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

Solar cells based on ZnO nanorods with thin In 2 S 3 shells have recently shown promising solar conversion efficiencies. Using optical-pump terahertz-probe (OPTP) spectroscopy, the charge separation across ZnO/In 2 S 3 interfaces is analyzed for ZnO nanorods with systematically varied In 2 S 3 absorber thicknesses, measuring transient photoconductivities with subpicosecond time resolution. Whereas for neat In 2 S 3 films the photoconductivity is dominated by fast multiple trapping and second order recombination, the ZnO/In 2 S 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 2 S 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.