A novel random terpolymer for high-efficiency bulk-heterojunction polymer solar cells

A new random terpolymer, coded LGC-D013, based on N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) as the acceptor and benzodithiophene (BDT) and terthiophene as the donor units, has been synthesized and characterized as a donor material in bulk-heterojunction (BHJ) organic photovoltaic (OPV) applications. The thermal, optical, and electrochemical properties of the LGC-D013 were characterized. The polymer has a deep highest occupied molecular orbital (HOMO) level of −5.56 eV and an optical band gap of 1.84 eV in film. The OPV based on LGC-D013:PC₇₁BM blend film demonstrated a power conversion efficiency (PCE) of 6.09%, with a relatively high fill factor (FF) of 72.55%. After 1,8-diiodooctane (DIO) treatment with a 3% volume ratio, the short circuit current density (J_sc) was improved from 9.48 to 11.29 mA cm⁻², and FF was improved from 72.55 to 73.13%, resulting in PCE improvement from 6.09 to 7.22%. The BHJ OPV using LGC-D013 as the donor polymer based on TPD and BDT with terthiophene showed an improved fill factor as high as 72%, which is higher than those of conventional TPD-BDT based polymers.