The undoped and Sn-doped Sb2Se3 films supported on Mo-coated glass substrates were prepared using a simple hydrothermal method. This process involved fine-tuning precursor ratios between tin sulfate (SnSO4) and potassium antimony tartrate trihydrate (K2Sb2(C4H2O6)2•3H2O). The solution preparation process used for the hydrothermal synthesis of Sb2Se3 films is depicted in Figure (Supporting information) and described in the experimental section. The potassium antimony tartrate trihydrate and selenourea precursors were dissolved in Milli-Q water (18.2 MΩ•cm) serving as Sb and Se sources, respectively. To prevent the formation of elemental selenium (Se 0 ), sodium sulfite (Na2SO3) was added into the aqueous solution to scavenge traces of oxygen. After the addition of sodium sulfite, a white precipitate was formed, primarily attributed to the increase in the solution's pH from 4.13 to 6.89. To improve reproducibility and achieve high-quality Sb2Se3 films, the white precipitation was removed from the solution by filtering. Powder X-ray diffraction (PXRD) was used to characterize the crystallographic identity of the white powders. The observed diffraction peaks were well indexed to Sb2O3 (Figure ). The Sb2Se3 films were obtained by placing Mo-coated glass substrates in the solution, followed by holding the reaction at 165 o C for different durations, as illustrated in Figure . The resulting film thicknesses for reaction times of 3 hours, 4 hours, and 5 hours are shown in Figure and are denoted as Sb2Se3-3h, Sb2Se3-Control, and Sb2Se3-5h, respectively. By adjusting the reaction duration, the thickness of the Sb2Se3 films was controlled, ranging from 200 nm to 400 nm. In this study, the optimal condition of 165 o C for 4 hours was selected for further analysis (see details below). To further elucidate the impact of sodium sulfite, a Sb2Se3 film was prepared without its addition. Figure exhibits the scanning electron microscopy (SEM) and X-ray diffraction (XRD) of this film. This film exhibits a nanowire structure that is unable to fully cover the Mo substrate, leading to a dark current during measurements. Furthermore, the XRD pattern indicates the formation of a secondary phase, Se 0 . A 30 nm TiO2 layer was deposited on Sb2Se3 films using atomic layer deposition (ALD).