A method for restoring the performance of electrochromic thin films

Abstract

The present invention discloses a method for restoring the performance of an electrochromic film, comprising: irradiating the electrochromic film with degraded performance, and applying a constant voltage to the electrochromic film while irradiating the light, so that the electrochromic film with degraded performance is restored to its initial performance. The method greatly improves the cycle stability and reversibility of the electrochromic material, and expands the application field of the "ion anti-capture" method.

Description

Technical Field

[0001] The invention relates to the technical field of electrochromic technology, and in particular to a method for restoring the performance of an electrochromic film. Background Art

[0002] Electrochromism is a phenomenon in which the optical properties of a material (reflectivity, transmittance, absorptivity, etc.) undergo stable and reversible color changes under the action of an external electric field, which is manifested in the appearance as a reversible change in color and transparency. This change can achieve a continuously adjustable ratio of the transmittance, absorptivity and reflectivity of the material. Amorphous WO3 is the most widely studied inorganic electrochromic material since the discovery of the electrochromic phenomenon more than 50 years ago. It has the advantages of high coloring efficiency, good reversibility, short response time, long life and low cost. In today's commercial electrochromic "smart windows", WO3 film is also the main optical functional part. Studies have shown that WO3 electrochromic films show a gradual attenuation of optical modulation ability in long-term electrochemical cycles.

[0003] The current academic report of the long-term action of constant current or constant voltage to induce ion anti-capture technology is a very innovative method. Its main content is to apply a constant voltage or constant current in the opposite direction of ion insertion to the cycle-degraded WO3 film. After a long-term electrochemical action (about 20 hours), the performance of the WO3 film can return to the initial cycle state. However, when using the constant current or constant potential method, the voltage usually needs to reach 5.7V (vs. Li / Li + Unless otherwise specified, the voltages mentioned below are vs. Li / Li + ) or even higher, and such high voltage for a long time will usually cause the organic electrolyte used in the cycle to decompose, which is not conducive to long-term use in real life.

[0004] Therefore, the prior art needs to be further improved and enhanced. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for restoring the performance of an electrochromic film, aiming to solve the problem that the existing use of high voltage to restore the performance of an electrochromic film will cause the organic electrolyte used in the cycle to decompose.

[0006] A method for restoring the performance of an electrochromic film, comprising: irradiating the electrochromic film with degraded performance, and applying a constant voltage to the electrochromic film while irradiating the light, so that the electrochromic film with degraded performance is restored to its initial performance.

[0007] Optionally, in the method for restoring the performance of an electrochromic film, the electrochromic film with degraded performance is irradiated with light, wherein the wavelength of light used for the irradiation is no greater than 405 nm.

[0008] Optionally, in the method for restoring the performance of the electrochromic film, the constant voltage is greater than the open circuit voltage of the electrochromic film.

[0009] Optionally, in the method for restoring the performance of an electrochromic film, the electrochromic film is a cathode electrochromic film.

[0010] Optionally, in the method for restoring the performance of an electrochromic film, the cathode electrochromic film contains an electrochromic metal oxide, and the electrochromic metal oxide is selected from any one of tungsten trioxide, titanium dioxide, tantalum pentoxide, molybdenum trioxide and niobium pentoxide.

[0011] Optionally, in the method for restoring the performance of the electrochromic film, the constant voltage is no greater than 4.5V.

[0012] Optionally, the method for restoring the performance of the electrochromic film, wherein the step of irradiating the electrochromic film with degraded performance with light and applying a constant voltage to the electrochromic film while irradiating the light, specifically comprises:

[0013] The electrochromic film with degraded performance and the auxiliary electrode are placed in an electrolytic cell and electrically connected to an electrochemical workstation respectively;

[0014] The electrochromic film with degraded performance is irradiated with light, and a constant voltage is applied to the electrochromic film with degraded performance by using the electrochemical workstation.

