Wide Band Gap Photovoltaic Polymer Based on Pyrrolo[3,4-f]benzotriazole-5,7-dione (TzBI) with Ultrahigh VOC Beyond 1.25 V

Pyrrolo[3,4-f]benzotriazole-5,7-dione (TzBI) is an effective electron-accepting (A) unit to construct photovoltaic polymers. Though TzBI-based polymers have realized promising photovoltaic performance and processed the low-lying HOMO (the highest occupied molecular orbital) energy levels, their open-circuit voltages (VOCs) are relatively below (<1.0 V). To extend the application of this kind of polymer in high VOC polymer solar cells (PSCs), here, we choose a famous wide band gap D−π–A type polymer donor P2F-EHp to match with an A2-A1-D-A1-A2 type acceptor BTA3. The P2F-EHp: BTA3-based photovoltaic device can obtain an ultrahigh VOC of 1.29 V but a low power conversion efficiency (PCE) of 4.62%. Subsequently, we further introduce fluorine atoms to BTA units and synthesize a new non-fullerene acceptor, named F-BTA3. The fluorination of the BTA units can increase the molar extinction coefficient, enlarge the charge transfer (CT) driving force, and suppress the bimolecular recombination. Consequently, the short-circuit current (JSC) and PCE of F-BTA3-based devices are increased by 71 and 81%, respectively, compared with the BTA3-based device. The PCE of 8.38% for P2F-EHp: F-BTA3 combination is also one of the highest values for PSCs with VOC beyond 1.2 V. Our results indicate that TzBI-based polymers can also realize high VOC and the fluorination of the A1 unit for A2–A1–D–A1–A2 type acceptor is an effective way to balance the JSC and VOC for PSCs.