Electrochromic Devices with Spatially Varying Sheet Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Large area electrochromic devices often exhibit slow and spatially non-uniform switching, known as the 'iris effect', due to voltage drops across transparent conductive coatings, leading to inconsistent transmissivity across the device.
Innovation Solution
A multi-layer electrochromic device with spatially varying sheet resistance in its electrically conductive layers, where the ratio of maximum to minimum sheet resistance is at least 2, allowing for coordinated and uniform switching across the device's area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage is applied across the conducting layers of a large area electrochromic device, then the device switches from a lightened state to a darkened state, but the switching is slow and spatially non-uniform due to voltage drops across the transparent conductive coatings
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, the coating has a first sheet resistance value in a first region and a second sheet resistance value in a second region, with the ratio between these values being at least 2. This spatial variation in electrical properties compensates for the voltage drops that occur during switching, ensuring uniform potential distribution and thus uniform switching across the entire device area, eliminating the iris effect while maintaining rapid response
2Area of stationary object
If the device area is increased for architectural applications, then the device can cover larger windows, but the iris effect becomes more pronounced due to higher resistivity and larger voltage drops
Solution Approach 1:
The patent addresses large area devices by implementing spatially varying sheet resistance values across the transparent conductive coating. This allows each region of the large device to have appropriately tailored electrical properties that compensate for position-dependent voltage drops, maintaining uniform transmissivity switching across the entire large area and eliminating the iris effect that normally worsens with increasing device size
3Ease of manufacture
If uniform sheet resistance is used across the conductive layer, then the device structure is simple and easy to manufacture, but the voltage drop causes non-uniform transmissivity with the greatest potential at the edges and least at the center
Solution Approach 1:
The patent resolves this contradiction by deliberately introducing non-uniformity in the sheet resistance of the transparent conductive coating. By having different sheet resistance values in different regions (with a ratio of at least 2), the design compensates for the natural voltage drop gradient in large area devices, achieving uniform transmissivity switching across the device while maintaining compatibility with standard manufacturing processes for creating spatially varying material properties
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
The device achieves rapid and uniform switching by controlling the voltage drop across the conductive layers, reducing the iris effect and ensuring consistent transmissivity across the entire device area.
Implementation Method 1
The first electrically conductive layer is transmissive to electromagnetic radiation having a wavelength in the range of infrared to ultraviolet and has 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 and a first electrically conductive layer on a surface thereof, 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.