Cu₂O thin films deposited by spray pyrolysis using diethanolamine and L-ascorbic acid as reducing agents

Cu2O thin films are of great interest due to their diverse applications. Spray pyrolysis is a low-cost and straightforward technique among the different methods used to deposit them. Precursor solutions using D-glucose as reducing agent and copper acetate have mainly been used. However, the D-glucose's remaining subproduct can detriment the films' properties and use in devices. In this work, precursor solutions using diethanolamine (DEA) or L-ascorbic acid (AA) as reducing agents to deposit Cu2O thin films are used for the first time. The effect on the structural, morphological, electrical, and optical properties of Cu2O thin films is shown for 0.25 M of DEA and 0.1 M of AA, which were the optimal molar concentrations to obtain homogeneous solutions, with 0.04 M of copper nitrate. The deposition temperature (T-d) determines the formation of Cu2O single phase. XRD analysis reveals films only constituted by Cu2O using DEA in the 280 degrees C <= T-d <= 310 degrees C and AA in the 280 degrees C <= T-d <= 290 degrees C ranges. These deposition temperatures are lower than the reported values (similar to 330 degrees C) using the same copper salt and glucose. This fact is associated with the reducing character of both agents since the obtained precursor solutions lead to an in-situ reduction. In addition, the films show minimum organic impurities content associated with the low volatilization temperature of the DEA and AA, which is desirable for their application in devices. The calculated bandgap energy (2.3-2.4 eV) for both types of films corresponds to nanocrystalline Cu2O. However, using L-ascorbic acid resulted in thin films with the lowest resistivity (10(2) Omega cm), attributed to an improvement in the crystallinity.