Effect of chlorination and position isomerization of benzotriazole-based acceptors on high-voltage organic solar cells based on dithienobenzodithiophene (DTBDT)-containing polymer donor

Abstract

Dithienobenzodithiophene (DTBDT)-based polymers exhibit good planarity, strong crystallinity, and high mobility. However, their application in organic solar cells (OSCs), especially in high-voltage systems, is very limited compared to that of benzodithiophene (BDT)-based analogs. Herein, we utilize a DTBDT-based polymer PE56 to pair with three wide-bandgap benzotriazole (BTA)-based nonfullerene acceptors (NFAs) and explore the potential for high-voltage OSCs. The chlorination on different positions of parent acceptor BTA5 produces BTA5-Cl and Cl-BTA5, where the Cl atoms are attached to the terminal benzyl ring and the bridge BTA unit, respectively. Due to the small energy offsets, PE56: BTA5, PE56: BTA5-Cl, and PE56: Cl-BTA5 achieved high open-circuit voltage (V_OC) of 1.25, 1.20, and 1.17 V, respectively. The gradually decreased V_OC values are attributed to the increased non-radiative recombination losses (0.17, 0.21, and 0.24 eV) caused by the chlorination and its position isomerization from terminals to BTA units. Chlorination could improve the miscibility between the donor and acceptor and thus form ordered molecular packing, facilitating photocurrent generation. The corresponding power conversion efficiency (PCE) increased from 5.44% to 9.71% and 11.18%. PE56: Cl-BTA5 achieved the highest PCE due to its efficient exciton dissociation, better charge transport, and suppressed charge recombination. Our results demonstrate that DTBDT-based polymer can be used in high-voltage OSCs, and the chlorination position of BTA-based NFAs greatly affects the photovoltaic performance.