Size-Controlled Synthesis of Cu2-xE (E = S, Se) Nanocrystals with Strong Tunable Near-Infrared Localized Surface Plasmon Resonance and High Conductivity in Thin Films

A facile method for preparing highly self-doped Cu2-xE (E = S, Se) nanocrystals (NCs) with controlled size in the range of 2.813.5 nm and 7.216.5 nm, for Cu2-xS and Cu2-xSe, respectively, is demonstrated. Strong near-infrared localized surface plasmon resonance absorption is observed in the NCs, indicating that the as-prepared particles are heavily p-doped. The NIR plasmonic absorption is tuned by varying the amount of oleic acid used in synthesis. This effect is attributed to a reduction in the number of free carriers through surface interaction of the deprotonated carboxyl functional group of oleic acid with the NCs. This approach provides a new pathway to control both the size and the cationic deficiency of Cu2-xSe and Cu2-xS NCs. The high electrical conductivity exhibited by these NPs in metal-semiconductor-metal thin film devices shows promise for applications in printable field-effect transistors and microelectronic devices.