Modulation of Three p-Type Polymers Containing a Fluorinated-Thiophene-Fused-Benzotriazole Unit To Pair with a Benzotriazole-Based Non-fullerene Acceptor for High VOC Organic Solar Cells

Three 6-fluoro-thieno[2′,3′:4,5]benzo[1,2-d][1,2,3]triazole (fBTAZT) containing copolymers, named as PfBTAZT-H, PfBTAZT-F, and PfBTAZT-Cl, were employed to pair with a benzo[1,2-d][1,2,3]triazole (BTA) based non-fullerene acceptor BTA3 for the applicaition in organic solar cells (OSCs). By introducing fluorine or chlorine atoms into the thiophene side chains on BDT units, the highest occupied molecular orbital (HOMO) energy levels of polymers shift down in sequence, and PfBTAZT-Cl shows an obvious blue-shift of absorption spectrum. PfBTAZT-F:BTA3-based OSC attains a VOC of 1.05 V, a JSC of 11.83 mA cm–2, and FF of 0.62, leading to a PCE of 7.69%, which are higher than that of PfBTAZT-H:BTA3 (VOC = 0.99 V, JSC = 11.60 mA cm–2, FF = 0.58, and PCE = 6.65%) due to its well-matched HOMO energy level, higher charge mobilities, and favorable film morphology. More surprisingly, chlorinated polymer PfBTAZT-Cl obtains the highest VOC of 1.20 V and PCE of 8.00%, which is attributed to the lowest HOMO energy level, l...