Positionally heterogeneous non-fully conjugated dimeric acceptors with unilateral conjugated π-bridge enable highly efficient and stable organic solar cells

Abstract

In this study, two non-fully conjugated dimeric acceptors, DYTC6T-V-out and DYTC6T-V-in, were designed and synthesized via a unilateral conjugated π-bridge strategy, introducing positional isomerism at the π-bridge site. DYTC6T-V-in exhibits a substantially higher dipole moment owing to its more distorted molecular conformation and larger small molecule subunit separation. This promotes more ordered molecular packing in the ternary blend film, thereby enhancing crystallinity, charge transport and charge collection. Conversely, the low dipole moment of DYTC6T-V-out results in reduced packing order in the corresponding blend film. Therefore, the ternary device based on DYTC6T-V-in achieved the best photovoltaic performance, achieving a PCE of 19.47%. Furthermore, the high molecular weight of the dimeric acceptors elevates their glass transition temperature(Tg), which enhances the morphological stability of the active layer. This work demonstrates the potential of employing a positional-isomer unilateral conjugated π-bridge strategy in non-fully conjugated dimeric acceptors, providing a promising approach to developing third components that synergistically improve both device performance and stability.