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 degrees C for 5 min; after that, the films were sintered in air at 250 degrees 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 degrees C range with steps of 25 degrees C. As revealed by X-ray diffraction data, the composition of the polycrystalline films depends upon the applied TA: i) CuO+Cu2O for T-A < 375 degrees C, ii) only Cu2O for T-A = 375 and 400 degrees C, and iii) Cu2O+Cu for TA = 425 degrees 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 degrees C are p-type with resistivity of 9.9 x 10(1) Omega-cm, mobility of 0.52 cm(2) V-1 s(-1), and carrier concentration of 1.2 x 10(17) 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.