TEAMUP

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

Find out more

Read the Article

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

Off

Traditional

White

A new kind of solar cell is coming: is it the future of green energy?

Anonymous — Thu, 30 Nov 2023 07:00:00 +0000

A new kind of solar cell is coming: is it the future of green energy? Anonymous (not verified) Thu, 11/30/2023 - 00:00

The TEAMUP Consortium, led by RASEI Fellow Mike McGehee, is highlighted in this Nature Feature.

Off

Traditional

White

TEAMUP Consortium funded to develop more stable and affordable tandem solar cells

Anonymous — Thu, 20 Apr 2023 06:00:00 +0000

TEAMUP Consortium funded to develop more stable and affordable tandem solar cells Anonymous (not verified) Thu, 04/20/2023 - 00:00

Daniel Morton

New consortium aims to accelerate the introduction of the next generation of solar panels

The TEAMUP consortium, that brings together researchers from Academic, Industrial and Federal Laboratories, seeks to identify and solve the factors that cause advanced perovskite materials to be unstable, paving the way for the integration into existing and future solar cells, boosting the efficiency of harvesting renewable solar energy.

Download the TEAMUP Press Release

Read the DOE Press Release

Press Release from Congressman Neguse

Feature in the Daily Camera

Solar Energy Technologies Office

Bertoni Research Group | ASU

Beyond Silicon

Holman Research Group | ASU

Kurtz Research Group | UC Merced

Luther Research Group | NREL

Marder Research Group | ��ý�Ļ��Ʒ

McGehee Research Group | ��ý�Ļ��Ʒ

Rolston Research Group | ASU

Sargent Research Group | Northwestern

Swift Solar

Tandem PV

Toney Research Group | ��ý�Ļ��Ʒ

In the last ten years a huge amount of research has focused on the use of Perovskite materials as semiconductors that can be tuned to harvest energy from the sun. Light from the sun excites electrons in the perovskite material, and through clever engineering these electrons can be harnessed to produce electric current. First introduced in the 1950s, modern solar panels use silicon as the semiconductor. Silicon requires a lot of energy to produce and is expensive to manufacture, factors which have driven many researchers to replace silicon with perovskite-based systems – however that technology is still someway off, and we need better solar energy systems right now.

Tandems for Efficient and Advanced Modules using Ultrastable Perovskites, or TEAMUP, a project that has just secured $9M in federal funding from the U.S. Department of Energy Solar Technologies Office (SETO), brings together a consortium of researchers from Academic (��ý�Ļ��Ʒ, Northwestern University, Arizona State University and UC Merced), Industrial (Swift Solar, Tandem PV and Beyond Silicon) and Federal Labs (the National Renewable Energy Laboratory), who have a near term solution for more efficient solar panels using a combination of the new perovskite-based systems and the existing silicon-based systems. So-called Tandem perovskite-silicon solar modules bring together the best of both technologies by putting a layer of perovskite on top of silicon-based devices, boosting the efficiency of capturing solar power. Because this approach builds on top of existing silicon-based technologies instead of completely replacing it, it can be more quickly realized and deployed, even potentially upgrading existing installations. Accessing these more efficient and affordable solar energy harvesting technologies is crucial for transitioning more communities to renewable energy sources in a fair and just fashion.

The tandem perovskite-silicon research community is currently working to answer three main questions on the path to commercialization; how to combine the perovskite and silicon devices (monolithic or mechanically stacked tandems), how to create and process the perovskite layer (vapor or solution processing) and how to make the tandem devices more stable and robust. The TEAMUP consortium has chosen not to limit their research focus by selecting one particular device strategy or processing approach and instead adopting a collaborative approach that brings together expertise across these disciplines to address the stability of tandem solar modules. By working together in this unique innovation ecosystem, one in which researchers who might otherwise be considered competitors can openly share the advantages and disadvantages of each approach, understanding of the challenges can be enhanced and realization of solutions that are applicable broadly, across the different strategies, can be accelerated.

Mike McGehee, the lead investigator from ��ý�Ļ��Ʒ says “We have an extraordinary team who bring many different types of expertise to the Consortium and I look forward to seeing what we can accomplish”. Colin Bailie, Founder and CEO of Tandem PV comments on the collaborative nature of this project “Tandem PV and Swift Solar have long sought to work directly together and with the broader US research community on common research topics that can be solved more quickly as a group. We are excited by the opportunity to work on the same team and not as competitors”.

“We have an extraordinary team who bring many different types of expertise to the Consortium and I look forward to seeing what we can accomplish” - Mike McGehee, TEAMUP lead PI

The key to long-term, real-world operation of these solar modules is the stability of these systems. Solar panels are expected to survive extreme conditions – the heat of the day and the cold of night can provide significant swings in temperature, humidity and general weather scenarios. Under these conditions the perovskite materials can degrade – in the same way that a metal can rust. This can cause reduction in performance efficiencies and lead to blistering in the solar modules. Researchers in TEAMUP are developing strategies to contain and protect the perovskite layers from degradation and enhance stability and real-world operation.

The teams have outlined a two-stage iteration process; innovation followed by comprehensive testing. The innovation stage will explore different perovskite materials, device structures and fabrication approaches. The testing stage will use a comprehensive suite of tools to simulate long-term use under real-world conditions and characterize how these new solar modules perform, the experience and understanding from which will be fed back into the innovation stage. By collecting data at every step of this feedback process TEAMUP will build detailed forecasting models capable of describing performance in real world conditions over a 25 year period, a critical tool in taking this technology to a commercial product.

The importance of the tandem module technology was highlighted by Colin Bailie “Perovskite-silicon tandems represent not only the opportunity to make solar more affordable for more communities in the US, but also a unique opportunity to return the United States to a position of leadership in solar manufacturing and develop a domestic manufacturing base around this new technology. TEAMUP’s success will ensure perovskite-silicon tandems are in a strong technological position as companies prepare for mass production”. Tomas Leijtens, Co-Founder and CTO of Swift Solar agrees “We’re excited to work with this diverse team to tackle the most pressing stability and performance challenges as we scale up perovskite solar technology. This consortium should help accelerate perovskite tandem commercialization in the US”.

Understanding and solving the degradation mechanisms that negatively impact stability in tandem perovskites is essential to demonstrating their feasibility to future investors and customers. By adopting an approach that is agnostic to both perovskite processing and device design, TEAMUP will develop solutions that can be applied across a wide cross-section of the perovskite industry.

RASEI led consortium of academic and industrial researchers focus on improving the stability of next generation solar panels

Off

Traditional

White