Flexible GaInP/Ga(In)As/Ge triple-junction space solar cells with a simple fabrication process based on Ge substrate thinning demonstrate power-to-mass ratios of 1.3 kW/kg

One the primary strategies in space photovoltaics is the development of flexible and lightweight solar cells with a high specific power. Rigid lattice-matched GaInP/Ga(In)As/Ge 3 J solar cells with a thickness of ∼150 μm for 100 mm (4-inch) Ge substrates with a power-to-mass ratio of 0.47 kW/kg currently represent the benchmark for space solar cells. This paper analyses the performance of these 3 J solar cells as a function of Ge substrate thickness under various scenarios of both front and back surface recombination velocity of the Ge subcell. In order to validate the modelling results, we manufactured GaInP/Ga(In)As/Ge 3 J solar cells thinned down to 50 μm from an original thickness of 150 μm following the same fabrication procedures as conventional thick cells and without back surface passivation nor back reflectors. Remarkably, the efficiency of the thinned cells is the same than the non-thinned ones, closely aligning the model predictions. We demonstrate a power-to-mass ratio of 1.3 kW/kg, despite the semiconductor structure not being optimized for the AM0 spectrum. Finally, we outline potential pathways for improving the performance of these 3 J solar cells to achieve nearly 2 kW/kg.