First Experimental Evidence of Amorphous Tin Oxide Formation in Lead-Free Perovskites by Spectroscopic Ellipsometry

The most promising lead-free options for producing perovskite solar cells are tin halide perovskite materials. Herein, while in situ monitoring the optical evolution of the material in humid air, spectroscopic ellipsometry is used to investigate the dielectric function of FASnI(3) layers (with and without additives) within the range of 1-5 eV. According to calculations based on the density functional theory that shows oxygen diffusion on FASnI(3) surfaces, the steady decrease in absorption coefficient in the band gap region (1.47 eV) and simultaneous increase in absorption in the 3-4.5 eV region suggest the production of amorphous tin oxide. Concurrently, X-ray diffraction reveals a clear degradation of FASnI(3). With the addition of sodium borohydride and dipropylammonium iodide, the optically active area of about 1.47 eV is preserved for a longer period while SnO2 production is prevented. Last but not least, FASnI(3)'s stability is investigated in dry N-2 environment and shown that it is optically durable for thermal operations up to 100 & DEG;C, particularly when additives are used.

Automated summary

The most promising lead-free option for perovskite solar cells is tin halide perovskite materials. Spectroscopic ellipsometry is used to investigate the dielectric function of FASnI(3) layers with and without additives, revealing a decrease in absorption coefficient in the band gap region and an increase in absorption in the 3-4.5 eV region, suggesting the production of amorphous tin oxide. By adding sodium borohydride and dipropylammonium iodide, the optically active area is preserved and SnO2 production is prevented. Additionally, FASnI(3) is optically durable up to 100°C when additives are used.