Low-cost material combination based on PTQ10 and completely non-fused nonfullerene acceptor for high VOC organic photovoltaics

It is a great challenge to develop low-cost photovoltaic materials, including p-type polymers and n-type small molecules, to fabricate organic photovoltaic (OPV) cells for outdoor and indoor applications. Among large number of nonfullerene acceptors (NFAs), non-fused NFAs have attracted much attention because of the ad-vantages of simple synthesis and easy chemical structure modification. Although the highest power conversion efficiencies (PCEs) of OPVs based on non-fused NFAs have reached 15%, the open-circuit voltage (VOC) is relatively low and hinders indoor application. Here, we designed a completely non-fused NFAs, Cl-BTA33, to combine with a classic low-cost polymer PTQ10. Compared with nonhalogenated BTA33, Cl-BTA33 possesses a higher molar absorption coefficient, stronger crystallinity, and tighter pi-pi stacking due to the stronger inter-molecular interactions. Under AM 1.5 M illumination, PTQ10:Cl-BTA33 combination realizes an improved PCE of 12.16% compared to PTQ10: BTA33-based device (PCE = 8.68%). The enhancement comes from the higher and more balanced carrier mobility, more efficient exciton dissociation, weaker charge recombination, more ordered molecular stacking, and more suitable phase separation. In addition, the large area (1.0 cm2) indoor OPV based on PTQ10: Cl-BTA33 achieves a high PCE of 24.28% under a 2700 K LED illumination at 1000 lx. This study proves that chlorination on the pi-bridge unit is a facile and effective strategy to modify the properties and improve the photovoltaic performance of low-cost, completely non-fused NFAs.