Artificial sunlight tool helps to test the properties of solar cells

Researchers have developed a laser-based instrument that generates artificial sunlight to help test solar cell properties and find ways to increase their efficiency.

The system from the US National Institute of Standards and Technology is said to simulate sunlight well across a broad spectrum of visible to infrared light. According to NIST the laser instrument can be focused down to a small beam spot – with resolution approaching the theoretical limit – and shaped to match any desired spectral profile. It is also claimed to be more flexible than conventional solar simulators such as xenon arc lamps or light-emitting diodes.

The new simulator is based on a white light laser that uses optical-fibre amplifier technology to boost the power and a photonic crystal fibre to broaden the spectrum. NIST researchers used the simulator to measure the efficiency of thin-film solar cells made of gallium arsenide, crystalline silicon, amorphous silicon and copper-indium-gallium-selenide, and the results are said to have agreed with independent measurements.

‘We can focus the light down to a spot less than 2μm in diameter, despite the wide spectral content. You can’t do this with sunlight,’ NIST researcher Tasshi Dennis said in a statement. ‘We then used this focused spot to scan across solar cell materials while monitoring the current the light generated. This allowed us to create spatial maps (images) of the response of a solar cell at the micrometre level.

The new instrument may help researchers understand solar cells’ optical and electrical characteristics, including defects and the impact of unusual designs.

In particular, the new simulator’s capability to make rapid, accurate spectrum adjustments will help characterise the most efficient solar cells, which use multi-junction materials in which each junction is tuned to a different part of the spectrum.

The instrument is designed to probe small research samples, individual concentrator solar cells and microstructures, not to determine the efficiencies of large solar cell panels and modules.

A paper authored by T. Dennis, J.B. Schlager and K.A. Bertness – A novel solar simulator based on a super-continuum laser for solar cell device and materials characterisation – has been published in IEEE Journal of Photovoltaics.