Diffusion activation energy of cadmium in thin film CuInGaSe2

Abstract

Diffusivity and activation energy of cadmium in copper indium gallium diselenide (CuInGaSe2 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.