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

Abstract

The most promising lead‐free options for producing perovskite solar cells are tin halide perovskite (Sn‐HP) materials. Here, while in situ monitoring the optical evolution of the material in humid air, we used spectroscopic ellipsometry to investigate the dielectric function of FASnI3 layers (with and without additives) within the range of 1–5eV. According to calculations based on the density functional theory that showed oxygen diffusion on FASnI3 surfaces, the steady decrease in absorption coefficient in the band gap region (1.47eV) and simultaneous increase in absorption in the 3‐4.5 eV region suggested the production of amorphous tin oxide (SnO2). Concurrently, X‐ray diffraction revealed a clear degradation of FASnI3. With the addition of sodium borohydride (NaBH4) and dipropylammonium iodide (DiPI), the optically active area of about 1.47 eV was preserved for a longer period while SnO2 production was prevented. Last but not least, we investigated FASnI3's stability in a dry N2 environment and showed that it is optically durable for thermal operations up to 100 °C, particularly when additives are used.This article is protected by copyright. All rights reserved.

Tailoring Single‐Mode Random Lasing of Tin Halide Perovskites Integrated in a Vertical Cavity

“…The combination of NaBH 4 and DipI additives produced a synergistic effect in FASnI 3 films increasing their stability, where the former was a reducing agent avoiding Sn +2 oxidation while the latter acted as a passivating agent, resulting in an enhancement of their optoelectronic properties under N 2 and ambient conditions, as discussed in previous works. 23,26 The commercial DBR mirrors (central wavelength 890 nm, supplied by Edmund Optics, Ref. 63 154, and Eksma Optics, Ref.…”

“…[24] The spectral position of the relatively narrow, 10 meV, ASE line is located at 1.37-1.39 eV, as observed in Figure 1b, which is redshifted by 10-30 meV with respect to the PL peak energy at ≈1.395 eV (888 nm), and 60-90 meV below the energy band gap at 1.46 +/-0.03 eV, as recently measured for these films by ellipsometry. [26] The multilayer structure of the microcavity was designed to tune M0 within the PL energies. In particular, the bandpass of the DBRs was chosen to be centered at 880 nm with a full width at half maximum (FWHM) >80 nm, see Figure S1 (Supporting Information), the thicknesses of FASnI 3 (d 1 ) and Au (d 3 ) were fixed to d 1 = 200 nm and d 3 = 30 nm, respectively, while d 2 , the PMMA thickness, was used as the tuning parameter for M0.…”