Organic Cation‐Dependent Degradation Mechanism of Organotin Halide Perovskites

Abstract

The applications of organotin halide perovskites are limited because of their chemical instability under ambient conditions. Upon air exposure, Sn2+ can be rapidly oxidized to Sn4+, causing a large variation in the electronic properties. Here, the role of organic cations in degradation is investigated by comparing methylammonium tin iodide (MASnI3) and formamidinium tin iodide (FASnI3). Through chemical analyses and theoretical calculations, it is found that the organic cation strongly influences the oxidation of Sn2+ and the binding of H2O molecules to the perovskite lattice. On the one hand, Sn2+ can be easily oxidized to Sn4+ in MASnI3, and replacing MA with FA reduces the extent of Sn oxidation; on the other hand, FA forms a stronger hydrogen bond with H2O than does MA, leading to partial expansion of the perovskite network. The two processes compete in determining the material's conductivity. It is noted that the oxidation is a difficult process to prevent, while the water effect can be largely suppressed by reducing the moisture level. As a result, FASnI3‐based conductors and photovoltaic cells exhibit much better reproducibility as compared to MASnI3‐based devices. This study sheds light on the development of stable Pb‐free perovskite optoelectronic devices through new material design.

Preparation of Methylammonium Tin Iodide (CH3NH3SnI3) Perovskite Thin Films via Flash Evaporation

“…In addition, also a chemical modification of the MASI is indicated from a strong decrease of lattice parameter ( a ≈ c = 6 009(5) Å, ΔV ≈ −12%), which could be expected from a decomposition under formation of MAI. The decomposition of MASI in air has been also been reported by Noel and Wang, showing the formation of MAI, with possible formations of amorphous tin oxide species.…”

Improving Performance of Lead‐Free Formamidinium Tin Triiodide Perovskite Solar Cells by Tin Source Purification

“…The increase of PL intensity represents increased radiative recombination process, which indicates that the density of trap‐state leading to nonradiative trap‐assisted recombination decreases. The carrier lifetimes fitted from time‐resolved PL curves manifest the reduction of defect density as well …”

Multichannel Interdiffusion Driven FASnI3 Film Formation Using Aqueous Hybrid Salt/Polymer Solutions toward Flexible Lead‐Free Perovskite Solar Cells

“…[8][9][10][11] Although the vast majority of the research is focused on APbX 3 materials, Sn-based perovskites are also of increasing interest because of the lower toxicity of Sn. [12][13][14][15][16][17][18][19][20][21] The CH 3 NH 3 SnI 3 has been explored in the majority of devices, but there are several important issues: (1) Sn 2+ is easily oxidized to Sn 4+ ; [16,22] (2) Poor quality films tend to form because of rapid crystallization during spin-coating. [16,23] Some have reported more stable devices employing [(NH 2 ) 2 CH]SnI 3 (FASnI 3 ), which presumably results from the enhanced interaction between Sn 2+ and larger sized FA + , making FASnI 3 an attractive candidate.…”