Thienopyrroledione and benzodithiophene/thiophene-based random terpolymer for polymer solar cells with improved fill factor

A new random conjugated terpolymer, coded as LGC-D054, was designed and synthesized. It is composed of N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) as an electron-accepting unit, and benzodithiophene (BDT) and terthiophene as electron-donating units into the polymer backbone. The optical, electrochemical, and photovoltaic properties of the terpolymer were investigated. The polymer displayed an optical bandgap of 1.81 eV, with a highest occupied molecular orbital (HOMO) level of −5.25 eV. The bulk-heterojunction (BHJ) polymer solar cell (PSC) with the blend film based on LGC-D054:PC₇₁BM exhibited a power conversion efficiency (PCE) of 4.46% with the short circuit current density (J_sc) of 8.71 mA/cm² and a relatively high fill factor (FF) of 61.21%. After introducing 1,8-diiodooctane (DIO), BHJ film showed better phase separation and larger domain size. Furthermore, this optimized morphology promotes improved hole and electron mobilities, leading to a promising PCE of 5.08% with improved J_sc of 9.08 mA/cm² and high FF of 66.02%.