Volatilizable Solid Additive‐Assisted Treatment Enables Organic Solar Cells with Efficiency over 18.8% and Fill Factor Exceeding 80%

Abstract Controlling the self‐assembling of organic semiconductors to form well‐developed nanoscale phase separation in the bulk‐heterojunction active layer is critical yet challenging for building high‐performance organic solar cells (OSCs). Particularly, the similar anisotropic conjugated structures between nonfullerene acceptors and p‐type organic semiconductor donors raise more complexity on manipulating their aggregation toward appropriate phase separation. Herein, a new approach to tune the morphology of photoactive layer is developed by utilizing the synergistic effect of dithieno[3,2‐ b :2′,3′‐ d ]thiophene (DTT) and 1‐chloronaphthalene (CN). The volatilizable solid additive DTT with high crystallinity can restrict the over self‐assembling of nonfullerene acceptors during the film casting process, and then allowing the refining of phase separation and molecular packing with the simultaneous volatilization of DTT under thermal annealing. Consequently, the PTQ10: m ‐BTP‐PhC6:PC 71 BM‐based ternary OSCs processed by the dual additives of CN and DTT record a notable power‐conversion efficiency of 18.89%, with a remarkable FF of 80.6%.