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

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.