Luminescent Harnessing of 2D Transition Metal Dichalcogenide Excitons

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are regarded as viable candidates for future high-performance optoelectronic and electronic devices due to their chemical stability, low dimensionality, direct bandgap and favourable electronic mobilities. Their direct bandgap facilitates strong light coupling, yielding photoluminescence (PL). Their quantum confined nature produces tightly bound excitons that exhibit intriguing many-body phenomena. 2D excitons may be transferred to other emissive materials in a heterostructure system. This has applications in e.g., photon harvesting with luminescent solar concentrators (LSCs). Newly prepared monolayers are however susceptible to chalcogen atom vacancies, which quench bright excitons and trap mobile charges, amounting to material with poor PL yields and low mobilities, which is of little practical use. Post-fabrication defect passivation schemes offer a means to recover and enhance optical and electronic properties of newly fabricated monolayers. This thesis presents a novel surface treatment based on oleic acid (OA) ligands, which unlike previously reported schemes, is applicable to both sulphide and selenide TMDs. As separate studies, we investigate the effects of OA on monolayer tungsten disulphide (WS2) and molybdenum diselenide (MoSe2). Steady state and time resolved PL (TRPL) microscopy uncover the photophysics of PL enhancement by OA treatment, and provides insights into the surface passivation mechanism. Electronic measurements of 2D TMD field effect transistors support the conclusions drawn from optical measurements. The following study reports exciton transfer from a 2D TMD absorber to a quantum dot (QD) emitter in a 2D-QD heterostructure. WS2 is harnessed as an optical antenna, from which excitons are funnelled to near infrared (NIR) lead sulphide-cadmium sulphide QDs. This describes the opposite process to what has been reported for similar hybrid systems, where 2D TMDs quench excitons. Steady state PL techniques confirm excitation energy transfer (ET), and the ET mechanism. TRPL studies reveal ET dynamics and confirm ET efficiency. Combining steady state PL and TRPL elucidates the ET pathway and competing loss channels. Finally, the concept of an LSC based on 2D-QD heterostructure luminophores is developed with the aid of Monte Carlo light transport simulations. Using an idealised luminophore model, Heterostructure LSC performance is compared to other LSCs based on typical luminophore materials namely, Lumogen Red 305 dye and NIR QDs.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2021

Author dc:creator

• Tanoh, Arelo

Advisor dc:contributor.advisor

• Rao, Akshay

• Transition Metal Dichalcogenides
• Energy Transfer
• Luminescence
• Excitons
• Quantum Dot

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/aca604d4-a111-4de3-9bf6-0b0df980f957/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0003-2494-5984
0000-0003-0320-2962

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/324763