Full-spectrum optical-beam-induced current for solar cell microscopy and multi-junction characterization

The design and application of a novel solar simulator based on a high-power, super-continuum laser is described in this work. The simulator light was focused to a spot approximately 8 μm in diameter, and used to create micrometer-scale spatial maps of full-spectrum, optical-beam-induced current in sample solar cells. Microscopic details such as grid lines, damage spots, and material variations were selectively excited and spatially resolved on GaAs and CIGS thin film cells. The simulator features continuous spectral coverage from the visible to the infrared, and the ability to be arbitrarily spectrally shaped. The spectral shaping capabilities were demonstrated by creating four unique output spectra for selectively light-biasing different layers of a multi-junction cell. The partial currents generated by a GaAs cell from spectrally sliced illumination were shown to be consistent with the external quantum efficiency of such a device. The simulator was also used to create blue-rich and red-rich spectra that were applied to the current-limited light biasing of a GaInP/GaAs tandem solar cell. By varying the spectral content, we were able to illustrate the current-limiting behavior of the junctions and confirm that the cell was top-junction limited.