Analysis and Growth Modeling of CuInSe2 Films by Electrodeposition for Photocell Applications

Abstract

CuInSe2 (CIS) thin films were deposited onto FTO/glass substrates by continuous current potentiostatic electrodeposition method. The aqueous deposition bath was prepared from a pH = 3.0 NaBF4 supporting electrolyte, containing CuSO4, In2(SO4)3, and SeO2 precursors. The characterization of these samples was done by scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffractometry, Raman spectroscopy, and optical spectroscopy. The experimental techniques have allowed the understanding of the atomic concentration dynamics of samples, and its relationship with the concentration of precursors. It was obtained p-type polycrystalline semiconductor samples, with 0.95 eV gap energy; the crystalline quality of these samples was also verified. Besides this, the nucleation and growth of CIS were studied during its electrochemical deposition on top of FTO, and vitreous carbon electrodes. Chronoamperometry I-t plots permitted the study of current transients, through classic nucleation models, which were used to understand the nucleation mechanism which occurred during the electrodeposition process, besides predicting some of its characteristic properties, as its diffusion coefficient, density of active sites, and nucleation rate constant per active site. Atomic force microscopy measurements were used to investigate the first stages of growth of these CIS films, deposited at different overpotentials. Preliminary devices CIS/In2Se3/FTO were mounted, with In2Se3 (IS) film also deposited by continuous current electrodeposition. Its electrical properties were analyzed, revealing a Schottky diode like behavior; there were observed light dependent open circuit voltage generation and resistance drop, disclosing promising characteristics for photovoltaic production.