Charge transport in colloidal nanocrystal films is mainly governed by the electronic coupling between nanocrystals. Since the bulky organic ligands on as-synthesized nanocrystals hinder charge transport, a common practice is to promote charge transport by replacing these long insulating native ligands with shorter ligands. This leads to a reduction in interparticle spacing that improves the electronic wavefunction overlap between adjacent nanocrystals.
Our group recently synthesized a new soluble precursor for SnSe that can also be utilized as a nanocrystal ligand. We first report on our precursor synthesis, which is carried out by reacting tin with dimethyl diselenide. We then characterize the precursor structure and its thermal decomposition product. Mass spectroscopy and nuclear magnetic resonance spectroscopy demonstrate that the precursor structure is tin(IV) methylselenolate, Sn[Se(CH3)]4. Differential scanning calorimetry and x-ray diffraction reveal that the precursor thermally decomposes into crystalline SnSe at 170°C.
This precursor creates avenues to make nanocomposites consisting of PbSe nanocrystals in a SnSe matrix. To explore this possibility, we carry out a solid-state ligand exchange of oleate capped PbSe nanocrystals with tin(IV) methylselenolate. We confirm the successful removal of oleate in this process with infrared spectroscopy. Heating of the nanocrystal films to 170°C transforms the precursor into SnSe and yields a PbSe-SnSe nanocomposite. In addition to these structural characterizations, we also report on our ongoing efforts to characterize carrier mobility, electrical conductivity, and Seebeck coefficient. We conduct these measurements using field effect transistor, van der Pauw, and differential thermovoltage techniques.