Dynamic Characterization of Charge Separation in WO$_{3}$–TiO$_{2}$ Nanoscale Heterojunction Investigated by the Transient Photovoltaic Technique

Abstract

The dynamic photo induced charge separation and transport properties of pulsed-magnetron-sputtered TiO 2 , WO 3 , and WO 3 -TiO 2 double-layer films were investigated using the transient photovoltage (TPV) technique. Effective charge separation and transport were observed for the WO 3 -TiO 2 heterojunction, which was about three times larger than those of the TiO 2 and WO 3 single-layer films. The TPV response of the WO 3 -TiO 2 heterojunction peaked at 28 ns with a recombination lifetime of 179 ns. These results suggested that the electron injection from TiO 2 under illumination was the dominant factor for the separation of photo induced charge carriers in the WO 3 -TiO 2 double-layer films.

Study on dynamics of photoexcited charge injection and trapping in CdS quantum dots sensitized TiO2 nanowire array film electrodes

“…18,19 The TPV enhancement of CdS/TiO 2 film (2 CBDs) is not only due to the UV-light absorption of TiO 2 overlapping that of CdS QDs in 2 CBDs (as shown in Figure 2(a)) but mainly results from the photoexcited electrons injected from CdS into TiO 2 due to the CB of CdS QD above the CB edge of TiO 2 (as shown in Figure 3). 15 In the following process, the transient intensity decreases gradually with the increase of CdS CBDs from 2 to 14 CBDs (similar to Fig. 2(b)).…”

“…In contrast, a negative TPV signal denotes that the top electrode is negative with respect to the back electrode. 14,15 In this case, the positive transient signal indicates that photoexcited electrons transfer to the FTO substrate, and photoexcited holes remain in TiO 2 nanowires, due to the upward shift of conduction band-edge of n-type TiO 2 . 3 Note that the transient signal of the composite CdS/TiO 2 film of 2 CBDs occurs at a timescale of about 2.5 Â 10 À8 s, which is a little slower compared to TiO 2 nanowire array film.…”

“…13 In our previous work, by using SPV, we have found that the built-in electric field of the interface essentially affects the separation and transport of the photoexcited charge in TiO 2 based on the conductive substrate. 14,15 In our present work, we focus on investigating the kinetic processes of photoexcited electrons injected from CdS QDs into TiO 2 nanowire arrays and photoexcited electrons trapped in QDs using the SPV and TPV technique. The experimental results indicate that the rate of electrons injected from CdS into TiO 2 is slower than that of the electrons trapped in the surface states of CdS.…”

Highly enhanced photocatalytic activity of WO3 thin films loaded with Pt–Ag bimetallic alloy nanoparticles

“…Here, we discuss it in detail based on the band structure and work functions. It was reported that the work functions (F) of WO 3 lm, metallic Pt, and metallic Ag are 5.7 eV, [45][46][47] 5.65 eV, 48 and 4.26 eV, 49 respectively. In addition, the work function of the bimetallic alloy can be expressed by the sum of the work functions of the two metal components, 50 which means that the work function of the alloy lies at a level intermediate between monometallic Pt and Ag (4.26 eV < F Pt-Ag < 5.65 eV).…”

Tungsten Oxide Nanostructures for Energy Storage and Field Emission Applications

“…The β factor enumerates the merit of field emission which strongly depends on several factors like emitter geometry, underlying substrate, conductivity, aspect ratio of nanostructure, inter electrode distance, spatial distribution of emitters etc. [12][13][14] The FN plot [ vs. ] (inset of Fig. 7a) exhibits a nice linear relationship in the high field region and suggests that the emission to be of F-N type.…”