Issue |
J. Eur. Opt. Society-Rapid Publ.
Volume 21, Number 1, 2025
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Article Number | 6 | |
Number of page(s) | 11 | |
DOI | https://doi.org/10.1051/jeos/2025001 | |
Published online | 28 January 2025 |
Research Article
Research on the photoelectrical properties of TiO2-doped V2O5/FTO nanocomposite thin films under thermal and electrical excitation
1
College of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, P.R. China
2
Shanghai Key Laboratory of Modern Optical System, Shanghai 200093, P.R. China
* Corresponding author: liyi@usst.edu.cn
Received:
25
October
2024
Accepted:
3
January
2025
The TiO2-doped V2O5/FTO nanocomposite thin films were prepared on the FTO substrates by sol-gel method and post-annealing process, and the MSM structural devices based on the prepared films were fabricated by sputtering, photolithography and etching techniques. SEM, XRD, and XPS were respectively used to study the morphology, structure and composition of the film, and the electrical and optical regulations of the device were measured by using spectrophotometry and semiconductor parameter analyzer. In the temperature range of 20–360 °C, the maximum modulation amplitude of the TiO2-doped V2O5/FTO film in the 400–1600 nm band was 18.282% and the modulation of the V2O5/FTO film was increased by 9.663% after TiO2-doping. The resistance of the FTO/V2O5-TiO2/FTO device reduced by 3–4 orders of magnitude by comparing with the FTO/V2O5/FTO device. The FTO/V2O5-TiO2/FTO device underwent semiconductor-metal state transition (SMT) around 259.91 °C. Under the applied voltage of 0–5 V, the maximum transmittance variations could reach 8.821%, 7.174% and 11.540% in 400–1600 nm band at the temperature of 20 °C, 40 °C and 80 °C, respectively. The outstanding optical and electrical regulation properties and the favorable cycling stability make the nanocomposite film expected to be applied in the field of optoelectronic devices.
Key words: V2O5 / Titanium dioxide / Nanocomposite film / Optoelectronic device
© The Author(s), published by EDP Sciences, 2025
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1 Introduction
With the development of modern society, while the living standards improve constantly, we begin to pay attention to the rational use of the earth’s resources and protect the earth’s ecological environment. In recent decades, exploring new materials for energy conservation and environmental protection has been the joint goal of the researchers. As a kind of transition metal, most oxides of vanadium have the semiconductor-metal phase transition (SMT) properties [1, 2], and they can exist at 2+, 3+, 4+, and 5+ valence, among which V2O5 has the highest oxidation valence state of 5+ [3], so it is the most stable vanadium oxide and undergoes the SMT effect at 257 °C [4]. V2O5 belongs to a natural n-type semiconductor, with an orthogonal crystal structure, a unique layered structure, a wide optical band gap (2.2–2.3 eV) and high absorption coefficient besides good thermal stability [5], these characteristics above make V2O5 become a popular material with a huge research value. V2O5 is mainly used in the production of high-hardness and wear-resistant materials such as glass and ceramics, and its high energy storage performance also makes it able to be applied in the preparation of lithium vanadate batteries. Because of the unique bipolar electrochromic discoloration properties [6], its application in the field of electrochromic devices become possible. At present, V2O5 has been used in energy storage [7], electrochromism [6], photoelectric detection [8], gas sensing [9], infrared detection [10] and other fields.
The fabrication of aperture nanostructures and the doping of other elements have been experimented to enhance the properties of V2O5 thin films [11–14]. Among them, the researches about TiO2-based doping have been widely completed in many fields such as the electrochromic devices and photocatalytic sensors. Lee et al. [15] used sol-gel method to make V2O5-TiO2 composite films and systematically examined their intercalation properties, and proved that V2O5 film with TiO2 addition might attribute to changes in microstructure, crystallinity and interaction force. Moura et al. [16] fabricated V2O5-TiO2 thin films by sol-gel method and deposited on fluorine-doped tin oxide (FTO) substrates by using the dip coating technique. The films shown an orthorhombic crystal structure with the thickness of 617 nm, and had an optical modulation of 35% at 633 nm after coloring and bleaching. Ivanova et al. [17] used sol-gel dip-coating technique to deposite TiO2-V2O5 composite thin films with V2O5 as the dopant. Results showed that V2O5-doping decreased the temperature of anatase-rutile transition of TiO2, the film were visually uniform and smooth, and the color efficiency (CE) could reach 15 cm−2 C−1 at the wavelength of 525 nm. Rehman et al. [18] prepared TiO2/V2O5/TiO2 multiple-layer-structure thin films by using electron-beam evaporation method. The films had a particle size of 20–40 nm with the optical bandgap of 3.51 eV, and showed an optical transmittance of ~78% in the visible region. In addition, Wang et al. [19] have prepared the one-dimension (1D) TiO2/V2O5 heterostructures by RF reactive magnetron sputtering method. The photodecomposition rate of Rhodamine B (RhB) by the 1D TiO2/V2O5 branched heterostructures under visible light was much faster than that of pure TiO2 nanofibers, the visible-light-induced catalytic activity of the 1D TiO2/V2O5 branched heterostructures was greatly improved. Sun et al. [20] synthesized a novel composite V2O5/BiVO4/TiO2 photocatalyst by using sequentially hydrothermal and adhering method. Comparing to pure TiO2 nanobelts and V2O5/BiVO4 nanorods, the V2O5/BiVO4/TiO2 composite film exhibited higher photocatalytic activity in decomposition of gaseous toluene under visible light irradiation (λ > 400 nm).
In addition, the metal-semiconductor-metal (MSM) structure under perpendicular voltage driven has been proved to enhance the optical and electrical properties of optoelectric devices [21–23]. Nowadays, most of studies focus on the electrochromic properties and the photocatalytic activities of V2O5 films, and there are few studies on the optical and electrical properties of V2O5 films before and after the phase transition happens. The reasons are probably that the devices based on V2O5 films usually have a high resistance at room temperature, and the thermal and electrical performances of them need to be further improved. Moreover, TiO2 is expected to refine the functions of V2O5 films as mentioned above. So it is envisaged that introducing nanoscale TiO2 powder to dope the V2O5 film, improving their performance under certain conditions. In this investigation, the TiO2-doped V2O5/FTO film is prepared by sol-gel method and post-annealing process with different proportions of TiO2, and the MSM structural device based on the prepared film is fabricated. Finally, the optical and electrical characteristics of the prepared films and the devices under thermal and electrical excitation are experimented.
2 Experiment
The preparation progress is shown in Figure 1. In this investigation, the 10 mm × 20 mm × 2.2 mm FTO conductive glass with the sheet resistance of 14 Ω was used as the substrate, while vanadium pentoxide powder (V2O5, analytical purity of 99.9%), nano titanium dioxide powder (TiO2, 20 nm, analytical purity of 99.9%) and hydrogen peroxide solution (H2O2, 30 wt%) were selected as the raw materials. The TiO2-doped V2O5/FTO film was prepared by sol-gel method. In priority, the rectangular FTO substrates were cleaned in acetone, absolute ethanol and deionized water in turn for 15 min each by using the ultrasonic cleaning machine (SK3300H). Drying them in the electric constant temperature drying box. Subsequently, V2O5 powder was slowly added into a beaker with H2O2 solution and stirring continuously for 10–15 min. In this process, the V2O5 powder and the H2O2 solution would undergo a violent exothermic reaction, releasing a large amount of oxygen. The reaction equations are listed as follow:
(1)
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Figure 1 The preparation process of the TiO2-doped V2O5/FTO film. |
After the reaction happened, added TiO2 powder in moderation, and continuously stirring for about 3 h to fully diffuse the TiO2 powder into the solution. While the stirring completed, the solution would become a gel with high viscosity. When the gel was made, placed the dried FTO substrate on the homogenizer, using the vacuum pump to inhale, absorbing the appropriate amount of gel with the rubber dropper and dropping it on the FTO substrate to make it be fully coated. Then, placed the sample in the annealing furnace after spin-coating at the speed of 4000 r/min, and the annealing temperature and time were set at 400 °C and 2 h respectively [24]. The resistivity of the TiO2-doped V2O5/FTO film is determined to be about 7.56 × 10−4 Ω cm. Besides, the pure V2O5/FTO film was fabricated by the similar process above as a contrast.
