Electrochromic Devices with Spatially Varying Sheet Resistance
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Solution Overview
Problem
Large area electrochromic devices experience slow and spatially non-uniform switching due to voltage drop issues in transparent conductive coatings, leading to the 'iris effect' where transmissivity varies significantly across the device.
Innovation Solution
A multi-layer device with a first substrate and a layered stack comprising a conductive layer and a current modulating structure, where the conductive layer has a spatially varying sheet resistance, ensuring uniform potential distribution across the device by patterning or grading the thickness/composition of the conductive layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage is applied across transparent conductive coatings in large area electrochromic devices, then the device switches from lightened state to darkened state, but voltage drop causes non-uniform potential distribution leading to the iris effect
Solution Approach 1:
The patent applies local quality by varying the sheet resistance of the transparent conductive coating across different regions of the device. Specifically, regions closer to the voltage application point have lower sheet resistance while regions farther away have higher sheet resistance. This spatially varying conductivity compensates for the voltage drop, ensuring more uniform potential distribution and eliminating the iris effect.
Solution Approach 2:
The patent changes the electrical parameter (sheet resistance) of the transparent conductive coating as a function of position. By grading the sheet resistance parameter across the device area, the system compensates for the inherent voltage drop in large area devices, achieving uniform switching without requiring uniform material properties throughout.
2Ease of manufacture
If transparent conductive coatings with uniform sheet resistance are used, then manufacturing is simplified, but switching becomes slow and non-uniform in large area devices
Solution Approach 1:
Rather than using uniform conductive layers throughout, the patent implements local quality by making the sheet resistance position-dependent. This allows the device to achieve fast, uniform switching performance in large areas while maintaining manufacturability through established deposition techniques that can produce graded or patterned resistance profiles.
3Area of stationary object
If the device area is increased for architectural applications, then the window covers larger surfaces, but the iris effect becomes more pronounced due to higher resistance
Solution Approach 1:
The patent solves the scaling problem by implementing local quality through spatially varying sheet resistance. In larger devices, regions farther from voltage application points naturally have higher resistance contributions, so these regions are compensated with higher local sheet resistance in the conductive coating. This ensures that the product of distance and resistance remains balanced across the entire large area, maintaining uniform switching regardless of device size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Facilitates rapid and uniform switching across the entire area of the electrochromic device, reducing the 'iris effect' and improving switching performance by controlling voltage drop.
Implementation Method 1
the current modulating structure comprising a material having a resistivity of at least 104 ohm-cm, the first electrically conductive layer having a sheet resistance, RS, to the flow of electrical current through the first electrically conductive layer that varies as a function of position in the first electrically conductive layer
Implementation Method 2
When a voltage is applied across these conducting layers the optical properties of a layer or layers in between change. Such optical property changes are typically a modulation of the transmissivity of the visible or the solar subportion of the electromagnetic spectrum
Data Source
AI summary
A multi-layer device comprising a first substrate, a first electrically conductive layer on a surface thereof, and a first current modulating layer, the first electrically conductive layer having a sheet resistance to the flow of electrical current through the first electrically conductive layer that varies as a function of position.