Enhancing solar cell efficiencies through strategic chlorination of quinoxaline-based D–A-type polymers

Abstract

In this study, we systematically incorporate chlorine (Cl) atoms to investigate the effects of chlorination on the photovoltaic performance of quinoxaline (Qx)-based donor–acceptor (D–A)-type polymers. First, we develop the unchlorinated reference polymer DBT-FQx by combining a thienyl-substituted dithienobenzodithiophene (DTBDT) donor with a multifluorinated quinoxaline (Qx) acceptor through a thiophene bridge. Next, Cl atoms are added to the thiophene side chains of the DTBDT donor, producing the chlorinated polymer DBTCl-FQx. Finally, we substitute the fluorine atoms at the 2,3-positions of the Qx acceptor in DBTCl-FQx with Cl atoms, resulting in the more chlorinated polymer DBTCl-ClQx. Notably, the photovoltaic performance of these polymers gradually improves with an increasing number of Cl atoms in the non-fullerene polymer solar cells. Devices based on the chlorinated polymers DBTCl-FQx and DBTCl-ClQx exhibit higher power conversion efficiencies (PCEs) of 14.01 % and 14.73 %, respectively, compared to the DBT-FQx reference (12.16 %). The improved PCEs are primarily attributed to enhanced open-circuit voltages due to deeper energy levels. Additionally, chlorination offers benefits such as better charge transfer kinetics, suppressed charge recombination, and superior morphological features of the devices. These findings underscore the potential of chlorination strategies for enhancing the photovoltaic performance of DTBDT–Qx-based polymer donors.