Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-020-03024-3 Comparative studies of CdS thin films by chemical bath deposition techniques as a buffer layer for solar cell applications A. Ashok 1  · G. Regmi 1  · A. Romero‑Núñez 1  · M. Solis‑López 1  · S. Velumani 1,2  · H. Castaneda 2 Received: 21 October 2019 / Accepted: 30 January 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Cadmium sulfide (CdS) buffer layer that decouples the absorber layer and window layer in thin-film solar cells was synthe- sized by two different chemical bath deposition (CBD) techniques with varying deposition parameters. X-ray diffraction (XRD) revealed that the CdS thin film crystallizes in a stable hexagonal wurtzite structure having a preferential orientation along (002) reflection plane with a crystallite size varying from 20 to 40 nm. First longitudinal optical phonon mode was identified at Raman shift of 305 cm −1 . Uniform, granular, continuous, and smooth surface with an average grain sizes (< 100 nm) as well as small roughness (< 9 nm) was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The symmetric composition of cadmium and sulfur along with larger grains (20 nm) was observed at higher deposition temperatures and times. The optical band gap of CdS samples obtained from process one was in the range of 2.3–2.35 eV, while the band gap by the second CBD process lay in between 2.49 and 2.65 eV, showing the most stable compound of CdS. The presence of a green emission band in photoluminescence spectra (PL) demonstrated that the CdS material has better crystallinity with minimum defect density. Hall effect studies revealed the n-type conductivity of CdS thin films with a carrier concentration values in the order of 10 16 cm −3 . Furthermore, CdS thin films fabricated by CBD process exposed better quality that might be more suitable material as a buffer layer for thin-film solar cells. 1 Introduction Historically, energy production and its consumption have been a keystone factor in the development of human civili- zation. The consumption of energy is interconnected with world population growth as well as characteristics of modern society like life expectancy, mean years of schooling, water access, and electrification level etc. [1]. The world energy production is mainly achieved by burning fossil fuels. How- ever, the use of fossil fuels has raised concerns due to its limited availability and environmental issues. The neces- sity to increase energy production for fulfilling the basic requirements without producing harmful gases becomes one of the most challenging problems that our civilization must encounter. To have a scenario of constant growth in population with the equilibrium between good quality of life, the needs of energy production, proportional distribution of energetics and a non-threatened climate, the use of the clean renewable source of energy is an essential as a forward step that humanity has to take in the energy production evolution. If we consume the energy sources in a similar trend, it is necessary to remember that in a near-future these resources (non-renewable) start to run out not only leaving behind a hole in the energy harvest but also increase the price geo- metrically [2]. These will directly affect the entire popula- tion of the world qualitatively. There is an acute worldwide concern to diminish the prob- lems of the energy crisis and global warming due to green- house gas emissions mostly obtained from non-renewable fossil fuels through combustion [3]. Among different renew- able energies (wind, hydropower, bioenergy, solar photovol- taic), the solar photovoltaic (PV) has achieved tremendous interest due to its most reliable, reliability, free availability with no pollution and fastest-growing market, by the fact that around 402 GW of total electricity generation capacity was installed by the end of 2017 and expected to reach 505 GW * S. Velumani velu@cinvestav.mx 1 Department of Electrical Engineering (SEES), Centro de Investigación y de Estudios Avanzados del IPN (CINVESTAV-IPN), Av. Instituto Politécnico Nacional 2508, C.P. 07360 Mexico City, Mexico 2 Department of Materials Science and Engineering, National Corrosion and Materials Reliability Laboratory, Texas A&M University, Texas, USA