# Investigation of Open Air Stability of CsPbBr3 Thin-Film Growth on Different Substrates
## 3 Results and Discussion  
### Structural Characterization  
As mentioned above, the magnetron sputtering sample holder was large enough to allocate all four substrates tested. In such a way, all perovskite films were deposited exactly in the same conditions. Nevertheless, the XRD patterns collected on the \"as-deposited\" samples differed, demonstrating the active role of the substrate. Figure 1 displays the XRD pattern recorded on freshly prepared thin films. It is worth noting that, in accordance with previous reports [22] on glass substrates (soda lime and silica), the thin films were characterized by the presence of a nearly pure, even if strongly textured, CsPbBr\({}_{3}\) phase. Strong texturing was highlighted by the disagreement between the intensity ratio of the experimentally observed peaks and the literature data. In magnetron-deposited thin films, the dominant orientations were (100) and (202) (Figure 1), while the plane (121) was almost neglectable, strongly differing from the typical powdery CsPbBr\({}_{3}\) pattern (COD 1533062). On the other hand, in the deposit growth on single-oriented polycrystalline gold, the CsPbBr\({}_{3}\) phase was a minor constituent, and other peaks, not attributable to the gold substrate, were detectable in the spectrum (Figure 1, blue line). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Substrate Type** & \begin{tabular}{c} **Chemical** \\ **Nature** \\ \end{tabular} & \begin{tabular}{c} **Mineralogical** \\ **Properties** \\ \end{tabular} & **Optical** & **Conductive** & \begin{tabular}{c} **Uses in PV and Optical** \\ **Devices** \\ \end{tabular} \\ \hline Silica glass & \begin{tabular}{c} SiO\({}_{2}\) \\ \end{tabular} & Amorphous & \begin{tabular}{c} Transparent \\ UV–Vis spectrum \\ \end{tabular} & No & \begin{tabular}{c} Optical windows \\ and general use \\ transparent \\ conductive substrate \\ \end{tabular} \\ \begin{tabular}{c} Soda-lime glass \\ \end{tabular} & \
\begin{tabular}{c} Commercial \\ grade glass \\ \end{tabular} &
\begin{tabular}{c} Amorphous \\ Polycrystalline \\ (111)-single-oriented \\ \end{tabular} & Reflective & Yes & Metallic back contact \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types of substrates used in this research. ITO, indium tin oxide; UV–Vis, ultraviolet–visible light; PV, photovoltaic. These differences were further highlighted during the ageing test. Figure 2 depicts the spectra of freshly prepared samples compared to those exposed to an aggressive environment (six days). Even at the end of the aging test (6 days of exposure), in the samples grown on soda-lime glass, silica glass, and ITO, CsPbBr\({}_{3}\) still constituted the dominant mineralogical phase (Figure 2a-c), while the sample deposited on (111)-oriented gold presented a large number of peaks, some of which could be attributed to moisture-induced degradation byproducts such as PbBr\({}_{2}\)[11; 26; 27]. Figure 1: X-ray diffraction (XRD) patterns of the “as-deposited” thin films. Full triangles indicate the CsPbBr\({}_{3}\) phase diffraction peaks. Figure 2: XRD patterns of the “as-prepared” (black lines) and aged (6 days, red lines) samples. As described in the legend, scatter symbols indicate the diffraction peaks for the most common byproduct phases: (**a**) quartz glass; (**b**) ITO; (**c**) soda-lime glass; (**d**) gold. Inset: zoom view of the region of the higher peak. The insets of Figure 2a-c display a superimposed zoomed view of the most intense diffraction peaks (CsPbBr\({}_{3}\) (202)) of the \"as-prepared\" and aged samples. The \"as-prepared\" film obtained on silica glass (inset Figure 2a) presented a symmetric and well-defined, even if broad, diffraction peak. After the aging process, the peak appeared with two narrow components. This phenomenon can be reasonably explained considering that, during the aging process, the temperature and moisture cause the degradation of the perovskite and the consequent formation of a second peak. Moreover, the growth of the crystallites caused sharpening of the peaks.