TITLE: Optoelectronic Materials and Devices for Next-Generation Displays and Retinomorphic Sensors

ABSTRACT: Recent advances in optoelectronic materials and device engineering are opening new frontiers in display technologies and visual sensing systems. As the demand grows for energy-efficient platforms, such as AR/VR glasses, electronic paper, and neuromorphic vision, there is a need for materials and devices that offer enhanced performance and simplified architectures. This dissertation addresses these needs by developing novel materials and device strategies for two emerging applications: power efficient displays and motion-sensitive photosensors. The first part focuses on emissive and non-emissive display technologies. Carbon dots (CDs), as environmentally friendly luminescent materials, offer a promising alternative to traditional phosphors and heavy-metal-based quantum dots for color-conversion LEDs. However, red-emissive CDs with large Stokes shifts remain scarce, posing a challenge for efficient excitation under blue or UV light. In this work, I developed novel red and green CDs with large Stokes shifts and demonstrated microscale multicolor patterning using CD inks, underscoring their strong potential for micro-LED displays. For non-emissive displays, the reversible electrodeposition and dissolution of MnO2 on transparent conducting substrates offers a promising mechanism for dynamic color modulation, but its application is often limited by slow kinetics and poor reversibility. To overcome these challenges, I introduced Fe2+ as a redox mediator in a less acidic electrolyte, which significantly enhanced both the switching speed and reversibility of the MnO2/Mn2+ redox reaction, thereby advancing the development of high-performance EC displays. Additionally, I investigated the EC properties of xylindein, a naturally derived fungal pigement, which exhibited a distinct multistep color transition from green to yellow to red, demonstrating strong potential for full-color EC display applications. In the second part of my research, I investigated retinomorphic sensors engineered for detecting fast-moving objects. These two-terminal sensors, integrating an organic bulk heterojunction photodiode with a dielectric capacitive layer, respond exclusively to changes in light intensity, enabling built-in motion detection and reducing data redundancy compared to conventional image sensors. I studied the underlying operating mechanisms and systematically optimized devcie performance by varying dielectric materials, with particular attention to dielectric thickness, active layer composition, and bias-induced charge polarization. Building on these insights, I developed a motion detection system composed of two retinomorphic sensors monolithically integrated on the same substrate and separated by a well-defined distance. As an object passes across the sensors, the resulting time delay between their responses allows accurate determination of motion speed. This architecture provides precise dynamic light sensitivity in a simplified design, offering a promising platform for future low-power neuromorphic vision systems.

MAJOR ADVISOR: Larry Cheng
COMMITTEE: Matthew Johnston
COMMITTEE: Harish Subbaraman
COMMITTEE: Oksana Ostroverkhova
GCR: Yuanzhe Liang