J. Eur. Opt. Society-Rapid Publ. 21, 6( 2025) 51
Figure 7. Transmittance spectra of( a) the pure V 2 O 5 / FTO film and( b) the TiO 2-doped V 2 O 5 / 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 V 2 O 5 / FTO film and the TiO 2- doped V 2 O 5 / FTO film.
259.91 ° C / 254.77 ° C, which represents the phase transition temperature of the device based on V 2 O 5 film with / without TiO 2-doping, respectively. Both of them are close to the typical phase transition temperature of V 2 O 5 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 / V 2 O 5- TiO 2 / FTO device decreases by 5.43 %, while 64.80 % of the FTO / V 2 O 5 / FTO device. Figure 8( e) displays the h( k)( 700 nm) of two devices under the thermal cycles. Obviously, the device based on the TiO 2-doped V 2 O 5 / FTO film has a more stable thermal cycling ability.
Figure 9 shows the transmittance spectra of the FTO / V 2 O 5-TiO 2 / FTO device and the FTO / V 2 O 5 / FTO device at 20 ° C, 40 ° Cand80 ° C under the applied voltage of 0 – 5 V, respectively. As shown in Figure 9( a)–( c), the transmittance of the FTO / V 2 O 5 / FTO device decreases when the applied voltage increases, while the transmittance of the FTO / V 2 O 5-TiO 2 / FTO device increases as the voltage increases as shown in Figure 9( d)–( f). The transmittance of the device based on the pure V 2 O 5 / FTO film decreases 5.777 % at most at 700 nm as the voltage rises to5Vat20 ° 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 TiO 2-doped V 2 O 5 / 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.
As mentioned above, TiO 2-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