High Efficiency (∼18%) Organic Solar Cells with 500 nm‐Thick Toluene Cast Active Layer by Aggregation Manipulation and Additive Engineering

Thick‐film organic solar cells (OSCs) are crucial for mass‐production: however, the efficiency of such cells is limited by the lack of morphological control afforded by methods that rely on high‐vapor‐pressure solvents. Herein, a systematic solvent and additive engineering strategy is reported for improving the performance of thick‐film (>300 nm) OSCs through aggregation modulation via solidification acceleration and electronic property enhancement. Two oligomers derived from the polymer donors PM6 and D18‐Fu are employed as solid additives to prepare the active layer. Characterizations reveal that the D18‐Fu‐derived oligomer exhibits stronger interactions with both the benzodifuran donor (D18‐Fu) and the acceptor (L8‐BO‐X), resulting in suppressed electron‐phonon coupling, more balanced donor–acceptor fibrillation, and enhanced face‐on molecular orientation. Devices treated with the D18‐Fu‐derived oligomer achieve a greater improvement in power conversion efficiency (PCE). Both additives enhance thickness‐ tolerance of the device owing to their structural compatibility with the D18‐Fu‐derived oligomer,‐ yielding superior performance. Notably, devices processed from toluene, a nonhalogenated solvent, demonstrate high PCEs with excellent thickness tolerance; the thick‐film device (500 nm active layer) exhibits an independently certified PCE of ∼18%, a record for thick‐film OSCs, with no significant loss in performance compared to its thin‐film (100 nm) counterparts (>19%).