Kiazadeh, A, Salgueiro D, Branquinho R, Pinto J, Gomes HL, Barquinha P, Martins R, Fortunato E.
2015.
{Operational stability of solution based zinc tin oxide/SiO2 thin film transistors under gate bias stress}, jun. APL Materials. 3:062804., Number 6
AbstractIn this study, we report solution-processed amorphous zinc tin oxide transistors exhibiting high operational stability under positive gate bias stress, translated by a recoverable threshold voltage shift of about 20{%} of total applied stress voltage. Under vacuum condition, the threshold voltage shift saturates showing that the gate-bias stress is limited by trap exhaustion or balance between trap filling and emptying mechanism. In ambient atmosphere, the threshold voltage shift no longer saturates, stability is degraded and the recovering process is impeded. We suggest that the trapping time during the stress and detrapping time in recovering are affected by oxygen adsorption/desorption processes. The time constants extracted from stretched exponential fitting curves are ≈106 s and 105 s in vacuum and air, respectively.
Aguas, H, Mateus T, Vicente A, Gaspar D, Mendes MJ, Schmidt WA, Pereira L, Fortunato E, Martins R.
2015.
{Thin Film Silicon Photovoltaic Cells on Paper for Flexible Indoor Applications}, jun. ADVANCED FUNCTIONAL MATERIALS. 25:3592–3598., Number 23
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Marques, AC, Santos L, Costa MN, Dantas JM, Duarte P, Gonçalves A, Martins R, Salgueiro CA, Fortunato E.
2015.
{Office paper platform for bioelectrochromic detection of electrochemically active bacteria using tungsten trioxide nanoprobes.}, jan. Scientific reports. 5:9910.
AbstractElectrochemically active bacteria (EAB) have the capability to transfer electrons to cell exterior, a feature that is currently explored for important applications in bioremediation and biotechnology fields. However, the number of isolated and characterized EAB species is still very limited regarding their abundance in nature. Colorimetric detection has emerged recently as an attractive mean for fast identification and characterization of analytes based on the use of electrochromic materials. In this work, WO3 nanoparticles were synthesized by microwave assisted hydrothermal synthesis and used to impregnate non-treated regular office paper substrates. This allowed the production of a paper-based colorimetric sensor able to detect EAB in a simple, rapid, reliable, inexpensive and eco-friendly method. The developed platform was then tested with Geobacter sulfurreducens, as a proof of concept. G. sulfurreducens cells were detected at latent phase with an RGB ratio of 1.10 ± 0.04, and a response time of two hours.
Santos, L, Nunes D, Calmeiro T, Branquinho R, Salgueiro D, Barquinha P, Pereira LÍ, Martins R, Fortunato E.
2015.
{Solvothermal synthesis of gallium-indium-zinc-oxide nanoparticles for electrolyte-gated transistors.}, jan. ACS applied materials {&} interfaces. 7:638–46., Number 1
AbstractSolution-processed field-effect transistors are strategic building blocks when considering low-cost sustainable flexible electronics. Nevertheless, some challenges (e.g., processing temperature, reliability, reproducibility in large areas, and cost effectiveness) are requirements that must be surpassed in order to achieve high-performance transistors. The present work reports electrolyte-gated transistors using as channel layer gallium-indium-zinc-oxide nanoparticles produced by solvothermal synthesis combined with a solid-state electrolyte based on aqueous dispersions of vinyl acetate stabilized with cellulose derivatives, acrylic acid ester in styrene and lithium perchlorate. The devices fabricated using this approach display a ION/IOFF up to 1 × 10(6), threshold voltage (VTh) of 0.3-1.9 V, and mobility up to 1 cm(2)/(V s), as a function of gallium-indium-zinc-oxide ink formulation and two different annealing temperatures. These results validates the usage of electrolyte-gated transistors as a viable and promising alternative for nanoparticle based semiconductor devices as the electrolyte improves the interface and promotes a more efficient step coverage of the channel layer, reducing the operating voltage when compared with conventional dielectrics gating. Moreover, it is shown that by controlling the applied gate potential, the operation mechanism of the electrolyte-gated transistors can be modified from electric double layer to electrochemical doping.
Pavan, M, Rühle S, Ginsburg A, Keller DA, Barad H-N, Sberna PM, Nunes D, Martins R, Anderson AY, Zaban A, Fortunato E.
