Perovskite Solar Cells Consisting of PTAA Modified with Monomolecular Layer and Application to All‐Perovskite Tandem Solar Cells with Efficiency over 25%

Abstract This study is on the enhancement of the efficiency of wide bandgap (FA 0.8 Cs 0.2 PbI 1.8 Br 1.2 ) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI 3 PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA 0.8 Cs 0.2 PbI 1.8 Br 1.2 PSCs. It is found that the surface‐modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA 0.8 Cs 0.2 PbI 1.8 Br 1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs ( E g = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all‐perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate.