Asymmetrically Trifluoromethylated Non-fused Electron Acceptor for High-Efficiency and Stable Organic Solar Cells

Fused-ring electron acceptors (FREAs) have advanced significantly in organic solar cells (OSCs) but suffer from complex synthesis and high production costs. As a cost-effective alternative, nonfused-ring electron acceptors (NFREAs) offer structural simplicity and easier synthesis, though typically at the expense of device performance. In this work, two asymmetric NFREAs, 3TT-CF₃ and 3TT-BCF₃, were synthesized via a modular strategy and applied in high-efficiency OSCs. The introduction of (trifluoromethyl)biphenyl substituent in 3TT-BCF₃ led to enhanced molecular rigidity, reduced energetic disorder and optimized blend morphology. When fabricated using the nonhalogenated solvent o-xylene, D18:3TT-BCF₃-based devices achieved a power conversion efficiency (PCE) of 16.11%, outperforming the 15.41% of 3TT-CF₃-based counterparts. This performance gain is attributed to improved short-circuit current density, fill factor and lower voltage losses. Moreover, 3TT-BCF₃ devices exhibited superior thermal and storage stability, efficient charge transport and favorable phase separation. These results highlight the potential of asymmetric molecular engineering in advancing cost-effective and high-performance NFREA-based OSCs.