If your smartphone doesn’t last the day, chances are the screen is largely to blame. The display is by far the most power-hungry component in your mobile device, but on your next phone it may give back some of the power it takes.

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Japanese device maker Kyocera, in a partnership with the French firm SunPartner Technologies, is showing off a prototype smartphone this week at Mobile World Congress, the largest trade show for mobile technology, with a screen that can actually charge the device both outdoors and indoors under bright lights.



Phones, like Samsung’s Blue Earth, have solar cells embedded on the back. But when using a phone, the back is obscured by your hand, and it's the screen that gets the most exposure to light. So Kyocera has incorporated transparent solar technology into the screen of its rugged Torque line.

The tech is thin enough to be incorporated into existing phones. The solar layer is less than 0.5 millimeters thick, according to a press release, and up to 90 percent transparent, so it doesn’t visibly interfere with the quality of an image. The solar layer lives below the touch layer in the phone screen, and houses transparent crystals that soak up light and a chip that converts the energy and feeds it into the phone battery.

The screen isn’t meant to be the phone’s primary power source. But for those who spend a lot of time outside, it could extend battery life substantially, or provide enough juice to make a short call in an emergency situation when there’s no charger available.



The device Kyocera is showing off this week at Mobile World Congress is only a prototype. “We have been examining the possibility of commercializing this technology based on the expected usage patterns of our rugged smartphone users,” writes Judah Reynolds, a corporate communications supervisor at Kyocera, in an email. But he says the technology’s charging abilities and efficiency at converting light to useable power will need to be improved before it makes it into a retail Kyocera phone.



At the moment the screen technology, dubbed Wysips Crystal by its French creators at SunPartner Technologies, generates 2.5 milliwatts of power per square centimeter under typical sunlight conditions, according to Matthieu de Broca, SunPartner’s marketing director. But he says the company expects to improve the technology and deliver up to 4 milliwatts by the end of 2015.

Even with those improved numbers, the solar layer won’t provide enough power to keep the phone going indefinitely if it is being used regularly. But today’s large screen phones have more surface area. If the technology continues to improve, it could allow a future device to deliver an infinite amount of standby time—so the phone’s battery won’t drain when it’s, say, just sitting on a desk near a window.



“When you get exposed to light, whether the product is on or off, you’re collecting energy,” says de Broca. “With ten minutes [of sunlight], you can get 100 minutes standby gain, which could also be about two minutes of additional talk time.”



The real limitation of power delivery is due to the fact that the crystals have to be transparent. An opaque panel would provide more power, but then of course, you wouldn’t be able to see the screen.



SunPower is also working on integrating its technology into cases and smart covers for phones and tablets. The company calls this technology Wysips Graphics, because the solar portion isn’t visible, and lets case makers create custom designs, just like with other phone cases and covers.



The solar-powered Kyocera Torque may not make it to market, but de Broca says they’re working to perfect the manufacturing process, and hope to see a solar-screen smartphone or tablet using Wysips Crystals by the end of 2015. He says the company’s solar cases could come as soon as this summer.



Kyocera is also working with French eBook company Bookeen to develop a solar-powered e-reader that can get all the power it needs from the sun or artificial light. According to a blog post on Bookeen’s website, the reading device should be available sometime next year.