A-DA'D-A non-fullerene acceptors for high-performance organic solar cells

Since the world-record power conversion efficiency of 15.7% was achieved for organic solar cells (OSCs) in 2019, the newly developed non-fullerene acceptor (NFA) Y6 with an A-DA ' D-A structure (A denotes an electron-accepting moiety, D denotes an electron-donating moiety) has attracted increasing attention. Subsequently, many new A-DA ' D-A NFAs have been designed and synthesized, and the A-DA ' D-A NFAs have played a significant role in the development of high-performance non-fullerene organic solar cells (NF-OSCs). Compared with the classical A-D-A-type acceptors, A-DA ' D-A NFAs contain an electron-deficient core (such as benzothiadiazole (BT), benzotriazole (BTA), quinoxaline (Qx), or their derivatives) in the ladder-type fused rings to fine-tune the energy levels, broaden light absorption and achieve higher electron mobility of the NFAs. This review emphasizes the recent progress on these emerging A-DA ' D-A (including Y-series) NFAs. The synthetic methods of DA ' D-fused rings are introduced. The relationships between the chemical structure of the A-DA ' D-A NFAs and the photovoltaic performance of the corresponding OSCs are summarized and discussed. Finally, issues and prospects for further improving photovoltaic performance of the OSCs are also proposed.