Research Highlight

Glowing graphene dots

doi:10.1038/nindia.2011.104 Published online 14 July 2011

Researchers have designed a new type of polymer-modified graphene quantum dot that could be useful for enhancing the efficiency of solar cells and producing better organic light-emitting diode (OLED) devices.

Quantum dots are interesting because they have a size-dependent optical response, exhibit efficient charge transport and are cheap to produce. However, cadmium-based quantum dots are toxic and hazardous, which prevents their use in large-scale device applications.

To find safe nanomaterials with similar properties as cadmium-based quantum dots, the researchers looked at graphene — a material that also facilitates good charge transport. They prepared graphene quantum dots (GQDs) from graphene sheets. The dots were of 1–2 layers and about 5–15 nm n size. Then they modified the dots with polymers to form three distinct materials: pure GQDs, aniline-modified GQDs (ANI-GQDs) and methylene blue-modified GQDs (MB-GQDs).

Upon irradiation with ultraviolet and visible light, the polymer-modified dots showed significant change in luminescence properties. The ANI-GQDs exhibited blue–white luminescence, whereas the MB-GQDs exhibited green luminescence.

The ANI-GQDs showed a decrease in resistance to charge transport, which improved the material's efficiency to harness solar energy. The study also found that the MB-GQDs dispersed in MEH-PPV saw an increase in charge carrier density, which provides a lower turn-on voltage and much higher efficiency than existing photovoltaic materials. Dispersing MB-GQDs in MEH-PPV provides more electrical transport paths, which enhances charge injection.

"Polymer-modified GQDs can be a cost-effective, environmentally friendly and more stable material for photovoltaics than current organic materials," says lead researcher Vinay Gupta.

References

  1. Gupta, V. et al. Luminescent graphene quantum dots for organic photovoltaic devices. J. Am. Chem. Soc. 133, 9960-9963 (2011) | Article |