Researchers at Yunnan University, the Southwest United Graduate School, the Fujian Institute of Research on the Structure of Matter (Chinese Academy of Sciences), and EPFL have demonstrated perovskite solar cells that operate submerged at depths of up to 10 meters, an application the team says extends underwater solar harvesting far beyond the shallow depths (2 m or less) explored in prior work.
The schematic diagram of submerged perovskite solar cells for underwater applications. Credit: Simin Ma, Yunnan University
The devices were field-tested at 10 m depth off the Weizhou Islands in the South China Sea, where large-area modules generated 324 mWh of electricity over two hours of submerged illumination - enough to charge lithium-ion batteries and power LEDs.
Sunlight attenuates sharply with depth in water, and by 10 m the surviving spectrum is a narrow blue-to-orange band very different from the full solar spectrum reaching a device on land. The team addressed this by using a wide-bandgap (~1.96 eV) lead halide perovskite whose absorption is spectrally matched to that underwater band, and built a custom underwater solar simulator with tailored optical filters to evaluate device performance realistically at various depths rather than relying on standard AM 1.5G testing alone.
To make the wide-bandgap perovskite itself efficient and durable, the researchers introduced polyhexamethylene guanidine hydrochloride (PHMG) as a crystallization additive. PHMG converts the perovskite from p-type toward n-type character, which the team reports improves electron extraction, suppresses halide ion migration, reduces defect density, and improves lattice stability. The resulting submerged perovskite solar cells (S-PSCs) reached a certified power conversion efficiency of 16.79% under standard AM 1.5G illumination, but 34.71% under the simulated 10 m-deep underwater spectrum - reflecting how much better the device is matched to underwater light than to full sunlight.
Stability testing backed up the lab results: the cells retained about 96% of their initial efficiency after 300 days of storage in a nitrogen glovebox, and showed almost no degradation after 1,160 hours under simulated 10 m submerged conditions. Accelerated aging tests projected a T80 lifetime of roughly 48,094 hours, or about 5.5 years, under those simulated conditions. The team then scaled the approach from small lab cells to large-area modules for the South China Sea field deployment, which they present as the first functional validation of perovskite photovoltaics operating at meaningful depth in real seawater rather than in a lab tank.
"Very few studies have been reported on underwater solar cells, and all of them are focused on very shallow water depths of only two meters or less, a scenario far from catering for requirements of practical application," said Wen-Hua Zhang of Yunnan University and the Southwest United Graduate School, the study's lead contact. "This work presents the first functional validation of submerged solar cells practically operating at a water depth of up to about 10 meters, greatly broadening their application scope." The team says it next plans to test at greater depths and to work toward standardized testing protocols for underwater photovoltaics, with an eye toward powering autonomous underwater vehicles, marine sensors, and submerged Internet-of-Things infrastructure.
