A2–A1–D–A1–A2 Type Non-Fullerene Acceptors with 2-(1,1-Dicyanomethylene)rhodanine as the Terminal Groups for Poly(3-hexylthiophene)-Based Organic Solar Cells

2-(1,1-Dicyanomethylene)rhodanine (RCN) is an important electron-deficient terminal unit to build non-fullerene acceptors (NFAs) having been realized high power conversion efficiency (PCE) beyond 12% with complicated p-type polymer as electron donor. However, the photovoltaic properties of RCN-based NFAs are unsatisfied when paired with the classic p-type polymer poly(3-hexylthiophene) (P3HT). In order to make a contribution in this regard, we designed two RCN-based small molecular acceptors with A₂-A₁-D-A₁-A₂ structure, BT3 and BTA3, where benzothiadiazole (BT) and benzotriazole (BTA) are bridged A₁ segments, respectively, to modulate the optoelectronic properties. As a result, P3HT:BTA3 solar cell exhibits a promising PCE of 5.64%, with a V_OC of 0.90 V and a fill factor (FF) of 0.65, which is obviously much better than that of P3HT:BT3 (PCE = 2.55%, V_OC = 0.72 V, FF = 0.61). The higher electron mobility of P3HT:BTA3 film indicates BTA3 tends to form a continuous pathway for electron transport even at a lower weight ratio of 1:0.3 than 1:0.5 for P3HT:BT3 film. Our results indicate that introducing a weak electron-withdrawing building block BTA is an effective strategy compared with the BT counterpart to improve the performance of RCN-based NFA devices.