Influence of Lithium Interstitial Doping on the Optoelectronic Properties of NiO and WO$_3$

First principles calculations through density functional theory (DFT)+$U$ method were performed to assess the effect of Li interstitial doping on optoelectronic properties NiO and cubic, hexagonal, monoclinic WO$_3$. The implications structural electronic their relationship with optical properties, such as dielectric response absorption coefficient in context electrochromism, are discussed. (i.e., electron doping) turns these materials metallic-like even for low concentration ($x<0.083$). In materials, largely influenced by intraband transitions. Compared NiO, Li-doped shows larger visible region while, respect WO$_3$, WO$_3$ exhibits an increment whole spectrum, particularly, infrared region. These results help understand changes observed electrochromic devices based materials.