Lithium doping in spray-pyrolyzed NiO thin films: results on their microstructural, optical and electrochromic properties

The Li-doped NiO thin films were prepared onto the plane glass substrates, and the FTO coated glass substrates for electrochromic characterizations, employing the spray-pyrolysis technique. These films were analyzed by a variety of characterization techniques. The structural characterizations reveal that the as-prepared films are of NiO with a cubic structure along with the (2 2 0) plane as the most preferred orientation of crystallite growth. The topographic characterizations show that the surface roughness changes with the varying lithium content. The bandgap energy values are found in the range of 3.40–3.65 eV. Two emission peaks, one corresponding to NBE and another related to the structural defects, are observed in the room-temperature PL spectra of the films. The coloration efficiency of the films improves upon Li doping and is optimum (34.84 cm 2 /C at 550 nm) for the 3 at.% Li-doped films. The CA analyses indicate that the coloration phenomenon in the films occurs faster in comparison with the bleaching process. The EIS data have been examined based on an equivalent electrical circuit model using fit and simulation analysis.