Hempel, H.; Redinger, A.; Repins, I.; Moisan, C.; Larramona, G.; Dennler, G.; Handwerg, M.; Fischer, S.F.; Eichberger, R.; Unold, T.: Intragrain charge transport in kesterite thin films - limits arising from carrier localization. Journal of Applied Physics 120 (2016), p. 175302/1-6
Open Access Version
Intra-grain charge carrier mobilities measured by time resolved terahertz spectroscopy (TRTS) in state of the art Cu2ZnSn(S,Se)4 kesterite thin films are found to increase from 32 to 140 cm2V-1s-1 with increasing Se content. The mobilities are limited by carrier localization on the nanometer-scale which takes place within the first 2 ps after carrier excitation. The localization strength obtained from the Drude-Smith model is found to be independent of the excited photocarrier density. This is in accordance with bandgap fluctuations as cause of the localized transport. Charge carrier localization is a general issue in the probed kesterite thin films which were deposited by coevaporation, colloidal inks and sputtering followed by annealing with varying Se/S contents and yield 4.9 to 10.0 % efficiency in the completed device.