Density Functional Theory (DFT)-Parameterized Multiscale Modelling on Properties and Electronic Transport in Metal Chalcogenide Nanocrystals (NC) and NC Solids
OPEN ACCESS
Loading...
Author / Producer
Date
2025
Publication Type
Doctoral Thesis
ETH Bibliography
yes
Citations
Altmetric
OPEN ACCESS
Data
Rights / License
Abstract
Benefiting from the low cost in manufacturing and high tunability in material properties, rapid development and enormous progress have been made over the past few decades from material synthesis to device fabrication for solution-synthesized semiconductor nanocrystals (NC), rendering them the unmatched choice for a wide range of advanced applications in electronic, optoelectronic, and thermoelectronic devices. By precisely controlling the constituent elements, size, shape, and surface termination of an individual NC, and engineering packing structures (ordered/disordered) of NC assemblies/solids, the optical/electronic properties and the performance of the devices incorporating NC solids can be readily adjusted. For applications requiring controllable charge carrier mobilities, further advancing the device performance requires a decent knowledge of impacts from NC composition and morphology as well as NC packing nonideality on the charge carrier dynamics and transport mechanism in NC solids determined by electronic NC-NC communication and charge-NC interaction.
Recent advancements in computational studies have been empowering a better understanding of structural/optical/electronic properties covering a length scale from individual NCs to NC solids. Among these methods, density functional theory (DFT)-based calculations and simulations on atomistic models of NCs prevail through the inclusion of atomistic complexity on the NC surfaces. In Chapter 1, we review
the various atomistic DFT-based methods that have been proposed to study NCs and their assemblies, highlighting the insights they provide for understanding the static and dynamic structural and elec-
tronic/optical properties of individual NCs and NC solids. Supported by the new experimental and more advanced DFT techniques, promising future perspectives can be expected for a better understanding in
more NC systems and empowering their applications in all fields. In this thesis, we focus on investigating charge carrier transport in NC solids. Choosing from a wide library of metal chalcogenide NCs,
we pick out lead sulfide (PbS) and mercury telluride (HgTe) NCs as two model systems. Both NC systems are widely used and proved great success in IR photodetecting and imaging, where high charge
carrier mobility is an essential metric for good device performance. By applying the same DFT-parameterized multiscale methodology armed with precise and robust atomistic models, we unveil how the size, shape, surface chemistry and packing condition of the NCs can impact on charge carrier transport in different NC solids, provide insights into the occurrence of complexity in charge transport mechanism (band-like or hopping), and prove the possible wide-applicability of this model on more other NC systems.
In chapter 2, with PbS NC as model system, where charge carrier transport limited to phonon-assisted hopping regime, we perform a DFT-parameterized kinetic Monte Carlo simulation on computationally constructed NC thin films with a range of disorders, including positional disorder, energetic disorder and deep electronic traps. We contribute by extracting and analysing statistics of the charge transients under a range of electric field biases to understand the impact of different types of disorder on charge carrier transport in NC solids. Based on the results, we propose several guidelines from NC synthesis to device
fabrication for controlling charge carrier mobility.
We further endeavor to transfer this model to exploit NC systems where charge transport mechanism is still unclear and debatable. Taken HgTe NC as an example, presence of both band-like and hopping transport are reported in the NCs above 10 nm in size. In order to elucidate the mechanism complexity in HgTe NC solids, we firstly build atomistic-precise models for HgTe NCs covering variety in NC shape, size and surface termination. As reported in Chapter 3, our atomistic model reproduce mid-gap-trap-free electronic structures of HgTe NCs, with the resulting structural, optical and electronic properties in line with experimental measurements. In Chapter 4, based on this atomistic model, we further contribute by explaining NC-charge interaction and showing evidence of charge delocalization among several HgTe NCs through DFT calculations of NC reorganization energy λ introduced by atomic rearrangement on NC
surface upon charging (polaron formation) and electronic coupling Vc between neighboring NCs. Under the influence of NC size, interparticle aligning orientation and facet-to-facet distance ∆ff, criteria for the occurrence and geometrical landscape of charge delocalization in randomly packed NC solids (implying band-like charge transport) are derived. Possible ways to improve charge carrier mobillity are then suggested accordingly. This model is proven to be well transferable to studying other mercury chalcogenide NCs.
Permanent link
Publication status
published
External links
Editor
Contributors
Book title
Journal / series
Volume
Pages / Article No.
Publisher
ETH Zurich
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
Organisational unit
03895 - Wood, Vanessa / Wood, Vanessa
Notes
Funding
201466 - FLARE – CSCS Tier 2 LHC Computing Infrastructure (SNF)
111111 - SNF-Forschungsprojekt (SNF)
NCCR MUST (183615) - NCCR MUST Verteilfonds (SNF)
111111 - SNF-Forschungsprojekt (SNF)
NCCR MUST (183615) - NCCR MUST Verteilfonds (SNF)
Related publications and datasets
Compiles: