Optimizing carbon nanotube deposition as an emissive layer in near-infrared organic light-emitting diodes applying ultrasonic spray coating techniques

Abstract

This thesis explores the use of single-walled carbon nanotubes (SWCNTs), specifically those with the (6,5) chirality, as emissive materials for near-infrared (NIR) organic light-emitting diodes (OLEDs). The work covers the full process from material preparation and chirality sorting to thin-film fabrication and device integration. SWCNTs were processed in both aqueous (surfactant-wrapped) and organic (polymer-wrapped) solvents using techniques such as aqueous two-phase extraction, gel chromatography, and shear-force mixing. A key focus of this work was the development of scalable film fabrication methods. Ultrasonic spray coating was optimized by tuning key parameters such as nozzle speed, nozzle-to-substrate distance, and flow rate to achieve uniform and controlled thin films. In addition, a simple solvent-washing approach using ethanol and methanol was developed to effectively remove surfactants, which otherwise hinder charge transport, while preserving the optical properties of the nanotubes. NIR-OLEDs based on both surfactantand polymer-wrapped SWCNTs were successfully fabricated, demonstrating emission around 1020 nm. Device performance was further improved through interface engineering, optimization of emissive layer thickness, and control of CNT concentration. This work establishes a scalable and sustainable platform for CNT-based NIR optoelectronic devices and provides guidelines for future improvements in device efficiency and fabrication strategies.