Adding solar cells to liquid-crystal displays could help recover a significant amount of energy that’s ordinarily wasted in powering them. Two research groups have created light filters that double as photovoltaic cells, a trick that could boost the battery life of phones and laptops.
Over 90 percent of the displays sold this year will use liquid-crystal display (LCD) technology. LCDs are, however, tremendously inefficient, converting only about 5 percent of the light produced by a backlight into a viewable image. The LCD in a notebook computer consumes one-third of its power.
This type of screen remains dominant because manufacturers can make LCDs inexpensively on a huge scale. More energy-efficient kinds of displays either are too expensive to manufacture or cannot produce high-quality images. “The LCD is very inefficient, but it works,” says Jennifer Colegrove, an analyst at Display Search, a market-research and consulting firm.
Two independent groups—one at the University of California, Los Angeles, the other at the University of Michigan—are tackling two of the biggest culprits of wasted light in LCDs: polarizers and color filters.
Polarizers filter out light that is incompatible with the liquid-crystal shutters in an LCD pixel, accounting for 75 percent of the total light wasted by LCD screens, and conventional color filters toss out two-thirds of the light that hits them. The two research groups have created plastic photovoltaic versions of these two display components, which convert light into electricity.
“We want to take an energy-wasting component that everybody uses and turn it into an energy-saving one,” says Yang Yang, professor of materials science and engineering at UCLA. Yang’s group created plastic solar cells that can act as polarizers. The researchers simply rub one layer in the solar-cell film with a cloth to align all the molecules in one direction. This alignment turns the cell into a polarizer that converts into electricity some of the light that doesn’t pass through.
Yang’s work is part of a three-year project being funded by Intel; in the coming year, his team plans to integrate the photovoltaic polarizer into a working display. In a paper published online in the journal Advanced Materials, the team reports that its polarizer can convert into electricity 3 or 4 percent of the light that’s normally wasted by a filter. Yang expects to get this up to about 10 percent by tinkering with the materials used.