolecular interactions. Correspondingly, LECs based on such host-guest cationic complex systems show substantially enhanced quantum efficiencies (power efficiencies) of up to 10.4% (36.8 lmW), representing a 1.5 times enhancement compared to those of pure host and guest devices. Such results indicate that the host-guest system is essential and useful for achieving highly efficient solid-state LECs.