A thermochemical understanding of the factors that govern the growth of chemical bath deposition of Cu₂O thin films

A simple room-temperature chemical bath deposition technique, inspired by the Felhling method, was used to deposit nanocrystalline cuprous oxide (Cu₂O) thin films. The process involved a mixture of copper sulfate, sodium potassium tartrate, and sodium hydroxide. A thermochemical analysis explored how pH and complexing agent concentration affected Cu(OH)₂ solubility and subsequent Cu₂O growth using species repartition diagrams. The study is conducted by fixing the [tartrate]/[Cu] ratio at 10, while varying pH, deposition time, and temperatures from room temperature to 80 °C. While oxide nucleation and growth began at pH = 9, denser and more uniform films formed at pH = 10 and 11, corresponding to the co-existing domain of copper hydroxo and copper tartrate complexes. Notably, regardless of pH, temperature, or reducing agent, the Cu₂O (111) facets appear to be selectively stabilized. The introduction of an aldehyde reducing agent such as glucose had little effect on the growth of Cu₂O layers at room temperature but promoted the formation of Cu⁰ at 80 °C.