[0015] Optionally, in the method for restoring the performance of the electrochromic film, the light is ultraviolet light and the irradiation time is 3-20 hours.

[0016] Beneficial effects: Compared with the prior art, the method of restoring the performance of the electrochromic film of the present invention uses a combination of light and constant voltage to act on the electrochromic film with degraded performance at the same time. Through the photoelectric synergistic effect, the trapped ions in the degraded electrochromic film can escape from the capture site and return to the electrolyte. Therefore, the photoelectric synergistic method can achieve the same film refreshing effect as constant current and constant potential, and can restore the WO3 film with degraded performance to the initial cycle stage. At the same time, it ensures that the electrolyte is not decomposed. And through verification, it can also be achieved on other cathode electrochromic metal oxides. This method greatly improves the cycle stability and reversibility of electrochromic materials, and expands the application field of the "ion anti-capture" method. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the method for restoring the performance of the electrochromic film in the embodiment.

[0018] Figure 2 The in-situ transmittance and charge capacity changes of WO3 film at 550nm wavelength before and after different anti-capture processes.

[0019] Figure 3 This is the spectrum change diagram of WO3 at 400-1100nm before and after the combined action of 285nm ultraviolet light and 4.0V constant voltage.

[0020] Figure 4 This is a graph showing the changes in in-situ transmittance and charge capacity of WO3 film at 550nm wavelength before and after the combined action of light of different wavelengths and 4.0V constant voltage.

[0021] Figure 5 This is a graph showing the changes in in-situ transmittance and charge capacity of WO3 film at 550nm wavelength before and after the combined action of 285nm ultraviolet light and 3.7V constant voltage.

[0022] Figure 6 This is a graph showing the changes in in-situ transmittance and charge capacity of WO3 film at 550nm wavelength under different CV cycle conditions before and after the combined action of 285nm ultraviolet light and 4.0V constant voltage.

[0023] Figure 7 This is a graph showing the changes in in-situ transmittance and charge capacity of TiO2 film at 550nm wavelength before and after the combined action of 285nm ultraviolet light and 4.0V constant voltage.

[0024] Figure 8 This is a graph showing the changes in in-situ transmittance and charge capacity of Nb2O5 film at 550nm wavelength before and after the combined action of 285nm ultraviolet light and 4.0V constant voltage.

[0025] Fig. 9 This is a graph showing the changes in in-situ transmittance and charge capacity of Ta2O5 film at 550nm wavelength before and after the combined action of 285nm ultraviolet light and 4.0V constant voltage. DETAILED DESCRIPTION

[0026] The present invention provides a method for restoring the performance of an electrochromic film. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] In order to solve the problem that the conventional constant voltage is used to restore the performance of the degraded electrochromic film, the organic electrolyte used in the cycle is easily decomposed.

[0028] This embodiment provides a method for restoring the performance of an electrochromic film, such as Figure 1 As shown, the method for restoring the performance of the electrochromic film includes: irradiating the electrochromic film with degraded performance, and applying a constant voltage to the electrochromic film while irradiating the light, so that the electrochromic film with degraded performance is restored to its initial performance.

[0029] Specifically, an electrolytic cell is provided, a small amount of electrolyte is injected into it, an electrochromic film with degraded performance and an auxiliary electrode are placed in the electrolyte, and electrically connected to an electrochemical workstation through a wire, that is, the electrochemical workstation can be used to provide a constant voltage for the electrochromic film with degraded performance. A light source, such as an ultraviolet lamp, is arranged outside the electrolytic cell. The ultraviolet lamp is used to vertically irradiate the electrochromic film with electrochemical cycle degradation with ultraviolet light through the electrolytic cell and a small amount of electrolyte, and at the same time, a constant voltage (CA) is applied to the electrochromic film using the electrochemical workstation, thereby achieving the effect of photoelectric interaction.

