Clément Livache

Résumé:

Colloidal semiconductor nanocrystals, and in particular colloidal quantum dots, are solution-processable materials that combine the robustness and high quality of inorganic semiconductors with the ease of processability of organic materials. This makes them excellent candidates for new generations of optoelectronic devices including detectors, LED and laser sources.¹ In the scope of their integration in such devices, spectroscopic approches are invaluable to understand fundamental photophysics, quantify relevant material parameters and drive synthesis optimization. In this talk, I will stress the importance of Auger decay control in nanocrystals. Auger recombination in high-quality nanocrystals is the principal non-radiative decay channel for multiexcitonic states. In Auger processes, an electron-hole pair (exciton) recombines by transfering its energy to a third carrier that get excited to higher energy levels.¹ In lasing applications, Auger recombination is detrimental since it very efficiently destroys population inversion. I will demonstrate how ultrafast spectroscopy can be used to understand the fundamental parameters of Auger, and I will present two novel approaches for the control of Auger relaxation lifetime over 6 orders of magnitude. Introduction of spin-exchange interactions in doped systems allows for considerable Auger acceleration below 500 fs,² leading to ultrafast electron photoemission with applications to photocathodes, photochemistry and potentially efficient solar cells beyond the Shockley-Queisser limit.^2,3 On the over side of the spectrum, the development of new compositional-graded core-shell structures allows for a dramatic increase of Auger lifetime beyond 2 ns,^4,5 opening the way to the integration of nanocrystals in the first prototypes of electrically-injected laser diodes.^6,7 

[1] Pietryga, Klimov et al. Chem. Rev. 2016

[2] Livache et al. Nature Photonics 2022

[3] Jin, Livache et al. Nature Materials – just accepted

[4] Lim et al. Nature Nanotechnology 2018

[5] Livache et al. submitted

[6] Ahn, Livache et al. Advanced Materials 2023

[7] Ahn, Livache et al. Nature – just accepted