PTQ10-Based Organic Photovoltaics with a High V_OC of ∼1.2 V via Chlorination of Benzotriazole-Based Nonfullerene Acceptors

Poly[(thiophene)-alt-(6,7-difluoro-2-(2-hexyldecyloxy)quinoxaline)] (PTQ10) is a low-cost and wide-bandgap photovoltaic polymer donor, which has received great attention for high-performance organic photovoltaics (OPVs). However, PTQ10-based devices with a high open-circuit voltage (VOC) are rarely reported, probably due to the lack of suitable wide-bandgap nonfullerene acceptors (NFAs). To expand the application of PTQ10 in high-voltage OPVs, here, we developed two A2–A1–D–A1–A2-type NFAs. Both BTA5-Cl and Cl-BTA5 are derived from the previously reported BTA5 by introducing chlorine atoms at the end-capped group (A2) or the bridged unit (A1), respectively. Chlorine substitution at different positions not only affects photophysical properties but also results in different power conversion efficiencies (PCEs) and energy loss (Eloss). Using tetrahydrofuran (THF) as a nonhalogenated processing solvent, the PTQ10:Cl-BTA5 combination realizes the highest PCE of 11.0%, with a VOC of 1.19 V and a fill factor (FF) of 70.4%. The PCE is obviously higher than those of the devices based on PTQ10:BTA5 (4.49%) and PTQ10:BTA5-Cl (8.78%), which can be ascribed to the optimal phase morphology and face-on orientation, together with the desired charge generation, transport, and collection. Our results indicate that chlorination is an effective method to modulate the properties of A2–A1–D–A1–A2-type NFAs for high-voltage and high-performance OPVs, and the substituted positions are also important.