New insights into the phosphine-free synthesis of ultrasmall Cu_2-xSe nanocrystals at the liquid-liquid interface

In this work, we first demonstrate a liquid-liquid interfacial strategy to prepare ultra small colloidal Cu_2-xSe NCs with blue fluorescence (<5 nm) under moderate conditions. Specifically, preparation of Cu_2-xSe NCs proceeds via a reaction of copper(ii) stearate [Cu(SA)₂] with NaHSe in the presence of phosphine-free oleic acid (OA) or oleylamine (OAm) as capping ligands at 95 °C at the toluene/water interface. The as-prepared NCs display a narrow size distribution compared with traditional high-temperature organic methods. Furthermore, a non-caustic and environmentally friendly ammonium thiocyanate (NH₄SCN) as a useful agent was introduced to replace the long-chain organic ligands for fabrication of NC-sensitized solar cells. The results indicate that the Cu_2-xSe NCs have potential applications in future optoelectronic devices.