NANOLED has demonstrated various breakthroughs compared to the state-of-the-art. The fabrication of a large array of single nanocrystals (NCs) with controlled position represents a considerable step forward, as the method for fabricating it is extremely versatile and it can be employed with a large variety of NCs with various shape and/or composition. In addition, the developed NCs positioning method allows correlating material's morphology to optical data and it is compatible with electrical injection. The combination of all these properties leads to an advanced and versatile platform that can be used for both fundamental studies as well as applications. The most crucial step for the controlled deposition of single NCs is increasing their size via a silica shell. Such approach is very versatile (as it can be applied to a variety of different NCs) and it enables a facile controlled deposition on patterned substrates. The research team has fully optimized such approach via advanced “design of experiments” methods and enhanced the reproducibility of the deposition process by employing a doctor blade technique on patterned substrates.
One the most critical step for the fabrication of electrically driven single-photon sources based on NCs is the fabrication of electrical contacts. Such final step is still under development as it is difficult to control and suffer from low reproducibility. So far, the research team has been able to obtain charge injection into 100 nm size patches of nanocrystals, additional research is required to inject charges in a single NC. Nonetheless, the 100 nm NC patches have been used to fabricate one of the smallest light-emitting diode based on NCs to date.
Other significant achievements have been obtained in material development. The team demonstrated that it is possible to carry out ligand-exchange on perovskite NCs in solid-state, thus improving the photoluminescence quantum yield compared to the pristine material and the standard ligand-exchange carried out in solution. Other major breakthroughs are represented by the novel IR-emitting materials prepared within the project framework, namely CsxMnBry NCs and InAs/Znse. The latter represents a considerable step forward compared to the state-of-the-art since the synthetic approach based on ZnCl2 leads to the formation of high-quality NCs with photoluminescence quantum yield above 60% and respective light-emitting diodes demonstrating an external quantum efficiency above 13%.
Considering the various results of the project, the research team has now developed a variety of tools that will lead to injected single-photon-sources based on deterministically positioned NCs. Such light-sources can also be fabricated with novel IR-emitting NCs. This is of particular importance given the relevance of single-photon-sources for quantum cryptography, a technology which operates with photons outside of the visible spectral range. Finally, the processing techniques and the new materials developed will allow the research team to fabricate novel nano-sized light sources (not only single-photon emitting devices) operating both in visible and near-infrared spectral ranges.
