Mixed solvents for reproducible photovoltaic bulk heterojunctions

Most efficient polymer solar cells are usually fabricated from toxic organic solvents, such as chloroform, chlorobenzene, or dichlorobenzene (ODCB). Here, we demonstrate a power conversion efficiency of 4.5% in solar cells with a new blue polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt- thiophene-2,5-diyl] (TQ1) mixed with PC ₇₁ BM and processed from mixed solvents of toluene and ODCB in a ratio of 9:1. Decreasing the content of ODCB makes device processing more compatible with the environment for large scale production, with 10% reduction of photocurrent compared to devices from pure ODCB under optimized conditions. In addition, less variation of photocurrent is obtained in solar cells processed from mixed solvents than from pure ODCB due to varying nanostructure in the blends, which is also critical for production.