Further improvement of the performance and stability of inverted perovskite solar cells (PSCs) is necessary for commercialization. Here, ferrocene derivative dibenzoylferrocene (DBzFe) is used as an additive to enhance the performance and stability of MA- and Br- free PSCs. The results show that the introduction of DBzFe not only passivates the defects in the film but also inhibits the ion migration in the film. The final device achieves a power conversion efficiency (PCE) of 23.53%, which is one of the highest efficiencies currently based on self-assembled monolayers (SAMs). Moreover, it maintains more than 96.4% of the original efficiency when running continuously for 400 h at the maximum power point.

Self-assembled molecules (SAMs) have been widely employed as hole transport layers (HTLs) that can improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, few SAMs are effective for wide band gap (WBG; Eg = 1.77 eV) PSCs. We found that [3-[4-(diphenylamino)phenyl]-9H-carbazol-9-yl]propylphosphonic acid (4dp3PACz) working as a monomolecular HTL is effective for WPG (FA_0.8Cs_0.2PbI_1.8Br_1.2) PSCs. The 4dp3PACz improved the quality of the perovskite film and reduced the defect density of the film, which reduced the nonradiative recombination and enhanced the carrier transport. 17.17% efficiency is reported. In addition, all-perovskite tandem solar cells consisting of the WBG PSC as the top cell gave 26.47% efficiency.

This study is on the enhancement of the efficiency of wide bandgap (FA_0.8Cs_0.2PbI_1.8Br_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 APbI3 PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA_0.8Cs_0.2PbI_1.8Br_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_0.8Cs_0.2PbI_1.8Br_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 (Eg = 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.