Quantitative PL imaging of thin film solar cells — Potential and pitfalls

Photoluminescence imaging as well as quantitative photoluminescence spectroscopy has been successfully applied to different solar cell materials, such as crystalline silicon and polycrystalline Cu(In, Ga)Se
₂
. These methods can be used to investigate spatial inhomogeneities, as well as for the contactless determination of quasi-Fermi level splittings, which are related to the open-circuit voltage in finished photovoltaic devices. The theory underlying the analysis of quantitative PL imaging is found to work reliably for more ideal semiconductors such as silicon, but can pose substantial problems for the more non-ideal semiconductors such as kesterite-type materials, where both the optical properties as well as the recombination process may vary widely from sample to sample. In this contribution we will evaluate different approaches to analyse quantitative PL imaging and discuss the potential pitfalls incurred, especially when the actual sample temperature during the measurement is not properly taken into account.