Driving thin film switchable optical devices
Controllers and control methods apply a drive voltage to bus bars of a thin film optically switchable device. The applied drive voltage is provided at a level that drives a transition over the entire surface of the optically switchable device but does not damage or degrade the device. This applied voltage produces an effective voltage at all locations on the face of the device that is within a bracketed range. The upper bound of this range is associated with a voltage safely below the level at which the device may experience damage or degradation impacting its performance in the short term or the long term. At the lower boundary of this range is an effective voltage at which the transition between optical states of the device occurs relatively rapidly. The level of voltage applied between the bus bars is significantly greater than the maximum value of the effective voltage within the bracketed range.
1. A method of transitioning an optically switchable device from a first optical state to a second optical state, the method comprising:
supplying an applied voltage (V app ) to the optically switchable device to transition the optically switchable device from the first optical state to the second optical state,
the optically switchable device comprising (i) bus bars separated by a distance of at least about thirty (30) inches and (ii) transparent conductive layers electrically connected with the bus bars,
wherein the V app is supplied to the bus bars of the optically switchable device,
wherein V app is controlled based at least in part on:
(a) a sheet resistance of the transparent conductive layers,
(b) the distance between the bus bars, and
(c) an instantaneous local current density in the optically switchable device,
wherein a magnitude of V app changes based on the instantaneous local current density as the optically switchable device transitions from the first optical state to the second optical state,
wherein application of V app to the bus bars results in an effective voltage of at least about one (1) Volt (V) at all locations between the bus bars of the optically switchable device.
2. The method of claim 1 , wherein V app has a magnitude between about 2.3 and 6 Volts (V).
3. The method of claim 2 , wherein V app has a magnitude between 2.5 and 5 Volts (V).
4. The method of claim 3 , wherein V app has a magnitude between 3.5 and 5 Volts (V).
5. The method of claim 1 , wherein the effective voltage remains below a maximum effective voltage of about four (4) Volts (V).
6. The method of claim 1 , wherein the effective voltage remains below a maximum effective voltage of about two and a half (2.5) Volts (V).
7. The method of claim 1 , wherein the bus bars are angled bus bars disposed at vertices of the optically switchable device, and wherein V app is controlled based at least in part on a geometry of the bus bars.
8. The method of claim 1 , wherein the distance separating the bus bars of the optically switchable device is at least about forty (40) inches.
9. The method of claim 1 , wherein the magnitude of V app is at least about half (0.5) Volt (V) greater than a maximum effective voltage that avoids damaging the optically switchable device.
10. The method of claim 9 , wherein the magnitude of V app is at least about one and a half (1.5) Volts (V) greater than the maximum effective voltage.
11. A method of transitioning an optically switchable device from a first optical state to a second optical state, the method comprising:
supplying an applied voltage (V app ) to the optically switchable device to transition the optically switchable device from the first optical state to the second optical state,
the optically switchable device comprising bus bars separated by a distance of at least about thirty (30) inches, and transparent conductive layers electrically connected with the bus bars,
wherein the V app is supplied to the bus bars of the optically switchable device, and
wherein V app is controlled based at least in part on:
(a) a sheet resistance of the transparent conductive layers,
(b) the distance between the bus bars, and
(c) an ohmic drop across each of the transparent conductive layers,
wherein a magnitude of V app changes based on the ohmic drop as the optically switchable device transitions from the first optical state to the second optical state,
wherein application of V app to the bus bars results in an effective voltage of at least about one (1) Volt (V) at all locations between the bus bars of the optically switchable device.
12. The method of claim 11 , wherein V app has a magnitude between about 2.3 and 6 Volts (V).
13. The method of claim 12 , wherein V app has a magnitude between 2.5 and 5 Volts (V).
14. The method of claim 13 , wherein V app has a magnitude between 3.5 and 5 Volts (V).
15. The method of claim 11 , wherein the effective voltage remains below a maximum effective voltage of about four (4) Volts (V).
16. The method of claim 11 , wherein the effective voltage remains below a maximum effective voltage of about 2.5 Volts (V).
17. The method of claim 11 , wherein the bus bars are angled bus bars disposed at vertices of the optically switchable device, and wherein V app is controlled based at least in part on a geometry of the bus bars.
18. The method of claim 11 , wherein the distance separating the bus bars of the optically switchable device is at least about forty (40) inches.
19. The method of claim 11 , wherein the magnitude of V app is at least about half (0.5) Volt (V) greater than a maximum effective voltage that avoids damaging the optically switchable device.
20. The method of claim 19 , wherein the magnitude of V app is at least about one and a half (1.5) Volts (V) greater than the maximum effective voltage.