Electrochromism of non-stoichiometric NiO thin film: as single layer and in full device

Electrochromic properties, known as a reversible modulation of the optical properties under an applied voltage, of NiO thin films are discussed in respect of the film stoichiometry. Using radio-frequency magnetron sputtering, non-stoichiometric NiO'' thin films of good crystallinity were grown at room temperature from low oxygen partial pressure [i.e., above 2 % P(O-2/Ar + O-2)]. A further increase in oxygen partial pressure leads to conductive brownish films containing a large amount of Ni3+. 2 %-Ni1-xO thin films exhibit significant EC performance in lithium-based electrolyte with a transmittance modulation of 25 %. If it is generally accepted that this optical modulation is due to an insertion of small cations, the presence of additional surface phenomena is also shown. The cycling of full device, based on the association of WO3 and NiO'' in temperature up to 60 degrees C and down to -35 degrees C confirms expected increase and decrease in capacity while surprisingly the optical switch from a transparent to a neutral gray color appears slightly modified.