Waste light captured from a mobile could charge its battery

A team from Cambridge University hopes to capture energy from organic light-emitting diodes (OLEDs) inside a phone by using thin-film photovoltaic (PV) cells built into the screen.

Prof Arokia Nathan, project leader and fellow of the Institute of Electrical and Electronic Engineers (IEEE), told The Engineer that only 30–40 per cent of light generated by OLEDs is projected out of the front of the average mobile phone screen, with much of it being lost through the edges of the OLED.

Nathan and his collaborators at Canadian company IGNIS Innovation have created a proof-of-concept device that can harness this wasted light using PV cells around the edges of the display.

‘Once we have captured the light in the solar cell, that generates an output. It’s not very high but it’s something useful nevertheless,’ said Nathan.

The team, which was first based at the London Centre for Nanotechnology at University College London, believes that the captured photons could be used to help charge the phone and, because the technology can capture ambient light as well, it could one day lead to a phone that never has to be plugged in.

With current technology, the solar cells could generate up to 5mW for a typical 3.7in (9.4cm) smartphone screen, according to team researcher Arman Ahnood.

The electricity generated by the solar cell is used to charge up a supercapacitor, which in turn is discharged into a battery. The supercapacitor is used because charging the battery directly would involve implementing complex circuitry.

‘The amount of electrical power that the capacitors are able to store depends on how they are implemented,’ said Ahnood.

According to Ahnood, the thin-film capacitors, fabricated at Cambridge University, store charge for a period that is long enough for the battery to consume it.

Nathan explained the next step is to seamlessly integrate the technology and look at how efficient the whole system will be when it is used in a working mobile phone.

The team is also exploring different circuit designs and other materials in order to improve the energy-harvesting system’s efficiency.

Ahnood added: ‘We are looking at other ways to scavenge as much energy as possible, such as through vibrations and even human movement.’