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.

The effects of humidity on the electrical properties of thermal inkjet-printed copper tetrasulfonated phthalocyanine (CuTsPc) films onto paper substrates are reported. DC electrical measurements revealed that sample resistance decreases from 10 12 X in moderate vacuum to approximately 10 7 X at highly water-saturated atmosphere. This behavior is attributed to the creation of water pathways on the cellulose fibers that allow ionic species such as impurities, protons (H ? ), and dissociated Na ? ions from the CuTsPc molecules, to flow. The contribution of the CuTsPc molecules and their dissociated Na ? ions on the sample resistance was elucidated analyzing the electrical response of bare and printed paper substrates. An increase of relative humidity levels (RH) from 10 % to 40-45 % revealed an increase of current of four orders of magnitude for printed samples, whereas less than one order of magnitude was registered for bare paper substrates. Electrical measurements as a function of temperature have shown that moisture can inhibit the semiconducting properties of CuTsPc. Thermal gravimetric studies revealed that approximately 11 % of mass accounting to the presence of water is released above 70°C, the same temperature in which the sample recovers its dry-state semiconducting behavior. The semiconducting properties of CuTsPc can also be observed upon white light illumination, whereas the charge carrier extraction is governed by the RH level. These results point out the important role of humidity on the electrical properties of paper-based organic, electronic, and optoelectronic devices.

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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.