McGehee

The case of the vanishing seeds: How curiosity-driven research is future-proofing “Smart Windows”

Daniel Morton — Tue, 27 Jan 2026 17:02:14 +0000

The case of the vanishing seeds: How curiosity-driven research is future-proofing “Smart Windows” Daniel Morton Tue, 01/27/2026 - 10:02

Daniel Morton

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Have you ever walked into a room on a glorious Colorado summer day and felt the heat radiating through the glass?

We usually solve this by cranking up the air conditioning or closing the blinds, losing our mountain view in the process. But what if the window itself could think? A team led by Mike McGehee, a Fellow at RASEI, describes research that improves the robustness of such a device.

For years researchers have been working on “smart windows”, devices that could “sense” the conditions outside and “react” to them. This investigation centers around a promising technology called Reversible Metal Electrodeposition (RME). The technical details of this process are complex, but you can understand the concept by thinking of it as a reversible coat of paint. At the flip of a switch, a thin layer of metal, in this case silver, spreads across the glass to form a layer that tints it, blocking out the heat and the glare. Flip the switch again and the silver dissolves back into a clear liquid, making the window transparent.

Buildings are responsible for consuming around 40% of all generated energy globally, much of which is expended in regulating the temperature, heating and cooling the building interior. Installing smart windows that can react to the environmental conditions could provide a very effective mechanism to reduce energy use and slash energy bills by automatically managing how much heat enters a room. It has been estimated that just by controlling the amount of sunlight that is let into a building through a window, we could cut energy bills by up to as much as 20%.

However, there have been a number of challenges to overcome in order to take this initial discovery from the lab to a product that can be deployed for use in buildings. One challenge is that early versions of these windows started out fast but grew “lazy” over time. After a few thousand uses the tinting / de-tinting process slowed, taking almost four times longer than it did on day one.

This is where the researchers undertook some detailed investigations to identify what was going on, and what could be done to fix it. A collaboration between the McGehee group (at the University of Colorado Boulder) and the Barile Group (at the University of Nevada) set out to find out exactly what was happening. The team decided to look closer, using a combination of high-powered x-rays and electrochemical tests. The windows were using tiny “seeds” of platinum to help the silver grow on the glass. Platinum is recognized for being tough and non-reactive, and so should be perfect as a nucleation point for the silver. Using these advanced techniques the team explored exactly what was happening to the platinum seeds during the clearing phase, when the silver “paint” is stripped away.

To their surprise, the platinum was not as tough as they initially thought. In the special liquid environment needed for the windows, the platinum seeds were actually dissolving and washing away when the window was switched to clear. As the number of seeds dropped, the silver had fewer locations to grow from, which was the cause behind the window tinting slowing.

This led the team to ask the question “What can we do to make the seeds more resilient?”, which led them to use gold in place of platinum. While gold and platinum are both precious metals, in water, which is the solvent used inside the window panels, gold is more stable and less susceptible to decomposition and dissolving. When they swapped the platinum seeds for gold ones, the results were immediate. Even after 7,500 cycles, the equivalent of years of daily use, the windows transitioned just as fast as the first time they were used.

These gold-based windows provide an exciting range of opportunities. Not only because of their improved stability over many thousands of cycles, but also because they can express multiple colors by varying the voltage, a feature of the size of the gold particles. This presents opportunities for their use in displays and communications devices. This technology offers a better, smarter window that could passively save significant amounts of energy if deployed in commercial and residential buildings. This work shows how the impact of making fundamental chemical changes can unlock the potential of new technologies.

January 2026

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Nickel-oxide hole-transport layers prevent abrupt reverse-bias breakdown and permanent shorting of perovskite solar cells caused by pinhole defects

Daniel Morton — Tue, 13 Jan 2026 00:25:38 +0000

Nickel-oxide hole-transport layers prevent abrupt reverse-bias breakdown and permanent shorting of perovskite solar cells caused by pinhole defects Daniel Morton Mon, 01/12/2026 - 17:25

EES SOLAR, 2026, ASAP

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Photophysical Properties and Phase Behavior of Ultrawide Photovoltaic Bandgap Cesium–Lead-Based Triple Halide Perovskites

Daniel Morton — Tue, 06 Jan 2026 00:19:00 +0000

Photophysical Properties and Phase Behavior of Ultrawide Photovoltaic Bandgap Cesium–Lead-Based Triple Halide Perovskites Daniel Morton Mon, 01/05/2026 - 17:19

CHEMISTRY OF MATERIALS, 2026, ASAP

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Enhancing the Cycle Life of Reversible Silver Electrodeposition Optical Devices with Durable Gold Seed Particles

Daniel Morton — Thu, 04 Dec 2025 18:40:58 +0000

Enhancing the Cycle Life of Reversible Silver Electrodeposition Optical Devices with Durable Gold Seed Particles Daniel Morton Thu, 12/04/2025 - 11:40

ACS APPLIED MATERIALS & INTERFACES, 2025, 17, 50, 68212-68217

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Six RASEI Fellows featured among the 2025 Clarivate highly cited researchers

Daniel Morton — Thu, 20 Nov 2025 16:09:48 +0000

Six RASEI Fellows featured among the 2025 Clarivate highly cited researchers Daniel Morton Thu, 11/20/2025 - 09:09

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Six RASEI Fellows highlighted as Clarivate Highly Cited Researchers in their 2025 list. Congratulations to Matt Beard, Joe Berry, Joey Luther, Mike McGehee, Mike Toney, and Merritt Turetsky!