[0030] In this embodiment, the constant voltage provided by the electrochemical workstation is a low voltage (relative to the existing constant voltage), and in principle, any voltage greater than the open circuit voltage of the electrochromic film can be used. In actual operation, the voltage value can be set to be slightly greater than the open circuit voltage of the electrochromic film.

[0031] In this embodiment, illumination is combined with constant voltage to act on the electrochromic film with degraded performance at the same time. Through photoelectric synergy, the electrolyte ions captured in the degraded electrochromic film can escape from the capture site and return to the electrolyte. Therefore, the photoelectric synergy method can achieve the same film refreshing effect as constant current and constant potential, and can restore the degraded WO3 film to the initial cycle stage. And through verification, it can also be achieved on other cathode electrochromic metal oxides. This method greatly improves the cycle stability and reversibility of electrochromic materials, and expands the application field of the "ion anti-capture" method.

[0032] The method for restoring the performance of the electrochromic film provided by the present invention is further explained and illustrated by means of specific preparation examples.

[0033] Example

[0034] 1. Preparation of electrochromic thin films

[0035] WO3 thin film was deposited on ITO glass using DC magnetron sputtering equipment. WO3 was deposited by reactive sputtering using a three-inch tungsten metal target. The sample stage was rotated during the deposition process to maintain uniform film thickness. During the film deposition process, the distance from the center of the target to the substrate was 110 mm, thus obtaining a transparent WO3 thin film.

[0036] 2. Electrochemical and optical characterization of WO3 electrochromic films

[0037] The WO3 film was electrochemically tested using a three-electrode system in a glove box (water and oxygen content were all less than 0.01ppm). The electrolyte was a 1M lithium perchlorate (LiClO4) propylene carbonate (PC) solution, the counter electrode and reference electrode were both Li foil, and the working electrode was the WO3 film. Cyclic voltammetry (CV) was used to perform long-term electrochemical cycles on the WO3 film. CV was performed in a voltage window of 2.0-4.0V, with a scan rate of 20mV / s and a scan number of 200-1000 cycles. Another CV cycle was a voltage window of 1.5-4.0V, a scan rate of 10mV / s, and a scan number of 20 cycles. The charge in each cycle can be measured by CV, and the use of This formula can be used to calculate the result. Where j is the current density, s is the scan rate, and V is the voltage. The time constant potential method (CA) is used to extract lithium ions trapped in the WO3 film. During the CA process, the direction of the constant potential is applied in the opposite direction of the lithium ions inserted into the WO3 film. The magnitude of the constant potential does not exceed 4.0V.

[0038] In-situ optical transmittance is recorded by spectrometer. The spectral range is 400-1100nm. The sample is placed in a rectangular quartz electrolytic cell, which is placed between a tungsten halogen lamp and a detector. The transmittance of light passing through the electrolytic cell filled with electrolyte is set to 100%. Both the full spectrum and the single wavelength spectrum are measured in-situ during the test.

[0039] 3. The photoelectric synergistic method can basically restore the performance of the degraded WO3 electrochromic film to its initial state.

[0040] The electrochemical cycle of WO3 was carried out in 1M LiClO4 PC solution using a three-electrode system. The electrochemical window was 2.0-4.0V and the scan rate was 20mV / s. After 20 hours of constant potential at 4.0V and 285nm UV irradiation, Figure 2 , Figure 3 As shown in the figure, both the electrochemical performance and the optical modulation ability of the tungsten trioxide film have basically recovered to their initial state. Figure 2 The results show that when only 4.0V constant voltage is applied, the film is not refreshed. Similarly, when only UV light is irradiated, the film still does not recover. This result shows that when low voltage and UV light irradiation act alone, they are unable to restore the electrochromic properties of WO3 film. Only light and electrochemical methods can do this.

