Heating‐induced aggregation control for efficient sequential‐cast organic solar cells: Photovoltaics: Special Issue Dedicated to Professor Yongfang Li

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 BTP‐eC7 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 face‐on π–π 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.