Furthermore, sputtering an uppermost fluorine-doped SnO2 film and a SiO2 film with FTO and SiO2 targets on the prepared film respectively, and then assembling it to form the MSM structure device after lithography and etching. Figure 2 displays the diagram of the device. The thicknesses of the FTO film and the TiO2-doped V2O5 film are about 350 nm and 420 nm respectively. 2 mm × 2 mm Au/Ni-Cr metallic contacts were used as the electrode. The device was formed to achieve transmittance modulation under perpendicular voltage driven.
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Figure 2 The structure of the device. |
3 Results and discussions
The 10%, 12%, 15%, 20% TiO2-doped V2O5/FTO films had been fabricated by the above crafts and the transmittance curves were examined at the wavelength of 700 nm under heating and cooling process from 150 °C to 330 °C, as shown in Figure 3. It can be seen that all films show excellent thermal phase transition characteristics. During the heating process, the transmittance of the TiO2-doped V2O5/FTO films under relative TiO2 ratios decreased 16.381%, 18.277%, 16.264%, 15.589% respectively, in which the prepared film with the proportion of 12% TiO2 showed the largest transmittance variation. It proves that the 12% TiO2-doped V2O5/FTO film has the better modulation characteristics, so the following experiments are carried-out by this kind of sample.
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Figure 3 Transmittance curves of the 10%, 12%, 15%, 20% TiO2-doped V2O5/FTO films at the wavelength of 700 nm. |
Figure 4 shows the SEM image of the prepared film tested at room temperature. In Figure 4(a) and (b), it can be found that the pure V2O5/FTO film was well fabricated with a dense surface. In Figure 4(c) and (d), it is observed that TiO2 nano powder has been evenly dispersed into the composite film. Figures show that TiO2 particles were predominantly found in proximity to grain boundaries with segregation behavior. The generation of pores may be related to the high annealing temperature during the preparation process. By comparison with Figure 4(a) and (b), it shows that the TiO2 nano powder has been doped into the composite film successfully.
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Figure 4 SEM micrographs of (a) (b) the pure V2O5/FTO film and (c) (d) the TiO2-doped V2O5/FTO film. |
The X-ray diffraction (XRD) profile of the pure V2O5/FTO film is shown in Figure 5(a). The diffractive angles of 26.36°, 33.64°, 37.64°, 51.40°, 61.48°, 65.34° correspond to (110), (101), (200), (211), (310) and (301) crystalized planes, respectively being consistent with the SnO2 standard card (JCPDS. NO. 46-1088). Figure 5(b) shows the XRD profile of the TiO2-doped V2O5/FTO film. The diffractive angles of SnO2 are almost consistent with the undoped film, and the diffractive angles of 20.12°, 21.56°, 31.02°, 40.92°, 42.38°, 54.48° correspond to (001), (101), (301), (002), (102) and (220) crystalized planes, respectively, which are consistent with V2O5 standard card (JCPDS. NO. 41-1426). The results indicate that the preparation of the TiO2-doped V2O5/FTO film has no effect on the crystal structure of FTO, and the main components of the film is composed of V2O5. The partial diffraction angle of (001) crystalized plane is finely shifted from 20.18° to 20.12° by comparing with the undoped film, which may due to the changing of the crystal structure of V2O5 after TiO2-doping. The grain size along the preferred orientation of V2O5 can be obtained according to the Scherrer formula:(2)
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Figure 5 XRD image of (a) the pure V2O5/FTO film and (b) the TiO2-doped V2O5/FTO film. |
Where D represents the grain size, k is the constant factor, λ is the wavelength of the X-ray, β is the full width half maximum (FWHM), and θ is the Bragg diffraction angle. After calculation, the undoped film has an average grain size of roughly 22.39 nm, while the doped film is about 27.51 nm.
