Rational selection of solvents and fine tuning of morphologies toward highly efficient polymer solar cells fabricated using green solvents

High-efficiency polymer solar cells (PSCs) based on a conjugated polymer named PBQ-4 were fabricated by employing 1,2-dichlorobenzene (o-DCB), o-xylene and anisole as primary solvents. We rationally selected three solvent additives, 1,8-diiodooctane (DIO), N-methylpyrrolidone (NMP) and diphenyl ether (DPE) to tune the morphologies of the blend films. The power conversion efficiency (PCE) of 8.47% and 7.62% were realized by using o-DCB/DIO and o-xylene/NMP as processing solvent, respectively. The PSC with a PCE of 8.37% was fabricated using the environmentally friendly solvents of anisole/DPE. To the best of our knowledge, the PCE of 8.37% is not only among the highest values reported for PSCs with E-g > 1.7 eV but also the highest value for a PSC processed using a biodegradable solvents with low toxicity. Therefore, these results open the new paths for the fabrication of highly efficient PSCs by green processes.