Lead Performer: Michael McGehee – Boulder, CO
DOE Total Funding: $410,689
Cost Share: $69,626
Project Term: October 1, 2017 – September 30, 2021
Funding Type: Cooperative Agreement
Dynamic windows, which have electronically controlled transmission, are highly desirable for increasing the energy efficiency of buildings via lighting, heating, and cooling savings. Replacing existing windows with well-functioning dynamic windows would result in ~2400 TBtu of energy savings across the U.S. residential and commercial sectors in 2030. However, the current production of dynamic windows is limited due to problems associated with durability, color, scalability, and high cost.
Most dynamic windows utilize electrochromic materials, which change their transmission properties upon application of a voltage, to modulate the transparency of a window toward visible and/or infrared light. The vast majority of research on dynamic windows over the past four decades has focused on transition metal oxides or polymeric materials as electrochromic materials. This project will utilize the reversible electrodeposition and dissolution of metals, which is an underexplored yet promising approach for dynamic window applications. Previous experiments demonstrate that 25 cm2 dynamic windows based on reversible metal electrodeposition possess minute-long switching times and maintain high optical contrast and uniformity over the course of at least 5,500 cycles. From just 15 months of research, the team has developed devices with metrics that already rival current electrochromic windows. Further research funded from EERE will enable the team to fabricate larger dynamic windows that are durable and inexpensive using this approach.
To uniformly elicit metal electrodeposition on a large scale, this project will employ invisible metal grid lines on the micron scale on both electrodes of the dynamic windows. Grid lines on the optically active working electrode will be used to decrease the sheet resistance of the transparent conducting oxide. Counter electrode grid lines will provide a uniform source of metal ions across the area of the device. The composition and geometry of these grid lines will be optimized to mitigate dendrite formation on the counter electrode such that these larger windows can be switched 50,000 times at 85°C without significant deterioration in performance in accordance with ASTM standards. In addition, the team will show large-scale device prototypes to window companies to receive advice about the most desirable optical properties of the electrodeposited metal and grid lines. Taken together, these strategies will allow the team to construct aesthetically pleasing 1-foot-long dynamic window prototypes using high throughput and inexpensive fabrication methods.
The dynamically tinting glazings are highly attractive for windows and skylights because they have a neutral color, offer a true privacy state and should be less expensive that electrochromic windows based on tungsten oxide. People are likely to purchase the windows because they will eliminate glare and provide excellent views. When they do, the windows will save a substantial amount of energy.
DOE Technology Manager: Marc LaFrance
Lead Performer: Michael McGehee, University of Colorado
- “Electrolyte for Improved Durability of Dynamic Windows Based on Reversible Metal Electrodeposition,” T.S. Hernandez, M. Alshurafa, M.T. Strand, A.L. Yeang, M.G. Danner, C.J. Barile, M.D. McGehee, Joule, (2020) DOI: 10:1016/j.joule.2020.05.008.
- “Design of Reversible Electroplating Cells for Energy-Saving Windows,” A.L. Yeang, T.S. Hernandez, M.T Strand, C.J. Barile, M.D. McGehee, ECS Meeting Abstracts, 1 (2019) 21-21.
- “Clear-to-Black Dynamic Windows with Minute-Long Switching Using Reversible Metal Electrodeposition,” S.M. Islam, T.S. Hernandez, M.D. McGehee, C.J. Barile, ECS Meeting Abstracts, 38 (2019) 1927-1927.
- “Hybrid Dynamic Windows Using Reversible Metal Electrodeposition and Ion Insertion,” S.M Islam, T.S. Hernandez, M.D. McGehee and C.J. Barile, Nature Energy, 4 (2019) 223-229.
- “Factors that Determine the Length Scale for Uniform Tinting in Dynamic Windows Based on Reversible Metal Electrodeposition,” M.T. Strand, C.J. Barile, T.S. Hernandez, T.E. Dayrit, L. Bertoluzzi, D.J. Slotcavage, M.D. McGehee, ACS Energy Letters, 3 (2018) 2823-2828.
- “Bistable Black Electrochromic Windows Based on the Reversible Metal Electrodeposition of Bi and Cu,” T.S. Hernandez, C.J. Barile, M.T. Strand, T.E. Dayrit, D.J. Slotcavage, M.D. McGehee, ACS Energy Letters, 3 (2018) 104-111.