One-step Electrodeposition of Metal Precursors from a Deep Eutectic Solvent for Cu(In,Ga)Se2 Thin Film Solar Cells

Electrodeposition and annealing (EDA) is a low-cost and promising growth route for Cu(In,Ga)Se2 (CIGSe). One of the main drawbacks of this method is the difficulty in controlling gallium deposition from aqueous electrolytes due to the interference of the hydrogen evolution reaction. Thus, to avoid this parasitic reaction and make the deposition more energy efficient we deposit from a deep eutectic solvent (DES). In this work we investigate the one step electrodeposition of copper, indium and gallium from the DES choline chloride:urea (ChCl:U – 1:2). The electrochemical behaviour of the ChCl:U-CuCl2-InCl3-GaCl3 system was studied by rotating disk electrode cyclic voltammetry. This analysis revealed several redox responses which related to the deposition and stripping of different Cux(In,Ga)y intermetallics. The morphology of the deposits depended primarily on the metal salt concentration in solution, since dendrites as well as compact layers were obtained. The metal precursor layers were successfully converted to CIGSe by selenisation, whilst avoiding Ga segregation. However, the maximum solar cell efficiency obtained was 2.7%. With this work we introduced a versatile one-step deposition method where the morphology of the precursor can be controlled by tuning solution composition and by introducing several potential steps during growth.