Results on the electrochromic and photocatalytic properties of vanadium doped tungsten oxide thin films prepared by reactive dc magnetron sputtering technique

Abstract

In this investigation, vanadium doped tungsten oxide (V : WO3) thin films are prepared at room temperature by reactive dc magnetron sputtering employing a tungsten–vanadium ‘inlay’ target. In comparison with pure sputtered tungsten oxide thin films, 11% vanadium doping is observed to decrease the optical band gap, enhance the colour neutral property, decrease the coloration efficiency (from 121 to 13 cm2 C−1), increase the surface work function (4.68–4.83 eV) and significantly enhance the photocatalytic efficiency in WO3 thin films. These observations suggest that (i) vanadium creates defect levels that are responsible for optical band gap reduction, (ii) multivalent vanadium bonding with terminal oxygen in the WO3 lattice gives rise to localized covalent bonds and thus results in an increase in the work function, and (iii) a suitable work function of V : WO3 with ITO results in an enhancement of the photocatalytic activity. These results on electrochromic and photocatalytic properties of V : WO3 thin films show good promise in the low maintenance window application.

Influence of Dopant Concentration on the Electrochromic Properties of Tungsten Oxide Thin Films

“…The CVs obtained appear very similar to those observed with well-defined electrochromic WO 3 films as already reported in literatures [16,17,43,52]. The overall features of the CVs are in agreement with the results reported for WO 3 films deposited by other techniques in a H 2 SO 4 medium [13,15,17]. It is reported that as the classical amorphous WO 3 films have a broad distribution of energetically different intercalation sites, its cyclic voltammograms do not display sharp current peaks for neither reduction (intercalation) nor oxidation (deintercalation) [53,54].…”

“…No peaks were found corresponding to the stretching modes of V 3 -O (520 cm -1 ), V 2 -O (650 cm -1 ) and V 5+ = O (1027 cm -1 ) [13].…”

“…If W content is high, the frequency at which the band appeared will also be high. There is a shift in the Raman bands to higher frequency due to the removal of water [13]. In addition there are some weak peaks around 184, 223, 270 and 330 cm -1 which are assigned as in the Table 1.…”

“…It is also reported that color neutrality can be obtained by vanadium doping in tungsten oxide. Optical absorption in these vanadium doped films is due to polaronic transition V 4+ V 5+ and W 5+ W 6+ in WO 3 [13]. The interaction between WO 3 and V 2 O 5 is unique because of the similarities of ionic radii and the structure in their highest oxidation state [14].…”

“…Composite WO 3 -V 2 O 5 films have been prepared by various techniques such as electronbeam evaporation [17], reactive DC sputtering [11,13], pulsed laser deposition [9] and chemical deposition like sol-gel [3]. Among the various thin film deposition techniques, RF magnetron sputtering has the advantage of being used for deposition of uniform films on larger area substrates as well as the flexibility of changing the deposition conditions [16].…”