Artificially controlled two-step electrodeposition of Cu and Cu/In metal precursors with improved surface roughness for solar applications

The very smooth surfaces of the multistacked metal layers fabricated by electrodeposition are particularly useful for obtaining the designed composition and the optimized composition distribution in CIGS solar cells. Thus, we employed an artificially controlled two-step electrodeposition method for the deposition of reproducible and smooth Cu layers on Mo substrates. First, the chronoamperometry at various applied potentials was investigated to confirm growth behavior at a direct constant potential. According to these results, a two-step process was designed: i) at the first step, high negative potential was applied for the formation of high density nuclei, and ii) at the second step, low negative potential was employed to promote the homogenous coalescence of the Cu nuclei. As a result, the root mean square (RMS) value of the Cu surface measured by atomic force microscopy was considerably decreased by up to 6.0 nm using the two-step process, compared to that fabricated using a single-step process. In addition, the relatively smooth In surface was observed on the Cu/In bilayers fabricated using the two-step process.