photo by: Josie Heimsoth/Journal-World

Graduate student Kushal Rijal stands with the lasers used in a used an experimental technique dubbed the “time-resolved two photon photoemission spectroscopy,” or TR-TPPE on Monday, July 22, 2024.

The University of Kansas has invested in numerous research projects to understand the mechanics of solar panels. Lately, however, some researchers are looking into improving sustainability and environmental friendliness.

The researchers have turned their own energy to several new topics, including improving organic semiconductors to replace silicon versions in harnessing the sun’s rays and finding new and better ways to recycle the panels at the end of their lives.

While solar panels provide almost 4% of the world’s electricity and remain a key solution for reducing carbon emissions, they can deteriorate and become less efficient over time. Typically, after 25 to 30 years, it’s more cost-effective to replace them. Experts anticipate that eventually, billions of panels will require disposal and replacement, and many say it’s a waste of valuable resources.

Additionally, solar panels can be made with products that have some disadvantages, like silicon, the same material found in everyday electronics. However, silicon solar panels come with some drawbacks, such as high costs and difficulties in mounting them on curved surfaces. Two research teams at KU are addressing both of these problems.

In addition to these projects, another KU project found that if you install panels on roofs with vegetation, the panels will produce an average of 1.4% more energy as compared with those over the white and black roofs. Another area of research focused on developing ultrathin and flexible solar cells – which convert sunlight into energy – with high efficiency using graphene, a single layer of carbon atoms.

Meanwhile, today a 10-kilowatt solar array sits on the roof of the Measurement Materials and Sustainable Environment Center, and it was funded as part of Westar Energy’s Solar Photovoltaic Project. The panels, expected to operate until at least 2040, provide an opportunity for students and faculty to gain experience with and conduct research using an operational solar array.

While the solar panel industry continues to develop, there are several steps these panels can take to become more environmentally friendly, and these KU researchers are striving to achieve just that.

A sustainable semiconductor

Although organic semiconductors have been used in electronics like cellphones, TVs and virtual-reality headsets, their application in commercial solar panels has been limited.

Organic solar cells don’t turn light into electricity as efficiently as the typical silicon solar cells. Where the silicon-based cells can convert about 25% of light energy into electricity, their organic counterparts have typically fallen around the 12% range. Recent advancements, however, are narrowing the gap.

A new class of organic semiconductors, called non-fullerene acceptors (NFAs), have reached a 20% efficiency rate. The scientific community has yet to determine how the NFAs outperform other organic semiconductors, but a team at KU is on the case.

Wai-Lun Chan, an associate professor of physics and astronomy, and his team, along with chemistry professor Cindy Berrie, uncovered a microscopic mechanism that partially explains the performance of an NFA.

photo by: Josie Heimsoth/Journal-World

Wai-Lun Chun and Kushal Rijal are able to perform the TR-TPPE measurement using the ultra-high vacuum photoemission spectroscopy system shown on Monday, July 22, 2024.

The researchers used an experimental technique dubbed the “time-resolved two photon photoemission spectroscopy” in their research. The technique tracks the energy of excited electrons and their relationship with solar cells.

“We are trying to study how these electrons behave in the case of (their interactions with) solar cells after they’re excited by light,” Chan said. “(Then) we can understand what kind of nanoscale structures would be needed to convert them to some kind of useful electrical current.”

To achieve this, the team put together a prototype material that was used in high performance solar cell devices. They use two different laser beams, one to excite the electrons by simulating what sunlight does, and the other to further excite those electrons out from the material. In this way, they can measure the energy of these electrons, which allows them to distinguish whether those electrons would contribute to the electrical current in an actual solar cell device, said graduate student Kushal Rijal.

With the help of this research, scientists can begin to uncover why this particular organic semiconductor is much more efficient than the rest, and help progress towards making these affordable and sustainable alternatives more available. The application of this organic semiconductor could serve in many applications that cannot be done with silicon, Chan said.

These organic materials used in the conductors can be customized to absorb light at specific wavelengths, allowing for the development of transparent solar panels or panels in various colors. These capabilities make organic solar panels particularly ideal for modern, eco-friendly, and sustainable buildings.

Recycling solar panels

Scientists at KU are using a $1.3 million grant from the U.S. Department of Energy to tackle an impending waste crisis by showing that solar panels can be recycled in an effective and environmentally friendly way.

Solar panels are made up of multiple layers, such as glass, adhesives, metals, and semiconductors. Extracting rare metals from panels at the end of their life is costly, time-consuming, and involves harsh chemicals. The U.S. National Renewable Energy Laboratory reports that fewer than 10% of decommissioned panels in the country are recycled.

photo by: Josie Heimsoth/Journal-World

Bala Subramaniam and Hongda Zhu are developing a new technology to easily separate the layers of solar panels, then use ozone to recover the valuable metals on Thursday, July 18, 2024.

“(If you) put panels in landfills, there would be problems just like with plastics,” said Bala Subramaniam, a professor of chemical engineering at KU and director of the Center for Environmentally Beneficial Catalysis. “There are environmental risks because solar panels use metals like tellurium and cadmium. Those could be toxic if they escaped into the environment, and plus, it’s not the solution to put them in a landfill.”

The research team plans to address this issue by creating a new technology for efficiently separating the layers and then utilizing ozone to recover valuable metals. They will initially develop and refine this process in the lab, followed by economic and environmental modeling to adapt the solution for industrial-scale application.

The research team is collaborating with the largest manufacturer of solar panels in North America, First Solar, on this project. First Solar is providing KU with samples to test out and for them to develop their technologies on, Subramaniam said.

“Currently, the conventional techniques that are being used are you just take the solar panel and then you just crush it in order to recover valuable metals,” Subramaniam said. “We don’t want to disperse them because they are valuable, and we want to reuse them again.”

Subramaniam said his team wants to help create a circular economy concept, which is a model of refurbishing and recycling existing materials as long as possible. There are multiple layers within a panel that people currently have to break through to obtain these metals. The teams hopes to minimize that effort and to maximize the recovery so these resources can continue to be used again.