The photovoltaic polarizers can harvest ambient light too, so they could potentially help charge a phone when it’s not in use. “When the phone sits, it could work in the background, collecting energy and recycling it back to the battery,” says Youssry Botros, program director at the Intel Labs Academic Research Office.
The second group, led by Jay Guo of the University of Michigan, is developing energy-harvesting color filters. Color filters are used in many types of displays, but the ones made by Guo’s team are appropriate for use in reflective “electronic paper” screens. These contain arrays of sub-pixels that absorb ambient light and then reflect red, green, or blue light.
Guo and colleagues combined a common polymer solar-cell material with a kind of color filter that his group invented last year. The photovoltaic color filter converts into electricity about two percent of the light that would otherwise be wasted.
Guo estimates that full displays incorporating this photovoltaic filter could generate tens of milliwatts of power, enough to make a difference to the life of a cell phone battery. The photovoltaic color filter is described in a paper published online in the journal ACS Nano.
“It’s an intriguing idea,” says Gary Gibson, a scientist developing reflective color displays at HP Labs in Palo Alto, California. Low brightness is a recurring problem for color electronic paper. If the color filter proves practical, says Gibson, energy harvested from ambient light could be used to power a backlight and make the display brighter.