Solvent-Coordinated Tin Halide Complexes as Purified Precursors for Tin-Based Perovskites

Abstract

A series of solvent-coordinated tin halide complexes were prepared as impurity-free precursors for tin halide perovskites, and their structures were determined by single-crystal X-ray diffraction analysis. Using these precursors, the tin halide perovskites, MASnI 3 and FASnI 3 , were prepared, and their electronic structures and photophysical properties were examined under inert conditions by means of photoelectron yield spectroscopy as well as absorption and fluorescence spectroscopies. Their valence bands (MASnI 3 : −5.02 eV; FASnI 3 : −5.16 eV) are significantly higher than those of MAPbI 3 or the typical hole-transporting materials 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenylamino)-9,9′-spirobifluorene and poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine). These results suggest that to develop the solar cells using these tin halide perovskites with efficient hole-collection properties, hole-transporting materials should be chosen that have the highest occupied molecular orbital levels higher than −5.0 eV.

Lead‐Free Tin‐Based Perovskite Solar Cells: Strategies Toward High Performance

“…Therefore, we recommend the sublimation of tin halides under inert atmospheres to eliminate any impurities, which is expected to improve the reproducibility of device performance. The purification of stannous halide precursors via solvent coordination reported by Wakamiya et al provides a convenient method that can be attempted in the fabrication of Sn‐based perovskites . A reducing atmosphere can also be adopted for handling such highly pure precursors to further prevent oxidation during film processing, as has been reported by Kanatzidis group .…”

Tin Halide Perovskites: Progress and Challenges

“…Charge transporting layers play an important role in the separation and extraction of photogenerated charges in PV devices. The conductivity of these materials may be p‐type, forming hole transporting layers (HTLs) or n‐type forming ETLs . Several conditions have to be met for these materials to be suitable for application in PSCs.…”

Realizing High Efficiency over 20% of Low‐Bandgap Pb–Sn‐Alloyed Perovskite Solar Cells by In Situ Reduction of Sn4+

“…It is believed that the Sn 4+ acts as p‐type dopants in the Pb–Sn‐alloyed perovskite films which induce deep trap states to boost nonradiative recombination . Unfortunately, even a highly purified commercial starting material SnI 2 (99.9%, trace metal) could contain up to 10 wt% of SnI 4 due to the technical difficulty of the complete removal of Sn 4+ during the synthesis, as reported by Wakamiya and coworkers recently . In addition, even though the storage of the starting material SnI 2 and the preparation of Sn‐based perovskite films is carried out under a N 2 ‐filled glove box, it is impossible to completely prevent oxygen exposure, so a certain degree of oxidation of Sn 2+ to Sn 4+ is still likely to occur during that time.…”