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Abstract. Zinc sulphide thin films were deposited on Corning glass substrates by the chemical bath deposition technique at different temperatures. The influence of the bath temperature and deposition time on the morphological and optical properties of the ZnS films are herein investigated. ZnS films were deposited by changing the bath-temperature from 50 ºC to 90 ºC, and deposition times from 60 to 160 min. Thin and transparent films were obtained with thicknesses from 10 to 90 nm with the increment of the bath temperature, meanwhile the band gap energy E g values diminishes from 4.15 to 3.4 eV. The quality of the ZnS film surfaces was also influenced by increasing the bath temperature, as showed by the reduced grain size and the increase of roughness, obtained from atomic force microscopy images. ZnS films of good optical quality were obtained at 90 ºC with a mean value of E g =3.56± 0.03 eV. IntroductionDue to its suitable optical properties, zinc sulphide (ZnS) emerges as an attractive semiconductor material for electronic and solar applications. ZnS thin films are commonly used as optical filter due to its appropriate band gap energy value of E g = 3.68 eV at room temperature [1][2][3]. They can also be used as buffer layer or as antireflective coating [4] for improving the efficiency of thin film solar cells. Efficiencies above 18 % have been reported for ZnS/Cu(In,Ga)Se 2 (CIGS) thin film solar cells [5]. Cadmium sulphide (CdS) has been typically used as buffer layer on CIGS thin solar cells to protect the Cu(In,Ga)Se 2 junction from possible damage during the zinc oxide (ZnO) sputtering deposition, which would cause unwanted modifications to the surface of the CIGS absorber. The efficiency of the CdS/CIGS solar cells drops at short wavelengths due to optical absorption losses from the CdS layer. The solar absorption can be improved by replacing the CdS film with other semiconducting material with a wider energy band gap. Because of its appropriate optical characteristics, ZnS arises as a good candidate for being used as a buffer layer in solar cell applications. The ZnS higher band gap energy (3.68 eV) [6] compared to that one of the CdS (2.42 eV) makes the ZnS wavelength range of transparency wider (above 330 nm) than the CdS one (above 520 nm) [8], increasing then the amount of sunlight on the photovoltaic conversion process. In addition, replacing CdS with ZnS is environmentally attractive by its non-toxicity. The effects of the chemical bath temperature on the ZnS rate of growth and of annealing temperature on the structural properties ZnS films have been studied [9,10]. In this work, ZnS thin films were deposited on glass substrates by the chemical bath deposition (CBD) technique varying the bath temperature and the deposition time, in order to study the influence of such parameters on the ZnS morphological and their optical properties.