Colloidal semiconductor quantum dots (QDs), also known as semiconductor nanocrystals, have attracted attention since their discovery just over 30 years ago, primarily because of their optical properties. The emission of sharp lines, similar to those of atoms, with a wavelength that can be tuned with slight changes in size and composition and the relatively low cost of synthesis makes QDs attractive for a range of optoelectronic as well as biomedical applications.

In this issue, we focus on a less explored aspect of QDs, that is, the electronic transport in three-dimensional arrangements of QDs, also known as QD solids. Just like a crystal consists of an ordered distribution of atoms, a QD solid is an ordered arrangement of QDs, which can be seen as artificial atoms, kept together by a variety of organic linkers. In a Review on page 1013, Cherie Kagan and Chris Murray explore the developments in the chemistry of QD solid assembly, which after several years has led to the observation of electron mobilities larger than 10 cm−2 V−1 s−1, indicative of an electronic band structure similar to that of high-mobility crystals. These values make the potential use of QD solids in a range of optoelectronic applications very promising.

Based on this potential, we asked Maksym Kovalenko, Jeffrey Urban and Arto Nurmikko, to discuss in a series of Commentaries (pages 994, 997 and 1001), the realistic potential of realizing commercially viable devices for applications in photovoltaics, thermoelectrics and light emission. The overall picture that emerges is that although the results are certainly promising, whether QD solids will be competitive with other materials considered for the various applications will depend on further improvement in device efficiency and costs.

Whether the electronic transport in QD solids will one day be used in commercial devices remains an open question. However, the concept that we can fabricate materials based on QDs, with new properties that can, in principle, be tuned at will by just using chemistry to vary the size of the constituents, their composition and their distance is simply tantalizing, and this should continue fuelling research for both fundamental and technological interest.