Abstract
Cu2ZnSnS4(CZTS) thin films were deposited on top of Molybdenum (Mo) coated soda lime glass (SLG) substrates using a single target rf magnetron sputtering technique. The sputtering parameters such as base pressure, working pressure, rf power, argon (Ar) gas flow rate, and deposition time were kept consistent throughout the experiment. The effect of different substrate temperatures, for example, room temperature (RT), 300°C, 350°C, 370°C, 400°C, and 450°C, was analyzed by studying their structural, electrical, and optical properties. As-sputtered films were then annealed at 460°C. X-ray diffraction (XRD) measurement revealed the structure to be kesterite with peak of (112) plane in both annealed and as-sputtered CZTS thin films. The crystallinity of the films improved with the increasing substrate temperature until 370°C. Secondary phases of MoS2,CuxMoSx,CuxSnSx,CuxS, and Cu6MoSnS8(hemusite) were also observed in the annealed CZTS films. Scanning electron microscopy (SEM) shows crystallite size of deposited CZTS thin film to be proportionally related to deposition temperature. The highest surface roughness of 67.318 nm is observed by atomic force microscopy (AFM). The conductivity type of the films was found to be p-type by Hall effect measurement system.
Highlights
Solar photovoltaic is rapidly becoming the leading choice as a clean electricity generation method
We have found that the as-sputtered films prepared at 370∘C exhibited strong preferential orientation of (112) plane, better crystallinity, and larger grain sizes than the other films sputtered at substrate temperature of 300∘C, 350∘C, 370∘C, 400∘C, and 450∘C [16]
We added CZTS thin films prepared at room temperature (RT) to investigate the effects on the properties followed by postdeposition annealing treatment of all the films
Summary
Solar photovoltaic is rapidly becoming the leading choice as a clean electricity generation method. CZTS possesses Kesterite crystal structure [5] and it is a p-type semiconductor which has a suitable band gap energy in the range of of 1.4-1.5 eV and large absorption coefficient over 104 cm−1 [6,7,8] Despite these interesting optical properties, so far a conversion efficiency of 12.6% has been achieved using a CZTSSe absorber layer by hydrazine chemical process [9]. Efficiency more than 10% in laboratory scale is imperative for research start-up of mini submodules and subsequent large modules Another popular route for CZTS polycrystalline deposition is sputtering of precursor followed by postdeposition heat treatment to promote crystal growth [14]. In order to quantitatively analyze the substrate temperature effect as well as the heat treatment induced alteration in the film, film crystallinity, grain size, elemental composition, and surface roughness were probed by various methods and the results are presented
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