Cuprous oxide thin films obtained by dip-coating method using rapid thermal annealing treatments

The transformation of cupric oxide (CuO) into cuprous oxide (Cu2O) thin films by rapid thermal annealing (RTA) treatments is studied. The CuO films were obtained by dip-coating from a precursor solution containing copper (II) acetate. The films are formed of ten coats, where each one was deposited with a withdrawal speed of 8 cm/min and dried in air at 250 °C for 5 min; after that, the films were sintered in air at 250 °C for 1 h. Under these conditions an average thickness of 240 nm is obtained. The RTA treatments on the CuO films were performed for 10 s with a heating ramp of 5 °C/s in vacuum at temperatures (TA) in the 325-450 °C range with steps of 25 °C. As revealed by X-ray diffraction data, the composition of the polycrystalline films depends upon the applied TA: i) CuO+Cu2O for TA < 375 °C, ii) only Cu2O for TA= 375 and 400 °C, and iii) Cu2O+Cu for TA ≥ 425 °C. Some physical properties of Cu2O films are: crystallite size ranging between 6.5 and 8.5 nm, direct forbidden band gap energy of 2.36 eV, and optical transmission around 75% for wavelengths larger than 520 nm. Cu2O films obtained at TA = 400 °C are p-type with resistivity of 9.9 × 101 Ω-cm, mobility of 0.52 cm2 V−1 s −1, and carrier concentration of 1.2 × 1017 cm−3. These properties of the RTA obtained Cu2O films make them a good candidate for application in solar cells of transparent conductive oxide (n-type)/Cu2O heterostructure type.