IDG News Service — Motorola has found a way to keep your mobile phone charged using only sunlight. The company recently received a patent for an LCD (liquid crystal display) that includes solar cells capable of charging the battery in a mobile phone or other portable device. The patent, which offered no hint of commercial product plans or timing, also outlines how solar cells can be added to OLED (organic light-emitting diode) and touch-screen displays.

The basic premise has been proposed before: A display screen is stacked over one or more solar cells, which are charged by the light passing through the display. But earlier designs allowed a relatively small amount of light to reach the solar cells, so little power was generated even in the best light conditions, Motorola researchers said in the patent.

The ultimate goal is to develop a device that could remain charged indefinitely, without requiring users to plug into a socket or carry external chargers. Until now, the major obstacle has been the LCD’s polarizer and reflective screen, which sends light back to the viewer. In earlier designs, the reflective screen allowed less than 6 percent of the available light to reach the solar cells, Motorola said.

To solve this problem, Motorola proposed using either cholesteric liquid crystal or polymer-disbursed liquid crystal in the display, instead of super-twisted nematic liquid crystals. This change in materials eliminates the need for both a reflective screen and polarizer in the LCD screen. As a result, Motorola claims as much as 75 percent of available light is able to reach the solar cells, providing a sufficient amount of power to charge the battery of a mobile device.

Motorola rival Nokia also recently applied for a unique U.S. patent: Nokia is working on technology to warn cell phone users of impending lightning strikes.