Comparative Analysis of Nonuniform Illumination and Chromatic Aberration in Triple and Quadruple Junction Solar Cells under Concentration Using SPICE

The optics of a concentrating photovoltaic (CPV) system typically provides nonuniform illumination on the subcells, affecting current profiles and consequently system efficiency. Using a two-dimensional, distributed resistance model, we estimate the impact of nonuniform illumination and chromatic aberration for an inverted metamorphic, triple junction solar cell (3J IMM) and a lattice-matched, four junction solar cell (4J LM). Both the multijunction cells have an optimized efficiency of 42.4% at 1000 suns under uniform illumination. The performance of the 3J IMM and the 4J LM is analysed at different peak-to-average irradiance ratios (PAR). The 3J IMM shows a higher sensitivity to nonuniform illumination and a loss in efficiency of 5.4% absolute at a PAR = 5.3 while the losses in a 4J LM account for 3.7% absolute efficiency reduction. To model the effects of concentrating optics, an optical train with an idealized Fresnel lens and a secondary truncated pyramid homogenizer is simulated using commercial ray tracing software using the AM1.5D spectrum. Losses due to concentrating optics, nonuniform irradiance profiles and chromatic aberrations are determined for both cells at various primary to secondary working distances. At a working distance optimal for the 4J LM, the neglect of chromatic aberration is found to overstate the CPV system efficiency by 1.4% absolute and at the optimal working distance for 3J IMM, neglecting chromatic aberration overstates the system efficiency by 2%.