New perovskite underwater solar cells can generate electricity at a depth of 10 metres, with an estimated operational stability of around 5.5 years.
Underwater solar cells, how far has the technology come?
Over the years, photovoltaic technology has crossed several physical boundaries, moving well beyond its traditional operating environment. After reaching space, where solar cells must withstand radiation, extreme temperature fluctuations and high vacuum conditions, researchers are now looking beneath the surface of seas and oceans.
This is not just about floating solar installations. Research is increasingly focusing on systems capable of operating below the water’s surface.
How deep can they go? A new study has set a record by developing underwater solar cells capable of generating electricity at a depth of 10 metres and operating continuously for an estimated 5.5 years.
Underwater photovoltaics, between limitations and potential
One obvious question is why researchers should invest time and resources in optimising underwater photovoltaics. Water is far from an ideal medium for transmitting light. Its molecules absorb, scatter and reflect photons in ways that create significant challenges for solar power generation.
More specifically, water completely absorbs light at wavelengths above 730 nm, including red and infrared light, while conventional silicon or cadmium telluride solar cells absorb photons above 800 nm, making them ineffective underwater.
The deeper solar cells are placed, the smaller the portion of the spectrum available for electricity generation becomes.
Despite these limitations, research in the field has continued for a simple reason. A range of aquatic applications, from aquaculture monitoring systems to underwater drones, require autonomous power sources.
“Very few studies have been published on underwater photovoltaic cells, and all of them focus on very shallow water depths of only two metres or less, a scenario far from meeting the requirements of practical applications,” explains Wen-Hua Zhang of Yunnan University in China and author of the new research. “This work presents the first functional validation of submerged solar cells capable of operating effectively at water depths of up to around 10 metres, greatly expanding their potential range of applications.”
New perovskite underwater solar cells
To achieve this result, Wen-Hua Zhang and his colleagues focused on lead halide perovskite photovoltaics, materials characterised by a high absorption coefficient and, importantly, a tunable bandgap.
For the experiment, the researchers used a wide bandgap of around 1.96 eV together with a specific additive, PHMG. The additive helped optimise crystallisation, improve energy-level alignment and reduce recombination losses.
Laboratory results showed a conversion efficiency of 16.79% under standard conditions, rising to an impressive 34.71% at a depth of 10 metres, where the available light spectrum is particularly well suited to the material.
The tests also indicated an operational stability of around 5.5 years at 25°C while submerged. Real-world trials with large-area modules confirmed that the technology could generate 324 mWh during two hours of underwater illumination at a depth of 10 metres, enough energy to charge lithium batteries and power devices such as LEDs.
“What surprised us most was the amount of electricity generated by our large-area modules under real-world conditions, at a depth of 10 metres, in just two hours,” Zhang says. “In addition, we were able to scale up from small laboratory cells to large-area modules. The combination of laboratory investigations and field experiments provides solid evidence that underwater photovoltaics can work.”
Researchers plan tests at greater depths
The research will not stop here. In future studies, Zhang’s team plans to test perovskite underwater solar cells at greater depths, investigating their operating limits and developing standardised testing protocols for underwater photovoltaics.
The study, Submerged solar harvesting with wide-band-gap perovskites for autonomous underwater energy systems, was published in Joule.
