Metastable properties of Cu(In1-xGax)Se2 with and without sodium

We compare the electronic properties of Cu(In1-xGax)Se-2 (CIGS, x=0.3) companion films with standard and nearly absent sodium levels. The films were examined over a wide range of metastable states produced by light-soaking. Admittance spectroscopy revealed that the activation energy of the dominant deep defect (hole trap) decreased monotonically from 300 to 60 meV with light-soaking time for samples with normal sodium, but remained nearly fixed (similar to 350 meV) for samples without sodium. Drive-level capacitance profiling indicated that the deep defect densities increased under light-soaking by roughly a factor of 20 for both samples and annealed at identical rates; however, the relative increases between the defect and hole carrier densities were dramatically different. (C) 2011 American Institute of Physics. [doi:10.1063/1.3553783]