BACKGROUND

Electrochromic (EC) devices are typically multilayer stacks including (a) at least one layer of electrochromic material, that changes its optical properties in response to the application of an electrical potential, (b) an ion conductor (IC) layer that allows ions, such as lithium ions, to move through it, into and out from the electrochromic material to cause the optical property change, while preventing electrical shorting, and (c) transparent conductor layers, such as transparent conducting oxides or TCOs, over which an electrical potential is applied to the electrochromic layer. In some cases, the electric potential is applied from opposing edges of an electrochromic device and across the viewable area of the device. The transparent conductor layers are designed to have relatively high electronic conductances. Electrochromic devices may have more than the above-described layers such as ion storage or counter electrode layers that optionally change optical states.

Due to the physics of the device operation, proper function of the electrochromic device depends upon many factors such as ion movement through the material layers, the electrical potential required to move the ions, the sheet resistance of the transparent conductor layers, and other factors. The size of the electrochromic device plays an important role in the transition of the device from a starting optical state to an ending optical state (e.g., from tinted to clear or clear to tinted). The conditions applied to drive such transitions can have quite different requirements for different sized devices or different operating conditions.

What are needed are improved methods for driving optical transitions in electrochromic devices.

SUMMARY

Various embodiments herein relate to methods for transitioning an optically switchable device using feedback obtained during the transition to control the ongoing transition and/or calibrating the tint states of optically switch devices using transfer functions. Certain embodiments relate to optically switchable devices having controllers with instructions to transition the optically switchable device using feedback obtained during the transition. Further, in some embodiments, groups of optically switchable devices are controlled together based on electrical feedback obtained during the transition. The optically switchable devices can be probed by applying certain electrical conditions (e.g., voltage pulses and/or current pulses) to the optically switchable devices. An electrical response to the probing can be used as feedback to control the ongoing transition.

In one aspect of the disclosed embodiments, a method of controlling an optical transition of an optically switchable device from a starting optical state to an ending optical state is provided, the method including: (a) applying a voltage or current for driving the optically switchable device to transition from the starting optical state to the ending optical state, where the applied voltage or current is applied to bus bars of the optically switchable device; (b) before the transition is complete, determining an electrical characteristic of the optically switchable device; and (c) using the determined electrical characteristic as feedback to adjust the applied voltage or current to further control the optically switchable device transition.

In a number of embodiments, the optically switchable device is an electrochromic (EC) window. Operation (c) may include substantially matching, during the transition, the tint level of the EC window to the tint level of a second EC window proximate the EC window. This allows more than one window to be controlled to matching tint levels.

Different types of feedback may be used. In some embodiments, the determined electrical characteristic includes an open circuit voltage across two electrodes of the optically switchable device. In these or other cases, the determined electrical characteristic may include a current flowing between two electrodes of the optically switchable device. In some examples, the determined electrical characteristic includes at least one of a voltage and a current, where operation (c) includes adjusting an applied current or voltage used to drive the transition based on the determined electrical characteristic to ensure that the optically switchable device is maintained within a safe operating current range and/or within a safe operating voltage range during the optical transition. The safe operating current range may have a maximum magnitude between about 70-250 μA/cm2. The safe operating voltage range may have a maximum magnitude between about 5-9V.

In certain embodiments, the determined electrical characteristic includes at least one of a voltage and a current, and (c) includes adjusting an applied current or voltage used to drive the transition based on the determined electrical characteristic to ensure that the optical transition is occurring at a rate of transition that is at least as high as a target rate of transition. In some cases, (c) includes adjusting the applied current or voltage based on the determined electrical characteristic to ensure that the optical transition occurs within a target timeframe. In these or other cases, the determined electrical characteristic may include at least one of a voltage and a current, and (c) includes adjusting an applied current or voltage used to drive the transition based on the determined electrical characteristic to determine whether the optically switchable device is at or near the ending optical state. Further, in some cases the determined electrical characteristic includes a current that occurs in response to open circuit voltage conditions applied to the optically switchable device.

In some cases, the method further includes determining a quantity of charge delivered to drive the optical transition, and based on the determined quantity of charge delivered, determining whether the optically switchable device is at or near the ending optical state. The method may also include receiving a command to transition the optically switchable device to a third optical state after initiation of the optical transition from the starting optical state to the ending optical state, where the third optical state is different from the ending optical state, where (c) includes adjusting an applied current or voltage used to drive the optical transition based on the determined electrical characteristic to thereby drive the optically switchable device to the third optical state.

In another aspect of the disclosed embodiments, a method of maintaining substantially matching tint levels or tint rates in a plurality of electrochromic (EC) windows is provided, the method including: (a) probing the plurality of EC windows to determine an electrical response for each window; (b) comparing the determined electrical responses for the plurality of EC windows; and (c) scaling a voltage or current applied to each of the plurality of EC windows to thereby match the tint levels or tint rates in each of the plurality of EC windows.

