Controlling growth chemistry and morphology of single-bath electrodeposited Cu(In,Ga)Se2 thin films for photovoltaic application

Single-bath electrodeposition of polycrystalline Cu(In,Ga)Se-2 thin films for photovoltaic applications is described. Cu(In,Ga)Se-2 was deposited onto Mo electrodes from low concentration aqueous baths containing CuCl2, InCl3, GaCl3, and H2SeO3. Buffering the solutions to pH similar to 2.5 stabilized bath chemistry and improved Cu(In,Ga)Se-2 film composition. Bath concentrations were shown to affect composition of deposited films, with a bath [Se4+]/[Cu2+] ratio of 1.75 required to maintain suitable deposited Se and Cu levels, while [In3+] could be adjusted to control deposited In and Ga. Deposited films initially exhibited significant cracking, which was prevented by lowering the [Se4+] in the bath, and contained Cu2-xSe as secondary phases, resembling cauliflower florets, embedded in the film surfaces. The formation of these secondary phases was overcome by pretreating the Mo electrodes with a short 1 min deposition from the Cu(In,Ga)Se-2 bath. This, coupled with a multipotential deposition regime, led to growth of smooth, compact, crack-free films of near stoichiometric values. Mechanisms of film growth and morphology control are discussed. All as-deposited films exhibit low crystallinity, and for device processing require recrystallization by annealing in an H2Se atmosphere. Promising preliminary results of electrodeposited Cu(In,Ga)Se-2 devices are presented. (C) 2006 The Electrochemical Society.