Properties of one-step electrodeposited Cu(In1-x9 Gax)Se2 thin films

One-step electrodeposition(ED) of Cu(In1-x9 Ga-x)Se-2 (CIGS) thin films on Mo/glass substrates from aqueous solutions containing CuCl2, InCl3, GaCl3, and H2SeO3 was studied. In order to stabilize the solutions, they were buffered using a potassium biphthalate/sulfamic acid mixture giving a bath of pH 2.5. The type of the solutions would influence Ga concentration in the CIGS films. In general, CIGS thin film is called stoichiometric compound when the molar ratio of Cu to In+Ga is 1, and when the ratio is in the range of 0.8-1, it is called near stoichiometric and slightly Cu-poor or In- rich CIGS compound. As-deposited films were near stoichiometric and slightly Cu-poor CIGS precursors with smooth, compact, crack-free surface by the optimization of the solution composition and the deposition condition. The electrodeposition mechanisms of CIGS on Mo substrates were studied by cyclic voltammetry. The results showed that Se4+ was first reduced to Se, and then Cu2+, In3+, and Ga3+ were deposited via the induced co-deposition mechanism at more positive potentials than they were reduced. As-deposited films were selenized and recrystallized at 550 degrees C in Se vapor with a Se source temperature of 280 degrees C, which improved crystal structure of the films and changed little the compositions of ED-CIGS thin films, but resulted in cracking of the films.