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

Abstract

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.