Institut des
NanoSciences de Paris
insp
insp
5.jpg

Soutenance de thèse de Junling Qu - Jeudi 29 avril 2021 à 10 h

Junling Qu, doctorant dans l’équipe Physco-chimie et dynamique des surfaces, soutient sa thèse le jeudi 29 avril 2021 à 10 h en visioconférence.

Colloidal semiconductor nanocrystals for optoelectronic applications : photodetectors and light emitting diodes

JPEG Left schematic of the HgTe LED. Right : infrared image of a wet biscuit illuminated by the HgTe LED.

Abstract

Nanocrystals with a dimension below their excitonic Bohr radius can provide size-tunable optoelectronic properties, enabling on-demand tailoring of properties for specific applications. Especially, the development of wet chemistry synthesis of colloidal nanocrystals makes them promising building blocks for the next-generation solution-processible low-cost optoelectronic applications including light emitting, sensing, and harvesting. My thesis targets two aspects of the nanocrystal-based devices : infrared photodetector and light emitting diodes (LEDs). My thesis is first focused on the heavy-metal-free infrared photodetection using either the intraband transition of self-doped Ag2Se nanocrystals or the plasmonic resonance of remotely doped ITO (tin doped indium oxide) nanocrystals. Before integrating them to photoconductive devices, I studied their optical and transport properties as well as their energetic configurations. I then test their infrared photodetection performance and rationalize their weak performance compared with their heavy metal counterparts. In the second part of my thesis, I advance to the all-solution nanocrystal-based LEDs in the visible and SWIR, with an emphasis on their practical application. The designed visible LED using CdSe/CdZnS nanoplatelets shows the lowest turn-on voltage and the longest lifetime for nanoplatelets based LEDs. I also provide insights on the origin of efficiency roll-off of the LED. Then, this LED is coupled with a homemade PbS broadband photodetector to achieve, for the first time, an all-nanocrystal based LiFi-like communication setup. For SWIR LEDs, HgTe is used as infrared emitter. By forming a HgTe/ZnO bulk heterojunction in the emitting layer, a bright SWIR LED capable of active imaging is obtained.

Jury

  • Dr. Dmitry Aldakov, CEA Grenoble, Rapporteur
  • Dr. Lionel Hirsch, Université de Bordeaux, Rapporteur
  • Prof. Bruno Masenelli, INSA Lyon, Examinateur
  • Prof. Davy Gérard, UTT Troyes, Examinateur
  • Prof. Corinne Chanéac, Sorbonne Université, Examinatrice
  • Dr. Emmanuel Lhuillier, INSP, Directeur de thèse