Asymmetric non-fullerene acceptors with balanced crystallization kinetics enabling a trade-off between charge generation and recombination in ternary organic solar cells

Abstract

The ternary strategy is an effective approach to enhancing luminescence properties and mitigating non-radiative recombination. However, achieving a simultaneous reduction in non-radiative recombination without sacrificing charge generation in organic solar cells (OSCs) remains a challenge. To address this, we designed two novel non-fullerene acceptors (NFAs) based on a quinoxaline core: asymmetric YQX-1O with a single branched alkoxy side chain and symmetric YQX-2O with dual branched alkoxy side chains. YQX-1O exhibits a wider bandgap and superior miscibility with the host acceptor, enabling balanced crystallization kinetics and an optimized blend morphology. This results in the simultaneous enhancement of V_OC and short-circuit current density J_SC, leading to a remarkable power conversion efficiency (PCE) of 20.0% in PM6:BTP-eC9:YQX-1O-based devices, with an improved V_OC of 0.864 V, a high J_SC of 29.25 mA cm⁻², and an FF of 79.05%. In contrast, YQX-2O, despite its wider bandgap, exhibits excessive molecular planarity and stronger self-aggregation, leading to unfavorable phase separation and limited device performance improvement. Our results highlight the critical role of asymmetric branched alkoxy side chains in regulating crystallization kinetics, which optimizes charge generation while suppressing charge recombination. Theoretical studies further confirm that balancing charge generation and recombination is key to optimal device performance.