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 co-doping 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.