Future solar cells will be cheaper and more energy-efficient to manufacture, while boasting better power output, thanks to an engineering breakthrough led by scientists at The Australian National University (ANU), UC Berkeley, and EPFL groups.
Conventional silicon solar cells, and semiconductors, are doped. During the manufacturing process, impurities are introduced into the silicon structure, in order to modulate its electrical properties.
In a turnabout breakthrough, the researchers found that they could achieve the same, if not better results, by sandwiching pure silicon between thin films of different materials (in this case, lithium fluoride and molybdenum oxide), rather than doping the silicon.
Lithium fluoride has a low binding energy of electrons, known as the work function, while molybdenum oxide's is very high. When the sunlight hits the silicon and creates an electron-hole pair, the electron is drawn to the lithium fluoride; the hole goes the opposite way. This basic mechanism is the basis of the electrical current.
"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 ANU Research School of Engineering, who conducted the study whilst on placement at UC Berkeley's Department of Electrical Engineering and Computer Sciences.
"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."
By eliminating doping and opting for layering instead, the researchers demonstrated the power of this new understanding of the physics of solar cells.
The research also yielded other benefits. It eliminates the need for the often-toxic chemicals that are used to dope conventional methods. Additionally, solar cells can be manufactured with a lower energy footprint, because unlike conventional doped cells that require heat above 800 degrees Celsius, the layering method allows solar cells to be manufactured at below 200 degree Celsius.
The new method has already yielded a solar cell which can achieve nearly 20 percent efficiency, which is better than the industry average. The researchers anticipate reaching over 25 percent efficiency using the same approach.