A see-through solar cell has been successfully fabricated by researchers at Tohoku University in Japan. It’s powerful – albeit tiny – and it might be coming to a building near you.

There’s been a few rumblings recently about some kind of imminent breakthrough in nuclear fusion, but the truth is we still have a way to go before this ultimate in clean energy is more efficient than, say, wind power.

For true nuclear fusion, we have to look to the sun (metaphorically, that is – please do not actually look at the sun.) Sitting at the center of our solar system, this gigantic ball of burning gas sends a total of 173,000 terawatts of solar energy our way. 

That’s over 10,000 times the world's total energy use, so it’s no wonder we’ve spent so much time and effort trying to harness it in the form of solar power. However, there are so many limiting factors to that: solar panels are generally big, opaque, and let’s face it: kinda ugly.

Now, the team from Tohoku University has changed that. They’ve developed a “near-invisible” solar cell, or NISC – engineers don’t have time to waste on extra syllables – that lets nearly 80 percent of light through. Theoretically, it could be placed anywhere, from the windows in your house to the screen on your smartphone – or even the skin on your body.

“Transparent solar cells (TSCs) have attracted considerable attention as they can overcome the limitations of traditional non-transparent solar cells,” explain the Tohoku researchers in a paper describing the study, recently published in Nature Scientific Reports.

“We successfully fabricated an NISC using ITO [indium tin oxide, one of the most widely used transparent conducting oxides] and monolayer tungsten disulfide […] as transparent electrodes, and photoactive layer, respectively.”

Using these materials – plus a thin layer of tungsten oxide between the ITO and the tungsten disulfide – the team made a solar cell that beats other transparent cells by several orders of magnitude. 

“The way in which we formed the solar cell resulted in a power conversion efficiency over 1000 times that of a device using a normal ITO electrode,” explained Toshiaki Kato, an associate professor at Tohoku University's Graduate School of Engineering and co-author of the paper, in a statement.

Now, of course, all that is useless unless the cells can be scaled up for use in actual solar panels – but luckily, the team looked into that, too.

“Even though a very high PCE [power conversion efficiency] could be obtained from a small device at a µm-scale, the P_T [total power] of the entire device would be considerably limited by the device size,” explains the paper. 

It’s not as simple as you might think: “scaling up by increasing the channel width and number of parallel connections cannot effectively increase P_T, and may sometimes cause the P_T to drop instead,” the researchers point out, meaning the team had to figure out a “suitable architectural design for large-scale device fabrication.”

“It was found that the aspect ratio […] [of the] device should be lower than the critical value of approximately 36,” the paper explains. “By further scaling up the device size by considering an optimal series–parallel connection structure, an extremely high transparency of 79% could be realized, with P_T reaching up to 420 pW [picowatts].” 

“This is the highest value within a TMD based solar cell with a few layers,” the paper concludes. “These findings can contribute to the study of TMD-based NISCs from fundamentals to truly industrialized stages.”