Hole-Transporting Polymers Containing Partially Oxygen-Bridged Triphenylamine Units and Their Application for Perovskite Solar Cells

A series of polymers composed of partially oxygen-bridged triphenylamine units was successfully synthesized by Suzuki-Miyaura or Migita-Kosugi-Stille cross coupling reactions. In addition to the polymer with directly connected triphenylamine units, P1, different π-spacers, were introduced into the polymer main chains including m-benzene, P2, p-benzene, P3, and bithiophene, P4. Photoelectron yield spectroscopy (PYS) results showed that the highest occupied molecular orbitals of these polymers lie above the valence bands of typical metal halide perovskites, suggesting efficient hole extraction from the perovskite. When used as hole-transporting materials in perovskite solar cells, the maximum power conversion efficiency (PCE) of P1–P4 reached 7.9% with LiTFSI additive, while the device of P1 and P4 without additive showed better PCE of 12.1% and 11.1%, respectively.