Australasian Science: Australia's authority on science since 1938

Solar Cells Ditch Doping

Scientists have developed a new silicon solar cell that promises cheaper manufacturing processes and better power output.

The research, published in Nature Energy (www.tinyurl.com/h88gvv6), did away with the chemical doping that conventional silicon cells rely on and instead used pure silicon sandwiched between thin films of different materials.

“For a lot of people this will broaden their idea of how silicon solar cells can be made,” said lead author James Bullock, a PhD student at the Australian National University who conducted the study while on placement at UC Berkeley.

“These cells can be made using a very simple low-temperature fabrication procedure, so they have the potential for cheaper processing whilst still having high efficiencies.”

The team’s best solar cell so far has achieved nearly 20% efficiency, which is better than the industry average, said co-author Prof Andres Cuevas of ANU. “There is nothing to say we can’t get to the world record efficiencies, over 25%, using this approach,” he said.

Instead of using doping impurities within the silicon structure to control the electronic properties, the team sandwiched a silicon wafer between layers of lithium fluoride and molybdenum oxide.

Lithium fluoride has a low binding energy of electrons while molybdenum oxide’s binding energy is very high. The difference means that when sunlight hits the silicon and creates an electron-hole pair, the electron is drawn to the lithium fluoride while the hole goes the opposite way, which creates an electric current.

The new design promises a lower energy footprint for solar cells because they can be manufactured below 200°C. Conventional doped cells must be made above 800°C. The cells also do not require the often-toxic chemicals used to dope conventional materials.

“This device is the result of a completely new understanding of the physics of solar cells,” said Prof Cuevas. “All those wonderful materials were sitting there, some of them already in our lab cabinets, but we had not realised how useful they can be.”