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Title: Photo-physics and applications of colloidal quantum dots
Author: Stubbs, Stuart Kenneth
ISNI:       0000 0004 2692 8114
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2010
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The work presented in this thesis was submitted to The University of Manchester for the degree of Doctor of Philosophy in June 2010 by Stuart K Stubbs and is entitled “Photo-physics and applications of colloidal quantum dots”. In this thesis the results of spectroscopic studies on various colloidal quantum dots, particularly related to the measurement and characterisation of multiple exciton generation are presented. Research conducted with Nanoco Technologies Ltd. that involved the design and development of hybrid quantum dot organic light emitting diodes for use in flat panel display technology is also presented. Cadmium selenide (CdSe), indium phosphide (InP), and lead sulphide (PbS) type I and cadmium selenide/cadmium telluride type II colloidal quantum dots were characterised using steady state photoluminescence and absorption spectroscopy. The fluorescence lifetimes of the decay of single excitons was measured in these quantum dots using time correlated single photon counting. An ultrafast transient absorption spectrometer was designed, built, and used to observe the picosecond dynamics of the decay of multiexcitons. These absorption transients were analysed in order to extract the quantum efficiency of producing multiple excitons per absorbed photon. The characteristic signature for multiple exciton generation was first found in CdSe using a time correlated single photon counting set-up. Results from the transient absorption spectrometer demonstrated efficient multiple exciton generation in InP for the first time as well as in PbS, where the efficiency was found to agree with values obtained by other research groups. The absorption transients taken for the type II CdSe/CdTe type II quantum dots demonstrated some novel decay dynamics that could not be attributed to the generation of multiple excitons. Quantum dot organic light emitting diodes were fabricated using Nanoco Technologies high quality cadmium based quantum dots and were shown to demonstrate bright, colour saturated emission originating from the quantum dot layer only. Using quantum dots of different sizes and structures red, green and blue devices were made and shown to be appropriate both in terms of brightness and chromaticity for the use as the red, green and blue pixels of a flat panel display. Because heavy metals like cadmium are restricted or banned from commercial products in many countries, Nanoco Technologies heavy metal free quantum dots, made from InP, were also incorporated in devices. Devices are demonstrated that emit from the quantum dot layer only, albeit at a lower luminance and efficiency than that found in the cadmium containing devices. This was the first demonstration of a heavy metal free, hybrid quantum dot organic light emitting diode.
Supervisor: Binks, David Sponsor: Advanced Photonics Research Institute, Gwangju Institute of Science and Technology ; University of Manchester
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Quantum dot ; Nanocrystal ; Multiple exciton generation ; Carrier multiplication ; Transient absorption ; QD-OLED