Over 20.5% Efficiency of Halogen-Free Solvent-Processed Organic Solar Cells Achieved by Anti-Solvent Strategy.

Halogen-free solvent processing is critical for the industrial-scale production of organic solar cells (OSCs) and environmental sustainability. However, such solvents typically result in suboptimal efficiency due to excessive molecular aggregation and unfavorable phase separation. To address this issue, an innovative anti-solvent (AS) strategy is proposed that accelerates photovoltaic material precipitation by timed introduction of orthogonal solvents to reduce solvent solubility and enhance volatilization, thereby avoiding prolonged aggregation. The resulting optimized phase separation and fibrous morphology facilitate exciton dissociation and charge utilization, enabling PM6:D18:L8BO-X-based OSCs to achieve a remarkable efficiency of 20.51% (certified as 20.12%), significantly higher than that of the conventional o-xylene-processed devices. The AS strategy also exhibits broad universality, with notable efficiency gains across diverse photovoltaic materials and solvent systems. Furthermore, scaling the AS strategy to methanol soaking for large-area fabrication yields a record module efficiency of 17.23%, which is one of the optimal performances reported for OSC modules with active areas exceeding 10.0 cm2. This work not only provides a practical solution for high-efficiency, eco-friendly OSC fabrication but also opens up new possibilities for their industrial-scale deployment.