Size and Phase Controlled Synthesis of CdSe/ZnS Core/Shell Nanocrystals Using Ionic Liquid and Their Reduced Graphene Oxide Hybrids as Promising Transparent Optoelectronic Films

Abstract

CdSe/ZnS core/shell nanocrystals were synthesized in a size and phase controlled manner using a series of ionic liquids; trihexyltetradecylphosphonium and 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, where R = ethyl, butyl, hexyl, and octyl. In particular, the longer alkyl side chains of the imidazolium cation induce the evolution from zinc blende nanodots to wurtzite nanorods. We suggest that the steric hindrance of the alkyl chains is responsible for the size and phase change of the nanocrystals. The noncovalent ionic liquid linkage of the CdSe/ZnS nanocrystals with the reduced graphene oxide (or single-walled carbon nanotubes) produced a strongly binding hybrid nanostructure, as evidenced by their efficient photocarrier generation. The nanorods demonstrated a higher photocurrent (similar to 2 times) than the nanodots under AM 1.5G irradiation. These reduced graphene oxide hybrid nanostructures offer the promise of producing outstanding transparent optoelectronic films on flexible substrates.