Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices

Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices

Kulkarni, A. (TU Delft ChemE/Opto-electronic Materials)
Siebbeles, L.D.A. (TU Delft TU Delft Library; TU Delft ChemE/Opto-electronic Materials)

TU Delft Library

2018

We studied charge carrier photogeneration, cooling, carrier multiplication (CM) and charge mobility and decay in: a) isolated PbSe nanocrystals in solution, b) films of PbSe nanocrystals coupled by organic ligands, and c) 2D percolative networks of epitaxially connected PbSe nanocrystals. The studies were performed using ultrafast pump-probe spectroscopy with optical or terahertz/microwave conductivity detection. The effects of electronic coupling between the nanocrystals on charge mobility were characterized by frequency-resolved microwave and terahertz photoconductivity measurements. Reducing the size of ligand molecules between nanocrystals in a film strongly increases the charge mobility. Direct connection of nanocrystals in a percolative network yielded a sum of electron and hole mobilities as high as 270±10 cm²V^-1s^-1. We found that a high mobility is essential for multiple electron-hole pairs formed via CM to escape from recombination. The coupling between the nanocrystals was found to strongly affect the competition between cooling of hot charges by phonon emission and CM. In percolative networks of connected nanocrystals CM is much more efficient than in films with ligands between the nanocrystals. In the e networks CM occurs in a step-like fashion with threshold near the minimum photon energy of twice the band gap.

carrier multiplication
charge cooling
charge generation
charge mobility
Nanocrystal

http://resolver.tudelft.nl/uuid:c7544346-a102-4be0-ba85-d3c13da03c17

https://doi.org/10.1117/12.2311452

SPIE

2018-11-21

9781510618725

Proceedings of SPIE: Advances in Ultrafast Condensed Phase Physics, 10673

SPIE Photonics Europe 2018, 2018-04-22 → 2018-04-26, Strasbourg Convention & Exhibition Centre, Strasbourg, France

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

conference paper

© 2018 A. Kulkarni, L.D.A. Siebbeles