Effects of Processing Parameters on Zinc Oxide Thin Films Prepared by Single Solution Deposition
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Effects of Processing Parameters on Zinc Oxide Thin Films Prepared by Single Solution Deposition Manuel F. Martinez1, Shaimum Shahriar1, Donato Kava1, Cheik Sana1, Vanessa Castaneda1, Jose Galindo1, and Deidra R. Hodges1 1 Electrical and Computer Engineering, The University of Texas at El Paso, El Paso, TX 79968, U.S.A. ABSTRACT Zinc oxide thin films were prepared via the sol-gel spin-coating method with the use of a spin processor. The film’s annealing parameters were varied to study their impact on the final film morphology and electrical properties. Characterization of the structural properties of the samples was carried on a X-ray diffractometer (XRD) and scanning electron microscopy. Electrical characterization was obtained with the use of a four point probe. Optical characterization of the samples was carried on a UV-Vis-NIR Spectrophotometer. Samples annealed under a cover are observed to have a higher transmission percentage on the visible light range while having a very small grain size and small relative resistivity. Samples annealed under standard atmospheric conditions show a larger grain size and resistivity, and correlated to it, a smaller transmission percentage. Samples annealed under vacuum prove to have a much more reduced optical, electrical, and structural properties when compared to the rest of the samples. INTRODUCTION Zinc oxide thin films are considered as promising candidates for perovskite thin-film perovskite solar cells. Zinc oxide nanocrystals have been used before in perovskite-based solar cells as an electron-selective contact (electron transport layer) that requires no sintering [1] either by depositing them into a mesoporous titanium dioxide (TiO2) scaffold [1][2], or by using them as a stand-alone layer for electron transport [1][3][4]. Both deposition methods have shown efficiencies in solar cells that range from 10.2% to 12.8% [1][3][4]. This material has been used in solar cells because of its wide band gap of 3.37 eV at room temperature and also because it exhibits high exciton binding energy (60 meV), which ensures an efficient excitonic emission and recombination up to room temperature [5]. This material also normally has a charge carrier concentration of 1016 to 1017 cm-3 [6]. Previous studies of the optoelectronic properties of this material were made by preparing samples with a wide variety of techniques such as spray pyrolysis, chemical vapor deposition (CVD), and RF sputtering. However, these techniques require the use of sophisticated equipment and setups that drive the costs of fabrication up [5]. For this reason, recent publications explore the fabrication of ZnO films prepared by the sol-gel method as an inexpensive, simpler, alternative to the use of the material in photovoltaics [7]. A tight control of the electrical and optical properties of zinc oxide thin-films can be achieved by the control of the change in dopant used and the oxygen adsorption by the film [8]. Furthermore, as Ladanov reported, a control of the growth parameters such as pressure, interacting gas
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