[0041] Figure 4To show the refreshing effect of different wavelengths of light and 4.0V constant voltage on the performance of WO3 film, 285nm, 305nm, 365nm, 405nm and 450nm wavelengths of light were used in succession with 4.0V constant voltage to act on the decayed tungsten trioxide film. Figure 4 As shown, both the regulation ability of 550nm wavelength light and the electrochemical cycling effect prove that when the constant voltage is 4.0V, the ion anti-capture effect of 305nm, 365nm and 405nm light is similar to that of 285nm ultraviolet light, and can restore the film performance, while the ion anti-capture effect of 450nm wavelength light is inferior to that of other wavelengths of light.

[0042] Figure 5 The results show that when the voltage is 3.7V and 285nm ultraviolet light is applied simultaneously, the film's performance is almost completely restored, both in terms of its ability to regulate 550nm wavelength light and its electrochemical cycling effect. However, when the voltage drops to 3.65V, the film's performance is also restored, but only halfway.

[0043] 4. The photoelectric synergistic method has a recovery effect on the decayed WO3 film under different cycle conditions.

[0044] The performance degradation of WO3 film varies under different cycle conditions, and the states of captured electrolyte ions in WO3 are also different, including shallow site capture, deep site capture, and irreversible capture. To verify whether the optoelectronic synergistic method has the same refreshing effect on WO3 decayed under different conditions, we continuously cycled the same tungsten trioxide film under the cycle conditions of 2.0-4.0V voltage window and 20mV / s scan rate for 500 and 1000 cycles, and 1.5-4.0V voltage window and 10mV / s scan rate for 20 cycles, and after each cycle stage, the decayed WO3 film was cycled for 20 hours using 285nm ultraviolet light irradiation and 4.0V constant voltage. Figure 6It shows that under the cycling conditions of 2.0-4.0V 20mV / s, the attenuation of the film charge capacity and the control ability at a single wavelength of 550nm after 1000 cycles is greater than that of 500 cycles. However, no matter whether the film is cycled 500 or 1000 times, it can almost recover to the initial cycle state after the joint action of photoelectric coupling, which shows that the shallow site capture generated under the cycling conditions of 2.0-4.0V 20mV / s is basically eliminated under the action of photoelectric synergy. The results of multiple actions of photoelectric synergy on the same sample also show that the photoelectric synergy method can refresh the film repeatedly. After the process of photoelectric synergy on ion anti-capture is completed, we continue to cycle the film under the cycling conditions of 2.0-4.0V 20mV / s for 100 cycles, and then cycle it under the cycling conditions of 1.5-4.0V, 10mV / s for 20 cycles. The in-situ spectral results at 550nm show that under this cycling condition, the control ability of the film in the bleaching state and coloring state is seriously decayed, and the number of ions inserted per cycle is also significantly reduced. Different from the previous case, the degradation of WO3 film under 1.5-4.0V 10mV / s cycling condition is due to the generation of deep site capture. After 20 hours of 4.0V constant voltage and 285nm UV irradiation, the film was cycled for 50 cycles under 2-4V 20mV / s cycling condition. Figure 6 It is shown in the figure that after the photoelectric method is implemented, the film returns to the cycle state under the same conditions as before the deep sites are generated. It can be seen that the film's cycle ability is basically restored to the state before the deep sites are generated, indicating that the photoelectric synergy method can also be used to release ions captured by the deep sites. The reason why it did not fully return to the initial cycle state may be that the generation of irreversible sites trapped a small number of ions inside and could not move.

[0045] 5. The photoelectric synergistic effect has a refreshing effect on the performance of other cathode electrochromic films.

[0046] Other cathode electrochromic films were deposited on ITO glass with square resistance by DC magnetron sputtering equipment. The target material was three-inch metal. During the deposition process, the sample stage rotated to keep the film thickness uniform. During the film deposition process, the distance from the center of the target to the substrate was 110mm, and a transparent metal oxide film was obtained.

