Diffusion of Fe in solar-grade Cu(In,Ga)Se2 layers was investigated over the temperature range from 200 to 600 C. Either natural or radioactive iron was diffused from the front-surface of Cu(In,Ga)Se2/Mo/soda lime glass samples. Penetration profiles of stable 56Fe and radioactive 59Fe were measured by secondary ion mass spectrometry and ion-beam sputtering in conjunction with activity counting, respectively. The Fe diffusivity could be described by:

D (cm2/s) = 1.6 x 10−4exp[-0.97(eV)/kT]

Taking into account Fe solubility data obtained from the secondary ion mass spectrometry profiles, evidence was provided that D was representative of diffusion along grain boundaries.

Fe Diffusion in Polycrystalline Cu(In,Ga)Se2 Layers for Thin-Film Solar Cells. N.A.Stolwijk, S.Obeidi, J.Bastek, R.Wuerz, A.Eicke: Applied Physics Letters, 2010, 96[24], 244101