A Novel Solution Process for the Synthesis of VO₂ Thin Films with Excellent Thermochromic Properties

Abstract

This article describes a novel and simple route to preparing VO(2) thermochromic films by using a VOCl(2) solution with poly(vinylpyrrolidone) (PVP). X-ray diffraction and Raman spectra showed that the VO(2) films deposited with PVP consisted of a nearly pure monoclinic/rutile (M/R) phase. Conversely, films prepared without PVP contained obviously impure crystalline phases. The as-prepared films with PVP showed excellent optical properties compared to those prepared by common gas-phase methods: an integral visible transmittance of 54.5% and an IR reduction (change in transmittance) of 41.5% at 2000 nm. The phase-transition temperatures were adjusted from 69 to 54 degrees C by tungsten doping. Equipment analyses revealed that PVP plays two roles in the film formation. First, it fundamentally acts as a film-forming promoter to improve physical gelation via interactions among oppositely charged carbonyl groups and amine groups of the polymer. Second, the negatively charged carbonyl groups can interact with VO(2+) to form a uniform mixed-gel film after solvent evaporation. Thus, the addition of PVP can stabilize the solution and improve the as-prepared film quality and phase purity. The current study suggests that the process has promise in applications of smart windows.

Thermal kinetic analysis of metal–insulator transition mechanism in W-doped VO2

“…. The difference in binding energy between O 1s and V 2p3/2 is 13.8 eV, which is in consistence with the 14.2 eV of VO 2 film fabricated by polymer-assisted deposition [22]. The above information confirms that the obtained vanadium oxide is stoichiometric.…”

Recent Advances in Nanostructured Vanadium Oxides and Composites for Energy Conversion

“…In polymer-assisted deposition (PAD), polymers (e.g., PVP, PVA) have been used to replace the integrated network of sol-gel, and inexpensive inorganic VO 2+ sources such as VOCl 2 and VOSO 4 can be used. [55] The solution-based precursors can be coated to form a homogeneous liquid film, followed by an annealing process. [56] Notably, solution-based deposition has unique advantages in controlling the surface structures of VO 2 (M) thin films.…”

Synthesis of doubly functional nanowhiskers from a colloid solution including a V–Ti complex precursor

“…The synthetic strategy consisted of growing the precursor clusters with the simultaneous attachment of (NH 4 ) 5 [(VO) 6 (CO 3 ) 4 (OH) 9 ]ÁTi(OH) 4 in solution (Fig. 1).…”

“…After further stirring for 1 h, the organic phase was separated to obtain the nanoparticle precursor, (NH 4 ) 5 [(VO) 6 (CO 3 ) 4 (OH) 9 ]Á10H 2 O [18]. The nanoparticle precursor was then added dropwise to the colloid solution including TTIP and PVP toluene solution with vigorous stirring over 5 h; it hydrolyzed on the surface of the nanoparticle precursor through a sol-gel reaction to obtain the V/Ti urchin-like (V/Ti) complex precursor (NH 4 ) 5 [(VO) 6 (CO 3 ) 4 (OH) 9 ]ÁTi(OH) 4 in PVP colloid solution. The sample of the colloid precursor was spin-coated onto glass (80 mm 9 80 mm) and then calcined in a tube Ti/VO 2 Nanowhisker Ti(OH) 4 Fig.…”

“…In hot weather, the VO 2 coating on the window would block most of the incident NIR solar radiation, preventing the room from heating up; in cold weather, the NIR radiation would pass through the coating to warm the room [8]. The wide variety of potential applications has attracted great interest from the research community [9,10].…”