Each year Clarivate, the parent company of Web of Science, performs an evaluation and selection process to identify and recognize researchers whose exceptional and community-wide contributions shape the future of science, technology, and academia globally. The evaluation is an evolving process, which employs criteria to address issues including hyper-prolific authorship, excessive self-citation, anomalous publication and citation patterns and profiles, in an attempt to ensure that recognized researchers meet the benchmarks they have developed.

This provides a mechanism to provide a snapshot of the global research landscape of current top-tier research talent, providing insights on global research and innovation trends.

In 2025 Clarivate designated 7131 Highly Cited Researcher awards to 6868 individuals. (Some researchers were recognized in more than one category).

This recognition highlights the cutting-edge research being done by the RASEI community. Congratulations again to our Fellows.

November 2025

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Toward Fullerene-Free PIN Perovskite Solar Cells

Daniel Morton — Wed, 19 Nov 2025 00:28:58 +0000

Toward Fullerene-Free PIN Perovskite Solar Cells Daniel Morton Tue, 11/18/2025 - 17:28

ACS ENERGY LETTERS, 2025, 10, 12, 6307-6317

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Boulder Climate Ventures Ignites Climate Tech Momentum with Fall Series

Daniel Morton — Thu, 16 Oct 2025 14:32:00 +0000

Boulder Climate Ventures Ignites Climate Tech Momentum with Fall Series Daniel Morton Thu, 10/16/2025 - 08:32

October 2025

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Fixing Solar’s Weak Spot: Why a tiny defect could be a big problem for perovskite cells

Daniel Morton — Mon, 15 Sep 2025 15:25:36 +0000

Fixing Solar’s Weak Spot: Why a tiny defect could be a big problem for perovskite cells Daniel Morton Mon, 09/15/2025 - 09:25

Daniel Morton

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Solar energy is a crucial part of our clean energy future, but a new, highly efficient solar material has a hurdle that needs to be addressed. A recent study reveals how a microscopic weak spot can lead to total device failure and what we can do about it.

A collaboration between a team led by RASEI Fellow Mike McGehee and scientists at the National Renewable Energy Laboratory (NREL), just published in the scientific journal Joule, provides evidence to help solve one of the key hurdles to large-scale manufacture of next generation perovskite solar cells.

Imagine you have a series of hoses connected end-to-end to water your garden. The water flows from the faucet, through each hose, and out the last nozzle. When every hose is getting enough water, the flow is strong and steady. This is like how a string of solar cells works on a solar panel; the sun’s energy makes electrons (the “water”) that flow through each cell, creating electricity.

But what happens if a single section of the hose gets kinked? The water can’t flow through it anymore, but there is still a lot of pressure coming from the faucet. The pressure will build up and eventually burst the weak spot in the kinked section. This is analogous to what happens when a section of the solar panel is shaded --- the cell becomes ‘kinked’. When just one part of a panel is shaded, the unshaded cells still generate electricity and “force” current backward through the non-producing shaded cell. This is known as reverse bias, and it can cause the shaded cell to permanently degrade and fail.

For conventional silicon-based solar cells, reverse bias is a known problem and engineers have developed a solution: a bypass diode. You can think of this as a small side-channel that allows the water to flow around the kinked hose, keeping the rest of the system running smoothly without building up damaging pressure.

However, the bypass diode solution doesn’t work for perovskite-based solar cells, a leading candidate for the next generation of more efficient and more affordable solar cells, because they are often too “weak”. One of the key pieces in the puzzle to solving this reverse bias problem in perovskite solar cells is understanding how the cell degrades when under reverse bias, and that is the focus of this research collaboration.

The McGehee group has a long history of success in creating and optimizing perovskite solar cells. Beginning in 2018, their focus shifted to a critical challenge: what happens when these cells are in the shade? Many researchers had already observed that even a small amount of reverse bias caused the materials to heat up and "melt," leading to rapid and permanent degradation of the perovskite.

While these observations were widely accepted, the exact reason for the degradation was a mystery and a subject of much debate. "These are complex systems, and it can be very hard to untangle what is going on," explained Ryan DeCrescent, one of the study's lead researchers. This is where the McGehee group's work came in—they set out to find the specific mechanism behind this destructive behavior.

"These are complex systems, and it can be very hard to untangle what is going on," explained Ryan DeCrescent

The perovskite layer is formed through an approach called solution processing. Solution processing is kind of like making a pancake, you make your batter and when you pour it onto a hot griddle several things happen: the water evaporates, the solids set, the thickness is determined by how much you add, and you often get gaps, or holes in your pancake. In these devices, the perovskite ingredients are put into a solvent. The solvent is then dropped onto the earlier layers of the device and warmed up, whereby the solvent evaporates and a film is formed, but often with defects, or gaps. Defects and pinholes are easily formed in such films. This is a particular issue for perovskites, since the precursor solution has low viscosity and during the heating stage defect formation is common.

