Researchers have made near-transparent solar cells that are efficient enough to charge a phone battery. The advance, published in the journal Proceedings of the National Academy of Sciences, is a glimpse at a future in which a phone or laptop screen could soak up the sun to power its battery. The technology could also lead to glass building facades and car windows that harness sunlight for electricity.

Today’s solar cells, made of crystalline silicon, are opaque, usually shiny blue or almost black in appearance. Scientists have been trying to develop see-through solar cells for years because they could expand the use of solar cells in unconventional applications such as windows and greenhouses. But both the transparency and the efficiency of see-through solar cells need improvement.

“The practical application still faces numerous hurdles,” Kwanyong Seo, a professor of energy and chemical engineering and his team at the Ulsan National Institute of Science and Technology write in the PNAS paper.

The issue is the metal wiring that conducts the electricity that the light-absorbing silicon produces. Conventional solar cells have metal wires on the both the front and rear sides. The wires are relatively wide at 3 to 5 mm and are visible on the surface of the cell. So the Korean team came up with a all-back-contact design for the electrodes. The electrode is a see-through metal film created on the rear side of the silicon cells.

To make the silicon layer itself transparent, the researchers riddle it with an array of microscopic holes. The team carefully calculated the diameter of the microholes and the spacing between them. That was crucial to ensure that the holes transmit all visible light and so that they are invisible to the human eye.

This carefully chosen design gave highly efficient and neutral-colored transparent solar cells. The cells have an efficiency of 15.8%. The researchers also made a module composed of 16 cells, which had an overall efficiency of 14.7%.

To demonstrate the new cells’ practicality, the team placed it on top of the glass screen of a Samsung Galaxy 9 phone and charged its battery under natural sunlight.

The researchers say that since all the processes they use except the microhole formation process are identical to commercial solar cell manufacturing, the transparent solar cells should be relatively easy to scale up to large-scale commercial-grade cells for building facades.

Source: Jeonghwan Park et al. All-back-contact neutral-colored transparent crystalline silicon solar cells enabling seamless modularization. PNAS, 2024.