Lead Chalcogenide Nanoparticles and Their Size-Controlled Self Assemblies for Thermoelectric & Photovoltaic Applications

We report a facile, room temperature synthesis of PbS, PbSe, PbSxSe1-x, and PbTe nanoparticles and their microscale assemblies by combining a chalcogen solution and a lead halide solution in select thiol-amine mixtures. Selection of appropriate thiol-amine pair and/or the use of appropriate amine to thiol ratio has demonstrated a size control on nanoparticle self-assemblies ranging from nano to microscale. Proper washing of these particles has yielded phase pure and compositionally uniform material with the absence of any carbonaceous ligands on the particle surface, making it attractive for electronic device fabrication. The resulting PbS material exhibits bandgap in the range of 0.6eV to as high as 1.2eV for various assembly sizes. These optical bandgaps confirm the retention of quantum confinement of PbS material even in self-assembled nano/micro structures, which could be an interesting phenomenon for future photovoltaic development. Along with carbon-free, quantum-confined self-assemblies, this chemistry also provides a room temperature and instantaneous reaction route to synthesize individually dispersed PbS and PbSe particles with long chain ligand capping similar to traditional synthesis routes. The PbSe material synthesized from this route shows the ability to alloy with PbS at room temperature in the entire composition range and also demonstrates thermoelectric performance comparable to existing undoped PbSe literature.