Investigating materials with nanoscale imaging and spectroscopy: Insights into perovskites and plasmonic substrates
Date
2025
Authors
Gartside, Hannah
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Abstract
The structure of an object is integral to its function. When considering nanostructured materials such as thin films of perovskites and gold nanoparticles, subtle differences in the structure can have a significant impact on their optical properties and function. In this thesis, high resolution optical imaging techniques were applied to study the properties of nanostructured materials. Laser scanning confocal microscopy (LSCM) was used to visualize phase segregation in mixed-halide perovskite through the formation of I-rich domains. An important component of perovskite solar cells (PSCs) is hole transport layers (HTLs) which are responsible for keeping electron-hole pairs separate as they are transported to their respective electrodes. As a contribution to the study of HTLs by Ahmed et al.1, near-field scanning optical microscopy (NSOM) was used to spatially visualize the distribution of no-contact areas in high molecular weight (HMW) and low molecular weight (LMW) Poly(triarylamine) (PTAA) through their photoluminescence (PL) distribution. NSOM was also used to characterize a rough gold substrate coated in 4-MBN. During an NSOM scan, a photochemical reaction of 4-MBN was observed to have occurred. Through Raman and tip-enhanced Raman spectroscopy (TERS) experiments, it was determined that the photochemistry occurred only when the probe was within the near-field of the surface. Some products of the reaction were tentatively assigned from TERS spectra. To understand the cause of the photodegradation, NSOM experiments were performed to investigate the possible presence of dark plasmons. Dark plasmons decay non-radiatively and are therefore extremely good at producing hot electrons which could have feasibly catalyzed the photodegradation reaction. Fano resonance was observed, and the near-field spectrum was blue-shifted relative to the far-field spectrum. This confirmed the activation of dark plasmons and suggested that they are the most likely cause of the observed photodegradation.
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Keywords
TERS, gold nanoparticles, SERS, Raman, NSOM, photochemistry, hot electrons, perovskite