Humans have harnessed energy from the Sun to create comfortable spaces for thousands of years. The Ancient Greeks and the Native Americans chose to orient their homes to face south to capture solar energy in thick stone walls that provided passive heating during cold nights. Today, energy-efficient buildings make use of their solar resource with a combination of photovoltaic cells that convert sunlight to electricity and building technologies that transmit light and heat from the sun indoors.

Windows are one of our most celebrated building technologies because they let us maintain our connection with the outdoors from the comfort of our offices and homes. Naturally, the next paradigm in sustainable architecture is a dynamic window with active solar control that adapts to the local climate in real-time. Dynamic glass technology promises massive energy savings through reduced lighting, heating, and cooling loads, improved comfort and well-being for occupants, and, importantly, the opportunity to finally rid the world of the blinds that we plaster over our beloved views.

Despite five decades of research and development, it has proved challenging to construct a dynamic window technology with the right color, contrast, and cost; until now. Reversible metal electrodeposition (RME) is an emerging solution that uses metal films to control light and heat flow in windows.  Since our first 25 cm² prototypes were described in a 2017 Joule article¹, our research team has been working hard to understand and solve the remaining challenges facing RME windows and, ultimately, validate the technology for commercial use. Our latest paper in Nature Energy describes the innovations that have enabled >900 cm² dynamic windows that boast neutral-color tinting and a wider range of visible and solar modulation than any existing technology. Please check out the video below for a demonstration of the technology across it entire dynamic range.

The fundamental advance in this work is the inclusion of polymer additives termed ‘inhibitors’ to our RME electrolyte to yield efficient, durable, and large-area dynamic windows. Polyvinyl alcohol (PVA), specifically, enables control over the morphology of the electrodeposited metal films by promoting plating of smooth and compact Bi-Cu films through an adsorption mechanism. The windows that employ the polymer inhibitor can readily tint to below 0.001% visible transmittance in less than 3 minutes and exhibit high infrared reflectance (>70%), color-neutral transmittance (C^* < 5), and an ultrawide range of optical and solar modulation. The polymer additive also eliminates harmful side reactions and allows us to switch our windows between clear and tinted states thousands of times with no observed degradation.

The use of metals in dynamic windows offers several important advantages over current state-of-the-art commercial technologies. Metals are the most conductive class of materials and exhibit strong interactions with light. The Bi-Cu films in our dynamic windows offer an intrinsic neutral color due to broad absorbance and reflectance over the visible spectrum compared to the sharp absorption features typical of electrochromic materials. The metal films reflect, rather than absorb, in the near-infrared (NIR) wavelengths which yields greater energy savings, especially in hot and sunny climates. And, the metal films completely block radiation over the entire solar spectrum after achieving ~100 nm thickness. The result is that RME dynamic windows exhibit an ultrawide optical range from clear glass (Tvis : 70%) to full blackout (Tvis: 0%) for maximal user control and comfort. In Figure 1, we compare the performance of RME windows to two state-of-the-art electrochromic technologies across the three most important metrics for windows: visible light transmittance (VLT), solar heat gain coefficient (SHGC), and color (a*,b*).

The RME window technology does not require expensive techniques like sputtering and can be processed on polymer films that will reduce the capital expense and enable retrofits. The superior optical performance, reduced complexity and expense, and proven scalability of the dynamic windows based on reversible metal electrodeposition make this technology an excellent candidate for providing the energy-efficient windows of the future. We founded Tynt Technologies to create beautiful indoor spaces that are more comfortable and sustainable. For more information, please visit us at tynt.io.

Link to Nature Energy article: Article Link

References:

1. Barile, C. J. et al. Dynamic Windows with Neutral Color, High Contrast, and Excellent Durability Using Reversible Metal Electrodeposition. Joule 1, 133–145 (2017).