Highly twisted ladder-type backbone bearing perylene diimides for non-fullerene acceptors in organic solar cells

A ladder-type π-system PDIPY that bearing perylene diimide and pyrene units have been developed for constructing non-fullerene acceptors. The vinyl bridged PDIPY dimer PDIPY-V and polymer PPDIPY-V have been synthesized via bromonation and Stille coupling recation. PDIPY-V and PPDIPY-V exhibit intense and broad absorption within 400-650 nm that complement the absorption spectra of the narrow bandgap polymeric donors. DFT calculation indicated that PDIPY-V and PPDIPY-V hold highly twisted structure, which prevent the formation of π−π stacking and crystallization in the aggregated states. The grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) investigations confirmed the amorphous nature of the pure films and the PDIPY-V/PPDIPY-V:PTB7-Th blend films. The PDIPY-V:PTB7-Th based photovoltaic device showed a poor performance due to the small LUMO offset of donor and acceptor. While the PPDIPY-V:PTB7-Th based device showed a high PCE of 5.20%, indicating the PDIPY derivatives are promising non-fullerene acceptors for polymer solar cells.