Photothermal and thermoelectric characterization of NDI and OPV based materials

Xu, Ziyao (2026) Photothermal and thermoelectric characterization of NDI and OPV based materials. PhD thesis, University of Glasgow.

Abstract

Growing global energy demand and increasing environmental concerns have driven the search for sustainable technologies capable of harvesting and converting renewable energy efficiently. While inorganic energy materials have traditionally attracted considerable attention because of their high energy-conversion efficiencies and excellent electrical conductivities, their limited flexibility, poor processability, and in some cases, high cost or low biocompatibility have encouraged growing interest in organic alternatives. Organic materials offer several advantages, including structural tunability, mechanical flexibility, solution processability, and biocompatibility. This thesis explores the development of organic photothermal materials, which convert light into heat, and organic thermoelectric materials, which convert heat into electricity.

In the first part of this work, six amino-acid-functionalised naphthalene diimide (NDI) derivatives were synthesised and studied as photothermal materials. UV–vis absorption spectroscopy confirmed the generation of radical anions and dianions upon 365 nm irradiation, and these reduced species were identified as the origin of the photothermal response. Their relative populations depended on irradiation time, with shorter exposure favouring radical anions and prolonged irradiation increasing dianion formation. As the self-assembled structures were strongly influenced by pH, the effect of pH on assembly behaviour and photothermal performance was systematically investigated. Thermal imaging was used to characterise photothermal performance, while small-angle neutron scattering revealed cylindrical assemblies in solutions and helped clarify the relationship between molecular structure and photothermal properties.

The second part focused on photothermal film formation for potential wearable applications. Pure NDI films were brittle and inflexible; therefore, glycerol was introduced as a plasticiser to improve flexibility and film homogeneity. Polymer matrices were further incorporated to stabilise the reduced species and extend photothermal performance. Two complementary methods were employed to evaluate film performance: thermal imaging to monitor temperature changes, and a Peltier-based setup to detect the potential signal generated by the temperature gradient of Peltier module. Together, these methods provided an effective means of assessing photothermal behaviour. In addition, the mechanical properties of the films could be tuned by varying the composition, improving their suitability for device design.

In the final part, organic thermoelectric materials based on phenylalanine-appended oligo(phenylene vinylene) (OPV-F)/carbon nanotube (CNT) composite composites were investigated. OPV-F was synthesised as a p-type thermoelectric material, and CNTs were incorporated to enhance electrical conductivity. Surface roughness parameters (Sq and Sdq) were analysed using 3D profilometry. The composites retained high electrical conductivity after CNT incorporation. Although pure CNT films exhibited high conductivity, their preparation and flexibility remained challenging, motivating the incorporation of OPV-F and polymer components to improve film quality and mechanical robustness. Overall, this thesis provides insights into the design of organic photothermal and thermoelectric materials and highlights the importance of structure property relationships in the development of flexible energy-conversion systems.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the China Scholarship Council.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Funder's Name: China Scholarship Council
• Supervisor's Name: Draper, Professor Emily R.
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86090
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 Jul 2026 13:29
• Last Modified: 13 Jul 2026 07:16
• Thesis DOI: 10.5525/gla.thesis.86090
• URI: https://theses.gla.ac.uk/id/eprint/86090

Related URLs

• Article DOI