Engineering Heat Flow in Two-Dimensional Perovskites via Metal and Spacer Cation Design

Two-dimensional (2D) organic–inorganic hybrid halide perovskites offer exceptional structural tunability and environmental stability arising from their layered architecture. However, their intrinsically anisotropic and poor thermal transport presents a critical bottleneck for device stability and operation. Here, we systematically investigate compositionally engineered thermal transport in a series of 2D perovskites through simultaneous variation of π-conjugated, semiconducting organic-spacer cations and metal cations using a noninvasive vibrational pump-visible probe (VPVP) platform. Time-resolved VPVP spectroscopy and microscopy independently quantify cross-plane and in-plane thermal diffusivities and the evaluation of anisotropic heat flow. We found that incorporation of semiconducting organic spacer molecules enhances cross-plane thermal transport while suppressing in-plane heat conduction, progressively reducing thermal anisotropy and approaching near-isotropic heat transport for extended conjugated organic spacers. Metal cation substitution further modulates thermal transport, with Sn-based 2D perovskites exhibiting enhanced thermal diffusivity relative to Pb analogues, whereas Ge incorporation introduces increased lattice anharmonicity arising from asymmetric metal-halide bonding, leading to weakened heat propagation. Correlating thermal diffusivities with structural parameters, including interlayer spacing and octahedral distortion, reveals that phonon transport in 2D perovskites can be rationally tuned through organic–inorganic lattice design.