Integrated solar cells on phone screens to chuck out plug-in charging

A group of Cambridge University researchers, under the able guidance of IEEE fellow Arokia Nathan, is nearing the final stages of developing smartphone screens with integrated solar cells. The team has just unleashed a prototype phone that can convert ambient light into power with the help of an array of solar cells on the device’s screen. The ultra thin solar cells are made from hydrogenated amorphous silicon.

Solar cells in smartphone screens

The technology aims to transform the way we use smartphones today. Once realized in its full sense, the phone can itself harvest the power required for its functioning, said Arman Ahnood, a member of the research team, at the Materials Research Society’s 2011 fall gathering in Boston. Eventually, we might have smartphones that need not to be plugged in to power outlets.

Since smartphones come with large displays, the photovoltaic (PV) cells would get large footprint to sit on the screen. The researchers have put the thin-film PV cells around the screen’s edges to harness even the light that seeps through the edges of an OLED screen. According to Ahnood, more than 60 percent of light generated on an OLED display oozes through its edges. Well, the new technology helps utilize the energy that will be wasted otherwise.

In harvesting power through integrated solar cells, the researchers faced some challenges. One problem was that the fluctuations in the voltage provided by solar cells might damage the phone’s battery. For fixing this problem, the team developed a thin-film transistor circuit to stabilize voltage variations and thus to extract energy more efficiently from solar cells.

In addition, for intermediate storage, the researchers designed a thin-film super capacitor in association with the energy group at the Cambridge’s Center for Advanced Photonics and Electronics. As a result, power harvested by the solar cells will not directly go to the battery; instead, it will be stored in an intermediary space.

The technology behind the solar powered smartphone is simply a combination of photovoltaics, transistors and supercapacitor. The system provides an average efficiency of 11 percent and peak efficiency of 18 percent. In other words, as the PV array converts five percent of ambient light to power under better lightning conditions, the system can produce as much as 165 MW per square centimeter. This way, the maximum output for a standard 3.7-inch smartphone screen will be 5 milliwatts, says Ahnood. Indeed, it is only a small fraction of the power required for a smartphone.

However, it is just a small example for the prospects of small-scale wireless power harvesting. The other CMOS-based switch-mode voltage regulators can provide better efficiency. However, the thing is that they are not suitable with the ultra thin screens of smartphones. Indeed, in future, we can expect similar researches to produce power for smartphones from built-in solar cells.

Via: IEEESpectrum