Modulating the middle and end-capped units of A2-A1-D-A1-A2 type non-fullerene acceptors for high VOC organic solar cells

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have been improved rapidly in the last few years, due to the development of excellent non-fullerene acceptor (NFA) materials. However, compared to the high PCE, the open-circuit voltage (V_OC) of OSCs is still relatively low. Recently, we have demonstrated that the “Same-A-Strategy” (SAS) is feasible to achieve high V_OC, where the same electron-accepting (A) unit is utilized to construct polymer donor and NFA. To investigate the structure-properties relationship, here we chose six benzotriazole-based NFAs (BTA1, BTA11, BTA3, BTA13, BTA7 and BTA17) with A₂-A₁-D-A₁-A₂ type molecular backbone, where indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) as middle electron-donating unit, rhodanine (R), 2-(1,1-dicyanomethylene)rhodanine (RCN), and malononitrile (M) as the terminal A_2, respectively. When paired with a p-type polymer J52-Cl containing BTA unit, OSCs based on six material combinations can realize ultra-high V_OC of 1.09–1.33 V with PCEs of 0.13–10.5%. The results indicate that the middle and end-capped units play a vital role to extend the application of SAS, and IDT and RCN are promising choices as the core and end-capped groups.