## 3 Results and Discussion  
The photo-sintered CZTS films have a large absorption wavelength range, as displayed in Figure 2, from 400 to 1400 nm. An optical band gap results from the extrapolated value hv in the x-axis at 0 of (\(\alpha\)hv)\({}^{2}\), providing the corresponding 1.6 eV that was used for the direct band gap materials. A strong absorbance was presented in the visible range, and a tail extended to longer wavelengths in the infrared region. In the visible range, CZTS has good absorption, indicating it as appropriate absorber layer of a photovoltaic device [17]. The photo-sintering process influenced the material characteristics similar to other studies [14, 18, 19]. Figure 3 demonstrates the surface of the as-deposited and photo-sintered CZTS films at various conditions. The as-coated CZTS film had a porous morphology with a uniform distribution of agglomerated grains and very small grains of several tens of nm. Generally, as the grain size and crystallinity improved, the CZTS surface was rougher and had island-like growth because of the increased bank voltage in the photo-sintering process. As illustrated in Figure 3, when the IPL energy increased, the particle sizes of the CZTS film also increased, which implies that crystallization occurred in the CZTS film. Increasing the energy density, duration, or repeat times causes serious destruction to the CZTS layer, as the high-energy density photo-sintered process causes peeling and cracking of the film. This damage significantly affects cell performance; so, optimization of sintering condition is necessary. Figure 1: A schematic diagram of the intense pulsed light system. For the analysis of the sintering effect to the CZTS films, the XRD analysis was performed. Figure 4 displays the XRD patterns of CZTS films at various treatment conditions. As illustrated, the peaks of the (112), (200), (105), (220), and (312) planes, corresponded to the kesterite structure and verified the presence of CZTS for as-coated along with photo-sintered films [20,21]. As demonstrated in the figures, the broadening of the peaks in the XRD analysis displayed small-sized particles and the films exposed to more energy tended to have larger NPs sizes. Also, the XRD pattern broadening for the film demonstrates the surface diffusion of NPs without changing its dimension. The intensity of the diffraction peaks changes following increased energy photo-sintering application. The intensity of the peaks indicating the (112) and (220) orientations present an improvement in crystallinity of the CZTS thin films, which gradually increases at 2.82 J/cm\({}^{2}\) and decreases at higher bank voltages of 2.96 J/cm\({}^{2}\) and 3.09 J/cm\({}^{2}\). This results in the transformation of the compound ratio and crystal structure, similar to the FE-SEM and energy dispersive X-ray analysis (EDX) results. The secondary phases consisting of ZnS, Cu\({}_{2}\)S, and Cu\({}_{3}\)SnS\({}_{4}\) are difficult to observe with XRD. As a result, Raman measurements of the CZTS thin film after treatment were performed, as illustrated in Figure 5. Raman spectroscopy provided a detailed analysis of the material compounds. The advantage of this measurement is observation of secondary phases that influence the performance of the CZTS solar cells  
Figure 3: FE-SEM images of the CZTS thin film. (**A**) As-coated, sintered with light intensity of. (**B**) 2.82 J/cm\({}^{2}\), (**C**) 2.96 J/cm\({}^{2}\), (**D**) 3.09 J/cm\({}^{2}\). Figure 2: UV-vis-NIR absorption spectra of the as-coated CZTS thin film and corresponding (\(\alpha\)hv)\({}^{2}\) vs. hv curve. because of difficulty in band alignment or mismatch in structure. A 532 nm laser was used to study the CZTS thin film at a range of 200-600 cm\({}^{-1}\). The formation was determined on the basis of one strong peak at 288 cm\({}^{-1}\) and two weak peaks at 368 cm\({}^{-1}\), which closely represent the kesterite CZTS structure in other reports, and the spectra did not indicate any other characteristics peaks or secondary phases [22].