2026-05-26 · Tags: solar energy, triboelectric, perovskite, nanotechnology, renewable energy
The eternal knock on solar power has been the same for decades: what happens when it rains? A team at the Institute of Material Sciences of Seville (ICMS) may have found an elegant answer — a 100-nanometer fluorinated coating that turns every raindrop into a tiny lightning bolt of electricity.
The Breakdown #
Researchers Fernando Núñez-Gálvez, Carmen López-Santos, and twelve colleagues published their findings in Nano Energy in late 2025. Their device is deceptively simple in concept: a perovskite solar cell topped with a thin layer of fluorinated polymer (CFₓ) deposited via plasma-enhanced chemical vapor deposition.
That coating does three jobs at once. First, it protects the notoriously moisture-sensitive perovskite layer from degradation — perovskite's Achilles heel. Second, it's over 90% optically transparent, so the solar cell works normally in sunlight. Third, and most interestingly, it acts as a triboelectric nanogenerator.
How Rain Becomes Electricity #
When a raindrop strikes the CFₓ surface, a phenomenon called contact electrification kicks in. The fluorinated polymer has an extremely high electron affinity — it strips electrons from the water on contact, leaving the droplet positively charged. As the drop spreads, recoils, and rolls off the hydrophobic surface, the shifting contact area creates a changing electric field. Electrodes connected to the solar cell's circuit harvest this as current.
The headline number is striking: a single raindrop impact can produce open-circuit voltage peaks of up to 110 volts. Enough, in lab tests, to light an LED.
The Catch (There's Always a Catch) #
That 110-volt figure needs context. It's an instantaneous peak measured with no load attached — the electrical equivalent of measuring a fire hose's pressure with the nozzle capped. The actual current is in the microamp range, and the power output peaks around 4 milliwatts per square centimeter. During sustained rain, average output drops to roughly 40 milliwatts per square meter.
For comparison, a standard solar panel in full sun produces 150 to 250 watts per square meter. That's a ratio of roughly 5,000 to 1.
The physics is unforgiving here. A heavy rainstorm (25 millimeters per hour) delivers about 0.35 watts per square meter of kinetic energy to a surface — and that's assuming 100% conversion efficiency, which no triboelectric device achieves. One back-of-envelope calculation puts it in sharp perspective: in Mawsynram, India, the rainiest inhabited place on Earth at nearly 10,000 millimeters of rain per year, a one-square-meter rain panel would generate about 0.138 kilowatt-hours per year. Worth roughly two cents. A solar panel of the same size would generate 150 to 200 kilowatt-hours, worth fifteen to twenty dollars.
So What's It Actually Good For? #
Not powering your house. But the Seville team isn't pitching it that way. Their target applications are far more modest and far more practical: IoT sensors, environmental monitors, autonomous smart-city devices, weather stations in remote locations — anything that needs a trickle of power in all conditions where replacing batteries is expensive or impossible.
A self-powered rain gauge that reports data every time it rains, powered by the rain it's measuring, is genuinely elegant. Soil moisture sensors in agricultural fields. Air quality monitors on streetlights that keep functioning through weeks of overcast skies. These devices need microwatts, not megawatts.
The CFₓ coating also held up well in durability tests — retaining over 85% output after 17,000 droplet impacts and maintaining 80% of initial performance after 300 hours of continuous illumination in humid conditions. The perovskite cell underneath kept more than 50% of its efficiency after 10 days of high-temperature, high-humidity stress, which, for perovskite, is actually encouraging.
A Crowded Field #
Seville isn't alone in this space. Zhong Lin Wang's group at the Beijing Institute of Nanoenergy and Nanosystems pioneered the concept of droplet-based triboelectric nanogenerators back in 2014. Tsinghua University demonstrated large-scale TENG arrays in 2023 with theoretical peak outputs of 200 watts per square meter under optimized conditions. Soochow University integrated TENGs directly with silicon solar cells as early as 2018. Groups in South Korea, Japan, and Hong Kong have all contributed variations.
What makes the ICMS work stand out is the triple-duty coating. Rather than bolting a separate energy harvester onto a solar panel — adding cost, complexity, and potential failure points — they engineered a single layer that simultaneously protects, improves, and harvests. The perovskite cell achieved 17.9% power conversion efficiency, which is competitive with commercial silicon cells.
The Honest Assessment #
Rain-powered solar panels won't replace conventional solar. The energy density of falling water is simply too low by orders of magnitude. But calling it a failure misses the point. The real innovation is a better perovskite solar cell — one that's more durable, more efficient in diffuse light, and happens to squeeze a few extra milliwatts out of the rain that would otherwise just sit there doing nothing.
For the billions of IoT devices that need to sip power for years without maintenance, that "nothing" might be exactly enough.
Research sourced from Núñez-Gálvez, F. et al., "Water-resistant hybrid perovskite solar cell - drop triboelectric energy harvester," Nano Energy 148, 111678 (2025). DOI: 10.1016/j.nanoen.2025.111678. Additional coverage from pv magazine, EurekAlert, and SciTechDaily.