A team of researchers from the National Institute of Standards and Technology (NIST) in the United States has created a laser-based instrument that simulates sunlight in order to test solar cell properties and further improve their efficiency.
The new simulator, as described in a paper published in the IEEE Journal of Photovoltaics, is based on a white light laser that uses optical-fibre amplifier technology to increase the power, and a photonic crystal fibre to broaden the spectrum. It is capable of simulating sunlight across the spectrum of visible to infrared light.
With the instrument, the NIST team were able 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 agreed with independent measurements.
The novel device is more flexible than conventional solar simulators such as xenon arc-lamps or light-emitting diodes, and it can be focused down to a small beam spot — with resolution approaching the theoretical limit — and shaped to match any desired spectral profile.
‘We can focus the light down to a spot less than two micrometres in diameter, despite the wide spectral content. You can't do this with sunlight,’ NIST researcher Tasshi Dennis explained. ‘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, its 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.
At the moment, 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. NIST researchers have been working to make the new simulator programmable and portable for use outside NIST.
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 characterization. IEEE Journal of Photovoltaics. Posted online May 26