Novel small-molecule hole transport materials: towards ideal packing and doping

Vella, Benjamin (2024) Novel small-molecule hole transport materials: towards ideal packing and doping. PhD thesis, University of Glasgow.

Abstract

Hole transport materials (HTMs) are crucial components in various types of electronic devices, particularly in energy conversion systems where they facilitate the rapid movement of charge from the active layer to the electrode. In light of the pressing need to shift away from unsustainable, non-renewable energy production through fossil fuels, developing low-cost energy-converting technology is of utmost importance for a more sustainable future.

Despite significant progress in the field of HTMs, characterised by a plethora of organic and inorganic materials being introduced monthly, the ‘ideal’ HTM remains elusive. This would represent a material that is cost-effective to produce, high-performing, reliable, and stable. The challenge stems from the intricate nature of the interactions between HTM structures and their behaviour in a film. All different elements of molecular structure contribute to the bulk charge transport properties, making it difficult to isolate individual influences from the observed net effect. Additionally, the need for chemical doping of HTM systems to increase carrier concentrations introduces further complexity, as the choice of additives and resulting doping reaction products profoundly impact the film characteristics. Spiro-OMeTAD, a widely used organic HTM in solar cell technologies, exemplifies these challenges, requiring chemical additives for adequate conductivity and suffering from poor film formation due to weak intermolecular interactions. It also suffers from costly synthesis and purification that hinder its widespread commercialisation.

Consequently, there is a pressing need for research to explore molecular structures designed to allow robust interactions between adjacent molecules in films, in order to overcome the shortfalls of Spiro-OMeTAD. In doing so, the links between molecular structure and bulk properties must be investigated. This thesis presents a series of HTMs synthesised through condensation chemistry, aiming to address some of the shortcomings of current HTM technologies and pave the way for more efficient and affordable solutions in electronic devices. These HTMs are used as a test bed to investigate the packing behaviour of linear organic HTMs, as well as their interactions with some common chemical additives that have non-trivial consequences on the final conductivity of the HTM film. The aim is to uncover structure-function relationships that will guide the smarter design of future HTMs. The three main chapters of this thesis consistently highlight a key observation: while chemical modifications to the HTM structure provide great control over its optical and electrochemical properties, they often lead to unexpected side effects in their oxidation and charge transport behaviour that necessitate further investigation. Comprehensive studies must therefore be conducted on any newly developed HTMs to uncover and mitigate these effects.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Cooke, Professor Graeme, Docampo, Dr. Pablo and Skabara, Professor Peter
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84804
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 13 Jan 2025 13:53
• Last Modified: 13 Jan 2025 13:53
• Thesis DOI: 10.5525/gla.thesis.84804
• URI: https://theses.gla.ac.uk/id/eprint/84804