Researchers in China have developed a perovskite solar cell that generates electricity efficiently in the dim, blue-green light of the deep ocean, achieving a record 34.71% power conversion efficiency at a simulated depth of 10 meters. The advance, led by Wen-Hua Zhang at Yunnan University and published in Joule, could enable self-sustaining underwater sensors, environmental monitors, and autonomous marine infrastructure that currently rely on batteries or tethers for power.
Conventional solar cells are optimized for the broad spectrum of sunlight at the surface, particularly the red and infrared wavelengths between 800 and 1150 nanometers. Water absorbs those wavelengths within the first few meters, leaving only a narrow band of blue and orange light spanning roughly 400 to 600 nanometers. Standard silicon, cadmium telluride, and 1.55 eV perovskite cells are therefore poorly matched to underwater illumination, a mismatch that has long stalled the deployment of solar-powered deep-sea equipment.
To address this, Zhang's team engineered a mixed-anion lead halide perovskite with a wide optical bandgap of about 1.96 eV, precisely tuned to absorb the blue-green window that penetrates deep water. Wide-bandgap perovskites are theoretically ideal for this application but suffer from severe degradation on land, where intense light and heat drive halide-ion migration, phase separation, and structural defects. Underwater, the naturally cool temperatures below 25 degrees Celsius and reduced light intensity act as an inherent shield against thermal degradation.
The researchers introduced a crystallization additive, polyhexamethylene guanidine hydrochloride (PHMG), into the perovskite matrix to address remaining internal defects. The polymer combines a water-repelling backbone with chemically active guanidinium cations that anchor into gaps in the crystal structure and bind tightly to lead and halide ions through hydrogen bonding. This dual-action mechanism raised the activation energy barrier for ion migration from 0.07 to 0.21 eV, effectively freezing phase segregation. Ultraviolet photoelectron spectroscopy revealed that PHMG also shifted the film's conductivity from hole-carrying to electron-carrying, creating a favorable energy slope at the surface that accelerates electron extraction and reduces energy losses from trapped charges.
Under standard terrestrial sunlight, the modified cell achieved a certified power conversion efficiency of 16.79%. Tested with a custom underwater solar simulator using multilayer interference optical filters, a small-area cell of 0.0895 square centimeters reached 34.71% efficiency under illumination equivalent to a depth of 10 meters. The team also built large-area modules with an active area of nearly 29 square centimeters, protected by multilayer encapsulation of polyisobutylene, cover glass, and epoxy resin that withstood extreme hydrostatic pressure and saltwater corrosion.
Deployed on a miniature robot in the open waters of the South China Sea near Weizhou Island, the modules harvested solar energy across varying depths. Even at 10 meters, with severely attenuated light, the system maintained stable electricity production, generating 324 milliwatt-hours to charge lithium-ion batteries that later powered a custom LED panel. Zhang noted that real ocean conditions, including waves, turbidity, and suspended organic matter, cause substantial fluctuations in output power, making field experiments indispensable for assessing real-world performance.
Accelerated thermal aging tests and Arrhenius degradation modeling predicted a long operational lifespan for the encapsulated devices. The work offers a path toward autonomous underwater vehicles, deep-sea sensors, and environmental monitoring platforms that could operate indefinitely without battery replacement or surface tethers, though further testing in diverse marine environments will be needed to confirm durability and scalability.
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