## 3 Results and Discussion  
Various perovskite films with an equimolar ratio of MAI:PbI\({}_{2}\), i.e., (1.0:1.0), (1.2:1.2), (1.5:1.5), and (1.6:1.6), were synthesized as described in the device fabrication section and characterized using SEM, XRD, UV-vis, and PL. First, the morphological characteristics of the perovskite films prepared on the glass substrates were examined via SEM, as shown in Figure 2a-d. The SEM image of (1:1) film formulation shows that the perovskite crystallization process did not reach completion, given the very small size of the grains buried in the midst of cracked islands comprised of a significant density of pinholes. Similarly, the (1.2:1.2) and (1.6:1.6) formulations showed improper perovskite crystallization, again with a high density of cracks and pinholes. However, the (1.5:1.5) film appears to be much better than the rest of the films due to a denser morphology with a far lower density of visible pinholes and cracks for this composition. Shown in Figure 2e are the XRD spectra of the fabricated absorber layers at these four compositions, and the results are in good agreement with prior reports [38]. The (1.5:1.5) film shows relatively intense peaks for the (110), (112), (121), (020), (220), and (222) planes with their intensity counts being higher than the other films, suggesting the better crystallinity of the (1.5:1.5) film, as compared to the rest of the samples; this in alignment with the SEM data taken for the (1.5:1.5) composition, where a compact morphology is evident (Figure 2c). While the presence of the PbI\({}_{2}\) impurity peak for the (1.0:1.0) and (1.2:1.2) formulations located at -12.5-13\({}^{\circ}\) is not ideal, this peak could also arise from the onset of post-synthesis degradation upon exposure to ambient conditions [39], or possible instrumentation resolution errors in measuring minute microgram resolution of precursor masses. Additionally, the magnified image of the XRD spectra for the (1:1) formulation at 13.14\({}^{\circ}\) is shown in the inset of Figure 2e, bottom panel. The crystallite size as it pertains to the (110) peak was calculated using the Scherrer relation, \(S=\frac{K\lambda}{S\cos\theta}\), where \(S\) is the estimated crystallite grain size, \(\lambda\) = 0.15406 A for the wavelength of the X-rays used in the diffractometer, \(\beta\) represents the full-width-half-maximum (FWHM) in radians, \(\theta\) is the diffraction Bragg angle, \(K\) is the Scherrer constant, which was taken to be -0.94, as characteristic of spherical crystals with cubic symmetry, which we assumed likely for our samples [40]. Based on the above analysis, the crystallite size for the films was calculated to be 43.4 nm (1.0:1.0) \(<\) 44.2 nm (1.2:1.2) \(<\) 45.5 nm (1.6:1.6) \(<\) 48.1 nm (1.5:1.5), as summarized in Table 1. Even though the variation between the sizes is very small based on this calculation, the data are consistent with the crystallite size being largest for the (1.5:1.5) film compared to the other films. Figure 2: The SEM images of the perovskite films fabricated on glass substrates using different equimolar concentrations of MAI:PbI\({}_{2}\): (**a**) (1.0:1.0), (**b**) (1.2:1.2), (**c**) (1.5:1.5), and (**d**) (1.6:1.6). (**e**) XRD spectra of the perovskite films synthesized on glass substrates at the increasing equimolar ratios of MAI:PbI\({}_{2}\) from bottom-to-top. Inset in the bottom panel shows the magnified region in XRD spectra for (1.0:1.0) film at 13.14\({}^{\circ}\) ascribed to the PbI\({}_{2}\) peak. The thickness profile of the films is shown in Figure 3, measured using atomic force microscopy (AFM). The nominal film thickness \(h\) for the (1.0:1.0), (1.2:1.2), (1.5:1.5), and (1.6:1.6) formulations was measured to be 287 \(\pm\) 97 nm \(<\) 317 \(\pm\) 72 nm \(<\) 337 \(\pm\) 58 nm \(<\) 346 \(\pm\) 66 nm, respectively.