In a further aspect of the disclosed embodiments, a method of transitioning a plurality of electrochromic (EC) windows at substantially matching tint rates is provided, the method including: (a) determining a transition time over which the plurality of EC windows are to be transitioned from a starting optical state to an ending optical state, where the transition time is based, at least in part, on a minimum time over which a slowest transitioning window in the plurality of EC windows transitions from the starting optical state to the ending optical state; (b) applying one or more drive conditions to each of the windows in the plurality of windows, where the one or more drive conditions applied to each window are sufficient to cause each window to transition from the starting optical state to the ending optical state substantially within the transition time.

In certain implementations, the method further includes: while applying the one or more drive conditions, probing the plurality of EC windows to determine an electrical response for each window, measuring the electrical response for each window, determining whether the electrical response for each window indicates that the window will reach the ending optical state within the transition time, and if it is determined that the window will reach the ending optical state within the transition time, continuing to apply the driving conditions to reach the ending optical state, and if it is determined that the window will not reach the ending optical state within the transition time, increasing a voltage and/or current applied to the window to thereby cause the window to reach the ending optical state within the transition time.

The method may further include when determining whether the electrical response for each window indicates that the window will reach the ending state within the transition time, if it is determined that the window will reach the ending optical state substantially before the transition time, decreasing a drive voltage and/or current applied to the window to thereby cause the window to reach the ending optical state at a time closer to the transition time than would otherwise occur without decreasing the drive voltage and/or current. The transition time may be based on a number of factors. For instance, in some cases the transition time is based, at least in part, on a size of a largest window in the plurality of EC windows. This can help ensure that the windows can all transition at the same rate.

The plurality of EC windows may be specifically defined in some cases. For instance, the method may include defining the plurality of EC windows to be transitioned based on one or more criteria selected from the group consisting of: pre-defined zones of windows, instantaneously-defined zones of windows, window properties, and user preferences. A number of different sets of windows can be defined, and the sets of windows can be re-defined on-the-fly in some embodiments. For example, defining the plurality of EC windows to be transitioned may include determining a first plurality of EC windows and determining a second plurality of EC windows, where the transition time determined in (a) is a first transition time over which the first plurality of EC windows are to be transitioned, and where the transition time in (b) is the first transition time, and further including: (c) after beginning to apply the one or more drive conditions in (b) and before the first plurality of EC windows reaches the ending optical state, determining a second transition time over which the second plurality of EC windows are to be transitioned to a third optical state, where the third optical state may be the starting optical state, the ending optical state, or a different optical state, where the second transition time is based, at least in part, on a minimum time over which a slowest transitioning window in the second plurality of EC windows transitions to the third optical state, and (d) applying one or more drive conditions to each of the windows in the second plurality of EC windows, where the one or more drive conditions applied to each window are sufficient to cause each window to transition to the third optical state substantially within the second transition time. In some embodiments, each window in the plurality of EC windows includes a memory component including a specified transition time for that window, where (a) includes comparing the specified transition time for each window in the plurality of EC windows to thereby determine which window is the slowest transitioning window in the plurality of ECA windows.

In another aspect of the disclosed embodiments, a method of calibrating a defined tint state of an electrochromic device is provided, the method including: (a) measuring the optical density for a plurality of hold voltages ranging between clear and tinted states; (b) determining a transfer function between one or more optical device parameters and the measured optical density of the device; (c) calculating one or more calibrated drive parameters using the transfer function, wherein the transfer function employs the use of one or more optical device parameters; and (d) configuring window control logic by substituting one or more predetermined drive parameters with the calibrated drive parameters. In some cases the transfer function determined in (b) can be used or modified to provide calibrated drive parameters for windows from which window parameters are measured.

In yet another aspect of the disclosed embodiments, a method of calibrating an electrochromic window or other optically switchable device is described that ensures the ending tint state of the device matches the intended tint state (sometimes referred to herein as a baseline tint state), thus reducing perceived differences in tint between adjacent windows. In certain embodiments, the method includes the following operations: (a) measuring one or more parameters of the electrochromic device, wherein the one or more measured parameters correlate with an unadjusted optical density at the specified tint state; (b) applying the one or more measured parameters to a transfer function to generate an calibrated drive parameter for the electrochromic device, wherein the transfer function was produced from a training set of electrochromic devices; (c) configuring window control logic for controlling one or more optical transitions and/or states in the electrochromic device, wherein in the configuring comprises applying the calibrated drive parameter; and (d) applying the calibrated drive parameter to the electrochromic device to induce the adjusted optical density at the specified tint state in the electrochromic device. In certain implementations the parameters measured in (a) and applied to the transfer function in (b) include optical parameters, electrical parameters, and environmental parameters.

These and other features will be described in further detail below with reference to the associated drawings.

