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  Strothkämper, C.; Schwarzburg, K.; Schütz, R.; Eichberger, R.; Bartelt, A.: Multiple-Trapping Governed Electron Transport and Charge Separation in ZnO/In₂S₃ Core/Shell Nanorod Heterojunctions. The Journal of Physical Chemistry C 116 (2012), p. 1165-1173

10.1021/jp2071748

Abstract:
Solar cells based on ZnO nanorods with thin In₂S₃4 shells have recently shown promising solar conversion efficiencies. Using optical-pump terahertz-probe (OPTP) spectroscopy, the charge separation across ZnO/In_2S_3 interfaces is analyzed for ZnO nanorods with systematically varied In_2S_3 absorber thicknesses, measuring transient photoconductivities with sub-ps time resolution. While for neat In_2S_3 films the photoconductivity is dominated by fast multiple trapping and second order recombination, the ZnO/In_2S_3 heterostructures exhibit slow electron injection dynamics occurring within hundreds of picoseconds, and long-lived charge-separated states. The transient photoconductivity of the ZnO/In_2S_3 core/shell system is analyzed with a correlated three component effective medium approach, yielding a significant decrease of the charge separation efficiency with increasing shell thickness.