Small-Molecule Donor/Polymer Acceptor-Based Organic Solar Cells Achieve >10% Efficiency

The small-molecule donor/polymer acceptor (SD/PA) system represents a promising but unconventional material pairing in organic solar cells (OSCs), offering notable morphological stability. However, the strong intermolecular interactions of the SD often lead to excessive aggregation during film formation, hindering exciton dissociation and charge transport, consequently limiting device performance. This study introduces a post-treatment strategy employing reverse thermal annealing (RTA) combined with conventional thermal annealing (TA) (RTA&TA) to modulate the morphology of BTR-Cl/PY-IT-based SD/PA-OSCs. The RTA&TA treatment effectively suppresses the aggregation of the SD, reducing the domain size from 73.92 to 52.80 nm. This morphological refinement enhances exciton dissociation efficiency, accelerates charge transfer, and suppresses recombination losses. As a result, the device power conversion efficiency is improved to over 10%, with the fill factor significantly increasing from 49.49 to 55.69%. This work confirms that RTA&TA is an effective pathway for optimizing morphology and boosting the performance of SD/PA-based OSCs.