Band engineering in monoclinic WO3 with C+H co-doping for optoelectronic applications: A hybrid functional study

Using the hybrid functional method, we systematically investigate the band engineering induced by C + H codoping in monoclinic WO3, and the associated effect on the optoelectronic functionality as well. First, we find that C substitution for O in WO3 improves the optical absorption through narrowing the band gap by 11% and introducing a curved intermediate level within the band gap (which functions as a stepping stone to relay the excited valence electrons to the conduction band). Further H incorporation into C-doped WO3 stabilizes the C substitution via clustering with C in the form of C-H and H-C-H chains, which reduces the band gap to less than 2 eV and simultaneously drives the deep C-induced intermediate level to be shallow. Such dopant clustering and the induced band engineering remarkably promote the optical absorption and optoelectronic functionality of WO3. The positive influence of dopant clustering has been fully analysed and discussed, and the favorability for forming C-H and H-C-H clusters in WO3 has been well presented through the detailed thermodynamic and kinetic analyses. The outcome of this work is expected to offer insightful guidance to tuning the properties of WO3 materials towards optoelectronic applications.