Homogeneous electrochemical deposition of in on a Cu-covered Mo substrate for fabrication of efficient solar cells with a CuInS2 photoabsorber

Highlights: ► Successful homogeneous deposition of indium on a Cu-deposited Mo/glass substrate. ► Effects of organic additives for efficient indium electrodeposition. ► Fabrication of a CuInS2 film having a good photoelectrochemical response. ► Achievement of high and reproducible sunlight-conversion efficiency. - Abstract: Electrochemical deposition of indium (In) on a copper-covered molybdenum-coated glass substrate from several acidic InCl3 solutions was studied for fabrication of CuInS2-based solar cells. When In was deposited using a simple acidic InCl3 solution at −0.80 V (vs. Ag/AgCl), island-shaped growth was observed, whereas a homogeneous In film was obtained from InCl3 solution containing citric acid and sodium citrate at −0.98 V (vs. Ag/AgCl). Electrochemical and structural analyses revealed that the citric acid additive had a function for smoothing the surface of the In deposit. The mixing with sodium citrate induced appreciable inhibition of H2 evolution during the In deposition, leading to high current efficiency of >90%. The CuInS2 film derived from the homogeneous In had a uniform thickness with a smooth surface, while the CuInS2 film obtained from the island-shaped In deposit showed a large variation in thickness with recessed areas. The CuInS2 film derived from the homogeneous In was showed better photoelectrochemical response than that of the film fabricated from the island-shaped In. As expected from these differences, the solar cell with an Al:ZnO/CdS/CuInS2/Mo structure derived from the homogeneous In film showed the best conversion efficiency of 7.8% with relatively high reproducibility.