PTB7:PC71BM bulk heterojunction solar cells exhibiting 9.64% efficiency via adopting moderate polarity solvent vapor annealing treatment

The effects of solvent vapor annealing (SVA) with different polar solvents on the performances of polymer solar cell (PSCs) was systematically investigated by applying seven polar solvents, including methanol, acetone, chloroform, o-dichlorobenzene, chlorobenzene, toluene and n-hexane. A 9.64% of power conversion efficiency (PCE) was obtained in the PTB7:PC71BM based PSCs with conventional structure of ITO/PEDOT:PSS/PTB7:PC71BM/LiF/Al by employing the moderate polarity chlorobenzene-SVA method, corresponding to an approximate 21% enhancement in PCE relative to the PSCs without SVA. The enhanced PCEs of PSCs with active layers undergoing chlorobenzene-SVA process are mainly attributed to the combined advantages of the increased absorption intensity, the higher and more balanced carrier mobilities, the upper migration of the PC71BM, and the excellent donor/acceptor phase separation interface in the active layer. Our work not only demonstrates that polar solvent SVA treatment is a much more efficient method of improving the efficiency of PSCs without time-consuming and laborious fabrication procedures, but also provides some feasible reference for the application of different polar solvent SVA treatment in photovoltaic field.