NTT DoCoMo has developed a solar-powered, waterproof mobile phone that
will go on sale from September. The solar hybrid can be recharged with
sunlight as well as electricity. Even if the battery has completely
lost its charge, just 10 minutes of solar recharging via a panel on the
phone’s body provides approximately one minute of talk time.
http://www.japantoday.com/category/technology/view/docomo-develops-solar-powered-handset