Stabilizing vanadyl acetylacetonate using imidazolium Ionic liquids for VO2 thermochromic thin films

Abstract

This study examines the role of different imidazolium ionic liquids (ILs) on the stabilization of vanadyl acetylacetonate, VO (acac)2, as a vanadium precursor by using UV-Vis spectroscopy. The possible stabilization mechanisms of VO (acac)2 in IL solution were investigated. Furthermore, a fabrication method is proposed to prepare monoclinic vanadium oxide VO2 (M) thin films using a mixture of ionic liquid and poly-ionic liquid (PIL). The ILs 1-ethyl 3 allyl imidazolium bis(trifluoromethansulfonylimide) ( [EAIM] [TFSI]), 1-ethyl 3-methyl imidazolium trifluoromethanesulfonate ( [EMIM] [TFO]) and 1-ethyl 3-methyl imidazolium acetate ( [EMIM] [AcO]) were investigated. It is shown that ( [EAIM] [TFSI]) has the best coordinating ability to VO (acac)2 for protecting the central vanadium atom from oxidation. For thermochromic film formation, the effect of annealing temperature (250°C – 400°C) and time (10 minutes - 120 minutes) on crystallization was studied using X-ray diffraction. The possible role of PIL decomposition on the formation and crystallization of VO2 (M) is discussed. The prepared films showed excellent thermochromic properties with 20.3 % solar modulation efficiency.