Multiple exciton generation in nano-crystals revisited: Consistent calculation of the yield based on pump-probe spectroscopy

TL;DR

This paper revisits the quantification of multiple exciton generation (MEG) in semiconductor nanocrystals, proposing a new methodology to accurately determine MEG yields from pump-probe spectroscopy data.

Contribution

It introduces a methodology to correctly scale transient absorption signals, improving the accuracy of MEG yield estimation in nanocrystals.

Findings

Modest MEG yields found in lead chalcogenide nanocrystals.

Incorrect assumptions can lead to significant errors in MEG yield estimation.

Proposed scaling factors improve the accuracy of pump-probe spectroscopy analysis.

Abstract

Multiple exciton generation (MEG) is a process in which more than one exciton is generated upon the absorption of a high energy photon, typically higher than two times the band gap, in semiconductor nanocrystals. It can be observed experimentally using time resolved spectroscopy such as the transient absorption measurements. Quantification of the MEG yield is usu- ally done by assuming that the bi-exciton signal is twice the signal from a single exciton. Herein we show that this assumption is not always justified and may lead to significant errors in the estimated MEG yields. We develop a methodology to determine proper scaling factors to the signals from the transient absorption experiments. Using the methodology we find modest MEG yields in lead chalcogenide nanocrystals including the nanorods.