Allylrhodanine-processed all-small-molecule organic solar cell achieves an 18.43% efficiency breakthrough

Solid additives (SAs) improve organic solar cells (OSCs) morphology and performance, yet, their efficiency in all-small-molecule (ASM) OSCs is limited by strong donor-acceptor crystallinity, and the underlying mechanisms remain unclear. Herein, structurally resembling the MPhS-C2 donor, 3-allylrhodanine (3-AR) as a SA enables precise control over the active layer morphology. Interesting, combined theoretical calculations and thin-film morphology analyses reveal 3-AR preferentially interacts with acceptor N3, thereby directing morphology evolution. Moreover, 3-AR effectively narrows the film formation window, suppressing lateral over-aggregation and crystallization, while promoting vertical donor-acceptor homogeneity. This optimized morphology synergistically facilitates efficient charge dissociation and collection, suppresses both bimolecular and trap-assisted recombination, and extends the lifetimes of excitons and charge carriers. Therefore, the 3-AR-treated MPhS-C2:N3 device achieves a remarkable power conversion efficiency (PCE) of 18.43% (certified 18.16%)-the highest reported for binary ASM-OSCs. This work shows additive efficacy is governed by balanced selective interactions, not by simplistic structural similarity.