Theoretical optimization and parametric study of n-on-p AlxGa1−xAs-GaAs graded band-gap solar cell

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Abstract
A comprehensive theoretical model of the graded band‐gap AlxGa1−xAs‐GaAs solar cell is used to optimize the n‐on‐p cell. The model includes power losses due to surface, bulk, and junction minority‐carrier recombination, series resistance, and photon reflection from an SiO antireflection coating of optimum thickness. The optimized cell has a junction depth/graded band‐gap layer thickness of 1.0 μm, respective donor and acceptor concentrations of 4×1017 and 2×1017 cm−3, and a surface AlAs mole fraction of x=0.35. The optimized graded band‐gap cell has an air‐mass‐zero efficiency of 17.7% (not corrected for a 13% front surface contact area) and is shown to be less sensitive than a similar n‐on‐p GaAs cell to material degradation in the form of decreased minority‐carrier diffusion lengths and increased surface‐recombination velocity.