Roles of solvent additive in organic photovoltaic cells through intensity dependence of current-voltage characteristics and charge recombination

Abstract

In this research, the enhanced power conversion efficiency of PBnDT-FTAZ:PC70BM bulk-heterojunction (BHJ) solar cells (over 7%), fabricated with a solvent additive (1,8-diiodooctane, 3%), was demonstrated. The appropriate ratio of solvent additive leads to a device with increased JSC, fill factor, and favorably controlled nanomorphology phase separation. Furthermore, the device with BHJ film fabricated with the solvent additive exhibited improved charge collection and simultaneously reduced charge recombination from a systematic light intensity analysis. The lack of Shockley-Read-Hall recombination at open circuit, the dominance of bimolecular recombination only when approaching open circuit, and an improved charge collection probability (95.5%) at short circuit contribute to high performance organic photovoltaic cells.