Heating-induced aggregation control for efficient sequential-cast organic solar cells

The aggregation and morphology within the photoactive layer is of considerable significance to boost the power-conversion efficiency (PCE) of organic solar cells (OSCs). Herein, heating-induced aggregation control of nonfullerene acceptor BTPeC7 during sequential casting was demonstrated. The large aggregates of BTP-eC7 can be significantly reduced by sequential casting of BTP-eC7 hot solution on the D18 fibrillar layer, and further eliminated by sequential casting of BTP-eC7 hot solution on the D18 fibrillar layer heated on hot substrate, leading to stronger faceon pi-pi stacking and appropriate phase separation within the photoactive layer to promote exciton dissociation and charge transfer. The maximum PCE of D18/BTP-eC7 solar cells can be enhanced from 8.1% of room temperature casting to 15.9% of hot solution, hot-substrate casting, therefore demonstrates that heating-induced aggregation and sequential-casting strategies are a promising approach in improving the performance of OSCs employing nonfullerene acceptors with limited solubility or strong crystallization ability.