Characterization of pulsed laser deposited Cu 2 ZnSnS 4 thin films for Solar cell

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Characterization of pulsed laser deposited Cu2ZnSnS4 thin films for Solar cell Tanaji P. Gujar1, Vaishali. R. Shinde1 and Ram S. Katiyar1 1

Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, USA

ABSTRACT In the present work we report the synthesis of Cu2ZnSnS4 (CZTS) films by pulsed laser deposition (PLD) and the effect of sulfur annealing on structure, composition, morphological and optical characterization of CZTS thin films. Raman spectra of the films exhibited the characteristics peaks of Kesterite structure. However, annealing caused to transfer the films from amorphous state into crystalline state. Scanning electron microscope (SEM) images revealed that as-deposited film exhibited a crack free, smooth, densely packed and homogeneous surface which was changed to rigid granular appearance after annealing. Energy dispersive X-ray spectroscopy (EDS) determined the compositions of the CZTS thin films which was near stoichiometry for the annealed samples. Ultraviolet–visible (UV–Vis) spectra showed the band gap of as-deposited film was 1.60 eV which was decreased to 1.40 eV after annealing. INTRODUCTION In the recent decade, power generation using the renewable energy sources such as photovoltaics has become crucial since the carbon free energy sources are the fundamental necessity of the present technology. Among the different generations of solar cells, the thin film technology has become more successful owing to the advantage of being cheaper but still efficient. The thin film solar cell (TFSC) consisting of polycrystalline Cu-chalcopyrites, such as CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS) and Cu(In,Ga)(S,Se) (CIGSSe), have been considered the most attractive TFSC due to their high conversion efficiency 20% by a three stage coevaporation technique [1,2]. However, the limited supply of the rare metals indium and gallium put the constraint on the mass production stage of the CIS and CIGS TFSC in the near future [3]. Cu2ZnSnS4 (CZTS) thin films are immerged as a strong competent and one of the most promising materials for low-cost TFSC since they consist of the abundant materials, and have a band-gap energy of 1.4–1.5 eV and an absorption coefficient of 104cm-1 [4]. So far, a power conversion efficiency record of 10.1% has been achieved for a Cu2ZnSn(S,Se) and 6.77 % for CZTS TFSC [5,6]. The CZTS thin films have been prepared by several experimental techniques such as sputtering [7], thermal evaporation [8], spin coating [9], electrodeposition [10, 11], spray pyrolysis [12], pulsed laser deposition (PLD) [13,14], and sulfurization of electron-beamevaporated precursors [15] etc. Among the various deposition techniques, PLD is a versatile technique where the films are deposited by ablation of target illuminated by the focused pulsed laser beam. During PLD the stoichiometry of the deposited film is maintained close to that of the used target, which is very important for the deposition of quaternary CZTS films for the solar cell performance. Thereby, PLD allow

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