Thermal Conductivity and Elastic Modulus in Two-Dimensional Hybrid Metal Halide Perovskites: From a Molecular Engineering Perspective

Device-level implementation of soft materials demands a comprehensive understanding of their thermal conductivity and elastic modulus to mitigate thermo-mechanical challenges and ensure long-term stability. Thermal conductivity and elastic modulus are usually positively correlated in soft materials, such as amorphous macromolecules, which poses a challenge to discover materials that are either soft and thermally conductive or hard and thermally insulative. Here, we show an anomalous correlation of thermal conductivity and elastic modulus in two-dimensional (2D) hybrid organic-inorganic perovskites (HOIP) by engineering the molecular interaction between organic cations. When replacing the organic cation from a softer alkyl ligand to a more rigid aryl ligand, we find that elastic modulus increases but thermal conductivity decreases, which provides a route to engineer thermal conductivity and elastic modulus independently. We further conducted molecular dynamics simulation to understand the molecular interactions and this anomalous dependence. Introducing chirality into the organic cation induces a unique molecular packing, leading to the same thermal conductivity and elastic modulus regardless of the composition for all half-chiral 2D HOIPs. This finding provides substantial leeway for further investigations in chiral 2D HOIPs to tune opto-electronic properties without affecting the thermal and mechanical stability.