Efficient ternary organic solar cells with energy cascade and Foerster resonance energy transfer by doping phosphorescent small molecule

In this work, we fabricated the ternary bulk hetero junction (BHJ) polymer solar cells (PSCs) by doping a phosphorescent small molecule bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium(acetylacetonate)[(tbt) 2 Ir(acac)] into the conventional active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). After doping (tbt) 2 Ir(acac), the short circuit current and fill factor are simultaneously enhanced compared with binary device and the power conversion efficiency (PCE) of P3HT:PC 71 BM based ternary devices is improved from 2.99% to 4.14%. More excellent photovoltaic performance of ternary PSCs is mainly attributed to enhanced charge transportation by appropriate energy cascade alignment and enhanced exciton harvesting by Foerster resonance energy transfer from (tbt)2Ir(acac) to P3HT.