Dear Colleagues,

Colloidal quantum dots (CQDs), semiconductor nanocrystals synthesised by solvent-based chemistry, have been studied intensively over the last three decades. Their small scale, typically a few nanometres, results in an optical band gap that is size-tunable by the quantum confinement effect. This property, coupled with their photo-stability and the low-cost and facile methods by which they can be produced and processed, has prompted their study as the light absorbing or emitting species for a number of important applications, including lighting and displays, third generation solar cells, lasers and image processing.

CQDs can be produced as homogeneous crystals of single materials and alloys, or as more complex structures. A shell or shells of different material can be grown around the original nanocrystal subsequent to its synthesis to produce a core/shell CQD. This spherical heterostructure enables the engineering of carrier wavefunctions, and hence of the photo-physical properties of the CQD. By choice of core and shell material with a suitable band alignment, and by control of the core size and shell thickness during growth, heterostructures can be produced that, for instance, localise electrons and holes in different regions, thus allowing control over the rate of radiative recombination, or maximise photoluminescence quantum yield (PLQY) by reducing the interaction of carriers with surface traps.

Indeed, it is becoming clear that the role of surface traps is key to the performance of CQDs for many applications. The nanoscale of CQDs means that a large fraction of the constituent atoms lie on the surface, where they may be under-coordinated. The resulting dangling bonds can lead to the formation of mid-gap states that trap carriers and act as a channel for non-radiative recombination, as well producing phenomenon such as photoluminescence intermittency, sometimes referred to as ‘blinking’. Such traps can be passivated to an extent by organic surface ligands, but steric hindrance can prevent these often bulky molecules from accessing every surface site. As described above, the growth of a suitable a shell can reduce the interaction of carriers with surface traps, but it can also reduce the efficiency with which they can be extracted to, for instance, contribute to the output of a CQD-based solar cell. However, in recent years the use of compact halide ions for surface passivation has proved particularly effective, resulting in near-unity PLQY and solar cell efficiencies in excess of 10%.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Dr. David Binks
Guest Editor

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• colloidal quantum dot
• nanoparticle
• nano crystal