Photoexcitation of PbS nanosheets leads to highly mobile charge carriers and stable excitons
Jannika Lauth (Leibniz Universität, Cluster of Excellence PhoenixD (Photonics, TU Delft - ChemE/Opto-electronic Materials)
Michele Failla (TU Delft - ChemE/Opto-electronic Materials)
Eugen Klein (Hamburg University of Technology)
Christian Klinke (Hamburg University of Technology, Universität Rostock, Swansea University)
S.S. Kinge (Toyota Motor Europe)
Laurens D.A. Siebbeles (TU Delft - ChemE/Opto-electronic Materials)
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Abstract
Solution-processable two-dimensional (2D) semiconductors with chemically tunable thickness and associated tunable band gaps are highly promising materials for ultrathin optoelectronics. Here, the properties of free charge carriers and excitons in 2D PbS nanosheets of different thickness are investigated by means of optical pump-terahertz probe spectroscopy. By analyzing the frequency-dependent THz response, a large quantum yield of excitons is found. The scattering time of free charge carriers increases with nanosheet thickness, which is ascribed to reduced effects of surface defects and ligands in thicker nanosheets. The data discussed provide values for the DC mobility in the range 550-1000 cm2 V-1 s-1 for PbS nanosheets with thicknesses ranging from 4 to 16 nm. Results underpin the suitability of colloidal 2D PbS nanosheets for optoelectronic applications.