2015.
{TiO2/Cu2O all-oxide heterojunction solar cells produced by spray pyrolysis}, jan. Solar Energy Materials and Solar Cells. 132:549–556.
AbstractHere we present for the first time a TiO2/Cu2O all-oxide heterojunction solar cell entirely produced by spray pyrolysis onto fluorine doped tin oxide (FTO) covered glass substrates, using silver as a back contact. A combinatorial approach was chosen to investigate the impact of the TiO2 window layer and the Cu2O light absorber thicknesses. We observe an open circuit voltage up to 350mV and a short circuit current density which is strongly dependent of the Cu2O thickness, reaching a maximum of {\~{}}0.4mA/cm2. Optical investigation reveals that a thickness of 300nm spray pyrolysis deposited Cu2O is sufficient to absorb most photons with an energy above the symmetry allowed optical transition of 2.5eV, indicating that the low current densities are caused by strong recombination in the absorber that consists of small Cu2O grains.
Nunes, D, Santos L, Duarte P, Pimentel A, Pinto JV, Barquinha P, Carvalho PA, Fortunato E, Martins R.
2015.
{Room temperature synthesis of Cu₂O nanospheres: optical properties and thermal behavior.}, feb. Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada. 21:108–19., Number 1
AbstractThe present work reports a simple and easy wet chemistry synthesis of cuprous oxide (Cu2O) nanospheres at room temperature without surfactants and using different precursors. Structural characterization was carried out by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy coupled with focused ion beam and energy-dispersive X-ray spectroscopy. The optical band gaps were determined from diffuse reflectance spectroscopy. The photoluminescence behavior of the as-synthesized nanospheres showed significant differences depending on the precursors used. The Cu2O nanospheres were constituted by aggregates of nanocrystals, in which an on/off emission behavior of each individual nanocrystal was identified during transmission electron microscopy observations. The thermal behavior of the Cu2O nanospheres was investigated with in situ X-ray diffraction and differential scanning calorimetry experiments. Remarkable structural differences were observed for the nanospheres annealed in air, which turned into hollow spherical structures surrounded by outsized nanocrystals.
Santos, L, Wojcik P, Pinto JV, Elangovan E, Viegas J, Pereira LÍ, Martins R, Fortunato E.
2015.
{Structure and Morphologic Influence of WO 3 Nanoparticles on the Electrochromic Performance of Dual-Phase a -WO 3 /WO 3 Inkjet Printed Films}, feb. Advanced Electronic Materials. 1:n/a–n/a., Number 1-2
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Fernandes, M, Leones R, Costa AMS, Silva MM, Pereira S, Mano JF, Fortunato E, Rego R, {de Zea Bermudez} V.
2015.
{Electrochromic devices incorporating biohybrid electrolytes doped with a lithium salt, an ionic liquid or a mixture of both}. Electrochimica Acta. 161:226–235.: Elsevier Ltd
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Wojcik, PJ, Santos L, Pereira L, Martins R, Fortunato E.
2015.
{Tailoring nanoscale properties of tungsten oxide for inkjet printed electrochromic devices}. Nanoscale. 7:1696–1708., Number 5: Royal Society of Chemistry
AbstractThis paper focuses on the engineering procedures governing the synthesis of tungsten oxide nanocrystals and the formulation of printable dispersions for electrochromic applications. By that means, we aim to stress the relevancy of a proper design strategy that results in improved physicochemical properties of nanoparticle loaded inks. In the present study inkjet printable nanostructured tungsten oxide particles were successfully synthesized via hydrothermal processes using pure or acidified aqueous sol-gel precursors. Based on the proposed scheme, the structure and morphology of the nanoparticles were tailored to ensure the desired printability and electrochromic performance. The developed nanomaterials with specified structures effectively improved the electrochemical response of printed films, resulting in 2.5 times higher optical modulation and 2 times faster coloration time when compared with pure amorphous films.
Branquinho, R, Salgueiro D, Santa A, Kiazadeh A, Barquinha P, Pereira L, Martins R, Fortunato E.
2015.
{Towards environmental friendly solution-based ZTO/AlOx TFTs}. SEMICONDUCTOR SCIENCE AND TECHNOLOGY. 30, Number 2, SI
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