Cotton-based nanocrystalline cellulose (NCC), also known as nanopaper, one of the major sources of renewable materials, is a promising substrate and component for producing low cost fully recyclable flexible paper electronic devices and systems due to its properties (lightweight, stiffness, non-toxicity, transparency, low thermal expansion, gas impermeability and improved mechanical properties). Here, we have demonstrated for the first time a thin transparent nanopaper-based field effect transistor (FET) where NCC is simultaneously used as the substrate and as the gate dielectric layer in an ‘interstrate' structure, since the device is built on both sides of the NCC films; while the active channel layer is based on oxide amorphous semiconductors, the gate electrode is based on a transparent conductive oxide. Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility ({\textgreater}7 cm 2 V −1 s −1 ), drain–source current on/off modulation ratio higher than 10 5 , enhancement n-type operation and subthreshold gate voltage swing of 2.11 V/decade. The NCC film FET characteristics have been measured in air ambient conditions and present good stability, after two weeks of being processed, without any type of encapsulation or passivation layer. The results obtained are comparable to ones produced for conventional cellulose paper, marking this out as a promising approach for attaining high-performance disposable electronics such as paper displays, smart labels, smart packaging, RFID (radio-frequency identification) and point-of-care systems for self-analysis in bioscience applications, among others.

Electrochemically 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.

In 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.

The 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.

Solution-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.

Aluminium-doped zinc oxide (AZO) is a common material used as a front contact layer on chalcopyrite CuInGaSe2 (CIGS)-based thin-film solar cells since it combines optimum optical and electrical properties with low cost and abundant elemental availability. Low-resistivity and high-transmission front contacts are required to develop high-performance CIGS solar cells. However, the durability of the cells is highly influenced by the corrosion resistance behaviour of the AZO layers. In this work, an exhaustive study of the aluminium-doped zinc oxide layers (AZO) deposited by pulsed DC magnetron sputtering (MS) has been performed. The optical, electrical and electrochemical corrosion resistance properties of the AZO layers have been evaluated as a function of the deposition pressure. The results show that adjusting the deposition pressure could develop AZO layers with very high electrochemical corrosion resistance in chlorinated aqueous media combined with optimum electrical and optical properties. Layers grown at 3×10−3mbar pressure present very high corrosion resistance values (in the order of 106 {\$}Ømega{\$}) and very high electrochemical stability, indicating no tendency for electrochemical corrosion degradation. Besides, these layers are highly transparent with an average transmittance in the visible range above 90{%} and with a low resistivity of 6.8×10−4 {\$}Ømega{\$}cm for a 1000nm films thickness, making them optimum candidate front contact for high-performance and high durability CIGS solar cells.

The present work reports the synthesis of zinc oxide (ZnO) nanostructures produced either under microwave irradiation using low cost domestic microwave equipment or by conventional heating, both under hydrothermal conditions. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, room/low temperature photoluminescence, and Raman spectroscopy have been used to investigate the structure, morphology, and optical properties of the produced ZnO nanorods. Identical structures with aspect ratio up to 13 have been achieved for both synthesis routes displaying similar final properties. The hexagonal wurtzite structure has been identified, and a red-orange emission has been detected in the presence of UV irradiation for all the conditions studied. Thermal stability of the as-prepared nanostructures has been evaluated through thermogravimetric measurements revealing an increase of superficial defects. The as-prepared ZnO nanorods were tested as UV sensors on paper substrate, which led to fast response (30 s) and rapid recovery (100 s) times, as well as sensitivity up to 10 indicating that these materials may have a high potential in low cost, disposable UV photodetector applications.

This 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.

Paper electronics is a topic of great interest due the possibility of having low-cost, disposable and recyclable electronic devices. The final goal is to make paper itself an active part of such devices. In this work we present new approaches in the selection of tailored paper, aiming to use it simultaneously as substrate and dielectric in oxide based paper field effect transistors (FETs). From the work performed, it was observed that the gate leakage current in paper FETs can be reduced using a dense microfiber/nanofiber cellulose paper as the dielectric. Also, the stability of these devices against changes in relative humidity is improved. On other hand, if the pH of the microfiber/nanofiber cellulose pulp is modified by the addition of HCl, the saturation mobility of the devices increases up to 16 cm 2 V −1 s −1 , with an I ON / I OFF ratio close to 10 5 .

Here 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.

The degradation of thin-film transistors (TFTs) caused by the self-heating effect constitutes a problem to be solved for the next generation of displays. Aluminum nitride (AlN) is a viable alternative for gate dielectric of TFTs due to its good thermal conductivity, matching coefficient of thermal expansion to indium–gallium–zinc-oxide, and excellent stability at high temperatures. Here, AlN thin films of different thicknesses were fabricated by a low temperature reactive radio-frequency magnetron sputtering process, using a low cost, metallic Al target. Their electrical properties have been thoroughly assessed. Furthermore, the 200 nm and 500 nm thick AlN layers have been integrated as gate-dielectric in transparent TFTs with indium–gallium–zinc-oxide as channel semiconductor. Our study emphasizes the potential of AlN thin films for transparent electronics, whilst the functionality of the fabricated field-effect transistors is explored and discussed.

pH is a vital physiological parameter that can be used for disease diagnosis and treatment as well as in monitoring other biological processes. Metal/metal oxide based pH sensors have several advantages regarding their reliability, miniaturization, and cost-effectiveness, which are critical characteristics for in vivo applications. In this work, WO3 nanoparticles were electrodeposited on flexible substrates over metal electrodes with a sensing area of 1 mm2. These sensors show a sensitivity of ?56.7 ± 1.3 mV/pH, in a wide pH range of 9 to 5. A proof of concept is also demonstrated using a flexible reference electrode in solid electrolyte with a curved surface. A good balance between the performance parameters (sensitivity), the production costs, and simplicity of the sensors was accomplished, as required for wearable biomedical devices.