Electrochromic response of pulsed laser deposited oxygen deficient monoclinic β-MoO3 thin films

Abstract

β-molybdenum trioxide (β-MoO3) films that crystallize in the monoclinic structure were successfully fabricated using pulsed laser deposition (PLD) technique by varying the partial pressure of reactive oxygen P(O2) gas ranges form 10−1mbar to 10−6mbar. The electrochromic (EC) properties of these films were presented in this report as a function of P(O2). The composition of the films was calculated from X-ray photoelectron Spectroscopy (XPS) and Electron energy dispersive spectroscopy (EDS) analysis. After Li+ intercalation, the films prepared at lower P(O2) (viz 10−4mbar, 10−5mbar and 10−6mbar) formed new stable phase of Li2MoO4 whereas no stable phase formation was observed in the films coated at higher P(O2) after Li+ intercalation. The EC studies revealed that the films coated at 10−2 mbar P(O2) had good coloration efficiency (η) of about 66 × 10−4 m2/C and 83% reversibility whereas the films coated with 10−6 mbar P(O2) showed lower coloration efficiency of 11 × 10−4 m2/C and 13% reversibility. But interestingly, the lower oxygen deficient film prepared at 10−1mbar had lower EC response compared to higher oxygen deficient film 10−2mbar. So, it is of interest to study comparatively the material properties of Li+ intercalated and de-intercalated 10−2mbar and 10−6mbar films (extreme values of EC properties). Analysis of these films suggested that the 10–20 wt% oxygen deficiency forms vacancies in the lattice which gave way to intercalate/deintercalate Li+ freely in to it. The EC performance of stoichiometric and more deficient MO films were found to be poor whereas few (10–20%) oxygen deficient MO films showed better EC performance.