UCLA Engineers Develop Transparent Photovoltaic Cells

A sample of transparent photovoltaic cell | Photo courtesy UCLA

Recent research at UCLA into polymer-based photovoltaic cells holds out the possibility that windows may someday be able to generate power from the sun. That's according to researcher Yang Yang, a UCLA professor of materials science and engineering, and director of the Nano Renewable Energy Center at California NanoSystems Institute (CSNI). An update on the team's research was published this month in the journal ACS Nano.

Yang and a team of researchers from CNSI, UCLA Henry Samueli School of Engineering and Applied Science, and UCLA's Department of Chemistry and Biochemistry have developed a photovoltaic cell that converts near-infrared radiation rather than visible light to electric power. The resulting photovoltaic cells allow two-thirds of the visible light hitting them to pass through, and operate at a 4% power conversion efficiency.

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Near-infrared radiation is essentially light with a wavelength too long for the human eye to detect it. By "tuning" their cells' photovoltaic sensitivity to this band of wavelengths, the researchers were able to generate power while allowing visible light to pass unabsorbed.

The main breakthrough Yang's team made was to replace standard PV cell electrodes, which are opaque, with a silver nanowire-metal oxide composite mesh, which conducts electricity while allowing light to pass through almost unhindered. The mesh works in tandem with a polymer photovoltaic layer, which Yang says can be created at a fraction of the cost of expensive crystalline silicon."Our new polymer solar cells are made from plastic-like materials and are lightweight and flexible," he said in a UCLA press release issued today. "More importantly, they can be produced in high volume at low cost."

A four percent power conversion rate means that for every 100 watts of near-infrared energy hitting the panels, four watts of electricity is produced. In real-world terms, a square-meter window of this transparent PV cell, in bright sunlight and tilted to face the sun directly, could power a 20 watt light bulb -- which is admittedly not the best application of the technology. This figure is impressive for the lab, but inexpensive standard thin-film PV cells offer 6% efficiency or better. Yang's team's cells don't offer standard rooftop PV much competition. But if the technology proves viable, such transparent PV cells could be used in a lot of situations where they'd complement rather than compete with conventional photovoltaics, from replacement windows in office buildings to computer screens that trickle-recharge your tablet or phone, or even vehicle windows that add a couple miles' range to your electric car. Yang's team's work bears further watching.

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