Development of soft electronic and optoelectronic fiber-based devices via the thermal drawing process

The development of soft electronic and optoelectronic systems is essential for the growth and industrial deployment of research fields such as smart textiles and wearables. However, it remains challenging to identify materials that reconcile the required mechanical attributes (e.g. softness and stretchability) with functional metrics essential to develop high-performance devices (e.g. electrical conductivity or photoconductivity). Moreover, it is equally important to find processing routes that can produce such devices at large scale and low-cost while ensuring an accurate arrangement of materials with disparate electronic properties into complex architectures with small feature sizes. In this thesis, we investigate the thermal drawing technique as a strategy to produce soft, multifunctional electronic and optoelectronic fibers. Originally developed for optical fibers, this process leverages the viscous flow of materials to transform macroscopic assemblies into long fibers while preserving the initial cross-sectional architecture. In particular, this work focuses on implementing the three fundamental pillars of soft optoelectronic devices within thermally drawn fibers: (i) Stretchable and electrically conductive materials serving as electrodes for charge collection and transport: Two composite systems relying on rigid and liquid fillers dispersed in a soft matrix are proposed, and their performance is demonstrated through various types of mechanical sensors. In particular, highly stretchable and conductance-stable electrodes are established in thermally drawn fibers by relying on liquid metal embedded elastomers. (ii) Transparent conductors that simultaneously enable light transmission and charge transport: The introduction of ionogels as a novel materials system in thermally drawn fibers is demonstrated. The versatility of this material enables a fine tuning of its mechanical, electrical and thermal properties to match the targeted attributes for specific applications. In particular, meters-long stretchable fibers encompassing a transparent and conductive core are produced, marking the first implementation of a transparent electrode in thermally drawn fibers. (iii) Stretchable semiconductors functioning as active layers with light-responsive properties: Blends of organic semiconductors with thermoplastic elastomers are envisioned as a facile route to produce soft semiconductors with low processing temperature that can be easily introduced into thermally drawn fibers. Each material system is first studied individually, then integrated into a single soft fiber demonstrating optoelectronic properties. This work paves the way towards the development of complex multi-functional soft fibers to fabricate smart textiles and wearables with advanced electronic and optoelectronic properties.