Physics Colloquium_

Talk by Prof. Roland Scheer Photovoltaics Group, Martin-Luther-University Halle-Wittenberg
Carrier lifetime and diffusion constant: How to determine solar cell material properties by time-resolved photoluminescence
Time-resolved photoluminescence (TRPL) is a simple contactless method with the primary goal to determine the effective lifetime of minority carriers in a semiconductor (short, the lifetime). The method is very interesting for quality control for solar cells. However, there are physical effects that cause the TRPL decay time not to simply equal the lifetime. To distinguish the influence of these physical effects it is necessary to perform time-resolved photoluminescence with varying experimental parameters, such as injection level, device temperature, or bias voltage.
If those experiments are re-enacted by computer simulation we can extract the wanted minority carrier lifetime and but also other quantities. For instance, increasing the injection level leads to bimolecular recombination and can be used to determine the majority carrier density. Increasing the device temperature reduces minority carrier trapping and can give the trap density. Changing the bias voltage in
TRPL on pn junctions (complete solar cells) may be used to determine the charge carrier mobility and thus the diffusion constant. Certainly, there remains the demand to determine the lifetime from a single measurement. This problem appears to have a viable solution.
1. M. Maiberg and R. Scheer, Theoretical study of time-resolved luminescence in semiconductor heterostructures.
1. Decay from the steady state. Journal of Applied Physics, 2014. 116(13): p. in print.
2. M. Maiberg and R. Scheer, Theoretical study of time-resolved luminescence in semiconductor heterostructures.
2. Pulsed excitation. Journal of Applied Physics, 2014. 116: p. 123711.
3. M. Maiberg, C. Spindler, E. Jarzembowski, and R. Scheer, Electrical characterization of Cu(In,Ga)Se2-solar cells by voltage dependent time-resolved photoluminescence. Thin Solid Films, 2014(0).http://dx.doi.org/10.1016/j.tsf.2014.09.022.

Prof. Dr. Roland Scheer (born 1959) studied electrical engineering and physics. He received his PhD at the Technical University Berlin with a thesis on chalcopyrite solar cells. From 1994 on he was leading scientist at the Helmholtz-Centre-Berlin. In 2002 he was visiting scientist at the National Institute for Advanced Industrial Science and Technology, Tsukuba, Japan. Scheer was co-founder of several companies, published more than 150 papers, and prepared a monograph on “Chalcogenide Photovoltaics” at Wiley. Since 2010 he holds the chair for photovoltaics at the Martin-Luther-University Halle-Wittenberg. His fields of interest are chalcogenide and other thin film solar cells covering structural and electronic properties of materials and devices.

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