The contribution of triplet excitons to the total singlet production yield in a sky-blue emitting co-polymer film

Abstract

In this work, the complex excited state dynamics of a sky-blue emitting co-polymer {poly-[9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine]} is determined, using a time-resolved gated spectroscopy method, which helps to investigate the origin of delayed fluorescence in thin film. It is clearly shown that delayed fluorescence arises from triplet–triplet annihilation mechanism, which opens an indirect pathway to generate singlet excitons. Experimentally, the delayed fluorescence yield varies from 20% at room temperature to 46 ± 2% at 20 K, suggesting that an alternative triplet harvesting mechanism is operative to convert the triplet into emissive singlet states.