RU2758579C2 - Method and software and hardware complex for controlling electrochromic devices - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electronic devices for controlling electrochromic products designed to regulate flows of light and radiant thermal energy. A method for controlling electrochromic devices with thin-film electrochromic layers separated by a layer of optically neutral electrolyte is proposed. At the beginning, an electrochromic device is subjected to multiple pre-operational effects with stabilized direct current within a permissible value of the current density in a coloring-pause, discoloration-pause mode with a gradual increase in voltage and registration of spectral-optical, temperature and volt-ampere characteristics, then, in an operating mode, the electrochromic device is switched according to a coloring-relaxation-pause-relaxation, discoloration-relaxation-pause-relaxation scheme, while, at stages of coloring and discoloration, the power of stabilized direct current is limited so that the current density does not exceed the maximum permissible value, at relaxation stages, electrodes of the device are opened, and the voltage on electrodes, light transmission and temperature of the device are controlled, at pause stages, electrodes are connected to a current stabilizer and the current, voltage on electrodes, light transmission and temperature of the device are controlled.

EFFECT: increase in the operational life of electrochromic devices, while maintaining initial parameters.

3 cl, 5 dwg

Description

The invention relates to electronic devices for controlling electrochromic products designed to regulate the fluxes of light and radiant thermal energy.

Electrochromic devices (ECD) are multilayer electrochemical cells capable of reversibly changing the optical properties under the action of an electric current due to the occurrence of topochemical redox reactions. ECU most often consists of transparent substrates, conductive layers, an electrochromic film, a counter electrode, and an electrolyte. The electrochromic oxide layer is located on a substrate, which is usually used as an industrial conductive glass; however, it is possible to use polymer films with a conductive ITO layer. Electrochromic materials have mixed ionic and electronic conductivity. They change their optical properties depending on the injection / extraction of charge (electrons and ions).

Electrochromic materials used in electrochromic devices are generally inorganic due to their thermal stability. It is expedient to use metal oxides as inorganic electrochromic materials. Most of these are known as structures built from MeO ₆ octahedra. At the moment, several oxide electrochromic materials are known, such as WO ₃ , V ₂ O ₅ , TiO ₂ , Cr ₃ O ₈ , NiO, MoO ₃ . Electrochromic devices with high staining efficiency are characterized by intense discoloration (transparency) with minimal energy consumption. In the general case, this effect is described by a reversible topochemical redox reaction, including the incorporation of lithium ions, described by the equation (for example, WO ₃ ): WO ₃ + xLi + xe↔Li _x WO ₃ .

At present, ECS based on a combination of thin electrochromic layers of WO ₃ and NiO are considered to be the most promising due to the combination of blue coloration for reduced WO ₃ and brown or black coloration for NiO. Films of these oxides are typical examples of cathode and anodic electrochromic materials, respectively. Electrochromic materials can exist in different phases and have crystalline, polycrystalline or amorphous structures depending on the annealing temperature, which determines different coloring / decolouring mechanisms.

Li-ion batteries are the closest to ECS in terms of the ongoing electrochemical processes. Like accumulators, the ECU stores the energy accumulated in the anode and cathode regions of the system without additional energy consumption, which allows it to maintain the selected level of light transmission. However, the main distinguishing feature of ECS is the need to manufacture all constituent materials from optically transparent components, which significantly complicates the production process. During operation, the active electrodes of the ECU during the course of electrochromic coloring / discoloration reactions undergo a regular change in the polarity of the power supply (up to 10 ⁸ cycles), which can lead to their overoxidation (re-reduction), accompanied by the degradation of electrochromic materials as a result of side electrochemical reactions. Local uncontrolled side thermodynamic electrochemical reactions over time can enhance the degradation of the active layers of ECS. This explains the large number of scientific publications and patents for inventions devoted to the study of ECS processes in order to increase their service life.

There are several main ways of loading ECS to avoid the above negative effects. So, for example, in patents EP 0475847, US 7277215, EP 0718667, US 4535329 it is proposed to work in the range of stability of the redox potential. The potential sensor is implemented using a third electrode. The use of a three-electrode system complicates the technological process of ECU production and increases costs due to additional research.

Also, to solve these problems, cyclic voltammetry is used (US Pat. RU 2492516). The complexity of this approach lies in the fact that ECUs manufactured using different technologies have different parameters, such as near-anode and near-cathode capacities and leakage currents, which cannot be measured by direct methods. The disadvantage of this approach is that in the process of loading the ECS, these parameters change, which does not allow the control controller to adequately assess the state of the ECS and ensure its operation.

