Structural, XPS, morphological and optical properties of annealed earth-abundant Cu 2 ZnSnS 4 thin ﬁlms grown by one step thermal evaporation L. Achour a , N. Khemiri a,* , M.A. Nasiri b , A. Cantarero b a Universit´e de Tunis El Manar, Ecole National d’Ing´enieurs de Tunis, Laboratoire de Photovoltaïque et Mat´eriaux Semi-conducteurs, 1002 Tunis, Tunisia b Universidad de Valencia, Instituto de Ciencia Molecular (ICMol), Catedr´ atico Jos´e Beltr´ an Martínez n ◦ 2, 46980 Paterna, Spain A R T I C L E INFO Keywords: Cu 2 ZnSnS 4 Annealing XRD Raman XPS ABSTRACT In this paper, we have conducted several characterizations on CZTS thin ﬁlms grown by thermal evaporation from calcined and non-calcined powder and vacuum annealed at 200 ◦ C and 250 ◦ C. Different characterizations were used to investigate the effect of powder calcination and annealing on the properties of CZTS. Structural analysis reveals that all the prepared CZTS ﬁlms have a kesterite structure with a preferential orientation along the (1 1 2) plane and an improvement of crystalline quality by using calcined powder. XPS results show a transition of the oxidation states from +2 to +4 for Sn and from +2 to +1 for Cu. These transitions occur for the samples elaborated from calcined powder at 900 ◦ C. All samples exhibited a high absorption coefﬁcient (10 4 cm  1 ). The optical band gaps of samples elaborated from uncalcined powder were 1.63 and 1.58 eV, whereas those of samples elaborated from calcined powder were 1.52 and 1.42 eV. 1. Introduction Thin ﬁlm solar cells (TFSC) emerged as the most attractive tech- nology since they have an interesting conversion efﬁciency up to 22.6 % for copper indium gallium selenide (CIGS) solar cells [1] and over 20 % in the case of CdTe [2]. But the obstacle for the development of CdTe and CIGS solar cells are the presence of toxic elements like cadmium (Cd) (on the other hand, Cd has an Earth’s crust abundance of only 0.25 ppm [3]) and the low abundance of indium (In) (In is a rare element, the Earth’s crust abundance is only a 0.15 ppm [3]). In the last decades, the research in thin ﬁlm solar cells had to overcome many requirements, among them the use of more sustainable materials and low fabrication costs [4]. Cu 2 ZnSnS 4 (CZTS) is considered as an excellent and promising semi- conducting material for photocatalysis and photovoltaic applications since it is only composed of earth abundant and safe elements [5–7]. Furthermore, CZTS is a potentially excellent absorbing layer since its absorption coefﬁcient is above 10 4 cm  1 and its direct band gap energy is around 1.45 eV, located in the optimal range of the solar spectrum [8]. However, the best efﬁciency achieved by CZTS based solar cell was 13.2 % with an open circuit voltage (V OC ) of 0.749 V and a short circuit current density (J SC ) of 23.40 mA/cm 2 [9]. This efﬁciency is much lower than that of CIGS or CdTe based solar cells [10]. Furthermore, Shockley and Queisser calculations indicate that CZTS can achieve a maximum theoretical efﬁciency of 32 % [11]. Low open circuit voltage (V OC ) and low short circuit current density (J SC ) are the main factors that limit the efﬁciency of CZTS based solar cells [12]. The main cause of this phe- nomenon is the high concentration of defects and secondary phases in CZTS ﬁlms [13]. There are several experimental and theoretical strate- gies to overcome this problem and consequently, increasing the efﬁ- ciency of CZTS solar cells. One approach was given by Paul et al. [14]. They propose to add a CdZnS layer on the absorber, with a ﬁnal structure Mo/CZTS/CZS/iZnO/ITO grown on soda lime glass (SLG). The calcu- lated efﬁciency was close to 20 %. Doumit et al. [15] have done recently another theoretical study, using COMSOL Multiphysics, of a CZTS/Si tandem solar cell with an anti-reﬂectance layer of In 2 O 3 on top. The calculated efﬁciency reaches the 22.8 %. But landing on the experi- mental results, the CZTS, and more generally, the (Ag,Cu) 2 Zn(Sn,Ge)(S, Se) 4 family of kesterite compounds give similar efﬁciency results, around 10–13 % [16]. The record efﬁciency of CZTSe solar cells has been given by a research group of the Chinese Academy of Sciences, it has been established in the 13.45 % [17,18]. In this work, we present an investigation on the structural and optical properties of CZTS thin ﬁlms in order to obtain CZTS ﬁlm with optimal characteristics. As experimental strategies, we used calcined and * Corresponding author. E-mail address: khemirinaoufel@gmail.com (N. Khemiri). Contents lists available at ScienceDirect Materials Science & Engineering B journal homepage: www.elsevier.com/locate/mseb https://doi.org/10.1016/j.mseb.2025.118389 Received 25 February 2025; Received in revised form 24 April 2025; Accepted 3 May 2025 Materials Science and Engineering B 319 (2025) 118389 Available online 6 May 2025 0921-5107/© 2025 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.