Colloidal nanocrystals for optoelectronics

Colloidal nanocrystals are chemically synthesized semiconductor nanoparticles. Their nanometric size gives them modified optical properties compared with bulk material. This modification is the result of quantum confinement. Quantum confinement represents a paradigm shift in the field of optical materials. For the first time, it became possible to modulate the spectrum via geometrical properties rather than by metallurgical processes involving alloying.

By modulating both size and composition, it is possible to obtain tunable optical properties from ultraviolet to THz. In particular, the luminescence of these nanocrystals has aroused great interest, for bio-imaging or quantum optics as a single-photon source. From 2013 onwards, it was the use of nanocrystals as fluorophores for displays that generated interest in these nanomaterials. Nanocrystals are set to become the standard for emitters in LCD displays, as they enable optical properties as good as OLEDs to be achieved at lower cost. The market for nanocrystals is worth over $100 million, with very strong growth prospects.

This first market has validated the entry of nanocrystals into the industrial world. The next challenge for these materials is to integrate them into optoelectronic devices, where they will be both optically and electrically active. From this point of view, nanocrystals hold great promise for low-cost components. Nanocrystals combine the performance and stability of inorganic materials with the processability of polymeric materials.

To achieve this goal, the conductive properties of nanocrystals need to reach the same level of maturity as optical properties. Obtaining conductive films from nanocrystals is critical to obtaining optoelectronic devices that are competitive with historical semiconductors. This involves controlling inter-box coupling, which is mainly linked to nanocrystal surface chemistry. Since 2009, major research efforts have made it possible to increase charge carrier mobility from 10 ^-6 cm ² V ^-1 s ^-1 at the end of synthesis to over 100 cm ² V ^-1 s ^-1 , making it possible to realistically envisage the manufacture of competitive optoelectronic components.

This article is organized as follows. In the first section, the chemical synthesis of nanocrystals is presented. This is followed by a presentation of the optical and transport properties of nanocrystal films. The final section discusses the integration of nanocrystals...