In‐Situ Removable Solid Additive Optimizing Active Layer and Cathode Interlayer of Organic Solar Cells

Abstract In situ removable (ISR) solid additive can employ cold sublimation process to optimize active layer morphology for organic solar cells (OSCs), thus remaining unique potential. Herein, a feasible guideline is proposed to discover a new ISR solid additive 1‐bromo‐4‐chlorobenzene (CBB), whose removing time ( T R ) is between those of reported ISR solid additives 1,4‐dichlorobenzene (DCB) and 1‐chloro‐4‐iodobenzene (CIB). The CBB with a moderate T R is beneficial for affording the optimal active layer morphology and achieving the highest power conversion efficiency (PCE) of 18.58% for D18:L8‐BO binary active layer, as supported by the most efficient exciton splitting, the fastest exciton transfer, and the most balanced carrier transports. Due to the unique ISR ability, DCB, CBB, and CIB are further proposed to optimize the aggregation of PDINN cathode interlayer. Particularly, the CBB‐ and CIB‐treated PDINN interlayers afforded the D18:L8‐BO based binary OSCs with excellent PCEs of 19.38% and 19.26%, along with remarkable fill factors of 80.98% and 81.37%, respectively. The CBB‐ and CIB‐treated PDINN interlayers can suppress non‐radiative recombination of the devices, resulting in higher open‐circuit voltage. This work not only provides an effective approach to flourish ISR solid additives but also expands the application of the ISR solid additive in OSCs.