The X-ray photoelectron spectroscopy (XPS) is performed to analyze the composition of the prepared films. Figure 6(a)–(c) show the general spectral line (0–1350 eV), O1s and V2p of the pure V2O5/FTO film, and Figure 6(d)–(g) exhibit the general spectral line (0–1350 eV), O1s, V2p and Ti2p of the TiO2-doped V2O5/FTO film, respectively. It can be seen in Figure 6(a) and (d) that the films does not contain other elements except O, V, Ti and C elements. In Figure 6(b) and (e), the peaks near 530 eV and 531.5 eV are associated with O2−, while O− near 533 eV. The appearance of O− peak division indicates that a small part of O elements have defects, resulting in the change from 2− ions to 1− ions. It can be found in Figure 6(b) that the O− peak appears a large reduction in contrast of Figure 6(e). The formation of oxygen vacancies is mainly related to the doping of TiO2 besides the residual HVO4. The above test results prove the existence of the vacancy. Theory and experiments show that the generation of vacancies makes the film more prone to a crystalline phase transition [25] and may improve the conductivity of the film. In Figure 6(c) and (f), the peaks near 517.6 eV and 525 eV of two orbital levels are associated with V5+, while V4+ near 515.8 eV and 523.8 eV. The less amount of V element presents 4+ state, which may be explained by the impurity of the V2O5 powder. The V5+ dominant peak and the V4+ inferior peak are in line with expectations. In Figure 6(g), the Ti peaks of occurring near 458.6 eV and 464.2 eV were 4+ ions, indicating that the TiO2 powder maintains its original morphology after incorporation.
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Figure 6 XPS spectra of the prepared films. (a) general spectral line (0–1350 eV), (b) O1s and (c) V2p of the pure V2O5/FTO film; (d) general spectral line (0–1350 eV), (e) O1s, (f) V2p and (g) Ti2p of the TiO2-doped V2O5/FTO film. |
Figure 7 displays the transmittance of the pure V2O5/FTO film and the TiO2-doped V2O5/FTO film in the wavelength range of 400–1600 nm at different temperatures from 20 °C to 360 °C. To ensure the measurement stability during the experiment, the heating rate was kept at 2 °C/min in measurement. Figure 7(a) shows the transmittance variations of the pure V2O5/FTO film in 400–1600 nm band. The film achieves a maximum transmittance of 62.084% at the wavelength of 700 nm at 150 °C. Figure 7(b) shows the transmittance variations in the 400–1600 nm band of the TiO2-doped V2O5/FTO film. The film achieves a maximum transmittance of 75.807% at the same conditions. As can be seen from the figure, the incorporation of TiO2 obviously improves the transmittance of the film at different temperatures. In the temperature range of 20–150 °C, the transmittance of both films gradually increases, speculating that the increasing trend is mainly due to the hydrophilic of the film [26]. In the temperature range of 150–360 °C, the transmittance of both films decreases, and it decreases most significantly from 250 °C to 300 °C, indicating that the phase transition has occurred in this range. The maximum optical modulation amplitude h(λ) is used to visualize the regulation properties of the films and it can be obtained by the following formula:(3)
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Figure 7 Transmittance spectra of (a) the pure V2O5/FTO film and (b) the TiO2-doped V2O5/FTO film under 20 °C, 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 360 °C; (c) The maximum optical modulation amplitudes of the pure V2O5/FTO film and the TiO2-doped V2O5/FTO film. |
Where Tmax(λ) and Tmin(λ) are the maximum and minimum transmittance of a certain wavelength under the test conditions, respectively. As shown in Figure 7(c), the maximum optical modulation amplitude of the pure V2O5/FTO film is 8.619% at 700 nm, and the average optical modulation amplitude in 400–1600 nm band is 4.450%. The maximum optical modulation amplitude of the TiO2-doped V2O5/FTO film is 18.282% at 700 nm and the average optical modulation amplitude in 400–1600 nm band is 7.423%. Comparing with the pure V2O5/FTO film. the maximum optical modulation of the film increases by 9.663% after TiO2-doping, and the average optical modulation from visible light to near-infrared band increases by 2.973%. It shows that the doping of TiO2 powder has improved the optical properties of the film under the changing of temperature. The increases of the transmittance are probably due to the bandgap broadening of the composite film and the blueshifting of optical absorption boundary caused by TiO2-doping.
