Multiple-Trapping Governed Electron Transport and Charge Separation in ZnO/In2S3 Core/Shell Nanorod Heterojunctions

Solar cells based on ZnO nanorods with thin In2S3 shells have recently shown promising solar conversion efficiencies. Using optical-pump terahertz-probe (OPTP) spectroscopy, the charge separation across ZnO/In2S3 interfaces is analyzed for ZnO nanorods with systematically varied In2S3 absorber thicknesses, measuring transient photoconductivities with subpicosecond time resolution. Whereas for neat In2S3 films the photoconductivity is dominated by fast multiple trapping and second order recombination, the ZnO/In2S3 heterostructures exhibit slow electron injection dynamics occurring within hundreds of picoseconds, and long-lived charge-separated states. The transient photoconductivity of the ZnO/In2S3 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.