(554a) Electrodeposition of Sn Alloys for Thin Film, Photovoltaic Applications From Citrate Electrolytes

The electrodeposition of different combinations of the elements of copper zinc tin sulfide (CZTS) and copper indium gallium (di)selenide (CIGS) from a citrate electrolyte are compared and their complexation with citrate species simulated, with a comprehensive mass balance model to assess the different complexed species with variable combinations of the metal ions. The partial current densities were determined for different combinations of metals (e.g., Sn, In, InSn, CuInSn) using a three electrode configuration with a constant applied potential deposition at room temperature. For example, the reaction rate of Sn was largely enhanced when codeposited with Cu. The surface morphology of SnInCu and SnCu deposition were rougher than Sn deposition. However, In was not equally enhanced and the ratio of Sn:In was altered with the codeposition of Cu. Thus, the enhancement was due to both an increase in surface area, due to a change in nucleation, and a kinetic effect. The concentration of the free citrate species (H₂AOH^- and HAOH^2-) were reduced when Sn was co-deposited with In and/or Cu which might have an affect on the surface morphology. The coupled kinetic behavior is akin to induced codeposition, where the codeposition of a more noble element, Cu, enhanced the deposition of one that is less noble, Sn.