The production of low cost sensors to monitor environment in some industrial sectors is a current need. In aviculture centers, for example, the concentration of ammonia gas is related to humidity, and it is necessary to control it to avoid contamination. With this need in mind, this paper presents the preparation and characterization of a low cost humidity sensor based on poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and polyaniline fully printed onto paper by a commercial HP printer. Using electrochemical impedance spectroscopy, an equivalent circuit containing resistive and capacitive parameters was proposed. The resistive parameter R1 is related to values of ambient humidity. The R1 values showed a sensitive response of 200% when relative humidity changes 80%, taking 10 min to reach saturation point. Moreover, the device showed good stability when humidity remained constant. These results indicate that the proposed device is suitable for applying as a humidity sensor that costs less than 1 Euro cent.
Paper electronics has emerged as an ecofriendly, light, low-cost, and recyclable material for the fabrication of flexible and printed transistors. In this study, we present fully printed organic electrochemical transistors using an active layer of PEDOT:PSS, carbon electrodes, cellulose-based electrolyte, and three different papers as substrates: bond, vegetal, and Lumi Silk, relating the electrical properties to the different morphologies of the paper surfaces. Each paper presents different regularity, diffusion capabilities, and roughness, with significant influence on the transistor performance. The more organized and smooth the surface, the better the electrical characteristics, the best of these being the Lumi Silk, with higher I
on/I
off ratio of 46, on-current of 8.3 × 10−5 A, V
on of 1.3 V, and power gain of 43.5 dB associated with ultra-low hysteresis of 0.1 V, high transconductance of −57.3 μS, and suitablity for flexible electronics and sensors applications.
Printed electronics is a reputable research area that encourages the search for simple alternatives of manufacturing processes for low-cost, eco-friendly, and biodegradable electronic devices. Among these devices, electrolyte-gated transistors (EGTs) stand out due to their simple manufacturing process and architecture. Here we report the study of printed electrolyte-gated transistors with in-plane gate architecture (IPGT) based on zinc oxide nanoparticles (ZnO-NPs). The drain, source, and gate electrodes with two different W/L channel ratios were fabricated using a screen-printed carbon-based ink. We also produced a conventional top-gate transistor as a control device, using the same structure as the IPGT described above by adding an ITO strip positioned over the electrolyte as the top-gate electrode. The IPGT with W/L = 5 presented a high mobility of 7.1 cm2V-1s-1, while the W/L = 2.5 device exhibited a mobility of 3.7 cm2V-1s-1. We found that the measured field-effect mobility of the device can be affected by the high contact resistance from the carbon electrodes. This effect could be observed when the geometric parameters of the devices were changed. Furthermore, we also found that the IPGT with W/L = 5 exhibited better values for mobility and transconductance than the top-gate transistor, showing that the IPGTs setup is a good promise for cheap and printed transistors with performance comparable to standard top-gate transistors.
The use of paper as a platform to manufacture organic electronic devices, electronic paper, has expanding potential for many applications because of several properties offered. In this work, we show a study of PEDOT:PSS printed by inkjet on bond paper, vegetal paper and sheets of PET. The relation between the surface density of the deposited material, morphology and resistivity was investigated for samples printed with a commercial Hewlett-Packard(HP) ® printer and Microsoft Word ® software. The amount of material deposited, i.e. surface density, was controlled using the print number in the same position and changing the gray scale used in the image formation. Changing the surface density of printed PEDOT:PSS, it is possible to produce a continuous film permeating the papers fibers. Sheet resistances obtained, when 7.0 mg cm À2 of PEDOT:PSS were deposited on the surfaces, were: (a) 413.2 kU/Sq for bond paper, (b) 5.6 kU/Sq for vegetable paper and (c) 2.3 kU/Sq for PET. The exponential dependence of sheet resistance with the surface density of printed material allows us to evaluate the strong influence of substrate roughness on PEDOT:PSS conductivity and to predict, for each one, conditions to minimize it.
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