Previous investigations have revealed that CH3NH3PbI3-based perovskites rapidly decompose on ZnO at elevated temperature. The thermostability of a perovskite film on ZnO was substantially improved with FAPbI3owing to the robust nature of FA compared with methylammonium (MA) in CH3NH3PbI3.

Organic hole-transporting materials (HTMs) are essential components of high-performance perovskite solar cells (PSCs). Three zinc-coordinated chlorophyll derivatives with bacteriochlorin, chlorin, and porphyrin macrocycles, namely, ZnBChl, ZnChl, and ZnPor, respectively, were newly synthesized and employed as HTMs in PSCs. The difference in the π backbones of these HTMs causes differences in their photophysical properties, and thus different hole-extraction abilities, as revealed by steady-state photoluminescence spectra. The power conversion efficiencies (PCEs) of PSCs with a typical mesoporous structure, fluorine-doped tin oxide/compact TiO 2 /mesoporous TiO 2 / CH 3 NH 3 PbI 3 /HTM/Ag, are 8.26%, 11.88%, and 0.68% for ZnBChl, ZnChl, and ZnPor, respectively. The small PCE of the ZnPor-based PSC is partially attributed to the small energy gap of the highest occupied molecular orbital (HOMO) levels between ZnPor and CH 3 NH 3 PbI 3 perovskite. Therefore, we increased this energy gap slightly by shifting the HOMO level of CH 3 NH 3 PbI 3 perovskite downward by incorporating formamidinium and bromide ions into the crystal lattice of CH 3 NH 3 PbI 3 . As a result, the PCE of the ZnPor-based PSC improved to 4.04%, and it exhibited a clearly normal current−voltage curve, indicating better energy alignment between ZnPor and the modified perovskite. In addition, the barriers both in the perovskite/ ZnPor interface and in the ZnPor layer originated from the delocalization of π-electrons on the symmetric aggregates determine the low PCE of ZnPor-based PSCs; this was deduced from measurements of atomic force microscope, ultraviolet photoelectron spectroscopy, and the electric impedance spectroscopy.

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