Cu2ZnSnS4 (CZTS) Thin Film Grown By Electrochemical Deposition For Solar Cell
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Date
2015-03
Authors
Mrzog, Elmoiz Marghni Mkawi
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Abstract
Cu2ZnSnS4 (CZTS) quaternary compounds have attracted much attention in the last few years as an abundant new low-cost and non-toxic material with desirable properties for thin film photovoltaic (PV) applications. In this thesis, a cost-effective solution processing method is developed for the fabrication of CZTS thin film absorbers by electrochemical deposition of Cu, Zn, and Sn precursors on molybdenum (Mo)-coated soda-lime glass (SLG) substrate, followed by a heat treatment in sulfur atmosphere. The effects of varying the electrochemical deposition parameters on the properties and growth of the CZTS thin films were investigated. The influence of the triangle wave pulse on the properties of the CZTS thin films improves the structural and morphological properties of samples by increasing the opportunities for different elements to come into contact. Additionally, using trisodium citrate as the complexing agent in the electrolyte solution reduced the difference between the reduction peaks of Zn and Cu by up to 0.25 V. The presence of sulfate salts in the electrolyte led to easy reduction of the metal ions, and improved the thin film produced. Four different precursor stacking sequences were examined, and the ordering of the precursors was found to have a significant effect on the properties of the resulting thin films. The influence of the annealing temperature (420–580 °C), sulfurization temperature (250–400 °C), and atmosphere (N2 and Ar (5%)) on the morphological and structural properties of the resulting CZTS films was studied. Annealing in N2 atmosphere was found to be necessary for grain growth. Using the same precursor chemistry, the aqueous synthesis of cubic and cuboid Cu2 ZnSnS4 nanocrystals by rotary evaporation solvothermal synthesis was investigated to confirm the crystalline state, direct band gap and absorption, and interplanar spacing of p-type CZTS. Characterization of the optimized sample (deposited with trisodium citrate) by X-ray diffraction (XRD) revealed a preferred orientation of the (112), (220), (200) and (312) planes, confirming the kesterite structure of CZTS. The sample had a homogeneous, compact morphology without any voids or cracks, and the grain size was more than 1.5 μm. The absorption coefficient of the films was over 104 cm−1, and their band gap was increased to 1.48 eV. The carrier concentration and their mobility in the CZTS films were 4.5 × 1020 cm−3 and 3.79 cm2 V−1 S−1, respectively. The best solar cell with a device structure of glass/Mo/CZTS/CdS/ZnO/Al:ZnO/Al derived from the obtained CZTS film exhibited a preliminary conversion efficiency of 2.94%. The present study demonstrates the possibility of fabricating CZTS thin films on molybdenum (Mo)-coated soda-lime glass (SLG) substrates by electrochemical deposition with potential applications in photovoltaic solar cells.
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Keywords
Thin films, Electric properties