Thiophene: An eco-friendly solvent for organic solar cells

In order to meet the demand of large-scale production of organic solar cells and concept of green chemistry, it is essential to develop environment friendly solvent to fabricate OSCs. In this paper, we utilize thiophene (TH) and diphenyl ether (DPE) as halogen-free processing solvent to optimize performance of OSCs based on PTB7-Th:PC71BM, and we choose chlorobenzene (CB) and 1,8-diiodineoctane (DIO) combination as comparison. For PTB7-Th:PC71BM blend film based on pure TH solvent, the blend film exhibits high photoelectron conversion, efficient exciton separate and charges collection and well developed morphology properties, thus, higher Voc, Jsc and FF were obtained than that of pure CB solvent. Furthermore, excellent photovoltaic performance was achieved with the addition of additive. The PCE of 9.02% from TH:5% DPE system was achieved without any thermal or solvent treatments (the pure TH processed devices PCE is 6.93%), while CB (with 2% DIO) based devices show a lower PCE of 7.41% (the pure CB processed devices PCE is 4.06%). The enhanced photovoltaic performance demonstrates that halogen-free solvent of thiophene provides a new strategy to large-scale fabrication of organic solar cells in future.