New transparent solar cell for window applications

Researchers at South Korea’s Ulsan National Institute of Science and Technology (UNIST) have created a transparent crystalline silicon solar cell by drilling micro-holes into the cell surface measuring about 100 μm in diameter.

The new cell, described in the study Neutral-Colored Transparent Crystalline Silicon Photovoltaics, published in Joule, was made by placing micro-hole-shaped light transmission windows onto a neutral-colored, transparent c-Si substrate with a thickness of about 200-μm. The cell would otherwise be intrinsically opaque.

“Before us, nobody tried to make transparent crystalline silicon with neutral colors,” the scientists said. Previous approaches, they further explained, were based on the fabrication of ultra-thin c-Si films, but due to limited absorption of long-wavelength light, the resulting PV cells had very low efficiencies.

The small micro-holes were designed to enable the transmission of all incident visible light through the substrate, resulting in a colorless substrate.  “The spacing of holes in the transparent c-Si substrate is maintained using a micrometer scale, enabling the spacing to be much smaller than 1.75 mm, such that the hole pattern will be invisible even at a distance of 30 cm,” the scientists said.

The research team also claims to have developed the most efficient transparent solar cell of its kind to date, with a conversion of efficiency of up to 12.2%. This compares with traditional UV- or NIR-absorbing transparent solar cells, which have usually efficiencies that top out at 2%.

“The transparent c-Si substrate shows a completely neutral color without a transmission cut-on wavelength, and its transmittance can be easily tuned by controlling the filling fraction,” the researchers wrote.

Their next step for this technology, which would be applied mainly to solar windows, is to scale up the solar cell to 25 cm2 (3.88 in2) and increase the efficiency to 15%. “We also need to have the mechanical stability and strength to apply our device to replace the current window in the building,” said research author, Kwanyong Seo.