Porous silica coating reaches 91.0% solar-glass transmission in lab

At a laboratory bench, a thin layer of porous silicon dioxide is being asked to do two jobs on a solar panel’s front glass: let more sunlight through and let more heat escape. Researchers from Karlsruhe Institute of Technology in Germany and the University of Namibia report that their best two-layer coating reached 91.0% solar transmittance and 90% mid-infrared emissivity, versus 89.8% and 87% for bare glass.

The mechanism is built into the material’s pore structure. The coating reduces optical reflection at the glass surface while increasing the glass’s ability to emit thermal radiation in the mid-infrared range, addressing two sources of loss identified by corresponding author Gan Huang. The team made the layer through a sol-gel process using silica precursors and a pore-forming template, then sintered the samples at 450 C for one hour.

Thickness is the trade-off. A single layer produced solar transmittance of 90.9% to 91.0%, while thicker coatings pushed emissivity as high as 96%—around 10% higher than bare glass—but reduced solar transmission through scattering. The strongest overall balance came from two layers containing 0.40 g of Pluronic F127.

And so what, concretely? The researchers observed a roughly 1.2-percentage-point gain in transmittance. Assuming photocurrent scales approximately linearly with transmitted sunlight, they estimate that a photovoltaic module with 20% efficiency could reach approximately 20.25% from this optical gain alone. That is a laboratory estimate, not a demonstrated module-level result.

The next test is outside the glass sample: the team plans to integrate the coating with complete photovoltaic modules and measure electrical output and operating temperature outdoors. It also wants scalable large-area coating methods suitable for industrial cover glass, along with long-term durability and possible anti-soiling studies.