PC₇₁BM as Morphology Regulator for Highly Efficient Ternary Organic Solar Cells with Bulk Heterojunction or Layer-by-Layer Configuration

The ternary strategy is one of the effective methods to regulate the morphology of the active layer in organic solar cells (OSCs). In this work, the ternary OSCs with bulk heterojunction (BHJ) or layer-by-layer (LbL) active layers are prepared by using the polymer donor PM6 and the non-fullerene acceptor L8-BO as the main system and the fullerene acceptor PC₇₁BM as the third component. The power conversion efficiencies (PCEs) of BHJ OSCs and LbL OSCs are increased from 17.10% to 18.02% and from 17.20% to 18.20% by introducing PC₇₁BM into the binary active layer, respectively. The in situ UV–vis absorption spectra indicate that the molecular aggregation and crystallization process can be prolonged by introducing PC₇₁BM into the PM6:L8-BO or PM6/L8-BO active layer. The molecular orientation and molecular crystallinity in the active layer are optimized by introducing the PC₇₁BM into the binary BHJ or LbL active layers, which can be confirmed by the experimental results of grazing incidence wide-angle X-ray scattering. This study demonstrates that the third component PC₇₁BM can be used as a morphology regulator to regulate the morphology of BHJ or LbL active layers, thus effectively improving the performance of BHJ and LbL OSCs.