Adjusting acceptor redistribution for highly efficient solvent additive-free polymer solar cells

A series of solvent additive-free polymer solar cells (PSCs) were fabricated with PBDT-TS1 : PC71BM (1 : 2, wt/wt) as the active layers; the performance of the PSCs can be enhanced by using MeOH:CH2Cl2 or MeOH: CB mixed solvent spin-coating treatment on the active layers. The maximum power conversion efficiency (PCE) of PSCs was increased from 6.69% to 7.21% or 7.76% by spin-coating the mixed solvents onto the active layers, respectively. The PCE improvement may be attributed to the increase in PC71BM elevated toward the top surface of the active layers during the mixed solvent spin-coating treatment. The redistribution of PC71BM in the active layers could also be indirectly confirmed from the variation of photoluminescence spectra and water contact angles of the corresponding films, as well as the J-V curves of electron-only devices.