RIVERSIDE, CA, Aug 4, 2025 – UC Riverside (UCR) researchers have developed an imaging method to reveal how advanced materials in solar panels and light sensors convert light into electricity. Their findings, published July 30, 2025, in the journal Science Advances, may improve the design of solar technology and fiber-optic communication devices.
Led by associate professors Ming Liu and Ruoxue Yan, the team at UCR’s Bourns College of Engineering created a three-dimensional technique that distinguishes between two processes in quantum materials. The first, known as the photovoltaic (PV) effect, is familiar from traditional solar panels. When light hits a semiconductor, photons knock electrons loose, and these electrons flow to electrodes to produce electricity.
The photothermoelectric (PTE) effect operates through a different mechanism. When light heats the electrons, these electrons become hotter than their surroundings. The temperature difference causes the energized electrons to move toward cooler regions, creating an electric current as they flow. Unlike the photovoltaic (PV) effect, where electrons move toward electrodes, electrons in the PTE effect tend to move away from electrodes.
“Before now, we knew both effects were happening, but we couldn’t see how much each one contributed and how they spatially distribute,” Liu said. “With our new technique, we can finally tell them apart and understand how they work together. That opens new ways to design better devices.”
The researchers tested their method on nanodevices made from molybdenum disulfide (MoS₂) paired with gold electrodes. This ultrathin semiconductor is under study for new electronics due to its optical and electrical traits.
Using a scanning technique that channels light through an atomic-force microscope tip, the team pointed where and how the PV and PTE effects took place at the nanometer scale. The PV effect appeared at the gold-MoS₂ junctions. However, the PTE effect spread further into the MoS₂ than what was anticipated.
“This goes against the conventional wisdom,” said Xu, the Ph.D. student who was the first author of the paper, added. “It shows that heat-driven effects can influence electrical output over much larger areas, even away from the metal contact.”
The team also tested the effect of adding a layer of hexagonal Boron Nitride (h-BN) above the MoS₂. Redirecting heat sideways through the MoS₂ boosted the PTE effect, increasing current production. “Normally, you try to keep heat localized,” Xu said. “But in this case, letting it spread out actually helped.”
To separate the PV and PTE contributions, the researchers varied the distance between the microscope tip and the sample. By tracking changes in current and breaking down the signal with multi-order harmonic analysis, they separated the two effects for the first time.
These advances could inform engineers designing smaller, yet efficient light detectors for fiber-optic systems or solar devices that convert both light and heat to electricity.
“The idea that we can fine-tune a photodetector’s performance using heat flow is really exciting,” Liu said.
Source: University of California, Riverside
About UC Riverside
The University of California, Riverside, (UCR) founded in 1954, is a public research university located in Riverside, CA. The campus offers 81 undergraduate majors, 48 master’s programs, and 42 doctoral degrees across three colleges, two professional schools, and two graduate schools. UCR reported a campus budget of about $1.3B in fiscal year 2023, with an endowment nearing $250M. It serves a diverse global community, with international students from over 65 countries. UCR employs approximately 3,576 faculty and staff across its campuses. UCR’s academic programs span engineering, science, humanities, business, public policy, and creative writing. UCR is engaged in research and industry partnerships in fields such as AI, robotics, environmental science, and public policy, supporting innovation and workforce development from its Riverside headquarters.