Wei Yan1 Tapajyoti Gupta1 Dang Tung Nguyen1 Yunpeng Qu1 Alexis Page1 Fabien Sorin1

1, Ecole Polytechnique Federale de Lausanne, Lausanne, , Switzerland

The integration of conducting and semiconducting architectures within thermally drawn thin and flexible fibers is emerging as a versatile platform for smart sensors and imaging systems, medical and biological probes, and advanced textile. Efficient photodetecting or thermal sensitive fibers in particular could bring a breath of new applications for advanced textiles. Thus far however, fundamental aspects of the microstructure formation and the interplay between microstructure and properties are poorly understood, leading to limited optical, electronic and optoelectronic performances of semiconductor-based fibers. Here, we first compare a regular annealing treatment of the as-drawn fiber with a laser annealing approach to tailor the microstructure of semiconductors in optoelectronic fibers. By judiciously controlling the laser parameters, we are able to fabricate an electrically addressed polycrystalline semiconductor domain with ultra-large grains, controllable crystallization depth as well as preferentially crystallographic orientations that allows the system to have the maximum carrier mobility[1]. We then turn to a simple and robust sonochemical approach applied to the amorphous semiconductor at ambient condition without any elevated temperature. The anisotropic surface energy of crystal planes in an organic solvent enables the controlled phase and orientation of monocrystalline nanowires that grow along the desired axis, directly in intimate contact with built-in electrodes[2]. The resulting nanowire-based fiber devices exhibit an unprecedented combination of excellent optical and optoelectronic properties in terms of light absorption, responsivity, sensitivity and response speed that compare favorably with other reported nanoscale planar devices. Most strikingly, this new approach facilitated high throughput and ultra-large area integration of nanowires into devices without the need for complex contacting procedures in the clean room, demonstrated by the growth of high-performance nanowire-based devices along the fiber length. Furthermore, we have demonstrated the unique capability of the functional fiber for fluorescent imaging based on a single fiber exhibiting simultaneous efficient optical guidance and excellent photodetecting performance. The improved control over the microstructure of the semiconductor in the multi-material fiber platform brings new insight into the field and opens unforeseen opportunities for advanced photodetecting probes and imaging systems, in bioengineering and healthcare, in remote and distributed sensing, energy harvesting, and advanced textiles.
[1] Wei Yan, et al. Microstructure tailoring of selenium-core multimaterial optoelectronic fibers. Optical Materials Express, 7 (2017) 1388. (Editor’s pick)
[2] Wei Yan, et al. Semiconducting nanowire-based optoelectronic fibers. Advanced Materials, 29 (2017) 1700681.