Ammonia(aq)-enhanced growth of cubic SnS thin films by chemical bath deposition for solar cell applications

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Ammonia(aq)‑enhanced growth of cubic SnS thin films by chemical bath deposition for solar cell applications U. Chalapathi1,2 · B. Poornaprakash1 · Won Jun Choi2 · Si‑Hyun Park1  Received: 26 March 2020 / Accepted: 25 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract SnS is a promising material for use in thin-film solar cells because of its suitable optoelectronic properties. So far, SnS thin films with a cubic crystal structure, prepared by chemical bath deposition, with long deposition times and low film thicknesses have been reported. Herein, we report the rapid fabrication of cubic SnS films by increasing the concentration of ammonia(aq) in the solution. SnS films deposited with low ammonia(aq) (0.1875 M) took 6 h to form 400 nm film, and the films were mixedphase. Increasing the concentration from 0.375 to 0.5625 M increased the film thickness from 600 to 1000 nm, with a deposition time of 6 h, and the formation of single-phase SnS. Further increase in the concentration from 0.75 to 0.9375 M decreased the deposition time to 4 h and increased the film thickness (1100–1300 nm). Again, increasing the concentration further to 1.125 M decreased the deposition time to 2 h and film thickness to 900 nm. Thus, increasing the concentration of ammonia(aq) increases the thickness of cubic SnS formed and decreases the deposition time. This work proposes a very useful technique for producing good-quality cubic SnS thin films in a short deposition time of 2–4 h. Keywords  SnS thin films · Cubic structure · Structural properties · Optical properties · Electrical properties

1 Introduction Over several decades, extensive studies have been carried out on promising solar cell materials to realize simple, nontoxic, earth-abundant, and efficient absorber layers to obtain high-efficiency solar cells. In this context, the kesterite semiconductors Cu2 ZnSnS4 (CZTS), Cu2 ZnSnSe4 (CZTSe), and Cu2ZnSn(S,Se)4 (CZTSSe) have emerged as alternative materials for Cu(In,Ga)Se2 (CIGS) and CdTe, whose efficiencies have reached approximately 22% [1, 2] but with limitations related to long runs and environmental concerns because of the presence of indium, which is expensive, and cadmium, which is toxic. The determined efficiencies of the kesterite solar cells are 11.8 %, 11.6 %, and 12.6% for CZTS, CZTSe, and CZTSSe [3–5], respectively. However, U. Chalapathi and B. Poornaprakash have equally contributed. * Si‑Hyun Park [email protected] 1



Department of Electronic Engineering, Yeungnam University, Gyeongsan 38541, South Korea



Center for Optoelectronic Materials and Devices, Korea Institute of Science and Technology, Seoul, South Korea

2

the problems associated with the presence of a large number of constituent elements include the formation of secondary phases ( Cux S, ZnS, and Cu2 SnS3 (CTS)), which results in the deterioration of efficiency [6]. Hence, CTS has been explored as an alternative to kesterite semiconductors because of the presence of fewer components. Solar cells based on CTS have achieve

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