Abstract
Ultrafast transient absorption spectroscopy is used to study subnanosecond charge dynamics in CdTe colloidal quantum dots. After treatment with chloride ions, these can become free of surface traps that produce nonradiative recombination. A comparison between these dots and the same dots before treatment enables new insights into the effect of surface trapping on ultrafast charge dynamics. The surface traps typically increase the rate of electron cooling by 70% and introduce a recombination pathway that depopulates the conduction band minimum of single excitons on a subnanosecond timescale, regardless of whether the sample is stirred or flowed. It is also shown that surface trapping significantly reduces the peak bleach obtained for a particular pump fluence, which has important implications for the interpretation of transient absorption data, including the estimation of absorption cross‐sections and multiple exciton generation yields.
Highlights
USIR is a digital collection of the research output of the University of Salford
This observation demonstrates that nonradiative recombination has been eliminated and surface traps have been completely passivated; the PLQY value for each sample studied is given in Table S1 (Supporting Information)
By measuring subnanosecond carrier dynamics in samples before and after a highly effective surface passivation treatment which can eliminate trapping, we have been able both to quantify the effect of trapping on the electron cooling rate and to show that hot carrier trapping can lead to a large reduction in the magnitude of the peak absorption bleach
Summary
USIR is a digital collection of the research output of the University of Salford. Where copyright permits, full text material held in the repository is made freely available online and can be read, downloaded and copied for non-commercial private study or research purposes. 1. Introduction are known to mediate nonradiative recombination, reducing the PL QY and lifetime, and enable the formation of trions and Colloidal quantum dots (CQDs) have potential application in PL intermittency, sometimes known as “blinking.”[7,8,9] Undera number of different technologies, including light emitting standing their role and distinguishing their effects from those diodes and solar cells.[1,2] Their appeal rests on both the facile, of other processes is complicated by the sample-specific contriscalable, and cost-effective solution-based methods by which bution of traps to charge dynamics, which can vary, depending they can be synthesized and processed, and the size tunability on preparation and handling, in ways that are not yet well of their emission wavelength and absorption edge, which ena- understood or controlled
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