Heat Transport in Disordered Binary Assemblies of Colloidal Metal-Halide Perovskite and Metallic Nanocrystals

Nanoscale thermal management is critical for colloidal nanocrystal solids, which have inherently low thermal conductivities. The thermal properties of metal-halide perovskite nanocrystals, in particular, remain underexplored. At the same time, while binary nanocrystal assemblies extend structural and electronic tunability, their impact on nanoscale thermal transport demands exploration. Here, we investigate the heat transport properties of disordered binary assemblies of colloidal CsPbBr₃ and Au nanocrystals. We undertake a combined theoretical and experimental study, including spatiotemporally resolved thermoreflectance microscopy experiments of heat propagation, finite element simulations of realistic spatial arrangements, and we develop an effective medium model for multicomponent nanocrystal films. Despite a three-hundred-fold difference in the bulk thermal conductivities of CsPbBr₃ and Au, the ligands dominate that of the colloidal nanocrystal film, rendering the perovskite-based system nearly as thermally conductive as an equivalent metal nanocrystal-based one. Superlattices of cubic CsPbBr₃ nanocrystals effectively maximize the core volume fraction and thereby the composite thermal conductivity for a given size and ligand. Indeed, introducing spherical Au nanocrystals to a cubic CsPbBr₃ nanocrystal assembly counterintuitively decreases the overall thermal conductivity by reducing packing density. However, thermal transport in the binary nanocrystal films is diffusive despite packing disorder and local CsPbBr₃:Au ratio variations, allowing nanoscale transport properties to extrapolate well to the bulk. These results highlight the complex interplay between composition, geometry, and interfacial effects in determining thermal transport in hybrid nanocrystal networks. We discuss these considerations in the context of thermal management for applications of nanocrystal solids.