Issue 45, 2016

Hot exciton cooling and multiple exciton generation in PbSe quantum dots

Abstract

Multiple exciton generation (MEG) is a promising process to improve the power conversion efficiency of solar cells. PbSe quantum dots (QDs) have shown reasonably high MEG quantum yield (QY), although the photon energy threshold for this process is still under debate. One of the reasons for this inconsistency is the complicated competition of MEG and hot exciton cooling, especially at higher excited states. Here, we investigate MEG QY and the origin of the photon energy threshold for MEG in PbSe QDs of three different sizes by studying the transient absorption (TA) spectra, both at the band gap (near infrared, NIR) and far from the band gap energy (visible range). The comparison of visible TA spectra and dynamics for different pump wavelengths, below, around and above the MEG threshold, provides evidence of the role of the Σ transition in slowing down the exciton cooling process that can help MEG to take over the phonon relaxation process. The universality of this behavior is confirmed by studying QDs of three different sizes. Moreover, our results suggest that MEG QY can be determined by pump–probe experiments probed above the band gap.

Graphical abstract: Hot exciton cooling and multiple exciton generation in PbSe quantum dots

Supplementary files

Article information

Article type
Paper
Submitted
01 Jun 2016
Accepted
19 Oct 2016
First published
19 Oct 2016

Phys. Chem. Chem. Phys., 2016,18, 31107-31114

Hot exciton cooling and multiple exciton generation in PbSe quantum dots

M. Kumar, S. Vezzoli, Z. Wang, V. Chaudhary, R. V. Ramanujan, G. G. Gurzadyan, A. Bruno and C. Soci, Phys. Chem. Chem. Phys., 2016, 18, 31107 DOI: 10.1039/C6CP03790A

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