Another way of loading ECS, which does not lead to its degradation, is to calculate the charge flowing in the structure of the sample by integrating the current in time, measuring the ECU voltage and limiting it to the safe limit of the redox potential, as, for example, in patents WO 2016115166, US 4512637 , RU 2492516. Also, a prerequisite for loading the ECU is the stabilization of direct current at a current density of about 50 μA / cm ² .

Closest to the proposed method and device is the method and device declared in patent RU 2655657 C1. In the method of controlling electrochromic light modulators with thin-film electrochromic and / or charge-buffer layers separated by an optically neutral electrolyte layer, the voltage arising on the electrochromic light modulator as a result of its forced charge / discharge with an electric current or self-discharge, correlating with optical transmission of the light modulator. The necessity and direction of the control action is determined by comparing the voltage across the electrochromic light modulator with the required operating voltage, determined based on the measurement of illumination and / or set by the user. The duration of the control action is limited by the moment of coincidence of the required operating voltage and the voltage on the electrochromic light modulator. The regulating action to increase the voltage across the electrochromic light modulator is direct current transmission in the forward direction from the anode to the cathode, and the regulating action to reduce the voltage is a short-term or permanent short-circuit of the anode and cathode. The value of the direct current density is selected depending on the area of the connected electrochromic light modulator in the range from 0 to 500 mA / cm ² . The range of values of the required operating voltage is limited by the difference in standard potentials of electrochemical reactions occurring in the electrochromic (anodic and / or cathodic) or charge-buffer layers at the current temperature of the light modulator. In the event of an emergency power outage, the electrochromic light modulator is returned to the state of maximum light transmission by short-circuiting the anode and cathode.

The main disadvantage of the known solution is that it uses the correlation of the optical transmission of the electrochromic light modulator with the voltage arising on it as a criterion for generating a regulatory effect. This criterion is necessary but not sufficient.

The disadvantage of this technical solution is the need for preliminary determination of the safe voltage of the redox potential for a specific ECS, which can change during operation, which will lead to inconsistent operation of the ECS and the control controller and early degradation of its layers.

Another disadvantage of the technical solution is the absence of a DC stabilization unit. The need for a current stabilizer is confirmed in the analogs discussed above, while the current density should not exceed a given value.

The disadvantages of the technical solution include the use of an emergency mode of the so-called "short circuit of the anode and cathode". In this mode, there is no need to reverse the polarity of the power supply of the ECU, but this approach is suitable for ECS with certain technical characteristics, in particular, with a high internal resistance and corresponding near-electrode capacitances. In other cases, a short circuit will lead to the destruction of electrochromic layers due to the flow of extreme currents and to the failure of the ECU. Also, the short-circuit mode assumes the presence of a certain potential on the electrodes of the ECU in the colored state, however, as a result of leaks, this potential will decrease over time, i.e. the relaxation process will take place, which will lead to incomplete discoloration of the ECH. In addition, as the authors of the patent themselves note, for reliable and safe operation of the controller, it is necessary to experimentally determine the electrophysical and electrochemical characteristics of the active layers of the ECS. Thus, the known solution does not provide long-term and safe operation of the electrochromic device.

The technical result of the claimed invention is to increase the service life of electrochromic devices while maintaining the original parameters.

The technical result is achieved by the fact that at first the electrochromic device is subjected to multiple pre-operational exposure to a stabilized direct current within the permissible current density in the coloring-pause, discoloration-pause mode with a gradual increase in voltage and registration of spectral-optical, temperature and current-voltage characteristics, determine the optimal operating range of the electrical energy supplied to the device, correlating with the light transmission, after which the device is switched in a mode specified by the user.

The pre-operational effect is carried out with increasing voltage so that the range of change in the light transmission of the electrochromic device is gradually increased from 5% to 75% compared to the initial value.

In the operating mode, the electrochromic device is switched according to the coloring-relaxation-pause-relaxation, bleaching-relaxation-pause-relaxation scheme, while at the stages of staining and bleaching, the current strength is limited so that the density of the stabilized direct current does not exceed the maximum permissible value, at stages relaxation, the electrodes are opened and the characteristics of the electrochromic device are controlled, at the pause stages the electrodes are connected to the current stabilizer and the characteristics of the electrochromic device are controlled.

