Growth Mechanisms of Electrodeposited CuInSe_2 and Cu(In,Ga)Se_2 Determined by Cyclic Voltammetry

摘要

Electrodeposition (ED) of CuInSe_2-based thin films from a buffered single-bath on de-sputtered Mo layers has been investigated. In order to understand the film growth, cyclic voltammetry (CV) was used to identify mechanisms leading to the formation of CuInSe_2 and Cu(In,Ga)Se_2. Similar CV data were observed for deposition from Cu-Se, Cu-In-Se, Cu-Ga-Se, and Cu-In-Ga-Se baths. A preliminary mechanism for CuInSe_2 and Cu(In,Ga)Se_2 film growth has been proposed from CV, composition and glancing incidence x-ray diffraction (GIXRD) data. Incorporation of In into the growing films occurs via reaction with H_2Se, formed by reduction of the initially deposited Cu_3Se_2, to form In_2Se_3, which is in turn rapidly assimilated into the film by reaction with copper selenides to form CuInSe_2. The incorporation of Ga may occur via a similar mechanism, however, the precipitation of Ga(OH)_3 can not be ruled out as a possible route for Ga uptake. All as-deposited ED CuInSe_2-based films have poor crystallinity and require annealing in H_2Se prior to device processing. Preliminary device results are presented, reporting a conversion efficiency of 6.5% and 6.2% for electrodeposited CuInSe_2 and Cu(In,Ga)Se_2, respectively.