Non-radiative recombination energy losses in Y-series asymmetric acceptor-based organic solar cells

Abstract

The molecular engineering of Y6 has marked a paradigm shift in the development of non-fullerene acceptors (NFAs) for organic solar cells (OSCs), enabling remarkable enhancements in power conversion efficiencies (PCEs) through its distinct A–DA′D–A architecture and optimized intermolecular packing. However, further advancement is hindered by persistent non-radiative recombination energy losses (ΔE₃), which predominantly originate from molecular relaxation and sub-gap charge recombination pathways. Among various structural optimization strategies, the implementation of molecular asymmetry has recently emerged as a promising approach to suppress ΔE₃ without compromising light absorption or charge transport. This review systematically summarizes recent progress in asymmetric Y-series NFAs, including modifications involving central cores, terminal groups, side chains, and multi-site asymmetrization. Emphasis is placed on the mechanistic understanding of how specific asymmetries influence molecular energetics, exciton dynamics, and non-radiative decay processes. Theoretical models and empirical correlations are discussed to elucidate the structure–ΔE₃ relationship. Finally, key challenges and prospective design principles for the rational development of next-generation asymmetric NFAs are outlined.