Advanced functional materials synthesis, characterization and tailoring for energy and optoelectronic applications
Translated title
Fortschrittliche Funktionsmaterialien: Synthese, Charakterisierung und maßgeschneiderte Anpassung für Energie- und Optoelektronische Anwendungen
Publication date
2025-12-01
Document type
Dissertation
Author
Pourmahdavi, Maryam
Advisor
Referee
Granting institution
Helmut-Schmidt-Universität/Universität der Bundeswehr Hamburg
Exam date
2025-11-26
Organisational unit
Publisher
Universitätsbibliothek der HSU/UniBw H
Part of the university bibliography
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File(s)
Language
English
Keyword
Semiconductors
Photo electrochemical water splitting
Hydrogen
Characterization
Abstract
Our modern world faces with two major hurdles: ongoing increasing demand for clean, renewable energy and heavy dependency on cutting-edge optoelectronic gadgets, from smartphones to energy conversion systems powering our sustainable future. Therefore, development of functional materials, which enable these technologies play a crucial role. This thesis explores the fascinating world of functional materials, specifically semiconductors, which are used as photoelectrodes in photoelectrochemical cells (PECs) to generate solar Hydrogen, investigating how we can precisely synthesize and characterize them, understand their properties down to the nanoscale and find out how various nano scale characteristics impact the macroscopic performance. This gained knowledge would ultimately enable us to design devices with enhanced performance in converting energy and powering optoelectronic.
Material's nanoscale microstructure significantly affects its properties and, eventually, macroscopic performance. The core of this research work is based on understanding and gaining insights into complex interplay of microstructure-properties-performance. Traditional characterization methods of materials often give us an averaged picture, covering the essential determining details of processes, which take place at specific times and points like grain boundaries or in different crystallographic structures. It is vital to resolve and understand these details at the nanoscale to improve the macroscopic performance. Therefore, this research focuses on employing cutting-edge characterization tools and developing novel data analysis techniques to zoom in on these nanoscale features and correlate them directly and precisely to the material's properties and overall device performance. Atomic Layer Deposition (ALD) was used as a promising method that enables us to synthesize ultra-thin films of materials layer by layer. This incredible precision is crucial for synthesizing protective layers on photoelectrodes for clean hydrogen production or for engineering delicate thin interfaces in power electronics. ALD was employed to synthesize and investigate two important semiconductor systems: titanium dioxide (TiO₂), a well-established model system in PEC, and aluminum nitride (AlN), a promising material for optoelectronics and potentially as an ultrathin protective coating for photoelectrodes.
For TiO₂, it was shown how the mixture of crystalline and amorphous structures within the film influences the charge carrier dynamics. Advanced microscopy techniques were employed, namely time-dependent Kelvin Probe Force Microscopy (KPFM), which can map surface potentials at the nanoscale (Figure 0), in combination with its macroscopic counterpart, the Kelvin Probe (KP). A novel data analysis technique was developed, which is a breakthrough in gaining insights into microstructure-property-performance interplay. This innovative approach enables us to extract time-resolved photovoltage data in a KPFM potential map pixel by pixel with ms time resolution, giving us a comprehensive, detailed picture of how different crystallographic regions contribute to the material's photoactivity. The findings clearly indicate that crystalline regions are considerably more efficient compared to amorphous areas at charge separation by generating a significantly higher photovoltage (~ 440 mV), highlighting the critical role of crystallinity and showcasing the capability of this developed novel data analysis technique to resolve it.
Material's nanoscale microstructure significantly affects its properties and, eventually, macroscopic performance. The core of this research work is based on understanding and gaining insights into complex interplay of microstructure-properties-performance. Traditional characterization methods of materials often give us an averaged picture, covering the essential determining details of processes, which take place at specific times and points like grain boundaries or in different crystallographic structures. It is vital to resolve and understand these details at the nanoscale to improve the macroscopic performance. Therefore, this research focuses on employing cutting-edge characterization tools and developing novel data analysis techniques to zoom in on these nanoscale features and correlate them directly and precisely to the material's properties and overall device performance. Atomic Layer Deposition (ALD) was used as a promising method that enables us to synthesize ultra-thin films of materials layer by layer. This incredible precision is crucial for synthesizing protective layers on photoelectrodes for clean hydrogen production or for engineering delicate thin interfaces in power electronics. ALD was employed to synthesize and investigate two important semiconductor systems: titanium dioxide (TiO₂), a well-established model system in PEC, and aluminum nitride (AlN), a promising material for optoelectronics and potentially as an ultrathin protective coating for photoelectrodes.
For TiO₂, it was shown how the mixture of crystalline and amorphous structures within the film influences the charge carrier dynamics. Advanced microscopy techniques were employed, namely time-dependent Kelvin Probe Force Microscopy (KPFM), which can map surface potentials at the nanoscale (Figure 0), in combination with its macroscopic counterpart, the Kelvin Probe (KP). A novel data analysis technique was developed, which is a breakthrough in gaining insights into microstructure-property-performance interplay. This innovative approach enables us to extract time-resolved photovoltage data in a KPFM potential map pixel by pixel with ms time resolution, giving us a comprehensive, detailed picture of how different crystallographic regions contribute to the material's photoactivity. The findings clearly indicate that crystalline regions are considerably more efficient compared to amorphous areas at charge separation by generating a significantly higher photovoltage (~ 440 mV), highlighting the critical role of crystallinity and showcasing the capability of this developed novel data analysis technique to resolve it.
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