Electrochemical behavior of CIGS electrodeposition for applications to photovoltaic cells

The electrodeposition mechanism of Cu(In,Ga)Se 2 (CIGS) thin films on ITO substrates was examined by using cyclic voltammetry (CV). The CV study was performed in unitary In, binary In-Se, ternary Cu-In-Se, and quaternary Cu-In-Ga-Se systems. CV of the Cu-In-Ga-Se system revealed a reduction peak at −0.6 V with the addition of GaCl 3 and showed that the current density was affected significantly by the concentrations of GaCl 3 and InCl 3 . This is probably due to the adsorption-site competition between In 3+ and Ga 3+ on the electrode surface. Energy dispersive X-ray spectroscopy confirmed the CV results. The composition of Ga in the CIGS films increased with increasing concentration of GaCl 3 in the electrolyte whereas the composition of In decreased sharply. The as-deposited films were annealed at 500 °C in a N 2 atmosphere for crystallization. XRD revealed three major peaks corresponding to the (112), (220) and (312) planes of CIGS chalcopyrite respectively. On the other hand, a secondary phase, such as In 4 Se 3 , was observed in the CIGS films containing a high In composition.