Dresden 2017 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 2: Focused Session: Inhomogeneous Materials for Solar Cells I

DS 2.3: Vortrag

Montag, 20. März 2017, 10:30–10:45, CHE 89

On the impact of material inhomogeneities on the time-resolved luminescence decay — •Matthias Maiberg, Torsten Hölscher, and Roland Scheer — Institute of Physics, Martin-Luther-University Halle-Wittenberg, 06120 Halle, Germany

Time-resolved luminescence is the method of choice for determination of material parameters, e.g. the minority carrier lifetime in a semiconductor. However, due to the size of the excited area the obtained data are mostly mean values averaged over a typical region of 10⁴ cm⁻². In our work, we study the impact of lifetime fluctuations, band gap inhomogeneities, and potential fluctuations on the time-resolved luminescence decay by means of three-dimensional simulation. It turns out that inhomogeneous charge carrier lifetimes will increase the luminescence decay time, if the ratio of the structure size and the average diffusion length is larger than 1. For ratios smaller than 1, however, inhomogeneous charge carrier lifetimes will lead to reduced luminescence decay times. In contrast to the strong impact of lifetime inhomogeneities, band gap fluctuations are shown to have a negligible effect on the luminescence decay. In the end, it is demonstrated that the effect of potential fluctuations, which numerous of the thin-film semiconductors are prone to, is rather similar to that of space charges in a semiconductor junction. In particular the decay time will always be smaller than the recombination lifetime due to occuring drift effects. For this reason, potential fluctuations may not explain the often observed long decay times in compensated semiconductors such as Cu(In,Ga)Se₂ or Cu₂ZnSnSe₄.