Exploring nanoscale light-matter interactions in sensors, OLEDs, and graphene

Abstract

This dissertation presents the comprehensive investigations of my exploration of nanoscale light-matter interactions within three innovative material systems: perovskite-based sensors, organic light-emitting diodes (OLEDs), and epitaxial graphene on silicon carbide (SiC). These materials with their unique optical and electronic properties are driving advancements in optoelectronic devices, offering new possibilities for applications in sensing, display technologies, and high-performance electronics. This research aims to elucidate how light interacts with each material at the nanoscale and to leverage these interactions for enhanced device functionality. In perovskite-based sensors, our study focuses on the high sensitivity and tunability of perovskite materials, examining their potential for detecting light, gases, and environmental changes. This research studies how the fundamental process of light being converted to electricity in both broad-band and narrow-band perovskite-based photodetectors can be used to measure the concentration of gaseous-phase oxygen, dissolved oxygen. and glucose oxidase. In OLEDs, this dissertation explores their fabrication on corrugated plastic substrates as well as planarized extraction plastic structures. Whereas conventional OLED devices have external quantum efficiencies (EQE) in the range of EQE ~20%, we report external quantum efficiencies of 61% for green OLEDs and 48% for white OLEDs on flexible plastic substrates with periodic corrugations planarized by a titanium oxide nanoparticle-embedded high refractive index resin. We also present a variety of corrugation patterns with pitch a ranging from 410 – 7800 nm and height/depth h ranging from 160 – 500 nm, with and without the use of an indexmatching fluid (IMF) to achieve EQE enhancements of 1.2x – 2x compared to flat reference substrates. Detailed analysis of OLED structures on plastic substrates with various corrugation patterns and in green, blue, and white OLED’s with various material composition reveals xx strategies to optimize brightness, contrast, and flexibility for improved display and lighting applications. The work also examines light-matter interactions in graphene, particularly in epitaxial graphene on silicon carbide (SiC), focusing on its extraordinary conductivity, transparency, and responsiveness to electromagnetic fields. Graphene’s optical characteristics at the nanoscale are analyzed to enhance its application in high-speed transistors, photodetectors, and quantum devices. In addition to pristine bilayer graphene (BLG), we further studied graphene with areearth metal intercalation, in this case with gadolinium (Gd), which can tune doping and opticalconductivity. Using the effective and efficient technique of scattering-type scanning nearfield optical microscopy (s-SNOM), this research captures high-resolution, sub-diffraction-limit images that shed light on the nanoscale optical behavior of these materials. By characterizing and optimizing light-matter interactions in: (i) perovskite-based sensors for oxygen and glucose sensing, (ii) green, blue, and white OLEDs on corrugated and planarized plastics, and (iii) pristine and Gd-intercalated epitaxial graphene on SiC characterized with scattering-type scanning near-field optical microscopy, this dissertation advances the understanding of nanoscale optoelectronics and provides a foundation for developing nextgeneration, high-performance devices in sensing, imaging, and display technologies. The investigations presented herein collectively enhance the knowledge of fundamental light-matter interactions in various heterostructure systems, open pathways for innovative applications in electronics and photonics, and provide valuable insights into novel phenomena, device design, and technological advancements in optoelectronic systems.