To further investigate the electrical performance of TiO2-doping effect to V2O5 films, the MSM structures were fabricated based on the 12% TiO2-doped V2O5/FTO film and the pure V2O5/FTO film as shown in Figure 2, yielding to the FTO/V2O5-TiO2/FTO device and the FTO/V2O5/FTO device. The resistance of the devices was measured at temperatures from 20–360 °C under heating/cooling conditions. According to Figure 8(a), the resistance of the FTO/V2O5/FTO device is 177.60 kΩ at 20 °C, while 149.35 Ω of the FTO/V2O5-TiO2/FTO device, as shown in Figure 8(b). Comparing with the former device, the resistance of the latter reduces by 3–4 orders of magnitude, which may due to the change of the band structure of the material caused by TiO2-doping, or the amount of the oxygen vacancies corresponds to Figure 6(e). During the heating process, the resistance-temperature curve displays a downward trend in three stages: slowly decreases from 20 °C to 220 °C, significantly drops from 220 °C to 290 °C, and slowly decreases again from 290 °C to 360 °C. The minimum resistance reaches 84.08 Ω at 360 °C, reducing to 56.29% by comparison with the initial resistance of the device. The fraction with a rapider descent rate indicates that the device undergoes the SMT effect, i.e. the thermally induced phase transition properties. To each acquisition point, the first derivative of resistance with respect to temperature is taken and Gaussian nonlinear data fitting is used to plot the curves. According to Figure 8(c), the curve takes an extreme point at 259.91 °C/254.77 °C, which represents the phase transition temperature of the device based on V2O5 film with/without TiO2-doping, respectively. Both of them are close to the typical phase transition temperature of V2O5 at 257 °C. During the cooling process from 360 °C back to 20 °C, the curve of two devices are basically similar to that of heating process. The slight deviation is probably because of the internal environmental influence of the heating device which leads to the inhomogeneity of the temperature-field distribution. To further verify the cycling stability of the devices, the above heating and cooling processes were performed for several times, and the resistance of the devices were recorded each five cycles. It can be seen in the Figure 8(d) that after 25 cycles, the resistance of the FTO/V2O5-TiO2/FTO device decreases by 5.43%, while 64.80% of the FTO/V2O5/FTO device. Figure 8(e) displays the h(λ) (700 nm) of two devices under the thermal cycles. Obviously, the device based on the TiO2-doped V2O5/FTO film has a more stable thermal cycling ability.
![]() |
Figure 8 Resistance of the MSM structure based on (a) the pure V2O5/FTO film and (b) the TiO2-doped V2O5/FTO film under 20–360 °C; (c) Two devices’ scatter plots and Gauss nonlinear fitting curves of first order derivative of resistance with respect to temperature; (d) The ratio of the resistance changes and (e) the h(λ) (700 nm) of two devices under thermal cycles. |
Figure 9 shows the transmittance spectra of the FTO/V2O5-TiO2/FTO device and the FTO/V2O5/FTO device at 20 °C, 40 °C and 80 °C under the applied voltage of 0–5 V, respectively. As shown in Figure 9(a)–(c), the transmittance of the FTO/V2O5/FTO device decreases when the applied voltage increases, while the transmittance of the FTO/V2O5-TiO2/FTO device increases as the voltage increases as shown in Figure 9(d)–(f). The transmittance of the device based on the pure V2O5/FTO film decreases 5.777% at most at 700 nm as the voltage rises to 5 V at 20 °C, while 6.949% and 6.822% at the same wavelength and voltage at 40 °C and 80 °C, respectively. The transmittance the device based on the TiO2-doped V2O5/FTO film increases 8.821% at most at 650 nm as the voltage rises to 5 V at 20 °C, while 7.174% and 11.540% at 650 nm and 750 nm at the same voltage at 40 °C and 80 °C, respectively.
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Figure 9 Transmittance spectra of the FTO/V2O5/FTO device and the FTO/V2O5-TiO2/FTO device at 400–1600 nm with the applied voltage of 0–5 V under (a) (d) 20 °C, (b) (e) 40 °C and (c) (f) 80 °C. |
As mentioned above, TiO2-doping can modify the width of band gap by gap-filling or atom-displacing. Under the action of heating and voltage-applying, the valence band electrons in the device have been formed into the carrier and have been bumped to the conduction band, which increases the carrier concentration and mobility in the device [27]. In this case, the ions and electrons borrow faster transitions in a large specific surface area created by the pore structure of the composite film [28], leading to the altered transmittance. The transmittance curves of two kinds of the devices show different changing tendency under voltage-applying, indicating that the correlation electric-modulation performance of the film has changed after TiO2-doping. From the result, the FTO/V2O5-TiO2/FTO device has better electrical modulation performance than the FTO/V2O5/FTO device.
