On July 31, 2025, researchers at the University of California, Riverside (UCR) unveiled a groundbreaking imaging technique poised to revolutionize the design of solar panels and light sensors. This innovative method precisely visualizes how cutting-edge nanomaterials convert light into electrical current, offering critical insights for developing more efficient and faster optoelectronic devices. Published in the journal Science Advances, the study, titled "Deciphering photocurrent mechanisms at the nanoscale in van der Waals interfaces for enhanced optoelectronic applications," marks a significant step forward in understanding fundamental energy conversion processes at the quantum level.

Led by Associate Professors Ming Liu and Ruoxue Yan from UCR's Bourns College of Engineering, the team developed a three-dimensional imaging approach capable of differentiating between the two primary mechanisms of light-to-electricity conversion in quantum materials. The first, the well-known photovoltaic (PV) effect, is the principle behind traditional solar cells, where photons dislodge electrons to create current. The second, the photothermoelectric (PTE) effect, involves light heating electrons, causing them to migrate from hotter to cooler regions and generate current. While both effects contribute to device performance, their individual contributions and spatial distribution were previously unclear.

"Before now, we knew both effects were happening, but we couldn't see how much each one contributed and how they spatially distribute," stated Professor Liu. "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 focused on nanodevices constructed from molybdenum disulfide (MoS2), a 2D semiconductor, integrated with gold electrodes. Utilizing a specialized scanning method that channels light through an atomic-force microscope tip, they mapped the PV and PTE effects down to the nanometer scale. A surprising discovery was the extensive reach of the PTE effect, extending much farther into the material than anticipated, challenging established theories. "This goes against the conventional wisdom," added Da Xu, the Ph.D. student and lead author. "It shows that heat-driven effects can influence electrical output over much larger areas, even away from the metal contact."

The team further demonstrated that introducing a thin layer of hexagonal boron nitride (h-BN) over the MoS2 could strategically redirect heat flow, significantly boosting the PTE effect. This manipulation aligns temperature gradients with the material's thermal response, enhancing current production. "Normally, you try to keep heat localized," Xu explained. "But in this case, letting it spread out actually helped." The novel analysis method, which varies the microscope tip-to-sample distance and employs multi-order harmonic analysis, allowed for the unprecedented isolation of these two effects in real space.

This innovation holds substantial promise for engineers designing compact light-detecting components in fiber-optic communication systems, where thermal management is paramount. It also paves the way for more efficient solar power technologies capable of harnessing both light and heat. "The idea that we can fine-tune a photodetector's performance using heat flow is really exciting," Liu concluded. The research underscores the complex interplay of light, heat, and electricity in advanced materials, promising further discoveries in the field.