Effect of annealing under different atmospheres of CZTS thin films as absorber layer for solar cell application
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Effect of annealing under different atmospheres of CZTS thin films as absorber layer for solar cell application Samia Chamekh1 · Naoufel Khemiri1 · Mounir Kanzari1,2 Received: 6 November 2019 / Accepted: 30 July 2020 © Springer Nature Switzerland AG 2020
Abstract The influence of annealing under several atmospheres on the structural and optical properties of C u2ZnSnS4 (CZTS) thin films was investigated. Thin films were deposited on ordinary glass substrates by vacuum thermal evaporation method. In order to optimize the growth of CZTS films, the samples were annealed under different atmospheres: vacuum, nitrogen (N2), Sulfur (S2) and under vacuum followed by sulfuration. The structural study of CZTS films was carried out using the X-ray diffraction. The spectra indicated the improvement of the crystalline quality of CZTS films after the thermal treatments. All annealed films exhibited a preferential orientation along the (112) plane. The optoelectronic properties of CZTS thin films were investigated using UV–Visible spectrophotometry. The optical study of annealed samples revealed a high absorption coefficient that exceeded 104 cm−1 and a band gap in the range of 1.48–1.56 eV. Keywords Cu2ZnSnS4 · Thermal evaporation · Annealing process · Optical properties · Structural properties
1 Introduction Currently, research in the solar cells field is one of the fastest growing renewable technologies [1]. Among various types of solar cells, CIGS ( CuInxGa1−xS(Se)2) and CdTe solar cells have attracted a lot of interest thanks to their high efficiencies 25 and 22.1% [2]. However, the reliability of CIGS and CdTe based solar cells is facing a hard task because of the scarcity of several constituents such as Indium (In) and germanium (Ga) [3] and the toxicity of Cadmium (Cd) [3, 4]. It is in this context, scientists were oriented in developing a new generation of thin film solar cells composed of low-cost and eco-friendly materials. Thanks to its optoelectronic properties, the quaternary chalcogenide family Cu2XSnS4 (X = Ni, Zn, Co, Mn, Fe) [5–7] are chosen to be the promising group of materials for use as absorber layer for photovoltaic application [6]. Among the chalcogenide family, the Cu2ZnSnS4 (CZTS) is
considered one of the most promising candidates owing to its p-type electrical conductivity, its high absorption coefficient of about 104 cm−1 in the visible light region [8, 9] and its direct band gap of about 1.5 eV [9, 10]. Many routes have been undertaken to elaborate CZTS thin films, whether chemical [11, 12] or physical techniques [13, 14]. Among all these techniques, the thermal evaporation under vacuum has the advantage of providing high purity film, high deposition rate and low cost elaboration [15]. There are various reports about CZTS solar cells, where they identified the key issues to determine the properties of the CZTS absorber layer such as phase diagram, crystal structure, chemical composition, secondary phases and optical properties. In 2019, Olgar [16] has investigated the effect of sulfuriz
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