In2S3 films have been successfully deposited on Corning glass substrates via chemical bath deposition (CBD) method using acetic acid as a novel complexing agent. The layers were grown by employing synthesis using indium sulphate and thioacetamide (TA) as precursors by varying TA concentration in the range of 0.1–0.5？M, keeping other deposition parameters constant. Energy dispersive X-ray analysis (EDAX) revealed an increase of S/In ratio in the films with the increase of TA concentration in the solution. The X-ray diffraction (XRD) analysis indicated a change in preferred orientation from (311) plane related to cubic structure to the (103) direction corresponding to the tetragonal crystal structure. The evaluated crystallite size varied in the range of 15–25？nm with the increase of TA concentration. Morphological analysis showed that the granular structure and the granular density decrease with the raise of TA concentration. The optical properties of the layers were also investigated using UV-Vis-NIR analysis, which indicated that all the In2S3 films had the optical transmittance >60% in the visible region, and the evaluated energy band varied in the range of 2.87–3.32？eV with the change of TA concentration. Further, a thin film heterojunction solar cell was fabricated using a novel absorber layer, SnS, with In2S3 as a buffer. The unoptimized SnS/In2S3/ZnO:Al solar cell showed a conversion efficiency of 0.6%. 1. Introduction Indium sulphide (In2S3) is one of the potential materials for various device applications. This includes development of photovoltaic [1, 2], photoelectrochemical solar cells [3], electronic [4], optical, [1, 5] and acoustic [6] dry cells, [7] which are displayed [8, 9] as photocatalysts for dye degradation [10] and water splitting [11]. This is mainly due to its chemical stability, wide energy band gap, and controllable electrical properties [12]. In photovoltaic solar cells, indium sulphide has been proved to be a promising buffer layer in the fabrication of thin film solar cells due to its lower toxicity compared to that of CdS [13]. In2S3 is an -type semiconductor that belongs to the III–VI group of compounds. Depending upon synthesis temperature and pressure, it exists in three crystallographic phases such as , , and . Among these phases, -In2S3 is the most stable phase at room temperature [14]. In2S3 films have been elaborated using a variety of methods such as spray pyrolysis [15, 16], chemical bath deposition (CBD) [17, 18], atomic layer deposition (ALD) [19–21], atomic layer epitaxy [22], electrodeposition [23], ion layer
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