Binary Organic Solar Cells with over 19 % Efficiency and Enhanced Morphology Stability Enabled by Asymmetric Acceptors

The simultaneous improvement of efficiency and stability of organic solar cells (OSCs) for commercialization remains a challenging task. Herein, we designed asymmetric acceptors DT-C8Cl and DT-C8BTz with functional haloalkyl chains, in which the halogen atoms could induce noncovalent interactions with heteroatoms like O, S, and Se, etc., thus leading to appropriately manipulated film morphology. Consequently, binary devices based on D18: DT-C8Cl achieved a champion power conversion efficiency (PCE) of 19.40 %. The higher PCE of D18: DT-C8Cl could be attributed to the enhanced π-π stacking, improved charge transport, and reduced recombination losses. In addition, the noncovalent interactions induced by haloalkyl chains could effectively suppress unfavorable morphology evolutions and thereby reduce trap density of states, leading to improved thermal and storage stability. Overall, our findings reveal that the rational design of asymmetric acceptors with functional haloalkyl chains is a novel and powerful strategy for simultaneously enhancing the efficiency and stability of OSCs.