Diffusion activation energy of cadmium in thin film CuInGaSe2

Diffusivity and activation energy of cadmium in copper indium gallium diselenide (CuInGaSe
2
or CIGS) thin films were investigated by annealing solar-grade SLG/Mo/CIGS/CdS samples of two different CIGS thicknesses at temperatures between 150° C and 325° C. Diffusion profiles of cadmium volume and grain boundary were investigated by dual-beam time-of-flight secondary ion mass spectroscopy. A relationship between the cadmium's volume and grain boundary diffusion coefficients and their activation energies at a given annealing temperature was established using LeClaire's grain boundary diffusion model. The data also provide evidence that cadmium diffusion may be strongly modulated by a gallium gradient seen both laterally at the interface and in the bulk in solar-grade CIGS material.