Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots

Andrew F. Fidler, Jianbo Gao, Victor I Klimov

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Understanding charge transport and recombination dynamics in photoexcited colloidal quantum dot (QD) solids is key to their applications in optoelectronic devices. Towards this end, we conduct transient photocurrent studies of films of electronically coupled, device-grade PbSe QD films. We observe that the photocurrent amplitude detected following excitation with a short 100 fs pulse is virtually temperature independent down to 6 K, suggesting a tunnelling mechanism of early-time photoconductance. The later-time signal exhibits clear signatures of thermal activation with characteristic energies that are surprisingly robust and independent of the exact type of QD surface treatment. We attribute this behaviour to the involvement of intrinsic fine-structure states and specifically the electron–hole exchange interaction, which creates an energetic barrier to electron–hole separation between adjacent QDs. At room temperature, which is well above the largest activation energy, relaxation of photoconductivity is dominated by non-geminate recombination involving mobile band-edge carriers of one sign and low-mobility carriers of the opposite sign (pre-existing and photoexcited) residing in intragap states. This process leads to memory-less dynamics when the photocurrent relaxation time is directly linked to the instantaneous carrier density.

Original languageEnglish
JournalNature Physics
DOIs
Publication statusAccepted/In press - Mar 20 2017

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photocurrents
quantum dots
time signals
optoelectronic devices
carrier mobility
surface treatment
photoconductivity
grade
relaxation time
fine structure
signatures
activation
activation energy
room temperature
pulses
excitation
interactions
temperature
energy

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots. / Fidler, Andrew F.; Gao, Jianbo; Klimov, Victor I.

In: Nature Physics, 20.03.2017.

Research output: Contribution to journalArticle

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