Green electrodeposition of ZnO as a TCO in terawatt solar cells

Electrodeposition of ZnO can be performed in an aqueous solution using a greener recipe, where the solution can be reused for multiple deposition runs. The solution in this greener recipe has only one function, i.e. to provide electrical conductivity for the deposition reactions. A Zn sheet serves as the anode, which dissolves during the deposition as the Zn source. O₂ is bubbled into the solution and reduced to OH- ions as the O source. This recipe minimizes concentration changes in the solution as deposition proceeds, making the solution reusable. An initial Zn²⁺ concentration of a few mM in the solution is required, not to serve as a Zn source but to facilitate the deposition and prevent precipitation of ZnO in the solution. Multiple deposition runs for ZnO films in the same solution have been demonstrated. X-ray diffraction, optical transmittance and absorption spectra reveal that all the ZnO films have similar structural and optical properties. They all display high transmittance of ~80% and low absorbance of ~10%.