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.