ChlorineEnabled Electron Doping in SolutionSynthesized SnSe Thermoelectric Nanomaterials

DOI: 10.1002/aenm.201602328 precursors,[4] doping proves challenging for solution-synthesized MC nanostructures.[5] Recently, post-synthesis halide treatment of nanocrystals in solution has been developed which involves switching halogens for long chain surfactant molecules absorbed on the surface.[2,6] In fact, sorption of halogens can be realized as part of a one-pot synthesis using metal halide precursors.[7] Although this strategy was initially developed for passivation of MC quantum dots against oxidation,[2,6,7] annealing or hot pressing halogen-coated nanoparticles allows halides to diffuse into the MC lattice and substitute for chalcogenide anions.[8] However, controlling doping levels is not straightforward and such methods can introduce rather high halide concentrations in small nanocrystals leading to reduced electrical conductivity.[8b] Hence exerting control over dopant concentration without sacrificing electrical performance is imperative. Thermoelectrics realize direct interconversion between thermal and electric energy, thus providing an important route An aqueous solution method is developed for the facile synthesis of Cl-containing SnSe nanoparticles in 10 g quantities per batch. The particle size and Cl concentration of the nanoparticles can be efficiently tuned as a function of reaction duration. Hot pressing produces n-type Cl-doped SnSe nanostructured compacts with thermoelectric power factors optimized via control of Cl dopant concentration. This approach, combining an energy-efficient solution synthesis with hot pressing, provides a simple, rapid, and low-cost route to high performance n-type SnSe thermoelectric materials.