Process and apparatus for switching large-area electrochromic devices

• US 20100172009A1
• Filed: 08/20/2009
• Published: 07/08/2010
• Est. Priority Date: 01/02/2009
• Status: Active Grant

• Current Assignee: Econtrol-Glas GmbH & Co. KG
• Original Assignee: Econtrol-Glas GmbH & Co. KG
• Inventors: Matthews, Jeremy
• Granted Patent: US 8,218,223 B2
• Time in Patent Office: Days
• US Class Current: 359/265
• CPC Class Codes: G02F 1/163 Operation of electrochromic cells, e.g. electrodeposition cells; Circuit arrangements therefor

Abstract

A method is disclosed for controlling switching of an electrochromic device comprising at least the following components: a first and a second electrode layer, a first and a second layer in which ions can be reversibly intercalated, and a transparent ion-conducting layer. At least one of the layers in which ions may be reversibly inserted is electrochromic. The optical properties of the device are modified when a potential is applied between the electrode layers. The potential applied is limited such that the maximum generated potential difference never exceeds the safe redox limits, and that the current does not exceed some predetermined limit. Switching of electrochromic devices in this manner allows for maximum device lifetime, while simultaneously optimising switching speed and transmission homogeneity. The method is characterised in that the potential applied to the electrode layers is varied in the form of a stepped ramp, during which time the current is measured constantly.

Claims

1. A process for switching an electrochromic cell comprising at least the following components:

a first and a second electrode layer;

a first and a second layer, in which ions may be reversibly inserted; and

an ion-conducting layer;

where at least the first layer, in which ions may be reversibly inserted, is electrochromic; and

where the first and the second layer, in which ions may be reversibly inserted, are counter electrodes to each other;

comprising the steps of;

measuring continuously the current (i_C) flowing through the cell if a voltage is applied to the electrode layers; and

varying the voltage in a stepwise fashion as a function of current, such that the voltage generated between the electrode layers is kept within predetermined temperature-dependent safe redox limits, so that the cell current is limited to predetermined temperature-dependent limits.

2. The process in accordance with claim 1, wherein the temperature dependence of the safe redox limit (U_EC) is calculated according to the equation:

U_EC=A+BT,

where T is the temperature of the electrochromic element and A and B are constants related to electrochromic device design.

3. The process in accordance with claim 1, wherein the temperature dependence of the maximum current limit (i_max) is calculated according to the equation

i_max=(j_max×

Area)F(T−

T₀),

where j is current density, Area is the active cell area, T is the temperature of the electrochromic element, and T₀ is a reference temperature, thereby the factor F allowing for modification of the current according to temperature, thereby allowing modification of switching speed with respect to temperature.

4. The process in accordance with claim 3, wherein the maximum current density (j_max) is calculated from the maximum allowed switching time, according to the equation

$j_{\max }=\left(\frac{Q_{\max }}{\mathrm{Time}}\right),$

where Q_max is the maximum charge density corresponding to the completely coloured state and (Time) is the maximum acceptable switching time.

5. The process in accordance with claim 1, wherein the effective resistance (R_eff) is calculated from cell dimensions and at least one material constant before starting the switching process.

6. The process in accordance with claim 5, wherein the effective resistance (R_eff) is calculated from cell width, where width refers to the separation between the electrode contact strips, height, where height corresponds to the length of the contacted edges, and at least one material constant (k), according the equation

$R_{\mathrm{Eff}}=\left(\frac{w}{h}\right)\times$

k .

7. The process in accordance with claim 6, wherein the maximum potential generated between the electrode layers is calculated from the applied contact potential (U_C), the cell current (i_C), and the effective resistance (R_eff).

8. The process in accordance with claim 7, wherein the maximum potential generated between the electrode layers is calculated according to the equation

U_f,max=U_C−

i_CR_eff.

9. The process in accordance with claim 8, wherein the temperature dependence of the safe redox limit (U_EC) is calculated according to the equation:

U_EC=A+BT,

where T is the temperature of the electrochromic element and A and B are constants related to electrochromic device design; and

further wherein the maximum voltage which may be safely applied to the electrode contacts is calculated from the temperature-dependent safe redox limit (U_EC), the cell current (i_C), and the effective resistance (R_eff).

10. The process in accordance with claim 9, wherein the maximum voltage which may be safely applied to the electrode contacts is calculated from the temperature-dependent safe redox limit (U_EC), the cell current (i_C) and the effective resistance (R_eff), according to the equation

U_C,max=U_EC+i_CR_Eff.

14. The process in accordance with claim 1, wherein the bleaching process, and therefore the charge extraction, is extended for a specific period of time, Δ

t_Bl is calculated according to the equation

Δ

t_Bl=(T_min−

T)×

F.

15. The process in accordance with claim 1, wherein the contact potential (U_C) applied to the electrode layers is varied in steps of 10-100 mV.

16. The process in accordance with claim 1, wherein both layers in which ions may be reversibly inserted are electrochromic.

17. The process in accordance with claim 1, wherein the first and the second electrode layer optically transparent.

18. An apparatus in accordance with claim 1, comprising:

a voltage source, applied to the cell contacts A and B;

means for measuring the applied contact potential (U_C);

a controller connected to the means for measuring the applied contact potential analysing the measured values;

an ammeter, providing for the cell current to be continuously measured;

a cyclic basis, enabling the measured values to be transferred to the controller; and

a temperature sensor, providing for temperature measurement of the electrochromic device,

wherein the controller is able to calculate the magnitude of the electrical potential to be applied to the cell contacts based on values of temperature, electrochromical potential limits and cell current.

19. The apparatus in accordance with claim 18, wherein the controller furthermore comprises a microprocessor and is able to perform calculations according to a switching algorithm, thereby controlling the entire switching process based on the use of the algorithm.

20. The apparatus in accordance with claim 18, wherein the temperature sensor is incorporated into the structure of the electrochromic device.

21. The apparatus in accordance with claim 18, wherein the voltage is applied to the cell contacts A and B by switching suitable relays.

11. The process in accordance with claim, wherein the applied cell potential is modified in a stepwise fashion, increased for coloration, decreased for bleaching, as long as the cell current remains below a predetermined current limit (i_max), until the maximum cell contact potential limit (U_C,max) is reached.

12. The process in accordance with claim 11, wherein the applied cell potential is modified in a stepwise fashion until the maximum cell contact potential limit (U_C,max) is reached, according to the equation

U_C,f=U_C,i+U_step,

with U_step being positive for coloration, and negative for bleaching.

13. The process in accordance with claim 11, wherein the applied cell potential is modified in a stepwise fashion after the maximum cell contact potential limit (U_C,max) is reached, according to the equation

U_C,f=U_C,i+U_step,

with U_step being positive for coloration, and negative for bleaching.