Triarylamine/Bithiophene Copolymer with Enhanced Quinoidal Character as Hole‐Transporting Material for Perovskite Solar Cells

Abstract Polytriarylamine is a popular hole‐transporting materials (HTMs) despite its suboptimal conductivity and significant recombination at the interface in a solar cell setup. Having noted insufficient conjugation among the triarylamine units along the polymer backbone, we inserted a bithiophene unit between two triarylamine units through iron‐catalyzed C−H/C−H coupling of a triarylamine/thiophene monomer so that two units conjugate effectively via four quinoidal rings when the molecule functions as HTM. The obtained triarylamine/bithiophene copolymer ( TABT ) used as HTM showed a high‐performance in methylammonium lead iodide perovskite (MAPbI 3 ) solar cells. Mesityl substituted TABT forms a uniform film, shows high hole‐carrier mobility, and has an ionization potential (IP=5.40 eV) matching that of MAPbI 3 . We fabricated a solar cell device with a power conversion efficiency of 21.3 % and an open‐circuit voltage of 1.15 V, which exceeds the performance of devices using reference standard such as poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine ( PTAA ) and Spiro‐OMeTAD .