Asymmetric A-D-π-A-type nonfullerene small molecule acceptors for efficient organic solar cells

There has been significant progress with regard to research on nonfullerene small molecule acceptors (SMAs) during the past several years. Typically, high-performance nonfullerene SMAs are based on symmetric A-D-A or A-pi-D-pi-A structural frameworks. In this study, a novel asymmetric nonfullerene SMA, TTPT-T-2F, with an A-D-pi-A structure is rationally designed and synthesized. In addition, a symmetric A-D-A-type nonfullerene SMA, IT-2F, and a symmetric A-pi-D-pi-A-type nonfullerene SMA, T-TPT-T-2F, are also synthesized for comparison. When PBT1-C is employed as a polymer donor, a promising power conversion efficiency (PCE) of 12.71% is achieved for TTPT-T-2F-based organic solar cells (OSCs), which surpasses those of devices based on IT-2F (PCE = 10.54%) and T-TPT-T-2F (PCE = 10.71%). Favorable phase separation toward efficient and more balanced charge transport accounts for the higher PCE achieved in the PBT1-C:TTPT-T-2F device. Our results demonstrate that a small molecule acceptor with an A-D-pi-A structural framework is a promising class of nonfullerene acceptors for OSCs.