Energy Generation

The Hidden Chemistry Inside Tomorrow’s Solar Cells

Daniel Morton — Thu, 23 Jul 2026 16:06:02 +0000

The Hidden Chemistry Inside Tomorrow’s Solar Cells Daniel Morton Thu, 07/23/2026 - 10:06

Daniel Morton

Researchers uncover why perovskite solar cells degrade under reverse bias, opening new pathways to longer-lasting solar technologies.

Researchers just figured out why perovskite solar cells break down surprisingly easily under partial shading, and how to stop it. Perovskite solar cells are among the most promising candidates for the next generation of solar technology. They can convert sunlight into electricity with remarkable efficiency while offering the potential for lower manufacturing costs than today’s silicon-based panels. Before they can be scaled and deployed, there are some critical challenges to be solved, including ensuring the cells remain stable for decades under real-world conditions. A central question has been what happens when a perovskite solar panel is pushed into an unusual electrical state known as reverse bias.

Like all solar panels, perovskite solar cells occasionally experience reverse bias, an unusual electrical condition that can occur when part of the solar panel is shaded while the rest is in full sunlight. It has long been known that reverse bias quickly damages perovskite devices, but the pieces were not all fitting together. Current flowing through the cell under reverse bias is at the heart of the problem, and there are two ways this can happen. The first is apparent if the materials have big defects, electrons bolt through those defects like lightning and fry the cell, an acute failure mechanism. The second mechanism happens even in cells where those large defects are avoided or covered up, current can flow by a process known as quantum tunneling; much like taking a short-cut through interfaces in the cell. This current flows everywhere and while it is less abrupt than electrons flowing through defects, it will cause degradation in the cell over time. This gradual problem is much harder to understand because seeing these subtler processes in the cell is not easy. Existing theories explained parts of the problem, but they couldn’t fully account for how quickly some cells degraded or why certain device architectures proved far more resilient than others. Something important was happening inside the device that researchers couldn’t yet see.

Late last year, in October of 2025, a report led by RASEI Fellow Michael McGehee, a Professor at the University of Colorado Boulder, in collaboration with researchers at the National Laboratory of the Rockies (NLR; then named NREL), that explored the underlying mechanisms of the abrupt failure mechanisms of perovskite films under reverse-bias was published in Joule. The team identified that the defects were the sites of failure and demonstrated how to create films without defects that were much more robust to exposure to reverse bias.

To explore and better understand the gradual mechanism for degradation Michael McGehee assembled a new team of collaborators with the required expertise, including the groups of Edward Sargent from Northwestern University, Neal Armstrong at the University of Arizona, David Ginger at the University of Washington, and Joey Luther another RASEI Fellow at NLR. Together they combined advanced time-resolved electrical measurements, device modeling and materials characterization to watch how perovskite solar cells responded under reverse bias conditions, just published in Joule. Rather than just observing the damage, they set out to answer the key question of what hidden process was driving it?

The layers inside a solar cell create an energy landscape that electrons must navigate to get through the cell. By design, the interfaces act as energy “mountains” separating two valleys where electrons can be. Under reverse bias, ideally electrons cannot get over (or through) the mountain; the mountain is wide enough to keep electrons where they belong, and no current flows. Using these advanced measurement techniques, the team, led by Kell Fremouw (a Graduate Student in the McGehee group) and Ryan DeCrescent (a Research Associate with the McGehee group) was able to investigate the current-flow and degradation mechanism in remarkable detail. They were able to uncover a hidden process that had largely escaped attention: Under reverse bias, electrochemical reactions inside the solar cell weren’t just moving charged particles around as previously thought, they were actually creating new mobile ions. As these newly created ions redistribute and accumulate near interfaces, they gradually reshape the energy mountain, making it thinner until quantum tunneling becomes easy, and making it much easier for damaging current to pass through. Essentially the shifting chemistry was changing the device physics, providing important insights into why some device architectures show electrical breakdown and degrade much faster than existing models could explain.

These observations underlined an important perspective about these devices. Rather than simply behaving as electronic devices that move electrical charge, the cells also function as tiny chemical systems, with electrochemical reactions reshaping their internal structure under certain conditions. The initial device physics governs the ion creation, and the ion creation changes the device physics; this is an important feedback loop that can accelerate degradation. Identifying the hidden chemistry gives the researchers a much clearer picture of why the degradation occurs, and possible ways to prevent it.

Based on these findings, the team was able to identify where to intervene. The answer isn’t to try and repair the damage after it has begun, but to stop the chemical reactions from starting in the first place. By improving on the ultra-thin transport layers inside the device, the so-called hole transport layer (or HTL), the researchers showed that they could block the reactions responsible for creating new mobile ions. This solution is one that doesn’t require new equipment or exotic new materials, the team used standard materials and procedures but ensured that the layer placed in the device was very smooth, improving the coverage of the layer. With the electrical landscape preserved, the pathway to damaging currents remains closed, helping the cells maintain their performance for longer.

