Band gap tuning of Cu(In,Ga)Se2 thin films by electrodeposition and their subsequent selenization using a rapid thermal annealing system

Abstract

Band gap tuning of electrodeposited Cu(In1-x,Gax)Se2 thin films through varying In3+ and Ga3+ concentrations in the electrolytic bath is demonstrated. Cyclic voltammetry was used to determine best Cu(In1-x,Gax)Se2 deposition potentials at the different bath conditions. Band gap tuning of Cu(In1-x,Gax)Se2 was achieved, through incorporation of varying In3+ and Ga3+ levels during film growth, in the range of 1 to 1.4 eV, corresponding to Ga content 0 ≤ Ga/(In + Ga) ≤ 0.64. Deposited films were characterized by EDS/SEM, XRD, and Raman spectroscopy to determine chemical composition, morphology, and crystal structure. Results show that as-deposited Cu(In1-x,Gax)Se2 thin films are of low crystallinity, with Se and Cu-Se compounds present as a secondary phase. Selenization of electrodeposited Cu(In1-x,Gax)Se2 films was performed using a rapid thermal processing system at 550 °C in an overpressure reactive atmosphere of N2/H2 (96%:4%) and elemental Se vapor. Selenization treatment promoted recrystallization and elimination of secondary phases, resulting in an increase in grain size while maintaining film composition. Processed films with Ga/(In + Ga) = 0.35 were processed into devices, achieving 2.6% efficiency.