Solar cells achieve new energy record

A team of Australian and US researchers has set a record for solar cell efficiency. The multi-cell array achieved an efficiency of 43%, beating the previous world record by 0.3%.

The University of New South Wales' (UNSW) Professor Martin Green, who led the effort, says solar cells only convert a fraction of the energy from sunlight into electricity.

"Sunlight is made of up of little particles and these particles have different energy," he says.

To create electricity, each photon of light must have enough energy to free an electron inside the solar cell. If the energy is low, the photon will bounce off the solar cell and no electrical current will be created.

"A standard cell can respond to photons of certain energy and above, but not below," says Green, who heads the UNSW ARC Photovoltaics Centre of Excellence.

Silicon, used in most solar cells, has a low threshold, ensuring most wavelengths of visible light will free an electron. But they are inefficient converters of short wavelengths such as blue light.

"Cells that have a lower threshold don't convert the light as efficiently as a cell that is matched to that colour," says Green.

To achieve a higher rate of conversion, the researchers used five different solar-cell types, matched to different wavelengths of light.

"Each cell has the maximum efficiency for one particular colour," says Green.

Using filters, the cell splits the incoming light into its different wavelength bands and sends it to the different cells.

The researchers developed a cell that efficiently converts red light into electricity. The other four cells were developed by two US groups based at the National Renewable Energy Laboratory and Emcore Corporation. Instead of silicon, these cells used combinations of gallium, indium, phosphorus and arsenic.

The previous world record of 42.7% was set using these four cells in combination with another cell from the University of Delaware.

Although the new design is very efficient, it is also expensive to produce.

Green is currently focusing his energy on improving the efficiency of single silicon cells.