An investigation of organic photovoltaics improvement via extension of the exciton lifetime

Abstract

The phosphorescent material tris(phenylpyrazole)iridium (Ir(ppz)₃) was doped into the bulk heterojunction (BHJ) layer of a 3-hexylthiophene-2,5-diyl and indene-C60 bisadduct blend to form more excitons in the triplet state. Triplet-state excitons have longer lifetimes than singlet-state excitons. Surface phase separation was determined via atomic force microscopy and the vertical distribution of various molecules was analyzed via secondary ion mass spectroscopy. Several annealing processes were applied to the BHJ layer doped with Ir(ppz)₃ to investigate the thermal stability of the film. The exciton lifetime in the BHJ film was characterized using femtosecond time-reserved photoluminescence.