# Investigation of Open Air Stability of CsPbBr3 Thin-Film Growth on Different Substrates
###### Abstract  
Originally developed out of scientific curiosity, lead halide perovskites are rapidly gaining success due to their broad tenability and ease of fabrication. Despite these advantages and the considerable progress made in the efficiency of perovskite-based devices, the stability of such materials remains a challenge. In this research paper, the role of substrate materials on which thin films of perovskites were deposited was examined, highlighting their critical importance for atmosphere-induced degradation. Indeed, CsPbBr3 thin films sputtered on glass (soda lime and quartz) and indium tin oxide (ITO) resulted more stable, while those deposited on polycrystalline gold-coated glass were much more prone to degradation in a temperature- and moisture-controlled (43% relative humidity (RH)) atmosphere.  
m 20202  
studied and promising fully inorganic perovskites thanks to its easy synthesis and profitable direct bandgap (2.3 V) [19].  
Generally speaking, CsPbBr\({}_{3}\) thin films, as well as other perovskites, are obtained via wet chemistry deposition by means of two different approaches: (a) (single step) both precursor salts are mixed together, in a stoichiometric ratio, in a common solvent, before allowing the solvent to evaporate, leaving behind the perovskite deposition, or (b) (two steps) the precursors are dissolved into different solvents, singularly deposited as thin films by spin coating, deep coating, or spray coating, and then thermally treated to form the perovskite [7; 20]. Unfortunately, these processes generally produce incoherent films, composed of tiny separated single crystals. This decreases the system efficiency since large grain boundaries increase the recombination rate. Deposition via melting both precursor salts in a quartz tube has also been proposed, but this approach turned out to be not suitable for industrial applications [21].  
Recently, our group proposed a new, easy, and fast process for the deposition of thin, uniform, and chemically homogeneous perovskite films using magnetron sputtering technology [22]. This vacuum-based technique does not require the use of solvents, and the thickness can be regulated by controlling the time and rate of sputtering, which can be monitored \"in situ\" by means of a microbalance. This allows depositing the film on virtually every type of solid substrate. However, the nature of the substrate on which the film is deposited is not totally indifferent. Its chemical nature, as well as its crystalline structure, does affect the perovskite's nucleation and growth mechanism, leading to chemically, optically, and morphologically different deposits.  
The aim of this work was to compare the stability of CsPbBr\({}_{3}\) thin films deposited onto different substrates when exposed to a moisture- and temperature-controlled atmosphere. According to suggested future applications, the perovskite films were grown on substrates commonly used for solar cells or optical devices: soda-line glass, quartz glass, (111)-single-oriented polycrystalline gold, and indium tin oxide (ITO). The evolution of the thin-film surface's chemical and mineralogical composition, as well as their optical properties, was evaluated and discussed as a function of exposure time to the aggressive environment.