Copper–indium–gallium–diselenide/molybdenum layers analyzed by corrected SIMS depth profiles

Abstract

Polycrystalline copper–indium–gallium–diselenide (CIGS) may act as absorber material for solar radiation in thin film solar cells. CIGS layers are grown on molybdenum back contacts deposited on glass or flexible substrates. During the preparation process, substrate elements diffuse across the back contact into CIGS. We investigate the diffusion into the CIGS/Mo layers by SIMS depth profiling corrected with respect to recoil mixing and atomic mixing. Detaching the CIGS/Mo layers from the substrate allows profiling the layers from surface-side and backside. Thereby, the intermixing effects caused by the sputtering process may be separated. Comparing the surface-side with the mirrored backside depth profile enables us to correct the distortion by recoil mixing, which is anisotropic and different for each element. The remaining profile, now only distorted by atomic mixing (isotropic for all elements), is then corrected with respect to the Mo profile at the interface, which is known to exhibit a step function. Finally, the corrected depth profile allows the determination of diffusion coefficients of impurities in the complex multinary compound system.