Conformational entropy tuning in nonfused-ring electron acceptors for low-cost and record-efficiency organic solar...

The commercial viability of organic solar cells (OSCs) is hindered by the trade-off between cost and performance. In particular, low-cost non-fused-ring electron acceptors (NFREAs) suffer from conformational disorder, limiting their photovoltaic performance. Herein, we strategically regulate conformational entropy (S _conf.) of NFREAs through the rational combination of intramolecular noncovalent interactions (INIs). The optimal candidate 3TT-SeS, identified through comprehensive density functional theory calculations, exhibits balanced Se···N and S···O INIs and demonstrates a significant reduction in S _conf. This strategy enables an exclusive single stable conformation and highly ordered molecular packing, thereby facilitating efficient charge transport. Consequently, the 3TT-SeS-based OSC achieved an outstanding power conversion efficiency of 19.26% (certified at 18.75%), setting a new benchmark for NFREA-based systems to date. More importantly, 3TT-SeS-based device demonstrates exceptional economic potential with an extremely low power generation cost of 0.77$ kW^-1, much lower than several high-performance FREA-based systems. Our work demonstrates a low-S _conf. design of NFREAs for cost-effective and high-performance organic photovoltaics.