Colloidal Ag₂SbBiSe₄ nanocrystals as n‑type thermoelectric materials

Materials with low intrinsic thermal conductivity are essential for the development of high-performance thermoelectric devices. At the same time, the solution processing of these materials may enable the cost-effective production of the devices. Herein, we detail a high-yield and scalable colloidal synthesis route to produce Ag₂SbBiSe₄ nanocrystals (NCs) using amine-thiol-Se chemistry. The quaternary chalcogenide material is consolidated by a rapid hot-press maintaining the cubic crystalline structure. Transport measurements confirm that n-type Ag₂SbBiSe₄ exhibits an inherently ultralow lattice thermal conductivity of ca. 0.34 W m^-1K^-1 at 760 K. Moreover, a modulation doping strategy based on the blending of semiconductor Ag₂SbBiSe₄ and metallic Sn NCs is demonstrated to control the charge carrier concentration in the final composite material. The introduction of Sn nanodomains additionally blocks phonon propagation thus contributing to reducing the thermal conductivity of the final material. Ultimately, a peak thermoelectric figure of merit value of 0.64 at 760 K is achieved for n-type Ag₂SbBiSe₄-Sn nanocomposites that also demonstrate a notable Vickers hardness of 185 HV.