Abstract
Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers to produce light-emitting diodes, solar cells and other devices. The efficacy of CQDs in these applications is reduced by the non-radiative recombination associated with surface traps. Here we investigate the effect on the recombination dynamics in CdTe CQDs of the passivation of these surface traps by chloride ions. Radiative recombination dominates in these passivated CQDs, with the radiative lifetime scaling linearly with CQD volume over τr=20–55 ns. Before chloride passivation or after exposure to air, two non-radiative components are also observed in the recombination transients, with sample-dependent lifetimes typically of less than 1 ns and a few ns. The non-radiative dynamics can be explained by Auger-mediated trapping of holes and the lifetimes of this process calculated by an atomistic model are in agreement with experimental values if assuming surface oxidation of the CQDs.
Highlights
Colloidal quantum dots (CQDs) have applications as the light emitting or absorbing species in a range of optoelectronic devices based on organic charge transporting layers, including light emitting diodes,[1] photovoltaic cells,[2,3,4] photodetectors,[3,5] holographic data stores and image processors.[6]
We report a study of the effects of chloride ion passivation on recombination dynamics in these CQDs
The spectra are largely unchanged by the treatment process, except for a red-shift of about l = 10 nm. This spectral shift on passivation has previously been shown to depend on the treatment time and the concentration of chloride ions used.[25]
Summary
Colloidal quantum dots (CQDs) have applications as the light emitting or absorbing species in a range of optoelectronic devices based on organic charge transporting layers, including light emitting diodes,[1] photovoltaic cells,[2,3,4] photodetectors,[3,5] holographic data stores and image processors.[6]. We have recently developed a technique that uses chloride ions to passivate CdTe CQDs that can result in near-unity PLQY that is, almost complete surface passivation.[25] In this work, we report a study of the effects of chloride ion passivation on recombination dynamics in these CQDs. The simplified recombination transient in the passivated CQDs allows the underlying charge dynamics to be studied free of the sample-specific influence of trapping, which hitherto has complicated analysis.
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