4 Conclusion
The TiO2-doped V2O5/FTO film was prepared by convenient and economical sol-gel method, and the photoelectric device with the MSM structure based on the prepared film was fabricated. The morphology, structure and composition of the film were studied, and the photoelectric properties of the device were further experimented. SEM results shows that the films have pores to improve conductivity, which corresponds to the O1s spectrum formation in XPS. XRD and XPS results show that TiO2 nano powder has been evenly dispersed into the film, and the film has shown a polycrystalline structure.
The TiO2-doped V2O5/FTO film undergoes a thermal phase transition near 259.91 °C, and the transmittance decreases substantially. The maximum modulation amplitude increases from 8.619% to 18.282%, increasing by 9.663% after 12% TiO2-doping. The resistance of the FTO/V2O5-TiO2/FTO device is 149.35 Ω at 20 °C. Comparing with the undoped thin-film devices, the resistance reduces by 3–4 orders of magnitude. During the heating process at 20–360 °C, the resistance decreases to 56.29%. The maximum transmittance variations of the FTO/V2O5-TiO2/FTO device in 400–1600 nm band with the applied voltage of 0–5 V can reach 8.821%, 7.174% and 11.540% at the temperature of 20 °C, 40 °C and 80 °C, respectively. By comparison with the FTO/V2O5/FTO device, the transmittance curves at the same conditions above are improved. All of the optical and electrical properties in this investigation have been cycled for several times, and the nanocomposite film shows excellent working stability.
Funding
This work was partly supported by the Foundation for Key Program of Ministry of Education China (Grant No. 207033), the National High Technology Research and Development Program of China (Grant No. 2006AA03Z348), the Shanghai Talent Leading Plan, China (Grant No. 2011-026), the Key Science and Technology Research Project of Shanghai Committee, China (Grant No. 10ZZ94).
Conflicts of interest
The authors declare no conflicts of interest.
Data availability statement
The research data are available on request from the authors.
Author contribution statement
The contributions of the authors are listed as follows:
Chang Xue-Investigation; Writing: original draft.
Yi Li-Conceptualization; Project administration; Supervision.
Haoting Zhang-Data curation.
Weiye He-Formal analysis.
Weiye Peng-Methdology.
Wenyan Dai-Software.
Zhen Yuan-Resources.
Ke Lin-Validation.
Wei Wang-Visualization.
Zhangqing Shi-Funding acquisition.
Hongwei Liu-Writing: review & editing.
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All Figures
![]() |
Figure 1 The preparation process of the TiO2-doped V2O5/FTO film. |
In the text |
![]() |
Figure 2 The structure of the device. |
In the text |
![]() |
Figure 3 Transmittance curves of the 10%, 12%, 15%, 20% TiO2-doped V2O5/FTO films at the wavelength of 700 nm. |
In the text |
![]() |
Figure 4 SEM micrographs of (a) (b) the pure V2O5/FTO film and (c) (d) the TiO2-doped V2O5/FTO film. |
In the text |
![]() |
Figure 5 XRD image of (a) the pure V2O5/FTO film and (b) the TiO2-doped V2O5/FTO film. |
In the text |
![]() |
Figure 6 XPS spectra of the prepared films. (a) general spectral line (0–1350 eV), (b) O1s and (c) V2p of the pure V2O5/FTO film; (d) general spectral line (0–1350 eV), (e) O1s, (f) V2p and (g) Ti2p of the TiO2-doped V2O5/FTO film. |
In the text |
![]() |
Figure 7 Transmittance spectra of (a) the pure V2O5/FTO film and (b) the TiO2-doped V2O5/FTO film under 20 °C, 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 360 °C; (c) The maximum optical modulation amplitudes of the pure V2O5/FTO film and the TiO2-doped V2O5/FTO film. |
In the text |
![]() |
Figure 8 Resistance of the MSM structure based on (a) the pure V2O5/FTO film and (b) the TiO2-doped V2O5/FTO film under 20–360 °C; (c) Two devices’ scatter plots and Gauss nonlinear fitting curves of first order derivative of resistance with respect to temperature; (d) The ratio of the resistance changes and (e) the h(λ) (700 nm) of two devices under thermal cycles. |
In the text |
![]() |
Figure 9 Transmittance spectra of the FTO/V2O5/FTO device and the FTO/V2O5-TiO2/FTO device at 400–1600 nm with the applied voltage of 0–5 V under (a) (d) 20 °C, (b) (e) 40 °C and (c) (f) 80 °C. |
In the text |
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