Electrochromic Window with Bragg Reflector for UV Protection
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Solution Overview
Problem
Traditional electrochromic (EC) window coatings are static and not well-suited for varying climates, and their performance degrades due to repeated exposure to UV radiation, leading to irreversible photochromic darkening and reduced optical dynamic range.
Innovation Solution
An electrochromic system comprising a working electrode, a counter electrode, and a solid-state polymer electrolyte, with a Bragg reflector to block UV radiation and a control unit that applies a sweep voltage to manage photoelectrochemically generated charge, preventing trapped charge from causing irreversible darkening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional EC materials are used to modulate visible light, then visible spectral control is achieved, but NIR radiation remains unchanged and UV exposure causes performance degradation
Solution Approach 1:
The patent segments the spectral control function by introducing a Bragg reflector layer that specifically handles UV and NIR radiation, while the EC material focuses on visible light modulation. This segmentation allows each component to address specific spectral regions, preventing UV-induced degradation of the EC material while maintaining visible light control functionality.
Solution Approach 2:
The Bragg reflector acts as an intermediary between the UV environment and the EC material. It reflects UV radiation away from the EC layer, protecting it from degradation while allowing the EC material to continue modulating visible light effectively. This intermediary structure resolves the contradiction by shielding the EC material from harmful UV exposure.
2Loss of energy
If static window coatings are used to reject solar heat gain, then energy efficiency in warm climates is improved, but adaptability to varying climates is lost
Solution Approach 1:
The patent transforms the static window coating into a dynamic system by incorporating electrochromic materials that can reversibly change their optical properties. The EC device can switch between transparent and colored states, allowing adaptive control of solar heat gain and visible light transmission based on varying climate conditions, occupancy, and time of day.
Solution Approach 2:
The system changes key optical parameters (transmittance, reflectance) of the window coating through electrochromic modulation. By applying voltage, the EC material changes its absorption and transmission characteristics across different spectral regions, enabling dynamic adaptation to different climate conditions and operational requirements.
3Illumination intensity
If photochromic darkening occurs due to UV exposure, then temporary shading is achieved, but irreversible performance degradation and reduced optical dynamic range occur
Solution Approach 1:
The Bragg reflector provides preliminary protection by reflecting UV radiation away from the EC material before it can cause photochromic darkening. This preventive action stops the harmful UV-EC material interaction at the interface, eliminating the root cause of irreversible degradation while allowing controlled visible light modulation.
Solution Approach 2:
The patent converts the potentially harmful UV exposure into a beneficial protective mechanism. The Bragg reflector uses the incident UV radiation to create a standing wave pattern that reflects UV energy away from the EC material, transforming the harmful UV field into a protective shielding effect that preserves EC material integrity.
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 system effectively controls photochromic darkening, enhances the durability of EC devices by periodically sweeping away photo-generated charge, and maintains optical performance across different spectral regions, improving long-term durability and energy efficiency in building windows.
Implementation Method 1
a Bragg reflector configured to selectively reflect UV radiation away from the working electrode
Implementation Method 2
EC window coatings undergo a reversible change in optical properties when driven by an applied potential
Data Source
AI summary
An electrochromic system and method for controlling photochromic darkening of an electrochromic device, the system including an EC device, a control unit, a voltage detector, and a power supply. The EC device includes a working electrode, a counter electrode, a solid-state polymer electrolyte disposed therebetween, and a Bragg reflector configured to selectively reflect UV radiation away from the working electrode. The control unit is configured to control a sweep voltage applied between the working and counter electrodes, such that the sweep voltage is applied when an open circuit voltage (OCV) between the working and counter electrodes is less than a threshold voltage.