Process and apparatus for switching large-area electrochromic devices

• US 8,218,223 B2
• Filed: 08/20/2009
• Issued: 07/10/2012
• 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
• Primary Examiner(s): CHOI, WILLIAM C
• Application Number:
  US12/544,311
• Publication Number:
  US 20100172009A1
• Time in Patent Office: 1,055 Days
• Field of Search: 359/265, 359/269, 359/270, 359/273, 359/275
• 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;

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

wherein 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 when a voltage is applied to the electrode layers; and

applying a voltage to the electrode layers and varying the applied voltage in steps of 10-100 mV as a function of current, such that the voltage generated between the electrode layers is kept within predetermined temperature-dependent safe redox limits, and the cell current is limited to predetermined temperature-dependent limits,

wherein the applied voltage is only increased if the cell current is less than a maximum cell current (i_max), determined according to

i_max=(j_max×

Area)+(T−

T₀)×

F,

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

2. The process in accordance with claim 1, wherein the temperature dependence of the safe redox limits (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 maximum current density (j_max) is calculated from a maximum acceptable switching time, according to the equation

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

5. The process in accordance with claim 4, 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 to the equation

6. The process in accordance with claim 5, wherein a maximum voltage generated between the electrode layers is calculated from an applied contact voltage (U_C), the cell current (i_C), and the effective resistance (R_eff).

7. The process in accordance with claim 6, wherein the maximum voltage generated between the electrode layers is calculated according to the equation

U_f,max=U_C−

i_CR_eff.

8. The process in accordance with claim 7, wherein the maximum voltage which may be safely applied to the electrode layers is calculated from the temperature-dependent safe redox limits (U_EC), the cell current (i_C), and the effective resistance (R_eff).

9. The process in accordance with claim 8, wherein the maximum voltage which may be safely applied to the electrode layers is calculated from the temperature-dependent safe redox limits (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.

10. The process in accordance with claim 1, wherein an applied cell voltage 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 a maximum cell contact voltage limit (U_C,max) is reached.

11. The process in accordance with claim 10, wherein the applied cell voltage is modified in a stepwise fashion until the maximum cell contact voltage limit (U_C,max) is reached, according to the equation

U_C,f=U_C,i +U_step,

with voltage step size (U_step) being positive for coloration, and negative for bleaching, and with final and initial voltages, U_C,f and U_C,i, respectively.

12. The process in accordance with claim 10, wherein the applied cell voltage is modified in a stepwise fashion after the maximum cell contact voltage limit (U_C,max) is reached, according to the equation

U_C,f=U_C,i−

U_step,

with voltage step size (U_step) being positive for coloration, and negative for bleaching, and with final and initial voltages, U_C,f and U_C,i, respectively.

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

t_Bl, which is calculated according to the equation

Δ

t_Bl=(T_min−

T)×

F,

wherein Δ

t_Bl is the additional bleaching time, T_min is a minimum temperature and T is the device temperature.

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

15. The process in accordance with claim 1, wherein the first and the second electrode layers are optically transparent.