Potential analysis of a rear-side passivation for multi-junction space solar cells based on germanium substrates

For future 4-junction Ge based multi-junction solar cells, the current generated in the Ge sub-cell gets very important. We developed an efficient rear-side passivation stack, which results in minority carrier lifetimes (teff) ≈ 200 ms and investigated its performance in an accelerated aging experiment (1 MeV electron irradiation). The aging caused a strong lifetime decrease down to teff = 4 ms, whereas the carrier mobility stayed constant. These experimental values provide the basis for Beginning-of-Life and End-of-Life solar cell simulations, which show that the potential of the rear-side passivation for 3-junction solar-cell performance is limited, but very promising for 4-junction solar cells.