Sn-Doped In₂O₃Nanoparticles as Thermal Insulating Materials for Solar–Thermal Shielding in the Infrared Range

Three-dimensional stacks of nanoparticles (NPs) are appealing building blocks for the bottom-up production of assembled films. We here focus on thermal transport in assembled films comprising Sn-doped In2O3 NPs (ITO-NP films) as thermal insulating materials because ITO-NP films are also expected to function as solar–thermal shields in the infrared range. Understanding the thermal transport in ITO-NP films is important in the rational design of efficient thermal insulation with low thermal conductivity. The ITO-NP films show a substantially suppressed thermal conductivity compared with ITO films because of increased boundary scattering of the heat carriers (phonons and free electrons) at their NP interfaces. This behavior is explained on the basis of the interface thermal resistances (ITRs) in ITO-NP films. These ITRs are key factors in determining the thermal transport mechanism related to the heat carriers strongly scattered at NP interfaces. This behavior is derived from the NPs consisting of an inorganic core encapsulated in a layer of organic ligands, which provides spatial separation between the NPs, resulting in reduced thermal transport. Thermal experiments and their modeling analysis provide a framework for understanding the thermal transport in ITO-NP films, potentially leading to the development of ITO-NP films with applications in both solar–thermal shielding and thermal insulation.