Controlling the Radiative Exciton Recombination Rate in Colloidal Nanocrystals and its Optoelectronic Applications

In recent years, colloidal semiconductor nanocrystals (NC’s) have attracted considerable attention due to their excellent optoelectronic properties such as tunable band-gap, enhanced photoluminescence quantum yield (PLQY) and high optical stability, which categorize them as a promising candidate to complement conventional technologies where tunable band-gap, large area, mechanical flexibility and low cost processing are required. Here we demonstrate how we can gain control over the exciton recombination rate, towards different applications such as lasers, LEDs, and solar cells. Manipulating the shape, the size and the structure of these materials we are able to precisely control the exciton lifetime from 500 ps up to 6μs. First we demonstrate that breaking the symmetry of the crystal we can enhance the emission rate and on the other hand by delocalizing the electron wavefunction we can suppress the e-h overlap leading to long lifetimes. Moreover, through strain induced piezo field we can further decrease the oscillator strength creating an indirect exciton in a Type-I hetero-structure. Coupling these nanocrystals with micro cavities we achieved single mode lasing with ultra-low threshold in weak coupling regime, and enhanced vacuum Rabi-splitting at room temperature in strong coupling experiments. Finally, on the other side of the spectrum we present novel chemical and physical routes to alter the electronic response of the nanocrystals towards efficient harvesting of short wave IR photo-generated excitons. In particular, we show a radical different approach to collect, the wasted so far, near IR electromagnetic radiation of the sun, complementing the current silicon technologies.

Ομιλητής: Σωτήριος Χριστοδούλου
Functional Optoelectronic Nanomaterials group
ICFO – The Insititute of Photonic Science
Av. Carl Friedrich Gauss 3
088600, Castelldefels (Barcelona)
Spain

Ώρα: Πέμπτη, 23 Φεβρουαρίου 2017, 11:00