Graphene Phototransistors Sensitized by Cu2–xSe Nanocrystals with Short Amine Ligands

Abstract

Recent attempts to employ colloidal semiconductor nanocrystals (NCs) as the sensitizing materials for hybrid NC–graphene phototransistors have provided a new effective photosensing platform. However, most of these devices are based on NCs containing either lead or cadmium, which would not be the most preferred material candidates for commercialization. Here, we demonstrate the use of colloidal Cu2–xSe NCs that do not contain lead or cadmium as the sensitizers for NCs–graphene hybrid visible phototransistors. Because the long olyelamine ligands originally attached on Cu2–xSe NCs are known to impede electronic process between NCs and graphene, the long ligands are replaced with short amines including octylamine, hexylamine, and butylamine. It is found that the NCs layer with shorter amine ligands yields a more prominent n-doping effect on graphene under illumination, which results in a systematic negative shift in Dirac voltage. More importantly, this leads to devices with larger photocurrent and larger lig...