The software and hardware complex for controlling electrochromic devices contains a control unit that determines the operating modes, a microcontroller with installed software that controls the switch units, voltage regulation, current stabilizers and receives data from the light transmission and temperature measurement units and measures the current and voltage levels. The power supply is connected to the voltage regulation unit, which receives a command from the microcontroller about the stabilized voltage level and supplies it to the current stabilizer unit for staining / discoloration modes. The switch unit connecting the electrochromic device to the current stabilizer unit 1 for staining / discoloration modes and to the current stabilizer unit 2 for pause modes is connected to the current and voltage measuring unit.

The essence of the claimed invention is illustrated by drawings, which show the following:

Figure 1 is a block diagram of the software and hardware complex, on which all blocks are indicated.

Figure 2 shows the dynamic current-voltage characteristic of the ECA at the initial stage of pre-operational electroforming.

Figure 3 shows the dependence of light transmission on energy consumption at the initial stage of pre-operational electroforming.

Figure 4 shows the dynamic current-voltage characteristic of the ECA at the final stage of pre-operational electroforming.

Figure 5 shows the dependence of light transmission on energy consumption at the final stage of pre-operational electroforming.

To test the method and program-technological complex electrochromic device with an active working of 2500 mm square were used ² comprising anodic electrochromic based layer TiO ₂ obtained by applying the sol-gel on the electrode (glass with a tin oxide coating doped with fluorine (FTO) ) using a centrifuge and annealed at a temperature of 300 ° C for 1 hour, the thickness of the electrochromic layer was 150 nm. Cathode electrochromic layer based on WO ₃ obtained by applying a sol-gel to an electrode (glass coated with fluorine-doped tin oxide (FTO)) using a centrifuge and annealed at 350 ° C for 1.5 hours, the thickness of the electrochromic layer was 200 nm. Electrical contacts to the electrochromic layers were applied along the perimeter of the glasses with silver conductive glue from Keller (resistance 0.06 Ohm⋅mm ² ). A model liquid solution of LiClO ₄ in propylene carbonate was used as the electrolyte, while the electrolyte thickness was limited by the thickness of the dielectric spacer, which was 0.5 mm. The ECU was sealed with CERESIT silicone sealant along the perimeter, while the layer thickness was 2 mm. After manufacturing, the sample was kept under a mechanical load of 200 g / cm ² for 36-48 hours at a temperature of 20-30 ° C. Several dozen samples were manufactured using this technology.

After holding the ECU under a mechanical load, the sample was subjected to a primary electrical action - pre-operational electroforming. The initial stage of ECU electroforming consisted in a multistage method of primary electrical impact, including the following stages: painting; pause; bleaching; pause.

The staining stage was characterized by the flow of a constant stabilized current with a density of up to 30 μA / cm ² during the time interval required to reduce the light transmission to 87% relative to the initial transmission in the near-IR region (the wavelength is 950 nm). Measurements of light transmission in the near-IR range can improve the measurement accuracy by 4-5 times compared to measurements in the visible range with a wavelength of 400-780 nm. In this case, the voltage on the ECU electrodes corresponds to the safe limits of the redox potential (up to 3.1 V) at a temperature of 22 ° C (the dynamic current-voltage characteristic is shown in Fig. 2). FIG. 3, number 1 denotes the dependence of light transmission on energy consumption before electroforming.

The pause after staining implies the ECU operation in the mode of connecting the ECU electrodes to the current stabilizer 2, while the current density level did not exceed 20 μA / cm ² (Fig. 2). The pause time interval was 60 s, which ensured the ECU discharge to a residual voltage of 5 mV.

The stage of discoloration is characterized by the flow of a constant stabilized current with a density of up to 40 μA / cm ² during the time interval required to increase the optical transmission to the initial level of light transmission (Fig. 2), while the voltage on the ECU electrodes corresponds to the safe limits of the redox potential (up to 3.1 V) at a temperature of 22 ° C.

The pause after bleaching implies the operation of the ECU in the mode of closing the ECU electrodes to the current stabilizer 2, while the current density level does not exceed 30 μA / cm ² (Fig. 2). The pause time interval was 120 s, which ensured the ECU discharge to a residual voltage of 3 mV.

The measurements of the characteristics (voltage, current, and light transmission in the near-IR region) were carried out every 500 ms, while the repetition frequency of the points on the recorded dependences characterizes the rate of the electrochemical processes in the ECU.

The criterion for the correct choice of the pre-operational exposure mode is the correlation of the speed and range of changes in light transmission with the amount of consumed electrical energy (Fig. 3.). Repeated repeated cyclic exposure leads to a decrease in energy consumption for dyeing - by 25%, discoloration - by 20%, which indicates the effectiveness of the initial stage of electroforming.

With a gradual increase in voltage, the working range of electrical parameters was reached, at which the final stage of electroforming was carried out, which consisted in a multistage method of repeated repeated electrical exposure in the painting-pause, discoloration-pause mode.

FIG. 2 and 4 show the dynamic current-voltage characteristics in the mode of pre-operational electroforming of the sample described above. FIG. 2 - the initial stage of electroforming; fig. 4 - the final stage of electroforming, with 1 cycle in FIG. 2 - characteristic of the unformed structure, 4 cycle in FIG. 4 shows a characteristic of a molded structure. The characteristics show 4 areas with negative differential resistance: staining, pause; discoloration, pause. Negative differential resistance is characterized by a violation of Ohm's law in such a way that with increasing voltage, the current decreases. An element with a negative differential resistance does not consume electrical energy, but gives it to the circuit, i.e. is the active element. This is due to some source entering its circuit that replenishes the supply of energy in the circuit. The nature of the negative differential resistance of various active elements is diverse, for example, in tunnel diodes, thyristors, gas-discharge plasma devices, devices with buffer charge-barrier layers. If the absolute value of the negative differential resistance is less than the sum of the positive resistances of the remaining elements of the circuit, then its role is reduced to partial compensation of losses in the circuit. If the negative resistance exceeds this amount, then this means that the state of the circuit is unstable and oscillations (oscillations of current and voltage) are possible, which is observed in the dynamic volt-ampere characteristics (Figs. 2 and 4).

To assess the work of the ECU, the dependence of its light transmission in the IR region on the consumed energy was made (Figs. 3 and 5). FIG. 3 - the initial stage of electroforming; fig. 5 - the final stage of electroforming with 1 cycle in FIG. 3 - characteristic of the unformed structure, 4 cycle in FIG. 5 shows a characteristic of a molded structure.

As a result of ECU cycling, the energy consumption for electrochemical staining / decoloration processes decreases, while the light transmission range increases. Repeated repeated cyclic exposure leads to a decrease in energy consumption at the final stage: for dyeing - by 3 times, for discoloration - by 34%. The positive effect of electroforming can be associated with a change in the outer electron shells of the atoms of the electrochromic layer of WO ₃ , with the appearance of waves of electron density, which promote the passage of lithium ions in the WO ₃ film and change its color. The characteristic of the pre-operational impact is the increase in the total ECU capacity by 8.3 times, while the total resistance decreases by 46 times. In this case, the activation of the electrochromic layers occurs, which makes it possible to increase the service life of the electrochromic device by 38%.

For the tested ECU sample, the optimal range of light transmission was from 92% to 30% (Fig. 5.). The operation of the ECU in this range made it possible to increase the operational life of the ECU without deteriorating its characteristics.

The efficiency for each section of the ECU operation (Fig. 5) was determined by the formula:

where:

ΔT is the interval of light transmission in this section of the dependence T = ƒ (E);

S is the active working area of the ECU;

ΔЕ is the energy interval spent on the electrochemical reaction process, providing the corresponding ΔТ interval of light transmission.

The overall efficiency increased at the initial stage: for staining - by 36%, for discoloration - by 20%, compared to unformed ECU, and at the final stage: for staining - 3 times, for bleaching - by 32%. In the pause mode after bleaching, the coloration process takes place due to the internal stored energy on the counter electrode.

After the pre-operational tests, the user sets on the control unit the required levels of light transmission and the ranges of the ECU operation time in the painted and discolored state, depending on the time of day.

The blocks of the complex work like this. The control unit is a computer for the electroforming stages and a control panel for the ECU operation modes. The microcontroller unit receives user-specified information from the control unit about the ECU operating modes and time, after which it controls the units: switch, voltage regulation, current stabilizer 1 for staining / discoloration modes, current stabilizer 2 for pause modes, and interrogates the current and voltage measurement unit for ECU electrodes and a block for measuring light transmission depending on the time of day. The microcontroller, depending on the ECU temperature, selects the optimal voltages and currents for the staining / decoloration modes for a given level of light transmission in the most efficient section of the ECU operation, determined by the minimum energy consumption at the final stage of pre-operational electroforming. In case of emergencies, the microcontroller switches the ECU to the relaxation mode.

The power supply provides a constant, stabilized voltage to the voltage control unit.

