A thieno[3,4-b]pyrazine-based A2–A1–D–A1–A2 type low bandgap non-fullerene acceptor with 1,1-dicyanomethylene-3-indanone (IC) as the terminal group

Abstract

As the most successful end-capped unit in conventional A–D–A type non-fullerene acceptors (NFAs), 1,1-dicyanomethylene-3-indanone (IC) plays a significant role in enhancing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Here, an A₂–A₁–D–A₁–A₂ type NFA of TP28, containing the bridge unit of thieno[3,4-b]pyrazine (TP) and the terminal unit of IC, is designed and synthesized. This is the first time that IC groups are introduced into the A₂–A₁–D–A₁–A₂ type NFAs. By selecting four kinds of common electron-withdrawing units including benzothiadiazole (BT), quinoxaline (Qx), benzo[d][1,2,3]triazole (BTA) and TP, we found that the steric hindrance of the A₁ unit may be the key factor in controlling the condensation reaction and only the TP unit could obtain the target molecule. Although the electron-donating capability of the central fluorene unit is relatively weak, TP28 exhibits a quite narrow optical bandgap of 1.47 eV. The PBDB-T:TP28 photovoltaic devices demonstrate a moderate PCE of 5.31%, revealing great potential of such kind of NFA for highly efficient bulk-heterojunction (BHJ) OSCs.