Researchers in South Korea have developed another potential option for transparent solar cells that can be used to replace or complement glass to help provide a more sustainable source of power for buildings, mobile devices, automobiles, and other applications.

Scientists at Incheon National University in Korea created a fully transparent solar cell that provides solar technology that appears invisible to the naked eye while also blocking potentially dangerous forms of light, said Malkeshkumar Patel, an adjunct professor in the Photoelectric and Energy Device Application Lab (PEDAL) of Incheon's Department of Electrical Engineering.

"A transparent solar cell (TSC) is a hidden solar cell bypassing the visible range light while absorbing harmful UV light to generate electric power," he told Design News. By appearing invisible and being transparent like typical windows, these cells can provide solar energy in numerous novel applications, Patel said.

The cell developed by the team, led by Incheon Professor Joondong Kim, demonstrated a power conversion efficiency of 2.1 percent, which is on par with comparable technology and a significant rate given that it harvests energy from a small part of the light spectrum, he said.

Indeed, while commercial solar cells offer power efficiencies as high as 24.4 percent, Patel said, they present their own challenges and limitations in terms of deployment and application.

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"The visible and IR photons from solar radiation captured for power production from large arrays installed in remote places, far from the urban area," he explained to Design News. "The use of conventional solar panels' opaque surface is critical to hinder comprehensive human-life utilization. These issues include stringent installation; integration limitations with emerging energy systems such as sensors, windows, and automobiles; the weight of the solar panels; and the panel's opaque nature, preventing everyday use."

Transparent solar cells, on the other hand, "produce electric energy with rich optoelectronic characteristics and see-through feature," Patel told us. The new cells developed by the team also are more environmentally friendly to produce in terms of their materials than commercially used silicon cells, he said.

Advancing the Technology

The Incheon team already has experience in developing transparent solar cells, and the new research builds on this work. Previously, scientists led by Kim developed a "dry" hybrid transparent voltaic device that uses metal-oxide semiconductors instead of solutions.

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"We applied the hybrid structure in our previous transparent solar cell technology," Patel explained to Design News. "We deployed zinc oxide [and] nickel oxide as n-type and p-type semiconductors and an ultra-thin layer of amorphous silicon as a light-absorption layer. These designed TSCs can offer the visible light wavelength transmittance value of 40 percent with a colorful appearance."

The latest transparent cell uses a combination of new and existing materials in combination for a different result, he said. The first is titanium dioxide (TiO2), a well-known semiconductor already widely used to make solar cells that also is environment-friendly and non-toxic material, absorbing UV light while letting through most of the visible light range.

The second material is nickel oxide (NiO), another semiconductor known to have high optical transparency and one of the most abundant elements on earth.

"In the currently developed TSCs, we deployed TiO2 and NiO as n-type and p-type semiconductors, exhibiting much higher transmittance of the visible wavelength photons (more than 60 percent)," Patel explained. "Interestingly, the large-size device using the heterostructure of TiO2/NiO shows excellent power conversion efficiency of more than 2 percent for the UV-wavelength photons."

To prove their cell's capability, the team powered an electric motor by parallel-connected two TSCs, with results suggesting that the TSCs are an invisible power generator, Patel said. "Moreover, the device also exhibited excellent broadband photodetection with a fast response speed, crucial for artificial eye development," he told us.

Researchers published a paper on their work in the Journal of Power Sources.

In addition to their application for smart buildings, the new cells also can be used in sensors, computing, and robotics to provide alternative and more environmentally friendly sources of power, Patel said.

In terms of robotics, the team envisions the technology being used to provide vision technology similar to how the human eye sees and senses the world, he said.

"TSCs can serve as an artificial eye for next-generation robotics, based on neuromorphic computing, due to the efficient UV sensing and broadband photoreceptive properties," Patel told Design News.

The next steps for the research include experimenting with the transparent cell's efficacy for these new applications, he added.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.