Influence of twisted or planar linkers on the performance of quasi-two-dimensional fused perylene diimide acceptors for organic solar cells

Quasi-two-dimensional (quasi-2D) fused perylene diimide building block is effective for constructing high-performance non-fullerene acceptors, while the exploration of their structure-property relationship remains critical, yet challenging. Herein, two quasi-2D non-fullerene acceptors (FPDI-V and FPDI-E) featuring vinylene or ethynylene linker were developed to reveal the effects of molecular geometry on photophysics, morphology and device performances. We observed that such minor chemical variations can lead to distinct difference on absorption spectra, energy levels, and the photovoltaic properties, but only have slight effects on crystallinity, molecular packing and film morphology. The resulting device based on PTB7-Th:FPDI-V delivered a power conversion efficiency of 7.53%, which is higher than those of FPDI-E based device (6.37%). The improved photovoltaic performance of FPDI-V with a twisted vinylene linker should come from the enhanced absorption coefficient, upshifted molecular energy levels, higher exciton dissociation rate, and weaker charge recombination. This result provides an updated idea for further designing and structural optimizing of quasi-2D non-fullerene acceptors.