accounting for most new capacity added to U.S. electric grids in 2024 - but the mid-1950s technology most often used to capture the sun's energy comes with environmental costs.
Manufacturing silicon solar panels is an energy-intensive process that requires toxic chemicals and creates recycling challenges. But lower-impact organic solar cells, made with less harmful materials, can break down too easily for large-scale deployment. According to Penn State researchers, adding a chemical derived from hydrogen and carbon may help organic solar cells become a more viable alternative. The team published their findings in the journal ACS Materials Au. The paper also earned recognition as part of the "2025 Rising Stars in Materials Science" issue from ACS Materials Au, to be published this month.
Led by Assistant Professor Nutifafa Doumon and doctoral candidate Souk Yoon "John" Kim in the Department of Materials Science and Engineering, the research centers on the solid additive 9,10-phenanthrenequinone (PQ). The researchers said their work shows the hydrocarbon derivative holds environmentally friendly possibilities for stabilizing and strengthening organic solar cells.
Also known as organic photovoltaics, the hydrocarbon-based technology can quickly wear down its ability to convert solar energy to electricity.
"PQ is also low-cost, commercially available, safer and simpler than many existing additives introduced in the manufacturing process," said Kim, who is advised by Doumon. "Better stability is a must for organic solar cells to become a more competitive option in the commercial market."
Incorporating PQ "may offer a practical pathway toward sustainable, scalable and durable alternative photovoltaics," he added.
Doumon, a faculty affiliate of the EMS Energy Institute in the College of Earth and Mineral Sciences, credited Kim for encouraging the study.
"It was John who first thought of using PQ as a nonvolatile option to improve the stability of organic solar cells - and avoid commonly used toxic additive," Doumon said. "PQ is commercially available, eco-friendly, tolerant of heat and it prevents rapid degradation in organic solar cells."
For their paper, the researchers made organic cells in varied structures, and with differing additives, in Doumon's lab at University Park. They tested the cells for longevity, resilience and efficiency under a range of temperatures and other environmental conditions, evaluating the cells for their ability to convert light energy over time.
Among their discoveries, the researchers found that PQ improved the efficiency of the cells - that is, the portion of light energy converted to electricity - in addition to longevity. They incorporated additives in what's known as the cell's active layer, which absorbs solar radiation.
The study results highlight the potential reliability and the commercial promise of organic solar cells as the energy industry looks to supplement silicon cells with need-based alternatives, according to the team. PQ helped organic solar cell devices retain more than 93% of their original power-conversion efficiency under sustained heat for 180 hours. That compares to 76% retention among devices with a commonly used toxic additive after the180 hours of use.
Even moderate stability improvements greatly reduce organic solar cell replacement frequency, waste and operating costs, the researchers said. Organic cells tend to be more flexible, lighter and less expensive to produce than their silicon counterparts - but with lifespans that are years shorter.
"We're not claiming that PQ solves all the problems," Doumon said. "Our findings are one step forward. We're looking at other solid additives for further study, to see where PQ falls in a broader spectrum of options."
The Materials Research Institute and the Institute of Energy and the Environment at Penn State partly funded the research. Assistant Professor Ivy Mawusi Asuo and past graduate students Pascale N'goran and Arthur Jin, all in the Department of Materials Science and Engineering, are co-authors.
