Continuum Laser Solar Simulator
This research leverages a new laser technology, the supercontinuum laser, to produce a programmable solar simulator that can rapidly configure to match nearly any solar spectral condition.
The design of the supercontinuum solar simulator is shown to the right. Light is produced from 400 nm to 2400 nm in sub-nanosecond pulses at a repetition rate of around 80 MHz. The total irradiance is sufficient to illuminate a 1 cm2 cell at more than 1-sun. The initial tests confirmed that solar cells respond to the simulator as they would to the sun, despite the pulsed nature of the source, and that the energy conversion efficiencies measured with the new simulator are in agreement with device measurements provided by our collaborators.
The most powerful feature of this simulator is that the entire spectrum is obtained with spatially coherent light, allowing optical manipulation with minimal loss. In particular, the light can be dispersed with prisms and reconstituted into a high-quality beam that is readily focused to a 2 µm spot. Using a fixed mask, the AM1.5 spectrum could be matched over the region from 450 nm to 2000 nm, as shown in the lower right. We are currently integrating a programmable spectral shaper and additional UV lasers to allow rapid switching (<1 s) and fully accurate solar simulation. With the supercontinuum simulator, we have recently demonstrated full-spectrum optical beam-induced current (OBIC) measurements on GaAs heterojunction and CIGS solar cells. The spectral splitting function was used to separately excite different spectral regions for the GaAs heterojunction for direct measurement of the current contributions from each region. The CIGS cell was spatially mapped to identify regions of high and low response, including regions with intentional damage. We plan to extend these studies to other materials and are open to new collaborations for testing the simulator's capabilities. Preliminary work has shown the ability of the solar simulator to light-bias multijunction solar cells to demonstrate the current limiting behavior.
The simulator has been tested with a variety of photovoltaic materials obtained from these collaborators: H. C. Yuan, NREL, Crystalline Si; Dan Friedman, NREL, GaAs heterojunction and multijunction; Lorelle Mansfield, NREL, CIGS; Bill Nemeth, NREL, amorphous Si.