Ultrafast Charge Transfer Cascade in a Mixed-Dimensionality Nanoscale Trilayer

Abstract

Innovation in optoelectronic semiconductor devices is driven by a fundamental understanding of how to move charges and/or excitons (electron-hole pairs) in specified directions for doing useful work, e.g. for making fuels or electricity. The diverse and tunable electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) and one-dimensional (1D) semiconducting single-walled carbon nanotubes (s-SWCNTs) make them good quantum confined model systems for fundamental studies on charge and exciton transfer across heterointerfaces. In nature, the photosynthetic apparatus achieves long-lived charge separation through a charge transfer cascade that consists of a series of thermodynamically downhill charge transfer reactions. Inspired by photosynthesis we create a unique mixed-dimensionality 2D/1D/2D MoS2/SWCNT/WSe2 hetero-trilayer. Photoexcitation of this trilayer heterostructure allows us to overcome both intralayer and interlayer exciton binding energies, resulting in coulombically unbound charges with microsecond recombination lifetimes. In contrast to previously demonstrated 2D/2D/2D trilayers based solely on monolayer TMDC layers, the very large charge mobilities and extended electron network of the 1D semiconducting SWCNT layer helps charges delocalize and diffuse away from the interface at which each type of charge is generated. Interestingly, the hetero-trilayer also appears to enable efficient hole transfer from SWCNTs to WSe2, which is not observed in the identically prepared WSe2/SWCNT heterobilayer, suggesting that new dynamic pathways may be opened by increasing the complexity of nanoscale heterostructures. Our work suggests "mixed-dimensionality" TMDC/SWCNT based hetero-trilayers as both interesting model systems for mechanistic studies of carrier dynamics at nanoscale heterointerfaces, and for potential applications in advanced optoelectronic systems.