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%).