PDI-based heteroacenes as acceptors for fullerene-free solar cells: importance of their twisted geometry

Abstract

Two perylenediimide (PDI) derivatives (FP₄TT2T and FP₄3T) with extended conjugation have been successfully synthesized. Due to their long fused D–A (D: donor and A: acceptor) molecular structures, PDI-based heteroacenes have rigid backbones and exhibit strong light absorption in the 300–600 nm range. With the contribution from the PDI moiety with strong electron affinity, the molecules possess low energy levels of LUMOs (ca. −3.7 eV), fitting well as acceptors for fullerene-free organic solar cells (OSCs). OSC devices containing FP₄TT2T and FP₄3T were fabricated and fully characterized. It is found that the geometric twist in PDI-based heteroacenes as acceptors could enhance the performance of OSC devices. OSCs based on FP₄3T with a more twisted geometry achieved a power conversion efficiency of 6.05%, which is higher than those based on the FP₄TT2T counterpart.