The voltage regulation unit receives a command from the microcontroller about the level of the required stabilized voltage and supplies it to the current stabilizer unit 1.

The current stabilizer unit 1 receives a command from the microcontroller about the level of the required stabilized current and supplies it to the switch unit and to the current and voltage measurement unit.

The unit for measuring the current and voltage on the ECU electrodes is interrogated by the microcontroller, after which the unit measures the current with a frequency specified by the user.

The switch unit connects the ECU to the power source or to the current stabilizer unit for the pause mode.

The current stabilizer unit 2 carries out the ECU discharge in the pause mode.

The light source was a 670 nm LED.

The operational mode contains the following stages of the ECU operation: coloring-relaxation-pause-relaxation; discoloration-relaxation-pause-relaxation.

The staining stage was characterized by the flow of a constant stabilized current with a density of up to 40 μA / cm ² during the time interval required to reduce the optical transmission to a user-specified level, while the voltage on the ECU electrodes was within the safe limits of the redox potential at a given temperature. The optimal work of the ECU was characterized by a change in light transmission to the ratio of the discolored state to the colored state within 3-4.

Relaxations imply ECU operation in idle mode, i.e. in the open state, while simultaneously measuring the voltage on the electrodes of the ECU, its light transmission and temperature.

The pauses imply the operation of the ECU in the mode of closing the ECU electrodes to the current stabilizer 2, while the voltage on the electrodes, light transmission and ECU temperature were recorded, the current level, the density of which did not exceed 40 μA / cm ² . The value of the local current density above 95-100 μA / cm ² leads to side thermodynamic processes that cause local irreversible destruction of optically active ECU layers.

The bleaching stage was characterized by the flow of a constant stabilized current with a density of up to 40 μA / cm ² during the time interval required to increase the light transmission to a user-specified level, while the voltage on the ECU electrodes remained within the safe limits of the redox potential at a given temperature.

For the tested ECU samples that underwent electroforming, 20,000 stepwise cycles were performed, after which the rate of topochemical reactions of coloring / discoloration decreased by no more than 2%, while the range of light transmission and power consumption did not change.

ECU samples, not subjected to electroforming by the claimed method, lost their performance after 300 working cycles.

Based on the test results of prototypes, the following conclusions can be drawn.

Due to the repeated pre-operational exposure of the electrochromic device to a stabilized direct current within the permissible current density, the power consumption in the working modes of staining and discoloration is significantly reduced. The multistage method of operation coloring-relaxation-pause-relaxation, discoloration-relaxation-pause-relaxation allows you to remove current surges when changing the polarity of the ECU supply, which provides an increase in the service life without degradation of the electrochromic layers. The combined stages of relaxation and pauses make it possible to avoid degradation effects caused by edge effects during operation of a large-area ECS. In addition, the stage of relaxation is the longest operating mode of the electrochromic device, which allows avoiding side redox processes and reducing the consumption of energy.

Claims (3)

1. A method for controlling electrochromic devices with thin-film electrochromic layers separated by a layer of optically neutral electrolyte, characterized in that at first the electrochromic device is subjected to multiple pre-operational exposure to a stabilized direct current within the permissible current density in the coloring-pause mode, discoloration-pause with gradual by increasing the voltage and recording the spectral-optical, temperature and current-voltage characteristics, then in the operating mode the electrochromic device is switched according to the coloring-relaxation-pause-relaxation scheme, bleaching-relaxation-pause-relaxation, while at the stages of staining and bleaching, the force of a stabilized constant current is limited so that the current density does not exceed the maximum permissible value, at the stages of relaxation, the electrodes of the device are opened and the voltage on the electrodes, light transmission and temperature of the device are monitored, at the stages of The bonds of the electrodes are connected to a current stabilizer and control the current, voltage across the electrodes, light transmission and temperature of the device. 2. The method according to claim 1, characterized in that the pre-operational effect is performed with increasing voltage so that the range of change in light transmission gradually increases from 5% to 75% compared to the initial value. 3. A software and hardware complex for controlling electrochromic devices, containing a control unit that determines the operating modes of the microcontroller, with installed software, controls the switch units, voltage regulation and current stabilizers and associated with the units for measuring current and voltage, light transmission and temperature, a power supply, connected to the voltage regulation unit, which receives a command from the microcontroller about the level of the required stabilized voltage and supplies it to the current stabilizer unit 1 for staining / discoloration modes, the switch unit connecting the electrochromic device to the current stabilizer unit 1 for staining / discoloration modes and to the block current stabilizer 2 for pause modes.

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