Residential/commercial buildings account for >40% of US energy demand 70% of electricity use, costing >$430 billion/year. If auto-darkening windows were available for building windows in warmer US regions, energy for cooling could be greatly reduced without effect on visibility. Now in ongoing and prior work, this firm has developed novel, auto-darkening electrochromic sunglasses based on unique, patented electrochromic polymers (see https://ashwin-ushas.com/electrochromic-sunglasses-goggles/). It is planned to commercially launch these end-2018. These have: (1) Very high light/dark (L/D) contrast (1%-70% Transmission, against air reference, dialable to any value in between), from use of nearly perfectly-matched, new, cathodically- and anodically-coloring (dual-polymer) Conducting Polymers (CPs). (2) High cyclability (>10K L/D cycles), long shelf life (>3 years), desirable color change (transparent to dark-blue-black), high durability. (3) Very thin (<0.4 mm), flexible durable lenses, naturally UV-blocking. (4) Unique, patented applied-voltage algorithm on Microcontroller (<$8) drastically reducing switching time (<2 s L?D, ~instantaneous D?L). (5) Fully automated, photosensor-based control based on ambient light. (6) Use rechargeable Li batteries, 72h continuous function with 12 L/D/L switches/hour before recharging; 15 µW/cm2, +/- 3.0 VDC. (7) Cost <$70 pair. (8) Superior to competing technologies: LCD-based electrochromic sunglasses (e.g. from ControlOne) and MOx-based electrochromic building windows (e.g. from Sage) have much poorer L/D contrast, lower stability and higher cost. The proposed work will adapt this technology to retrofit building windows, based on preliminary work we already carried out since 2014 (prototype for automobile windshields delivered to General Motors in 2017). The key issue in adapting this to large-area building windows is that there is a large conductivity drop across distances of more than ~10 cm on the transparent conductive substrates used (ITO/Mylar), such that the slower color transition across larger areas from the electrical contact points is visible. Prior work in our labs, and advances in technology since 2013, have overcome this key issue. Although the actual solution arrived at is proprietary, it can be stated here that it involves laying down very-high-conductivity grid lines on the large-area ITO/Mylar substrates, much like those on a car rear-window defroster, except that these lines are invisible to the eye due to their dimension and composition. A windshield-dimension prototype was delivered by us to GM in 2017; this demonstrated that the grid lines were completely compatible with the electrochromic CPs. The technology for large-scale, inexpensive production of these has been outlined. The proposed work will further develop this technology specifically for building-window application. It will include testing a multitude of grid-line methods, refinement of electrochromic properties, all necessary Controllers for automated window operation, and methods of large-scale commercial production.
