This research leverages a new laser technology, the super-continuum laser, to produce a programmable solar simulator that can rapidly configure to match nearly any solar spectral condition.
The design of the super-continuum solar simulator is shown below. Light is produced from 450 nm to 2400 nm in sub-nanosecond pulses at a repetition rate of 80 MHz. The total irradiance is sufficient to illuminate a 1 cm2 cell at more than 1-sun. Initial tests have 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 can also be readily focused to a 2 µm spot. Using programmable spatial light modulators (SLMs), the AM1.5 reference spectrum could be matched over the region from 450 nm to 1750 nm, as shown in the upper right. With external optics, the simulator output has been concentrated to an irradiance of more than 600 suns to illuminate small-area multi-junction concentrator solar cells. Spectral conditions representative of changes in time of day, time of year, weather, and location have also been generated. The spectral control has also been used to perform light biasing of multi-junction solar cells to demonstrate junction current limiting. By focusing the simulator beam to a micrometer-scale spot, we have demonstrated full-spectrum optical beam-induced current (OBIC) measurements on GaAs heterojunction and CIGS solar cells. The uniformity of the current production from the surface of the GaAs cell was mapped. 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.