Synthesis of fluorinated benzotriazole (BTZ)- and benzodithiophene (BDT)-based low-bandgap conjugated polymers for solar cell applications

Abstract

A series of donor–acceptor (D–A) polymers (P1–P3) based on benzodithiophene (BDT) and electron-accepting benzotriazole (BTZ) units containing thiophene linkers with/without alkyl side-chains were designed and synthesized via Stille coupling polymerization method. The effects of polymers with multiple fluorinated BTZ groups on their thermal, optical, electrochemical, and photovoltaic properties were investigated. These polymers possessed the highest occupied molecular orbital (HOMO) levels ranged −5.38 to −5.6 eV and the lowest unoccupied molecular orbital (LUMO) levels ranged −3.55 to −3.57 eV, which covered broad absorption ranges with low optical bandgaps. The bulk heterojunction (BHJ) polymer solar cell (PSC) devices containing an active layer of D-A polymers blended with different weight ratios of electron-acceptor [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) were explored under 100 mW cm−2 of AM 1.5 white-light illumination, where the maximum power conversion efficiency (PCE) value of 3% (with Jsc = 7.70 mA/cm2, FF = 54.04, and Voc = 0.72 V) was obtained in the PSC device consisting of polymer P3.