Abstract
Recent studies have demonstrated the advantage of developing pressure-sensitive devices with light-emitting properties for direct visualization of pressure distribution, potential application to next generation touch panels and human-machine interfaces. To ensure that this technology is available to everyone, its production cost should be kept as low as possible. Here, simple device concepts, namely, pressure sensitive flexible hybrid electrodes and OLED architecture, are used to produce low-cost resistive or light-emitting pressure sensors. Additionally, integrating solution-processed self-assembled micro-structures into the flexible hybrid electrodes composed of an elastomer and conductive materials results in enhanced device performances either in terms of pressure or spatial distribution sensitivity. For instance, based on the pressure applied, the measured values for the resistances of pressure sensors range from a few MΩ down to 500 Ω. On the other hand, unlike their evaporated equivalents, the combination of solution-processed flexible electrodes with an inverted OLED architectures display bright green emission when a pressure over 200 kPa is applied. At a bias of 3 V, their luminance can be tuned by applying a higher pressure of 500 kPa. Consequently, features such as fingernails and fingertips can be clearly distinguished from one another in these long-lasting low-cost devices.
Highlights
Since their introduction at the end of the last century, organic semiconductors and organic electronic devices have demonstrated their potential as low-cost alternatives to the state-of-the-art inorganic devices[1,2,3,4]
The simple device architecture that we introduce consists of an inverted organic light-emitting diodes (OLEDs) device in which the top anode, which is commonly deposited by thermal evaporation, is replaced by a hybrid flexible and pressure sensitive electrode composed of PDMS, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and silver nanowires (AgNWs)
Chen et al proposed to use alternative materials such as polyethylene terephthalate (PET) as flexible substrates to deposit AgNWs/PEDOT:PSS hybrid electrodes which could be used in capacitive pressure sensors with the following device architecture: PET/AgNWs + PEDOT:PSS/PDMS/ AgNWs + PEDOT:PSS/PET16
Summary
Since their introduction at the end of the last century, organic semiconductors and organic electronic devices have demonstrated their potential as low-cost alternatives to the state-of-the-art inorganic devices[1,2,3,4]. By applying pressure on the flexible electrode, electrical contact is generated locally which induces a change in the apparent color of the electrochromic material This approach utilizes a much simpler device architecture compared to the concept presented by Wang et al the electrochromic pressure-sensitive devices require a relatively long color-switching time (largely over 1 s) and no bright emission can be observed from the devices (they cannot be used in the dark). Compared to the evaporated electrodes, the solution-processed ones exhibit a higher transmittance and introduce the possibility to obtain pressure-sensitive pressure sensing When these electrodes are used as anode in inverted OLED architectures, our all-solution-processed devices prepared using scalable and low-cost fabrication techniques exhibit strong luminance at relatively low voltages and open the way to the generation of interactive electronic skins and pressure sensors
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