UCLA

Slapping solar panels on your humble abode may not seem like the height of fashionable home design, but what if you could just use your windows to gin up a little juice?

Researchers at the University of California, Los Angeles (UCLA) claim they’ve developed a transparent solar cell that’ll do just that, absorbing solar radiation through something like a glass-fitted opening without compromising your ability to see through it.

But one of the key features of the UCLA team’s discovery is that it generates energy by using a “photoactive plastic material” that absorbs primarily infrared light, as opposed to visible, creating electricity by tapping radiation no human eye can see.

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The upside of designing the cells to primarily capture infrared energy in lieu of visible? The cells are “nearly 70% transparent to the human eye,” says the UCLA press office. In other words, based on the press snaps the university’s handing around, imagine windows fitted with this material to at most look slightly tinted.

And the benefits would, in theory, extend well beyond windows. According to the research team leader and UCLA engineering professor Yang Yang, “These results open the potential for visibly transparent polymer solar cells as add-on components of portable electronics, smart windows and building-integrated photovoltaics and in other applications.”

Imagine charging your smartphone, laptop, tablet or pair of head-mounted “smart glasses” by simply laying any of those devices somewhere near a source of infrared energy.

Yang claims the team’s polymer solar cells (PSCs) are made from “plastic-like materials” and that they’re “lightweight and flexible,” adding that they can be produced inexpensively in high volume.

How’d they do it? By placing an infrared sensitive polymer on the top layer of the film.

A team of UCLA researchers from the California NanoSystems Institute, the UCLA Henry Samueli School of Engineering and Applied Science and UCLA’s Department of Chemistry and Biochemistry have demonstrated high-performance, solution-processed, visibly transparent polymer solar cells through the incorporation of near-infrared light-sensitive polymer and using silver nanowire composite films as the top transparent electrode. The near-infrared photoactive polymer absorbs more near-infrared light but is less sensitive to visible light, balancing solar cell performance and transparency in the visible wavelength region.

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What’s more, the team was able craft a new kind of conductive material — made of silver nanowire and titanium dioxide nanoparticles — to replace the material (made of metal) used previously. The only downside: power-conversion efficiency is just 4%, meaning the electricity generated would be considerably less than that of a traditional solar panel.

But wait, haven’t we already heard about electricity-generating windows? Indeed we have: Last October, 3M announced it had developed a transparent film-like material that, during peak sunlight hours, could generate enough power from a square meter to charge a smartphone — about 20% of the total energy generated by a standard solar panel.

The issue with 3M’s product is that it blocks around 80% of visible and 90% of infrared light, making it an obviously poor choice for high visibility-desired installs, say you wanted to place PSC tech over your house’s bay windows.

When I asked UCLA’s Yang to comment on 3M’s technology, he acknowledged that both his team’s and 3M’s products were based on an “organic” solar cell, but — lacking access to their methods and materials — declined to make more detailed comparisons. He did confirm the opacity and coloration differences, noting that “The 3M solar cell has a light-green color, whereas ours is nearly fully transparent.”

UCLA’s press statement adds that the reason alternative PSC materials often yield low visible light transparency is because “suitable polymeric PV materials and efficient transparent conductors were not well deployed in device design and fabrication.”

That assumes you wouldn’t want to block visible light (or invisible heat), of course. 3M’s solution could, for instance, double as a shading/heat-blocking tool, were it placed somewhere more appropriate for that function.



The UCLA team’s research is published in the academic journal ACS Nano (subscription required).

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