Broadband Cooling Spectra of Hot Electrons and Holes in PbSe Quantum Dots

Broadband Cooling Spectra of Hot Electrons and Holes in PbSe Quantum Dots

Spoor, F.C.M. (TU Delft ChemE/Opto-electronic Materials)
Tomić, Stanko (University of Salford)
Houtepen, A.J. (TU Delft ChemE/Opto-electronic Materials)
Siebbeles, L.D.A. (TU Delft ChemE/Opto-electronic Materials)

2017

Understanding cooling of hot charge carriers in semiconductor quantum dots (QDs) is of fundamental interest and useful to enhance the performance of QDs in photovoltaics. We study electron and hole cooling dynamics in PbSe QDs up to high energies where carrier multiplication occurs. We characterize distinct cooling steps of hot electrons and holes and build up a broadband cooling spectrum for both charge carriers. Cooling of electrons is slower than of holes. At energies near the band gap we find cooling times between successive electronic energy levels in the order of 0.5 ps. We argue that here the large spacing between successive electronic energy levels requires cooling to occur by energy transfer to vibrational modes of ligand molecules or phonon modes associated with the QD surface. At high excess energy the energy loss rate of electrons is 1-5 eV/ps and exceeds 8 eV/ps for holes. Here charge carrier cooling can be understood in terms of emission of LO phonons with a higher density-of-states in the valence band than the conduction band. The complete mapping of the broadband cooling spectrum for both charge carriers in PbSe QDs is a big step toward understanding and controlling the cooling of hot charge carriers in colloidal QDs.

carrier cooling
carrier dynamics
electronic structure
nanocrystal
quantum dot
transient absorption spectroscopy

http://resolver.tudelft.nl/uuid:565aa8d9-eee5-49fa-a10b-856a4b7ac917

https://doi.org/10.1021/acsnano.7b02506

1936-0851

ACS Nano (online), 11 (6), 6286-6294

Institutional Repository

journal article

© 2017 F.C.M. Spoor, Stanko Tomić, A.J. Houtepen, L.D.A. Siebbeles