Wide‐Bandgap Donor–Acceptor Copolymer Based on BDTTz Donor and TPD Acceptor for Polymer Solar Cells Using Fullerene and Nonfullerene Acceptors

Abstract

A donor–acceptor copolymer based on thiazole substituted benzodithiophene (BDTTz) (donor unit) and thieno[3,4‐c]pyrrole‐4‐6‐dione (TPD) (acceptor unit) P(BDTTz‐TPD) denoted as P132 is investigated. P132 shows an absorption profile from 300 to 680 nm and the low‐lying highest occupied molecular orbital (HOMO) energy level of −5.54 eV. P132 as donor along with fullerene derivative (PC71BM) or nonfullerene denoted as BThIND‐Cl as acceptor are used for the fabrication of polymer solar cells. The P132:BThIND‐Cl‐based polymer solar cell shows high open‐circuit voltage as compared with P132:PC71BM which is attributed to the upshifted lowest unoccupied molecular orbital level of BThIND‐Cl and low energy loss. Moreover, P132:BThIND‐Cl attains higher short‐circuit current than that for P132:PC71BM which is attributed to the broader absorption spectra and low optical band gap of BThIND‐Cl, which leads to high light‐harvesting ability of the P132:BThIND‐Cl active layer. The polymer solar cells based on P132:PC71BM and P132:BThIND‐Cl attain power conversion efficiencies of 7.03% and 15.52%, respectively. The charge transport is more balanced in P132:BThIND‐Cl and results in a high value of fill factor. Small energy loss in P132:BThIND‐Cl‐based PSCs is attributed to the low HOMO offsets between P132 and BThIND‐Cl.