Characterization of reactively sputtered molybdenum oxide films for solar cell application

Molybdenum oxide (MoO3) thin films were prepared via Radio Frequency (RF) sputtering at different ambient composition and post-deposition annealing. The effects on the structural, optical, and surface properties of the deposited films were investigated. The ambient oxygen concentration O2/(O2 + Ar) was varied from 10% to 100% at 10 mTorr. Post deposition anneals were performed in Ar at 300–500 °C. The films were analyzed using glancing incidence x-ray diffraction (GIXRD), UV/Vis/NIR spectrophotometry, and x-ray photoelectron spectroscopy (XPS). As-deposited films have amorphous structures, independent of the oxygen partial pressure. Annealing at 300 °C in air resulted in crystallization of the molybdenum oxide films to the monoclinic β-MoO3 phase. Samples annealed at 400 and 500 °C were identified as pure orthorhombic α-MoO3 phase with (020) preferred orientation. High resolution XPS studies showed the presence of Mo6+ (MoO3) and Mo5+ (Mo4O11) oxidation states at the surface of as deposited and low temper...