According to Ahnood, only 36% of the light produced by an OLED display is projected out and the rest is wasted. This wasted light, which is scattered or "bleeding" from the edge of the display, can be harnessed with photovoltaic cells, built into the screen itself.
Ahnood's system currently has an efficiency of 11%, producing a total output of five miliwatts on a typical 3.7-inch device, which is far from what a smartphone needs. According to this research (PDF link), a typical smartphone uses up to several hundred miliwatts, and as much as 68.6 miliwatts in a suspended state.
However, Ahnood believes the efficiency can be increased significantly, to the point where this system could extend battery life by a few hours.
To smartphone owners, which often call their devices "6 o'clock phones," since their battery only lasts until late afternoon with normal usage, these couple of hours could make a big difference.