[0047] The electrochemical cycle of TiO2 was carried out in 1M LiClO4 PC solution using a three-electrode system. The electrochemical window was 1.25-4.0V and the scan rate was 20mV / s. Figure 7 As shown in the figure, after 250 electrochemical cycles, the charge capacity of TiO2 and its ability to regulate light with a wavelength of 550nm decreased significantly. After 20 hours of constant potential at 4.0V and 285nm ultraviolet light irradiation, they both returned to the initial cycle state.

[0048] The electrochemical cycle of Nb2O5 was carried out in 1M LiClO4 PC solution using a three-electrode system. The electrochemical window was 1.5-4.0V and the scan rate was 20mV / s. Figure 8 As shown in the figure, after 650 electrochemical cycles, the charge capacity of Nb2O5 and its ability to regulate light with a wavelength of 550nm decreased significantly. After 20 hours of constant potential at 4.0V and 285nm ultraviolet light irradiation, they both returned to the initial cycle state.

[0049] The electrochemical cycle of Ta2O5 was carried out in 1M LiClO4 PC solution using a three-electrode system. The electrochemical window was 1.5-4.0V and the scan rate was 20mV / s. Fig. 9 As shown in the figure, after 200 electrochemical cycles, the charge capacity of Ta2O5 and its ability to regulate light with a wavelength of 550nm decreased. After 20 hours of combined action of a constant potential of 4.0V and 285nm ultraviolet light irradiation, they returned to the initial cycle state. Even the regulation ability in the first few cycles after the photoelectric synergistic effect was greater than that in the initial cycle.

[0050] In summary, the present invention provides a brand-new method to enable cathode electrochromic films such as WO3 and TiO2 to return to their initial state after decay, greatly improving the cyclability and reversibility of the electrochromic film. It should be noted that similar recovery effects cannot be produced only when illumination and a relatively low constant voltage are applied, and photoelectric effects must be combined. When using the photoelectric synergistic method, the wavelength range of the light is ≤405nm, and when the energy of the light is large enough, the voltage is greater than the open circuit voltage of the film. For example, the performance of the WO3 film can be restored by the combined action of 285nm ultraviolet light and a constant voltage of 4.0V. Subsequently, it can be applied to the recovery of the performance of multilayer thin-film electrochromic devices (including substrate, transparent bottom electrode layer, electrochromic layer, electrolyte layer, ion storage layer and transparent top electrode layer), which has certain operability, innovation and foresight.

[0051] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for restoring the performance of an electrochromic film, characterized in that: include: Exposing light to a cathode electrochromic film containing an electrochromic metal oxide whose performance has degraded, and applying a constant voltage to the electrochromic film while irradiating the light, so that the electrochromic film whose performance has degraded is restored to its initial performance; The wavelength of light used is no greater than 405 nm.

2. The method for restoring the performance of an electrochromic film according to claim 1, characterized in that: The constant voltage is greater than the open circuit voltage of the electrochromic film and less than the electrolyte decomposition voltage.

3. The method for restoring the performance of an electrochromic film according to claim 1, characterized in that: The cathode electrochromic film contains an electrochromic metal oxide, and the electrochromic metal oxide is selected from any one of tungsten trioxide, titanium dioxide, tantalum pentoxide, molybdenum trioxide and niobium oxide.

4. The method for restoring the performance of an electrochromic film according to claim 1, characterized in that: The constant voltage is no greater than 4.5V.

5. The method for restoring the performance of an electrochromic film according to claim 1, characterized in that: The step of irradiating the electrochromic film with degraded performance with light and applying a constant voltage to the electrochromic film during the irradiation specifically includes: The electrochromic film with degraded performance and the auxiliary electrode are placed in an electrolytic cell and electrically connected to an electrochemical workstation respectively; The electrochromic film with degraded performance is irradiated with parallel light, and a constant voltage is applied to the electrochromic film with degraded performance by using the electrochemical workstation.

6. The method for restoring the performance of an electrochromic film according to claim 5, characterized in that: The light used for the illumination is ultraviolet light, and the irradiation time is 3-20 hours.

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