Anisotropic Thermal Transport in Quasi-2D Ruddlesden-Popper Hybrid Perovskite Superlattices

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Abstract
Two-dimensional hybrid metal-halide perovskites (2D-MHPs) have emerged as important solution-processed semiconductors with favorable optical and electronic properties for diverse applications in photovoltaics, optoelectronics, and spintronics. The quasi-2D layered structures, featuring large acoustic impedance mismatches between the organic and inorganic sublattices, are expected to result in distinct and anisotropic thermal transport properties along the cross-plane and in-plane directions. Here, we introduce transducer-free vibrational-pump-visible-probe (VPVP) approaches that enable accurate quantification of anisotropic thermal transport properties in various archetypical single-crystalline 2D-MHPs. Specifically, using VPVP spectroscopy and VPVP microscopy, we measure the anisotropic thermal diffusivities of 2D-MHPs with systematically varied Pb-I octahedral layer thicknesses, as well as organic spacer types and lengths, revealing how these structural parameters alter the cross-plane and in-plane thermal transport properties in distinct ways. While diffuse interface scattering plays an important role in dictating cross-plane thermal transport, in-plane thermal transport is primarily determined by phonon transport within interconnected inorganic layers. Density functional theory incorporating four-phonon scatterings provides further insight into the low thermal conductivity and modest thermal conduction anisotropy in 2D-MHPs. Our work demonstrates a new all-optical and noncontact method, which requires minimal sample preparation and allows direct visualization of cross-plane and in-plane thermal transport, potentially compatible with sample environments. The demonstrated VPVP approaches can advance understanding of thermal transport in 2D-MHPs as well as wide-ranging hybrid and polymeric semiconductors beyond 2D-MHPs.
Funding Information
  • National Science Foundation (DMR-2313648)
  • National Science Foundation (CBET-2315077)
  • National Science Foundation (2138259)
  • National Science Foundation (2138286)
  • National Science Foundation (2138307)
  • National Science Foundation (2137603)
  • National Science Foundation (2138296)
  • National Science Foundation (2415101)
  • National Science Foundation (DMR-2317008)
  • National Science Foundation (CBET-2445361)
  • U.S. Department of Energy
  • Basic Energy Sciences (DE-SC0022082)
  • Research Opportunities Initiative, University of North Carolina
  • Office of Naval Research (00014-24-1-2045)
  • Brookhaven National Laboratory (DE-SC0012704)
  • Pittsburgh Supercomputing Center (mat220006p)
  • Pittsburgh Supercomputing Center (mat220008p)

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