Experimental verification of AlGaAs reflectors optimised for InGaP/GaAs/Ge triple-junction cells

Spectrally selective multilayer reflectors incorporated into InGaP/GaAs/Ge triple-junctions can provide a targeted absorption boost for the middle cell, which can then be thinned to increase the cell’s radiation tolerance for space applications. However, epitaxial growth limits material choice, which limits the reflected bandwidth of a typical quarter-wave reflector. Our previous computational work has identified optimised reflectors designs as a function of GaAs subcell thickness and reflector layer count to compare design strategies for increasing the bandwidth. Here, we grow and compare three of these reflectors with 41-layers, optimised for 1500 nm GaAs subcells: a standard quarter-wave stack with one target wavelength, a double stack with two target wavelengths, and a linearly-varied stack. The specular reflectance of the three reflectors is measured. Four 1500 nm GaAs cell samples will also be grown and processed – three with epitaxial reflectors and one without. The EQE and IV characteristics of these cells will be compared to identify the impact of the reflectors on cell performance and compare against modelling predictions.