Effect of cation ratios and monoethanolamine on the morphology of solution processed Cu 2 ZnSnS 4 films
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.173
Effect of cation ratios and monoethanolamine on the morphology of solution processed Cu2ZnSnS4 films Jitendra Kumar, Sarang Ingole Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur208016, India
Abstract
Thin films of Cu2ZnSnS4 have been synthesized through solution chemistry. The correlation between film morphology and the ratio of cations (copper, zinc and tin) and the amount of monoethanolamine (MEA) in solution has been investigated. The stoichiometric ratio of cations resulted in films comprised of fine grains (~165 nm) with large crystals (~ 1 − 2 m) spread over its surface. The films corresponding to copper poor and zinc rich solutions were comprised of grains having uniform size (~300 nm). The addition of MEA to precursor solutions resulted in a significant drop of pinholes in the films, however, at the same time grain size decreases to 50 − 200 nm range depending on the amount of MEA present in the precursor solution.
INTRODUCTION Over the last decade Cu2ZnSnS4 (CZTS) has been under intense investigation as an alternative to Cu2(In,Ga)Se2 due to perceived limitations associated with the relatively limited availability of constituent elements indium (In) and gallium (Ga). The use of relatively abundant elements zinc (Zn) and tin (Sn) in CZTS makes this material promising for cost-effective photovoltaics (PV). Also, it possesses a high absorption coefficient (104 cm-1) and direct band gap (1.5 eV) which is optimum for PV applications [1,2] . Synthesis of CZTS thin films has been carried out via various techniques like sputtering [1], electrodeposition [3], nanoparticle-based ink [4] and solution chemistry [5]. Out of these, solution chemistry is quite attractive since it involves relatively lower temperatures, no need for a high vacuum. However, challenges associated with the solution route are the control over impurities, stoichiometry, and morphology. There have been several studies for CZTS film synthesis via solution route; these involve mixing of Cu, Zn and Sn salts along with a source of sulphur (S) into a
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suitable solvent and coating such a solution onto a substrate [6,7]. A few studies have also employed monoethanolamine (MEA) as a complexing agent [8,9]. In this context, present work reports a correlation between the relative amount of Cu, Zn and Sn salts and CZTS film morphology. Along with this, an investigation for the effect of MEA amount in solution on CZTS film morphology has been carried out. EXPERIMENTAL DETAILS Materials Copper chloride dihydrate (CuCl2.2H2O), zinc chloride hydrate (ZnCl2.01H2O), tin chloride (SnCl2.2H2O) were purchased from Alfa Aesar. MEA and 2-methoxyethanol (2ME) were from Loba Chemie, India, and
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