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

Du Chen1,2, Thu T. M. Chu3, Yanyan Li1,2, Shunran Li1,2, Qixuan Hu4, Jee Yung Park1,2, Tyler Wang2,5, Luoqi Dai3, Ming Lu6 et al.

Mengxia Liu2,7, Letian Dou4,8, Xiaotong Li3, Yi Xia9, and Peijun Guo1,2,*

  • *Contact author: peijun.guo@yale.edu
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Phys. Rev. X 15, 041054 – Published 22 December, 2025

DOI: https://doi.org/10.1103/kh5d-jrxw

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 in situ 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.

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Popular Summary

Understanding and controlling the flow of heat is important for improving the performance and stability of devices such as solar cells and light-emitting devices. We developed an all-optical and nondestructive method to measure how heat flows in 2D hybrid perovskites. Taking advantage of the infrared light absorption of the organic sublattice and the sensitivity of visible light reflectance to lattice temperature, our devised pump-probe scheme tracks the spatiotemporal temperature decay after impulsive infrared thermal excitation. We found that heat moves very slowly across the layer-stacking direction due to the organic-inorganic packing, whereas heat transfer along the layer is tied to the intrinsic properties of the constituent building blocks. This work provides a comprehensive view of anisotropic heat flow in 2D hybrid perovskites, informing strategies for tailoring these properties through structural design. The all-optical approach is versatile, useful for other layered or nanoscale hybrid and polymeric materials. This opens exciting possibilities for characterizing and engineering heat flow at the microscopic level.

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Phys. Rev. X 15, 041054– Published 22 December, 2025
  • Received 20 August 2025
  • Accepted 1 December 2025
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