A voltammetric study of the electrodeposition chemistry in the Cu + In + Se system

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The mechanism of formation of CuInSe 2 thin films on a glassy carbon surface during voltammetric scanning was examined in detail for the first time using a combination of Pourbaix analyses, cyclic and hydrodynamic voltammetry of the binary In + Se and Cu + Se systems, along with cyclic photovoltammetry, i.e. cyclic voltammetry combined with periodic white light illumination of the electrode/electrolyte interphase, on the ternary Cu + In + Se system. A sulfuric acid matrix containing SeO 2 and uncomplexed Cu 2+ and In 3+ ions was used in all cases. The data on the binary systems were consistent with the facile formation of a Cu 2− x Se solid phase in the Cu+Se system and a kinetically sluggish interaction between In and Se in the In+Se case. An internally consistent mechanistic scheme is proposed for the ternary system involving the concurrent formation of the Cu 2− x Se phase, its subsequent reduction coupled with the 6 e − reduction of H 2SeO 3 to H 2Se, and finally the underpotential assimilation of In into the solid phase leading to the photoactive chalcopyrite semiconductor, CuInSe 2. The cathodic decomposition of the initially formed Cu 2− x Se is shown to be a key to subsequent assimilation of In and formation of CuInSe 2. The photocathodic response observed for this thin-film formation was diagnostic of a Cu-rich ternary composition and consequent p-type behavior for the conditions pertaining to this study.