Terpinolene processed PTB7:PC71 BM blend film for polymer solar cells: a non-aromatic and non-chlorinated solvent predicted by Hansen solubility parameters

Terpinolene (TPO), a natural and safe substance for food and cosmetic additives, was selected as a solvent to replace chlorobenzene (CB)-type solvents for solution processing of polymer solar cells (PSCs). Hansen solubility parameters (HSPs) of TPO, with delta(d), delta(p), and delta(hb) of 16.8, 2.75, and 2.5 MPa1/2, respectively, were obtained by first-order group approximation, and the calculated Relative Energy Difference of 1.08 for TPO to PC71 BM suggested that TPO could be a good non-aromatic and non-chlorinated solvent for solution processing of fullerene based PSCs. Pristine PTB7 and PC71 BM films spin-casted from TPO showed very smooth surfaces, with small root-mean-square roughness of 0.824 and 0.565 nm, respectively. In addition, CB- and TPO-processed PTB7:PC71 BM blend films showed comparable UV absorption spectra, photoluminescence quenching behaviors, and surface morphologies. In PSCs, the TPO-processed active layer displayed a good power conversion efficiency of 6.42%, close to that of CB-processed device. Our results suggest that TPO would be a promising solvent for environment-friendly fabrications of PSCs.