III-V-Semiconductor Subcell Absorbers in Silicon-Based Triple-Junction Solar Cells

Tandem solar cells are required for higher photovoltaic module efficiencies and thus reduced costs and land demand. This thesis was concerned with the development of a two-terminal III-V//Si triple-junction solar cell. Two compound semiconductors, AlGaAs and GaInAsP, were investigated. The samples were grown lattice matched on GaAs substrates using metalorganic vapor phase epitaxy. GaInAsP exhibited a high performance with a minimum loss to the radiative limit of 18 mV in a rear-heterojunction solar cell. An optical parameter morphing method was optimised to generate continuous refractiv index data for arbitrary absorber compositions. The robustness of the method was experimentally confirmed by a comparison to literature values as well as spectral ellipsometry, external quantum efficiency, and reflection measurements. With the complex refractive index data the target absorber thicknesses in multi-junction solar cells were adjusted by transfer matrix modelling to achieve current match between the subcells. The triple-junction solar cell achieved a power conversion efficiency of 35.9 % under the AM1.5g solar spectrum, the highest efficiency for monolithic silicon based cells to date.