Zinc Sulfide Thin Film: Structural, Morphological and Optical Study for Photovoltaic Applications

Abstract

Zinc sulfide (ZnS) thin films have been deposited on commercial glass substrates by simple chemical bath deposition technique (CBDT). The Structural, morphological and Optical characteristics of as-deposited films were investigated for the photovoltaic applications. X-ray diffraction study shows the polycrystalline nature of the thin film. The grain sizes obtained by XRD & SEM were well matched. SEM study gives the average grain size between 87nm and 137nm. FTIR and UV-Vis measurement showed that the films had more than 65% transmittance in the wavelength larger than 350 nm, and the fundamental absorption edge shifted to shorter wavelength. Optical study shows the energy band gap ranging from 3.54 to 3.71 eV. The physical conditions were kept identical while growing all the samples. It was found that ZnS films are suitable for various optoelectronic/photovoltaic applications.

Introduction

Zinc Sulfide (ZnS) thin films offer advantages over Cadmium Sulfide (CdS), including a wider band gap (3.6 eV vs. 2.4 eV) and better lattice matching with CIGS absorbers, making ZnS suitable for optoelectronic and optical applications such as LEDs, reflectors, and dielectric filters.

Deposition Technique:
ZnS thin films were prepared using Chemical Bath Deposition (CBD), a simple, low-cost, and scalable method suitable for large-area substrates. CBD allows control over film thickness, deposition rate, and uniformity by adjusting solution pH, temperature, and reagent concentrations.

Experimental Details:
Films were deposited from a solution of zinc acetate and thiourea in alkaline ammonia on cleaned glass substrates at ~70°C. Post-deposition, films were washed and dried. Structural, morphological, and optical properties were characterized using XRD, SEM, FTIR, and UV-Vis spectroscopy.

Results:

• Structural: XRD confirmed ZnS nanocrystals with hexagonal structure and grain sizes of 8–113 nm.

• Morphological: SEM showed uniform, crack-free films with nanocrystalline grains in a fibrous-like structure.

• FTIR: Bands at 694–706 cm?¹ indicated Zn–S stretching; other bands corresponded to O-H, C-H, and N=N vibrations.

• Optical: UV-Vis spectra revealed high transmittance and a blue-shifted absorption edge (~250–400 nm). Band gap values ranged from 3.54–3.71 eV, increasing as crystallite size decreased, consistent with quantum confinement effects.

Conclusion

Nano-crystalline Zinc sulfide (ZnS) thin films have been successfully prepared by using CBD technique. The crystallite sizes measured by XRD studies are found to be within 87nm to 137 nm. XRD shows that samples are of hexagonal phase which is important for device performance. SEM studies shows presence of long tubes and irregular distributions of particles. FTIR spectroscopy shows the bonding peaks and the percentage transmittance, the films were found to have high transmittance in the range between 60 to 75% in the UV-VISNIR regions; so average 65% transmittance in the wavelength larger than 350 nm are very suitable for use as the buffer layer of thin film solar cells with CuInS2 absorber layer by replacing CdS hence ZnS films are suitable for use as the buffer layer of the CIS solar cells, and it is the viable alternative for replacing CdS in the photovoltaic cell structure. These films could be effective as thermal control window coatings for cold climates and antireflection coatings. The UV absorption studies on films clearly show an increase in band gap with reduction in particle size as compared to bulk materials, and this fact supports the formation of nanocrystallites in these films.

References

[1] A.F.Cattell, A.G. Cullis, Thin Solid Films, 92, 211-217 (1982) [2] Z.Porada, E.S.Osiowska, Thin Solid Films, 145, 75-79 (1986) [3] B. Elidrissi, M. Addoua, M. Regragui, A. Bougrine, A. Kachouane, J.C. Bernède, Mat. Che. & Phy., 68,175-179 (2001) [4] M.Rabah, B.Abbar, Y.Al-Douri, B.Bouhafs, B.Sahraoui, Mat.Sci. &Eng., B100,163-171 (2003) [5] Monroy E., Omnes F. & Calle F., Semicond. Sci. Technol., 18, 33–51 (2003). [6] Y. S. Kim, S. J. Yun, App.Sur.Sci. 229,105-111 (2004) [7] N. Karar, Suchitra Raj, F. Singh, Karar et al. / Journal of Crystal Growth, 268, 585-589 (2004). [8] I. O. Oladeji, L. Chow, Thin Solid Films 474, 77– 83 (2005) [9] A.Z. Arsad et al Ceramics International Vol. 50, 7B, 11776-11786 (2024) [10] Kishore, N. S. Saxena, V. K. Saraswat, K. B. Sharma, T. P. Sharma, J. Opto. Adv. Mat., 8, 1641 – 1642 (2006) [11] T. R. Marisol, R.G. Bárbara, D. R. Rodrigo, C.Gerardo, J. Chil. Chem. Soc., 52, 3 (2007) [12] B. S. Remadevi, R. Raveendran, A. V. Vaidyan, Prammana J. Phy., 68, 679-678 (2007) [13] Vijay B. Sanap, International Journal of NanoScience and Nanotechnology, Volume 12, Number 1, 1-9 ISSN 0974-3081 (2021). [14] I. B. Jemaa, F. Chaabouni, A. Ranguis, J. Alloys Compd. 825, 153988 (2020). [15] F. Göde, Optik 197, 163217 (2019). [16] S. Moghe, A. Acharya, R. Panda, S.B. Shrivastava, M. Gangrade, T. Shripathi, V. Ganesan, Renewable Energy 46, 43 (2012).

Copyright

Copyright © 2025 V. B. Sanap. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.