Nanostructured device based on coated ZnO layer as a window in solar cell applications

This work highlights some physical properties related to the influence of aluminum, tin and copper incorporation on nano-structured zinc oxide (ZnO:M; M:Al, Sn and Cu) thin films prepared by ultrasonic spray pyrolysis technique (USP) on glass substrate at 350 +/- 5 degrees C. For the as-grown layers, M-to Zn-ratio was fixed at 1.5 %. The effects of metal doping on structural, morphological, optical and electrical properties were investigated. X-ray diffraction pattern revealed that the as-prepared thin films crystallized in hexagonal structure with (0 0 2) preferred orientation. The surface topography of the films was performed by atomic force microscopy. AFM images revealed inhibition of grain growth due to the doping elements incorporation into ZnO matrix, which induced the formation of ZnO nanoparticles. Optical measurements showed a high transparency around 90 % in visible range. Some optical parameters, such as optical band gap, Urbach energy, refractive index, extinction coefficient and dielectric constant were studied in terms of doping element. Particularly, dispersion of refractive index was discussed in terms of both Cauchy and single oscillator model proposed by Wemple and DiDomenico. Cauchy parameters and single oscillator energy E-0 as well as dispersion energy E-d were calculated. Finally, electrical properties were investigated by means of electrical conductivity and Hall effect measurements. The measurements confirmed n type conductivity of the prepared thin films and a good agreement between the resistivity values and the oxidation number of doping element. The main aim of this work was the selection of the best candidate for doping ZnO for optoelectronics applications. The comparative study of M doped ZnO (M: Al, Sn and Cu) was performed. High rectifying efficiency of the Al/n-ZnO/p-Si/Al device was achieved and non-ideal behavior was revealed with n > 4.