Sun-Free Photovoltaics: Materials Engineered to Give Off Precisely Tuned Wavelengths of Light When Heated

ScienceDaily (July 31, 2011)

• MIT researchers have made a button-sized power generator fueled by butane that can run three times longer than a lithium-ion battery of the same weight; the device can then be recharged instantly, just by snapping in a tiny cartridge of fresh fuel.
• It has long been known that photovoltaic (PV) cells needn't always run on sunlight.
• thermal emitter that radiates only the wavelengths that the PV diode can absorb and convert into electricity, while suppressing other wavelengths
• Celanovic is confident that with further work his team can triple the current energy density. "At that point, our TPV generator could power your smartphone for a whole week without being recharged," he says.

I found this story by way of PC magazine, which had a story about Elon Musk.  That story was linked from Next Big Future.   By the way, the link wasn't direct, I had to dig a little to find it.

One may wonder if such a system can be scaled up, so that it can be made into a battery which could power an automobile.