Cu2O thin films obtained at low temperature by mono-ethanolamine decomposition in open atmosphere

Abstract

Cu2O thin films were obtained from CuO films at drying temperatures lower than 290 °C and times shorter than 10 min in open atmosphere. A rapid transformation of CuO films to Cu2O films at 260 °C evidenced the existence of a useful reduction mechanism that was studied. A metal precursor solution was prepared from the mixing of copper acetate and monoethanolamine in isopropanol. Thin films of 5 layers were deposited by the dip-coating method at a withdrawal speed of 6 cm/min. Each layer was dried in a furnace at 230, 260, 275 or 290 °C for 5, 7 or 10 min. X-ray diffraction, reflectance and transmittance in the UV–Vis region and, specular reflectance in the infrared showed that CuO films are obtained at 230 °C. However, Cu2O with good crystallinity and transparency is produced with drying at 260 °C and above, for 10 min and less. Band gaps for CuO and Cu2O films were 1.28 eV and 2.18 eV, respectively. FTIR, resistivity and SEM studies evidenced a reduction mechanism that transforms CuO to Cu2O. The effect is caused by monoethanolamine decomposition into several other reducing compounds, mainly copper carboxylates. Even though some authors have reported similar precursor solutions with monoethanolamine, none have obtained Cu2O in open atmosphere, nor have they explained the organic reaction pathways involved. With the help of other reducing organic compounds, the phenomena can be exploited to produce Cu2O films from CuO ones at milder processing conditions, thus enabling applications for flexible electronics.