A new breed of screens for cell phones, now in development, is getting back to nature. 
Qualcomm and others are promoting new screen technology for handhelds and mobile devices that can stay on all day without sapping battery life, thanks to the sun or liquids. As a result, a cell phone equipped with such a screen could continually broadcast stock quotes, news stories or show a music video to go along with a built-in MP3 player. Currently, phone screens stay dark mostly by necessity.
The difference is that the new screens don’t need to be backlit, as do current screens. Instead, they are primarily illuminated by light from the sun or the movement by liquids inside the screen. New cell phone screens battery-friendly | CNET News.com