Synthesis of Cu2-xSe Nanocrystals by Tuning the Reactivity of Se

In this paper, we demonstrated a modified hot-injection method to synthesize high-quality Cu2-xSe nanocrystals (NCs) in liquid paraffin without using the hazardous and unstable alkylphosphines as the ligand of Se. The key of this method is the capability for tuning the reactivity of Se at the stage of formation of Cu2-xSe nuclei. The low reactivity of Se facilitated the decomposition of copper(H) acetylacetonate into Cu2O, whereas the increase of Se reactivity promoted the reaction between Cu and Se. By control of the experimental variables, such as reaction time, Se concentration, reaction temperature, and, particularly, the addition of the noncoordinating solvent of Se, high-quality Cu2-xSe NCs were prepared. The resultant Cu2-xSe NCs possessed an indirect band-gap absorption around 1050 nm, potentially applicable in photovoltaic investigations. As an example, the optoelectronic properties of Cu2-xSe NCs were investigated, which showed a promising increase in photocurrent under AM 1.5 illumination. Because the current method was convenient and environmentally friendly, it was believed that this work would facilitate the development of a preparation technique and industrial application of copper-based photovoltaic devices.