Band alignment driven efficient electron transfer and enhanced photoelectric property of gold nanoclusters sensitized graphene quantum dot composites

Gold nanoclusters (Au NCs) have received much attention due to their promising applications in many fields including optical imaging, catalysis, biomedical science and, more recently, energy conversion. Herein, we have constructed a model composite of Au NCs and graphene quantum dots (GQDs), and investigated the band alignment of their energetic levels, efficient electron transfer, and enhanced photoelectric properties of Au NCs/GQDs composites. The introduced Au NCs not only make up for the deficiency of light absorption of GQDs in the visible light region but importantly function as the electron donor to sensitize GQDs and improve the photoelectric properties of the composite. The results from steady-state and time-resolved measurements demonstrate a dramatically quenched fluorescence and a shortened lifetime of Au NCs in the composites, owing to the efficient electron transfer from Au NCs to GQDs. The electron transfer efficiency determined from the dynamical analysis is consistent with that of steady-state fluorescence quenching. The type-II band alignment of Au NCs and GQDs moieties effectively promotes the charge separation of excited Au NCs moieties and the electron transfer to GQDs. As a result, the photoelectric current of Au NCs/GQDs composite is enhanced by 2.69 and 4.80 times that of individual Au NCs and GQDs, respectively. These findings demonstrate a feasible strategy for constructing photoelectric composites with Au NCs as the sensitizer and carbon-based QDs as the electron acceptor and also provide photophysical insights into the structure-property relationship of Au NCs-based composites. [Display omitted] •We have designed and constructed the photoelectric composites using Au NCs as sensitizer and GQDs as electron acceptor.•Type-II band alignment effectively promotes the charge separation of excited Au NCs.•Steady-state and transient spectral observations demonstrate the efficient electron transfer from Au NCs to GQDs.•The photoelectric current of Au NCs/GQDs composite is enhanced by 4.80 times that of GQDs.