To better understand the impact of these defects on the performance of the solar cells under reverse bias you need to take a really good look at them. Central to this work is a suite of tools that enabled exceptional examination of the perovskite layer. “A large part of this work was really setting ourselves up to look very carefully at these surfaces” said DeCrescent. Four main techniques were employed to better understand the defects: Electroluminescence (EL) imaging with a high-resolution camera, Scanning Electron Microscopy (SEM), Laser-Scanning Confocal Microscopy (LSCM) and Video Thermography. The strategy was to compare ‘before, during, and after’ pictures of devices that had been exposed to reverse bias. The high-resolution camera showed that “weak spots” in the device were the origin of degradation. To better understand “perfect” device behavior and efficiently scan a large number of samples (~100), the team setup a large number of very small devices, creating thin films with an area of just 0.032 mm^2. To put that in perspective, each device was about the width of two human hairs. The small size of these devices meant that it was possible to create devices that were defect-free, since it is hard to create defect-free films on a larger scale. Through this combination of a large sample size, and advanced imaging, the team was able to rapidly explore many different types of defects.

This approach of using advanced imaging proved to be an incredibly effective way not only to identify the defects but also to understand exactly what happens to them. "Video thermography and electroluminescence imaging are really powerful techniques for such devices; for example, defects that are sometimes difficult to spot really stand out using these approaches," explained Ryan. Using the thermography technique the defects glow brightly, and in the electroluminescence technique the defects show as dark. Using these techniques in combination provided a very reliable and effective way of mapping the defects. The techniques clearly revealed where the degradation was occurring.

The team’s evidence strongly supports the argument that defects, like pinholes and thin spots in the perovskite layer, are the precise locations where reverse-bias breakdown begins. The thermography images showed that these sites are where the material rapidly heats up and melts, essentially shorting between the two contact layers. In contrast, defect-free devices showed remarkable stability, surviving hours of reverse bias without any significant degradation.

This level of detailed understanding is crucial for the future of this technology. The team's research provides a clear path forward for scientists and engineers: to develop more robust and stable perovskite solar cells, they must prioritize making pinhole-free films and using more robust contact layers to prevent this kind of abrupt and permanent thermal damage.

This work represents a critical step in the journey toward commercializing perovskite solar cells. It highlights the fact that detail-driven, rigorous scientific approaches are needed to understand complex problems. With this knowledge in hand, scientists can now engineer devices that are designed for longevity, ensuring these promising materials can fulfill their potential.

September 2025

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Powering the Future: U.S. Students Gain International Experience Through Photovoltaics Research in Berlin

Daniel Morton — Tue, 26 Aug 2025 19:43:01 +0000

Powering the Future: U.S. Students Gain International Experience Through Photovoltaics Research in Berlin Daniel Morton Tue, 08/26/2025 - 13:43

Lauren Scholz

A summer of international research concludes as U.S. students contribute to solar innovation in Berlin while gaining hands-on training and global scientific perspective through the NSF-IRES Program.

We are proud to celebrate the successful completion of our first cohort of students bound for Berlin as part of the National Science Foundation International Research Experience for Students (NSF-IRES) Program in metal-halide perovskite photovoltaics. Over the course of ten intensive weeks, nine students from universities across the United States immersed themselves in collaborative research at Humboldt-Universität zu Berlin and Helmholtz-Zentrum Berlin. Their work focused on advancing next-generation solar technologies—specifically, the development and optimization of metal-halide perovskite solar cells.

This timely exchange supported critical progress in the field of photovoltaics, where metal-halide perovskites offer promising pathways to higher efficiency and more versatile solar solutions beyond the limits of conventional silicon-based technologies. By engaging directly with leading German research teams, students not only deepened their technical knowledge and experimental skills but also gained valuable cross-cultural experience and a global perspective on scientific collaboration.

Selected for their academic excellence and commitment to renewable energy innovation, the participants—ranging from undergraduate to graduate level—contributed to a variety of interdisciplinary projects in chemistry, physics, materials science, and engineering. Their contributions helped strengthen the scientific partnerships between U.S. and German institutions and demonstrated the impact of international collaboration in addressing global climate and energy challenges.

Find out more about the 2025 IRES Cohort

2025 NSF IRES-Perovskites participants. Pictured (left to right): Megan Davis, Keya Amundsen, Jiselle Ye, Jack Schall, Keenan Wyatt, Kell Fremouw, Leo Beck, Gabriel Graf. Not pictured: Arial Brookhart.

August 2025

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How non-ohmic contact-layer diodes in perovskite pinholes affect abrupt low-voltage reverse-bias breakdown and destruction of solar cells

Daniel Morton — Tue, 26 Aug 2025 01:55:56 +0000

How non-ohmic contact-layer diodes in perovskite pinholes affect abrupt low-voltage reverse-bias breakdown and destruction of solar cells Daniel Morton Mon, 08/25/2025 - 19:55

JOULE, 2025, 102102

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