Effects of different polar solvents for solvent vapor annealing treatment on the performance of polymer solar cells

The effects of different polar solvents on the performance of solvent vapor annealing treated polymer solar cell (PSC) with a structure of ITO/ZnO/PTB7: PC71BM/MoO3/Ag was systematically investigated by applying different polar solvents, including methanol, ethanol, dimethylsulfoxide, acetone and isopropanol. By analyzing the variation of PSC performance and the morphology of active layer, we found that both the solubility parameters (Delta) and viscosity of solvent were playing an important role in controlling the morphology of PTB7: PC71BM blend. Especially, the PSC treated by methanol with high Delta and low viscosity exhibited a remarkable enhancement of power conversion efficiency from 6.55% to 8.13%. The performance improvement was mainly due to the formation of the nanoscale crystallization of PTB7: PC71BM blend and the moderated aggregation of PC71BM, resulting in efficient charge separation, balanced charge transport and suppressed charge recombination. (C) 2014 Elsevier B.V. All rights reserved.