Composite side chain induced ordered preaggregation in liquid state for high-performance non-halogen solvent processed organic solar cells

Abstract

Eco-friendly organic solar cells (OSCs) have become a promising choice for commercialization, particularly emphasizing the importance of using non-halogenated solvents. However, non-halogenated OSCs with high-performance remain limited due to the uncontrollable preaggregation behaviors of photovoltaic materials in these solvents. Here, composite side chain engineering was shown to enhance photovoltaic performance of non-halogenated solvents processed OSCs by developing two small molecular acceptors, C10ch-F and C10ch-Cl, and to study the preaggregation behavior in toluene. Through a combination of in situ absorption analyses and molecular dynamics simulations, we demonstrated that the cyclohexyl moiety at the tail of the linear chain acted as a fixative, effectively mitigating the entanglement of the amorphous long chains and prolonging the kinetics of film formation process, resulting in reinforced molecular packing with a preferential face-on orientation. With effective charge generation, transport, and collection, C10ch-Cl-based device from Tol showed an impressive PCE of 18.4 % and 19.2 % in the binary and ternary systems. Moreover, the PCE remained at 80 % of its initial value after 790 h of continuous illumination, indicating excellent photostability. The uncovered preaggregation and realized excellent performance obtained through the composite side chain strategy may allow for further synthetic advances, potentially leading to significantly improved eco-friendly OSCs.