Daniel Morton — Mon, 05 Jan 2026 19:31:00 +0000

Locking in Solar Power: How a Stronger Interlayer Boosts Perovskite Cell Durability Daniel Morton Mon, 01/05/2026 - 12:31

New Molecular Designs Extend the Life and Efficiency of Next-Generation Solar Cells

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Posted on the RASEI website with permission and minor modifications from the piece published by David DeFusco on the UNC Chapel Hill Applied Physical Sciences Site here.

A new study published in Science led by researchers at UNC-Chapel Hill, with collaborators from the Renewable and Sustainable Energy Institute (RASEI), explains why perovskite solar cells—fast-rising rivals to traditional silicon panels—tend to break down under prolonged heat and sunlight, especially ultraviolet light, and reveals a promising strategy to dramatically slow that damage.

The work focuses on a thin “interlayer” that sits between the electrode and the perovskite material inside a solar cell. This layer is only a single molecule thick, but it plays an outsized role in how long the device lasts.

“These interlayers are meant to help charges move efficiently out of the perovskite and into the circuit,” said Chengbin Fei, first author of the study and a postdoctoral researcher in UNC’s Department of Applied Physical Sciences. “But we found that some of the same chemical features that make them useful can also cause long-term damage if they’re not tightly attached to the electrode.”

Many high-performance perovskite solar cells use interlayers based on phosphonic acids. These molecules stick to a transparent electrode made of indium tin oxide, or ITO, and help pull positive charges out of the perovskite. Until now, most researchers assumed these layers were harmless once installed. Fei and his colleagues discovered that this is not always true.

The researchers found that some of these tiny helper molecules aren’t firmly stuck to the solar cell’s surface. When the cell gets hot or sits in sunlight that includes ultraviolet rays, those that are loosely attached molecules can break free. Once that happens, they start interfering with the solar material itself. They trigger harmful changes inside the cell: key ingredients fall apart, iodine-related components react in damaging ways and lead turns into a form that no longer works properly. Over time, all of this damage adds up and causes the solar cell to produce less and less electricity.

“In simple terms, the acid part of these molecules can act like a slow poison,” said Fei. “At high temperatures and under UV light, it accelerates chemical reactions that the perovskite just can’t tolerate.”

To understand what was happening, the researchers used a range of techniques, including spectroscopy and X-ray measurements, to watch how the materials changed over time. They found that stronger acids caused faster damage and that UV light made the reactions much worse. This explained why devices that look stable at first can fail after hundreds or thousands of hours outdoors.

The key advance came when the researchers at UNC and the University of Colorado Boulder created a new version of this thin helper layer containing a combination of two molecules that sticks much more tightly to the electrode surface. Seth Marder, the senior author at the University of Colorado-Boulder and Director of the Renewable and Sustainable Energy Institute (RASEI) says “the molecule our team developed was designed to not only interact with the electrode surface but more strongly with its neighboring molecules. Consequently the molecules stay more securely in place, reducing the reactive parts that can break away and damage the solar material that is deposited on top ”. As a result, the layer still helps charges flow out of the cell, but it no longer triggers the damaging reactions that shorten the cell’s lifetime.

Simply put, “when the molecule is firmly locked onto the surface, it can’t wander into the perovskite and cause trouble,” said Fei. “That simple change makes a huge difference over time.”

Solar cells made with the new interlayer design showed striking improvements and met a key performance milestone. Under harsh test conditions—85 degrees Celsius, continuous bright light that included UV and constant operation—the devices ran for nearly 3,000 hours before losing just 10 percent of their efficiency. That level of durability has not been reported before for this type of perovskite solar cell.

The molecule our team developed was designed to not only interact with the electrode surface but more strongly with its neighboring molecules. Consequently the molecules stay more securely in place, reducing the reactive parts that can break away and damage the solar material that is deposited on top.
- Seth Marder

The researchers also scaled up their approach to small solar modules, closer to what might be used in real products. These “minimodules,” about the size of a postcard, reached power conversion efficiencies above 22 percent and kept working for more than 2,000 hours under the same stressful conditions, which is considered very high performance for this type of solar technology.

Jinsong Huang, senior author of the paper and UNC Louis D. Rubin Distinguished Professor, said the results address one of the most important barriers to commercialization. “Efficiency alone is not enough,” he said. “For perovskite solar technology to succeed outside the lab, it must survive heat, light and time. This work shows a clear chemical pathway to make that happen.”