Process And Device Technologies For Wearable Electronics Based On Silver Nanowires

The capacity of the real-time sensing,recording and analysis of the wearable electronics makes it being possible to communicate with the human whenever and wherever they needed,which is related to our daily life.However,the performance of the traditional wearable electronic is less than satisfactory,the requirements of more fit body shape,compatibility with the human skin,and higher sensitive to body signal and more convenient are needed as the electronic equipment "wear" on the human body.This thesis investigates the low temperature solution processed silver nanowire(AgNW)flexible/stretchable conductive films for pressure,strain sensors and organic solar cells.New deposition technology and innovative structures were developed in this thesis to improve the flexibility,sensitivity,lifetime and portability of the devices.The internal connection of conductive films and the pressure and strain sensors and organic solar cells was explored by combining with the surface morphology,photoelectric and mechanical properties of the conductive film,which provides a new way for the further development of wearable sensors and solar cells.The main research contents include:(1)A suitable process of the conductive film was developed on a flexible substrate.With ultra-high aspect ratio(>2000:1)AgNWs and ethanol diluted poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)(PEDOT:PSS)as the processing material,highly conductive,transparent and mechanical flexible conductive films were prepared.The conductive film was applied in the flexible capacitive pressure sensors and solar cells.The sensitivity of the achieved pressure sensor was 2 times higher than the sensor with indium tin oxide(ITO)electrode.The 4×4 pressure sensor was proved the capability of the electrodes for spatially electronic signal collection and transmission.The fabricated flexible OPV device has a power conversion efficiency(PCE)of 1.83 %,which prove the potential of the electrodes for multilayer integration in optoelectronic device applications.(2)The results of the stability of AgNW-PEDOT:PSS composite conductive film show that the hygroscopic and acid properties of the common PEDOT:PSS lead to poor stabilities of the composite films,due to the conductivity degradation of PEDOT:PSS by the water absorption and the acid corrosion of AgNWs by PEDOT:PS.By using the organic alkali of the guanidine modified neutral-pH PEDOT:PSS as the over-coating layer,the long term shelf-life time,thermal and current stressing stabilities are all significantly improved without sacrifice of transparency,electrical conductivity and mechanical flexibility.The stable conductive films and porous polydimethylsiloxane(PDMS)film with ammonium hydrogen carbonate foaming agent were used to constructured the capacitive pressure sensors.The results show that the sensitivity of sensor with porous PDMS film was about 6 times higher than the device with bulk PDMS film,and the range of sensor with high sensitivity was also been extended.The sensors were placed at the wrist and the insole,the real-time monitoring of the wrist pulse and the plantar pressure distribution was achieved,which contribute to the development of the sensors in human healthcare application.(3)The surface roughness of the AgNW conductive film was improved using the peel-off process.By adjusting the size of the AgNWs,the hardness of the polymer and the separation layer,the influence of the surface morphology of the AgNW/polymer conductive film was investigated.The results show that the low aspect ratio AgNWs is more likely to be transferred to PDMS film with large surface roughness.By using the thermal cross-linked poly(methyl methacrylate)(PMMA)with high shore hardness and a thin layer of sodium hydroxide(NaOH)on the glass,the high aspect ratio AgNWs can be transferred.The AgNW/PMMA film shows low surface roughness,high conductivity,transparency and mechanical flexibility.The AgNW/PDMS films were applied in the pressure sensor,which shows a 2 times higher sensitivity than the device using aluminum foil as the electrodes.The AgNW/PMMA film was applied in solar cells.First,the performance of the solar cells was improved by introducing ZnO cathode interlayer.Then,the neutral-pH PEDOT:PSS and graphene oxide(GO)compound was introduced at the AgNW interface,which shows a similar performance compared to the acid PEDOT:PSS device.(4)The large area AgNW conductive films was fabricated using bar coating method.The photoelectric properties of bar coated films was investigated.By reducing the thickness of the PDMS substrate,The fabricated AgNW-PEDOT:PSS/PDMS strain sensor presented a sensitivity more than 20 times higher than that of conventional strain sensors based on a thick(800 ?m)PDMS film,and also high optical transparency of nearly 80% and light weight,which are desired features for developing unperceivable and invisible sensors in wearable applications.The sensor was finally demonstrated for real-time monitoring of human fingers and neck motion.The capacitive pressure sensor is prepared using fabricated light-weight conductive films,the sensitivity of the pressure sensor was improved and the weight of the sensor was reduced.The sensor was demonstrated for the real-time monitoring of the human wrist pulse and breathe.