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.