Artificial Skin Based On Flexible Transparent Electrodes For Visualized Tactile Sensing

Electronic skins that can conformally wrap irregular surfaces and spatially map and sense various stimuli have been the forefront of development of optoelectronics. Piezoresistivity, capacitance and piezoelectricity are traditional transduction methods widely used in pressure sensors which can by external equipments convert pressure signal into analog electronic signals containing the details of pressure signal. Nowadays, people demand a more intuitive way for human–machine interaction, however, user interfaces based on a human-readable output(e.g., visible light) have not been explored. The transparent electrodes(TEs) used in electronic skin for pressure visualization require excellent optoelectronic properties, superior mechanical flexibility, low cost and high-throughput production. Indium tin oxide(ITO) is the most commonly used transparent conductor. The high transmittance of ITO at low sheet resistances and mature technology is the primary reason for the popularity of ITO. However, ITO cannot meet the further needs for TEs in many applications due to its scarcity of supply, its ceramic and high temperature processes. Compared the various alternatives with ITO, such as carbon nanotubes, graphene and conducting polymer, Ag nanowires(NWs) are both commercial and achieve performance equivalent to ITO. Herein, we introduce an electronic skin for tactile visualization with Ag NWs TEs. The main research contents and results are as follows:1. By means of the optimization of polyol process, the Ag NWs with 1000 aspect ratio were synthesized in the one-pot reduction route. After the synthesis, the nanoparticles and short Ag NWs that inevitably contaminate the NWs produced by a polyol synthesis can be purified with a simple, scalable selective precipitation process. As a result, high quality Ag NWs ink with no impurity was obtained. When coated from an ethanol-based ink on a polyethylene terephthalate(PET) film to make a transparent conducting film, purified Ag NWs treated by room-temperature plasma exhibited a transmittance of 91 % at 22 Ω/sq. Experimental results clearly revealed that the sheet resistance of the Ag NWs/PET film could nearly maintain constant under different bending conditions, showing good tensile properties. In addition, the Ag NWs/PET film conductivity in the original state coinciding with that after 2000 cycles indicates the Ag NWs/PET film has good stability.2. The double-sided display flexible alternating-current electroluminescent device(ACEL) was fabricated based on zinc blende structure ZnS:Cu particles(6-9 μm) and Ag NWs/PET film. The photoluminescent spectra of AECL device was measured and the electroluminescent mechanism of ZnS:Cu particles was studied. The double-sided display flexible ACEL device had good luminous stability and note that its ACEL intensity enhanced when increasing applied voltage or frequency.3. On the basis of double-sided display flexible ACEL device, the touch sensor,the brightness of which enhanced with the increasing of pressure, was obtained after the pyramidal microstructure was introduced to the light-emitting layer. Electronic skin for tactile visualization with transparent flexible electrodes may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices because of its characteristics of fast response, high stability, high reversibility, multi-touch and cuttable.