Practical target values of Shockley-Read-Hall recombination rates in state-of-the-art triple-junction solar cells for realizing conversion efficiencies within 1% of the internal radiative limit

摘要

In order to identify the cause of the difference between actual efficiency and the theoretical limit in state-of-the-art triple-junction solar cells, we investigate the internal luminescence efficiency in the depletion region ( eta intdep). The average internal luminescence efficiency of the whole subcell volume ( eta int over bar ) is obtained experimentally, and the eta intdep is deduced by numerical calculations using rate equations. We find that eta int over bar and eta intdep agree well in the low-recombination current regime including the maximum power point. This indicates that the non-radiative recombination loss at the maximum power point strongly depends on the recombination in the depletion region. Furthermore, we determine the actual Shockley-Read-Hall recombination coefficient in the depletion region, A(dep), which is proportional to the effective density of recombination centers. Our analysis reveals the target values of A(dep) required for realizing conversion efficiencies that are within 1% of the internal radiative limit. The analysis also clarifies the extent of reduction of the effective density of recombination centers (in the depletion region) that is required to realize a given target efficiency.