Publication date: 27th June 2014
In quantum dot (QD) solar cells it has already been shown that the incorporation of graphene enhances the photocurrent due to its extraordinary electron transport properties. However, only few experimental studies, mainly carried out with cadmium-based QDs, were focused on the understanding of the electronic interaction between the QDs and graphene sheets in the composite.[1-3] Therefore, we developed QD-graphene hybrid inks with highly efficient charge transfer from the QDs to graphene, based on different QD and graphene synthesis procedures and coupling strategies. The key point is to enhance the graphene light absorption by broadening the spectral range with NIR PbS QDs.[4] We have prepared stable hybrid solutions using ligand-modified PbS QDs, and chemically reduced graphene oxide (RGO) or liquid-exfoliated graphene (GLE) (from graphite as carbon source).
When keeping a constant concentration of QDs in solution, we observed that their PL emission properties were quenched when decreasing the degree of reduction of the graphene (which was verified with XPS), and increasing the concentration of the graphene-based materials. The strongest quenching effect has been observed using GO-based materials. This can be ascribed to a greater electron-accepting and interacting capacity of the GO derivatives.[1, 2] Apart from the optical characterization, the TEM images of the QD-graphene composites show that it is possible to modulate the QD coverage and dispersion on the graphene sheets varying the coupling strategy used to prepare the hybrid ink.
References:
[1] I.V. Lightcap et al., Fortification of CdSe Quantum Dots with Graphene Oxide. Excited State Interactions and Light Energy Conversion. J. Am. Chem. Soc. 2012, 134, 7109-7116.
[2] S. Kundu et al., Fluorescence Dynamics and Stochastic Model for Electronic Interaction of Graphene Oxide with CdTe QD in Graphene Oxide-CdTe QD Composite. J. Phys. Chem. C 2013, 117, 23987-23995.
[3] S. Guo et al., Photoinduced Electron Transfer Between Pyridine Coated Cadmium Selenide Quantum Dots and Single Sheet Graphene. Adv. Funct. Mater. 2013, 23, 5199-5211.
[4] I. Moreels et al., Z., Size-Tunable, Bright, and Stable PbS Quantum Dots: A Surface Chemistry Study. ACS Nano 2011, 5, 2004-2012.
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