Lehigh Physicists Pioneer Quantum Material for Solar Efficiency Breakthrough

Physicists at Lehigh have developed a quantum material, atomically thin CuxGeSe/SnS, which is positioned as a leading candidate in a new class of materials aimed at significantly enhancing solar panel efficiency.

The development holds promise for advancing solar technology to meet the increasing global demand for clean energy.

A simulated prototype employing this material in the active layer of a solar cell exhibited an average photovoltaic absorption rate of 80%, a high generation rate of photoexcited carriers, and an external quantum efficiency (EQE) reaching an unprecedented 190%-a measure that far exceeds the theoretical Shockley-Queisser efficiency limit for silicon-based materials and pushes the field of quantum materials for photovoltaics to new heights.

"This work represents a significant advancement in sustainable energy solutions, showcasing innovative approaches that could revolutionize solar energy efficiency and accessibility in the near future," said Chinedu Ekuma, professor of physics.

Ekuma, along with doctoral student Srihari Kastuar, published their research in the journal Science Advances.

Since publication, the potential breakthrough development has received glowing coveragefrom

science-focused news outlets across the globe. Ekuma also recently presented the findings at a gathering of scientists convened by the U.S. Department of Energy, where the research was met with enthusiasm.

A Quantum Leap in Solar Efficiency

The remarkable efficiency of the material is largely due to its unique "intermediate band states," which are specific energy levels within the material's electronic structure that optimally convert solar energy. These states feature energy levels positioned within subband gaps-ranging from approximately 0.78 to 1.26 electron volts-ideal for efficient sunlight absorption and charge carrier production. In addition, the material performs especially well with high levels of absorption in the infrared and visible regions of the electromagnetic spectrum.

Typically, traditional solar cells achieve a maximum EQE of 100%, correlating to the generation and collection of one electron for each photon absorbed. However, the Lehigh-developed material utilizes intermediate band states to capture photon energy typically lost in conventional cells, including energy lost through reflection and heat production.

"Our engineered material excels beyond other intermediate band semiconductors as it hosts IB states without significant alterations to the crystal structure or the introduction of defects," explained Kastuar. "The intercalated copper atoms induce effects typically achieved through heavy-doping."

The novel material was developed using "van der Waals gaps," minuscule spaces between layered two-dimensional materials that can host atoms, molecules or ions. By intercalating zerovalent copper atoms between layers of germanium selenide (GeSe) and tin sulfide (SnS), the researchers tuned the material properties to enhance its photovoltaic performance.

But is it practical?

Ekuma, an expert in computational condensed matter physics, developed the simulated prototype as a proof of concept after extensive computer modeling of the system demonstrated theoretical promise.

Although integrating the newly designed quantum material into current solar energy systems will require further research and development, Ekuma pointed out that the experimental technique used to create these materials is already highly advanced.

Scientists have, over time, mastered a method that precisely inserts atoms, ions and molecules into materials, and encouraging results from a fabricated sample of the material were reported shortly after Ekuma's initial publication.

A team of experimentalists, including scientists from Worcester Polytechnic Institute and the University of California-Davis, fabricated a sample of the material and conducted a variety of advanced analyses to characterize its properties.

Those results, published in the journal Applied Materials and Interfaces, concluded that intercalating zero-valent copper into layers of GeS was indeed a promising strategy offering "profound effects" for the enhanced functioning of photoelectric devices and solar energy conversion systems.

"Its rapid response and enhanced efficiency strongly indicate the potential of Cu-intercalated GeSe/SnS as a quantum material for use in advanced photovoltaic applications, offering an avenue for efficiency improvements in solar energy conversion," Ekuma said.

Beyond enhanced performance in solar applications, the material offers additional advantages in terms of environmental sustainability. Copper and germanium are well-established materials that are less toxic than lead-based materials used in some solar panels. In addition, GeSe is an accessible resource, six times more abundant than antimony (Sb), an element currently used in many thin-film solar cells.

"Our material is a promising candidate for the development of next-generation, high-efficient solar cells, which will play a crucial role in addressing global energy needs," Ekuma said.

The research was funded in part by a grant from the U.S. Department of Energy.

Story by Dan Armstrong

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