German researchers are developing new types of power cells that could mean mobile phones will never have to be recharged at the mains again.
Casio, Siemens and other manufacturers of phones and PDAs are already building prototype devices that use the new power cells, developed at the Department for Energy Technology at the Fraunhofer-Institute.
The plan is to replace rechargeable batteries in mobile devices with a miniature version of the hydrogen fuel cell used to power electric cars, and recharge it with a super-efficient solar cell built into the devices.
Until now, the tiny amount of space available in a mobile phone or PDA was too small to allow integration of fuel cells and solar cells, Fraunhofer researchers told ZDNet.
And it is a race against time: as mobile electronic devices shrink in size and increase in functionality, they draw more power. Manufacturers of solar cells meanwhile continue to raise the efficiency of their products - some have achieved an efficiency of almost 25 percent - but they are still much too expensive for the mass market.
Power of the sun
Now researchers at the Fraunhofer Institute's Solar Energy Systems ISE in Freiburg, Germany, have managed to find a way of combining these conflicting factors.
Their high-performance solar module, which is due to have its first public showing next week in Hanover, Germany, is integrated in the lid of a Casio palmtop, and makes the device completely autonomous of external electrical supplies.
"The decisive factor," said Dr Christopher Hebling, head of the Micro-Energy Technology group at the ISE, "is that the device can run on solar power alone even under low lighting levels. At a normal workplace, you have only three percent of the brightness of summer sunshine. Even down to a level of one percent, the electrical voltage provided by our solar module remains virtually constant; in conventional cell types it would have long since broken down."
The high output rating of over 35 milliamps per square centimetre in direct sunlight is attributable to the solar module's special design.
"The 14 individual cells of single-crystal silicon overlap like roof tiles," said Hebling. "In this way, the cells make optimum use of the limited available space, and achieve an efficiency of more than 20 percent."
The surfaces of solar cells with such a conversion efficiency are coated with an electrically insulating layer of silicon oxide or nitride. This non-conducting material needs to be removed again at specific points to allow attachment of the electrical contacts - a previously complex and expensive process.
Again, the Fraunhofer researchers have arrived at a new solution: a special laser zaps away the coating from the designated contact points. Such innovations have enabled the researchers to reduce the total number of process steps by eighty percent, making the solar cells cheap enough to become a viable alternative to other sources of energy.
The Fraunhofer Department of Energy Technology is due to show the first functioning micro fuel cell for use in smartphones and PDAs. Four Germans at the Fraunhofer Department based in Plymouth, Michigan, have developed what what they call a series-ripe gas cell system.
Like solar cells, this system offers attractive advantages compared to rechargeable batteries: significantly higher storage capacity, long lifetime, flat and variable designs, and extremely low self-discharge.
Visitors to the fair will see the fuel cell powering a camcorder. The cell has an output of ten watts with a voltage of eight volts, is hardly larger than a matchbox and combines a polymer membrane fuel cell with a hydrogen storage unit. Longer operating times can be achieved by fitting a larger storage unit.
Fraunhofer first demonstrated this with a laptop at the Hanover Trade Fair in 1998. Among the development-partners for this prototype were Siemens PC Systems (now Fujitsu Siemens) and Aventis.
