Promising molybdenum trioxide films for optically detectable gas sensor and solar cell applications

Abstract

Sub-stoichiometric molybdenum trioxide (MoO3−x) thin films were grown by thermal evaporation techniques on glass, single crystal silicon Si and Fluorine doped Tin Oxide (FTO) glass substrates with different thicknesses. It was found that, Oxygen vacancies play an important role on properties of MoO3−x films. The structural properties of these films were analyzed by means of x-ray diffraction, energy dispersive analysis of x-ray, scanning electron microscopy. The film surface uniformity and smoothness with thickness was tested using the surface roughness measurement for MoO3−x films grown on glass and FTO. The optical properties of all presented films were investigated using UV–vis–near-infrared (NIR) spectrophotometer Optical transmittance and reflection of MoO3−x film were measured in the wavelength range from 200 to 2500 nm. MoO3−x film with 500 nm thick was tested optically for gas sensor applications. The effect of chlorine exposure on the optical transmittance of MoO3−x film with 500 nm thick deposited on glass was studied. Transmittance degradation as increasing the period of exposure was observed, indicating to the high sensitivity of MoO3−x to chlorine gas. The electrical resistivity and Seebeck coefficient of MoO3−x film with 500 nm thick were measured. Low resistivity (∼10−3 Ω.cm) and high transmittance (∼78%) in the visible spectrum of the film of 100 nm thick deposited on FTO coated glass substrate recommended it to be promising as transparent conductive electrode for solar cell.