Enhanced Photovoltaic Performances via Chlorine Substitution on Alkylphenyl Side Chains of a Conjugated Polymer

Owing to the enhanced intermolecular interaction, aromatically chlorinated polymers have been energetic to the molecular design and innovation of pi-conjugated polymers for efficient organic solar cells (OSCs). Herein, two structurally similar copolymer donors (Z1 and Z2) based on benzodithiophene (BDT) on alkylbenzene conjugated side chains without and with chlorine atoms were designed and synthesized. Two copolymers possessed similar absorption spectra ranging from 380 to 620 nm and approximated optical band gap (Egopt). Compared with the nonchlorinated polymer Z1, polymer Z2 substituted by chlorine in the meta-position of the alkylphenyl group endowed it an enhanced pi-pi stacking and favorable morphology, which brought the OSCs the significantly enhanced photocurrent and fill factor as well as hole/electron mobility. When the nonchlorinated copolymer Z1 showed a power conversion efficiency (PCE) of 12.03%, the chlorinated copolymer Z2 obtained a higher PCE of 15.11%. The results provide more insight into the role of the chlorinated alkylphenyl side chains in designing new conjugated polymers to promote the performance of OSCs.

Automated summary

Due to enhanced intermolecular interaction, aromatically chlorinated polymers play a crucial role in the molecular design and innovation of pi-conjugated polymers for efficient organic solar cells (OSCs). In this study, two structurally similar copolymers (Z1 and Z2) were designed and synthesized, based on benzodithiophene (BDT) with alkylbenzene conjugated side chains, one without chlorine atoms and the other with chlorine atoms. The chlorine substitution in Z2 led to enhanced pi-pi stacking and favorable morphology, resulting in significantly improved photocurrent, fill factor, and mobility compared to Z1. The chlorinated copolymer Z2 exhibited a higher power conversion efficiency (PCE) of 15.11% compared to the nonchlorinated copolymer Z1's PCE of 12.03%. These findings provide valuable insights into the role of chlorinated alkylphenyl side chains in the design of new conjugated polymers for enhanced OSC performance.