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 (VOC) of OSCs is still relatively low. Recently, we have demonstrated that the Same-A-Strategy (SAS) is feasible to achieve high VOC, 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 electrondonating unit, rhodanine (R), 2-(1,1-dicyanomethylene)rhodanine (RCN), and malononitrile (M) as the terminal A2, respectively. When paired with a p-type polymer J52-Cl containing BTA unit, OSCs based on six material combinations can realize ultra-high VOC 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.

Automated summary

The use of the Same-A-Strategy (SAS) to construct polymer donors and non-fullerene acceptors (NFAs) using the same electron-accepting unit has proven feasible in achieving high open-circuit voltage (VOC) in organic solar cells. The study indicates that the middle and end-capped units of benzotriazole-based NFAs play a vital role in extending the application of SAS, with IDT and RCN identified as promising choices for the core and end-capped groups.