Photoelectronic applications for fluorescent carbon dots derived from hydrothermal synthesis

The use of carbon nanomaterials is of growing interest in next generation devices for a wide variety of applications, and one of particular recent interest in the ields of biosensing, photocatalysis and photovoltaics is the carbon dot (CD). This particle can be created in a wide variety of synthesis methods and as a class of material possess exceptional optoelectronic properties that are highly tunable and dependent on a variety of environmental factors. This gives them a large scope for optimisation and novel applications.
One such synthesis method that produces carbon dots is hydrothermal carbonisation (HTC), which has the added beneits of being sustainable, facile and adjustable. The method uses relatively low temperatures and reaction times for significant yields, with a wide variety of precursors applicable including waste biomass. The complexity of the reaction processes is not to be underestimated and the formation mechanism of carbon dots is poorly understood, especially as these are thought to vary with the precursor, solvent and other parameters. Due to the significant polydispersity and morphological heterogeneity of the particle this method has also been neglected in the literature, but the process could be a very promising and scalable improvement to multiple technologies.
A thorough understanding of the optoelectronic and formation mechanisms is crucial to the tuning and optimisation of carbon dots towards diferent applications and is proposed to be studied in more detail. The resulting control of the HOMO and LUMO levels for photocatalytic and photovoltaic applications through size and morphology control will allow them to be used as high quantum yield sensitisers for these applications. Further, these allow them to be tailormade to sensitise a variety of different substrates with a variety of band gaps and allow minority carrier injection across the interface into these devices. This includes the potential ability to design and optimise tandem heterojunction cells
where the size of the carbon dot is the major varying factor between layers, increasing efficiency per unit area. Carbon dots can also be applied to solar cells as a form of ield efect passivation for active layers in a variety of substrates due to their tunable negative charge in addition to light collection, rather than surface shadowing, properties. Uses as replacements for quantum dots made from toxic metals is another possibility in Gratzel cell structures, in addition to novel setups.
Overall, there is significant room to explore the most exciting possibilities in the applications sphere for carbon dots. Understanding the fundamental mechanism of formation and of their unique optoelectronic properties is essential to the
facile manipulation of these particles. Investigations into the control of these properties as well as more fundamental studies, such as single particle fluorescence and in-situ hydrothermal synthesis TEM, will help to elucidate this. Additionally, novel applications in optoelectronics including photocatalysts and photovoltaic cells are desirable and achievable to develop the next generation of these devices that combine high performance with sustainability.