Design of textile-based electronics for energy harvesters and pressure sensors

Abstract

The main theme of this research is the development and applications of textile-based electronics, especially, energy harvesting and sensing devices. Textile-based electronics have attracted considerable attention owing to their facile processing, cost effectiveness, and large-area processibility. Furthermore, the inherent properties of textile, such as light weight, flexibility, comfortability, and breathability, can provide outstanding performance and versatility to the practically integrated device In this study, the low temperature processed textile-based perovskite solar cells, micro- and nanofiber nonwoven fabric-based triboelectric nanogenerators (TENGs), and PEDOT-coated conductive textile-based pressure sensors, which are textile-based electronics that can be applied to various fields such as wearable devices and smart home care systems, were investigated. First, the prototype of reliable perovskite solar cells was fabricated on the textile substrates using only the printing methods. We observed that embedding a thin layer of PU effectively improves the processability of the woven fabric substrate; thus, we allowed multiple solution-processed thin layers to be formed on the textile substrate. Consequently, perovskite solar cell devices fabricated on the textile substrate exhibited a PCE of 5.72% with good ambient stability up to 300 h, retaining > 80% of their initial PCE. Although this efficiency is inferior to that of glass-substrate based devices, an all-solution-processed, printable, ITO-free device with 5.72% efficiency is promising for practical applications of perovskite solar cells. Further materials research and optimization of the device and the process would lead to improved device performance. Second, we developed highly porous, breathable and flexible T-TENGs, which are consisted of melt-blown PP nonwoven and TPU nanofiber mats, for wearable devices. The effects of the basis weight of nonwoven PP on the triboelectric performance of TENGs were investigated. Structural characterization revealed that the micro-sized PP nonwoven has a relatively large pore size and high permeability in comparison to that of its counterpart, TPU nanofiber mat, and the porous structure and thickness of nonwoven PP were affected by the basis weight. Owing to the highly porous nonwoven structure with a high air volume, the interface layer between the two counter triboelectric layers were not fully in contact even when they were integrated. Thus, the T-TENG could harvest energy under different external forces and frequencies. Under walking and running motions, TPU/PP50-based T-TENG provided an output voltage and current of 110.18 ± 6.06 V and 7.28 ± 0.67 µA, respectively. Furthermore, the energy generated by T-TENG-based insole could be used to directly light up 57 green LEDs sustainably. Thus, we fabricated a facile, breathable, and flexible generator fully based on fibers, which can be applied in wearable devices. In addition, the manufacturing method of the triboelectric layer of T-TENG is low-cost and amenable to mass production. Third, the real-life applications of a reliable textile-based pressure sensor were investigated using a developed conductive textile. A PEDOT thin film-coated textile was prepared by VPP with various concentration of FeCl3 solution, and it was confirmed that a FeCl3 concentration higher than 13% did not affect the conductivity. The morphology and surface resistance of the washed samples and repeatedly folded samples were investigated. The washed samples for more than 40 min showed uniform surface morphology and resistance because only a PEDOT layer remained due to complete removal of impurities. Furthermore, the mechanical durability was determined by real-time monitoring of the sensor response to static (every 200 cycles) and dynamic pressures (2,000 cycles) under repeated tests. The fabricated PEDOT conductive textile exhibited fast response (52 ms) and recovery times (22 ms), and the sensor response was extremely stable even at a 3 Hz cycle. The fabricated textile-based pressure sensor could precisely measure both dynamic and static pressures even during mechanical impact as well as the pressure of irregular objects such as hand, iron, and packing tape. The results imply that the developed sensors, which have various advantages such as light weight, low cost, large area productivity, flexibility, low thickness, and excellent washing and mechanical durability, can be widely utilized in a various field requiring large-area, bending, or washing such as homecare systems and wearable electronics.