Citation: Stanchik, A.V.; Asmalouskaya, T.N.; Rakitin, V.V.; Gremenok, V.F.; Gapanovich, M.V.; Trukhanova, E.L.; Zubar, T.I.; Trukhanov, A.V.; Trukhanov, S.V. Morphology and Crystal Structure of Cu 2 NiSn(S,Se) 4 Thin Films Obtained by an Electrodeposition-Annealing Process. Coatings 2022, 12, 1198. https://doi.org/10.3390/ coatings12081198 Academic Editor: Heping Li Received: 20 July 2022 Accepted: 14 August 2022 Published: 17 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). coatings Article Morphology and Crystal Structure of Cu 2 NiSn(S,Se) 4 Thin Films Obtained by an Electrodeposition-Annealing Process Aliona V. Stanchik 1,2, *, Tatsiana N. Asmalouskaya 2 , Vladimir V. Rakitin 3 , Valery F. Gremenok 1,2 , Mikhail V. Gapanovich 3 , Ekaterina L. Trukhanova 1, *, Tatiana I. Zubar 1 , Alex V. Trukhanov 1 and Sergei V. Trukhanov 1 1 Scientific and Practical Materials Research Center, National Academy of Sciences of Belarus, 220072 Minsk, Belarus 2 Department of Information and Computer Systems Design, Belarusian State University of Informatics and Radioelectronics, 220013 Minsk, Belarus 3 Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia * Correspondence: alena.stanchik@bk.ru (A.V.S.); el_trukhanova@mail.ru (E.L.T.) Abstract: Today, an actual task of photovoltaics is the search for new light-absorbing materials for solar cells, which will make them more efficient and economically affordable. Semiconductor Cu 2 NiSn(S,Se) 4 (CNTSSe) thin films are promising materials due to suitable optical and electrical properties. This compound consists of abundant, inexpensive, and low-toxicity elements. However, few results of studying the properties of CNTSSe films have been presented in the literature. This paper presents the results of studying the morphology, phase composition, and crystal structure of the CNTSSe films, which were first obtained by high-temperature annealing of electrodeposited Ni/Cu/Sn/Ni precursors on glass/Mo substrates in chalcogen vapor. The films were studied using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It has been found that sequential electrochemical deposition makes it possible to obtain the Ni/Cu/Sn/Ni precursors of the required quality for further synthesis of the films. It is shown that high-temperature annealing in chalcogen vapor in air makes it possible to synthesize stable polycrystalline CNTSSe films. The obtained results confirm that the production of CNTSSe films is suitable for use in solar cells by the proposed method, which can be improved by more precise control of the precursor composition and annealing conditions. Keywords: metal precursors; electrodeposition; annealing; chalcogen; CNTSSe; thin films; morphology; crystal structure 1. Introduction Today, the most common solar cells (SCs) are based on silicon and thin films of copper indium gallium selenide and cadmium-telluride due to their high efficiency [1]. However, silicon solar cells have one of the highest costs due to the difficult and energy-intensive manufacturing technology [2]. The copper indium gallium selenide and cadmium-telluride thin films are composed of toxic, low abundant raw materials, and expensive elements. This is predicted to severely limit the production, mass deployment, and economic sustainability of SCs [3,4]. Thin films based on earth-abundant, inexpensive, and low-toxicity elements, specifically Cu 2 ZnSnS 4 , Cu 2 ZnSnSe 4 , and Cu 2 ZnSn(S,Se) 4 solid solutions, have been ex- tensively researched as absorber materials in recent years [5,6]. These compounds have attracted much attention due to their optimum optical band gap values (about 1.0–1.5 eV) and high absorption coefficients (~10 4 cm −1 ) for potential application in thin-film SCs [5,6]. The efficiency of SCs based on Cu 2 ZnSnSe 4 , Cu 2 ZnSnS 4 , and Cu 2 ZnSn(S,Se) 4 films is 11.95% [7], 11.0%, and 12.6% [1], respectively, with a theoretical possible efficiency of about 30% [8]. The low open-circuit voltage and fluctuations in the band gap of the Cu 2 ZnSn(S,Se) 4 films due to their structure and narrow single-phase region of existence Coatings 2022, 12, 1198. https://doi.org/10.3390/coatings12081198 https://www.mdpi.com/journal/coatings