Central core substitution optimized molecular aggregation and photovoltaic performance in A-DAD-A type acceptors

With the development of A-DA'D-A (D: electron-donating unit; A: electron-withdrawing unit) type acceptors, the performances of organic solar cells (OSCs) have reached a new stage. The central core of A-DA'D-A molecules exhibits a significant impact on molecular planarity and stacking. In this research, the conjugated central core of A-DA'D-A type molecules was extended to the two-dimensional (2D) direction, and the influence of alkyl chains on the 2D-central cores on molecular structure and device performances was explored. Compared with TPTC6 containing alkyl chains, TPTC0 without alkyl chains showed stronger intermolecular interactions and crystallinity, which realized advantageous phase separation in the blend film, leading to more effective charge separation and transport. Therefore, devices based on TPTC0 exhibited an excellent power conversion efficiency (PCE) of 17.70%. In contrast, the blend film exhibited a high energetic disorder due to the poor miscibility between PM6 and TPTC0, resulting in decreased VOC compared with TPTC6. In this work, the influence of alkyl chains on molecular stacking and crystallinity in 2D-expanding conjugated materials was discussed in detail, which would promote the development of related research.