Study of Si doped VO 2 thin films for solar thermal applications

Doubling of the Phase Transition Temperature of VO2 by Fe Doping

“…For practical use, various transition temperatures of VO 2 are desired to fulfill the different demands depending on the applications. For illustration, a phase transition temperature ( T PT ) of around 30 °C is suitable for thermochromic smart windows, whereas a T PT above 110 °C is required for solar thermal collector optimization. , Great efforts have been devoted to accomplishing the modulation of T PT , and doping is the most widespread and efficient approach for achieving this objective. Relying on a Mott-driven transition mechanism, high-valence dopants act as donors of free electrons to the VO 2 conduction band and decrease the T PT , while substitution of V 4+ with lower-valence ions such as Fe 3+ , Al 3+ , and Cr 3+ stabilizes the intermediate phase M2 and slightly increases the T PT . − W 6+ has been considered as one of the most effective donor-like dopants, decreasing the transition temperature by 24 °C per 1 mol % .…”

Element doping: a marvelous strategy for pioneering the smart applications of VO2

“…For highly efficient solar collectors, T MIT above 90 °C is required. 13 Other applications, including solar and electronic devices, also regard elevated T MIT as the premise. Disappointingly, the number of studies on element doping for increasing T MIT is far less than that for decreasing T MIT .…”

“…At lower doping level, the lattice distortion induced by ion radius mismatch is responsible for the lower T MIT , while more h + carriers are injected into VO 2 at high doping level and thus give rise to the increased T MIT . 42 In addition to the elements discussed above, Si, 13 Ti, 22 N 14 and rare earth elements (like Ce, 25 Tb 42 ) exhibit relatively weak capabilities in raising the T MIT of VO 2 , as shown in Table 2. Finally, to aid understanding, we present the reported phase transition temperature (experimental data) of element-doped VO 2 in Fig.…”

“…The results of many studies have shown that external atoms generally reduce the phase transition amplitude of VO 2 by 1–2 orders of magnitude. 13,23,29,56,77,94,101–103 Especially, for some elements, such as Cr, 91,101 H, 29 Ni, 103 and N, 76 a high doping level can even lead to the disappearance of the switch effects. High defect concentration can be used to explain such a phenomenon.…”

“…For instance, smart windows require excellent thermochromic properties of VO 2 near room temperature, while a higher T MIT is necessary for solar thermal collectors, electronic devices, etc . 12,13 By varying the doping level or element type, the modulation amplitude and direction of properties can be varied. Even controlling the insertion position of atoms has been reported; nitrogen atoms are inserted into the VO 2 lattice in the O position or the interstitial position depending on the NH 3 in the reaction chamber.…”