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Photonic structures allow reducing the thickness of photovoltaic (PV) devices while improving their photocurrent, thereby enabling high-efficient, low-cost, and mechanically flexible solar cells. Wave-optical front structures have shown to be promising for integration in various thin-film PV technologies, as those based on silicon or perovskite semiconductors, due to a combination of: (1) Broadband absorption amplification—wavelength-sized structures provide geometrical index-matching for the impinging light, strongly reducing reflection while boosting the photons' path length within the absorber via scattering. (2) Improved electrical performance—their incorporation in the transparent contact can enable higher electrode volume, thereby improving the cells' voltage and fill factor. Such a location can also prevent increasing the cells' roughness, therefore not contributing to recombination. (3) Enhanced stability—particularly in perovskite cells, the front photonic structures block most of the harmful UV radiation that degrades such devices. Colloidal lithography methods have revealed to be highly cost-effective for the nanopatterning of such structures, allowing compatibility with industrial scalability and low-cost requirements.

A novel Photovoltaic-Electrochemical (PV-EC) integrated system is designed, capable of converting CO2 into carbon-based fuels, in which “smart” synergetic effects between the two technologies are explored, such as thermal coupling (TC) and electronic regulation (DC-DC), that can strongly improve the energetic performance. We show that, when thermally-coupled, the PV and EC cells exhibit a symbiotic behaviour: the solar-to-fuel efficiency stays almost temperature-independent due to improved reaction kinetics, which compensates for photovoltaic thermal losses. The electronic regulation is equally important, because it guarantees that all power provided by PV generation is channelled to the EC load. When conjugated with TC, the DC-DC converter can boost production up to 50% beyond the TC improvement. For operating temperatures in the 40-90°C range, combined TC and DC-DC can boost production by up to 586% and 42.9% for Perovskite/Si double-junction and mono-crystalline Si solar cells, respectively. These solutions are tested in two PV-powered pathways for methane production: 1-step, CO2 →CH4, and 2-step, CO2 →Syngas→CH4; where in the latter the intermediate syngas is converted to methane through catalytic hydrogenation. Despite the advantageous simplicity of the direct production (1-step) of methane, the comparison between the two paths showed that the second route achieves close to 20% higher annual yield.

grant agreement No 763989 UID/CTM/50025/2019 PTDC/NAN-OPT/28430/2017 PD/BD/143031/2018 SFRH/BD/148078/2019 Photonic micro/nano-structures in the wave-optics regime have shown to be a promising strategy for effective broadband light capture in ultra-thin devices, opening a window of opportunity for cheap, efficient, lightweight and flexible photovoltaics (PV). Here we design, from an optical standpoint, a novel industrially-attractive concept where light trapping is obtained by conformably depositing the solar cell materials onto previously-patterned photonic substrates. This solution is applied and optimized for perovskite solar cells (PSCs) with distinct thicknesses of the perovskite absorber - the conventional (500 nm) and ultra-thin (300 nm) in view of enhanced flexibility - yielding photocurrent improvements up to 22.8% in superstrate cell configuration and 24.4% in substrate-type configuration; thereby coming relatively close to the fundamental Lambertian limits. Furthermore, these structures also show an omni-direction optical response for incidence angles up to 70° for all cases, therefore demonstrating the viability of this light trapping method for implementation in flexible PV devices operating under bending. The photonic-enhanced ultra-thin solar cells designed here ultimately support the reduction of material usage in PSC technology, which is especially beneficial to mitigate lead usage, without impacting the device's performance. preprint published

Expanding the single molecule detection, enabled by laser-induced graphene (LIG) technology, for portable and on-site analysis, a dual molecule system with a two-working electrode architecture was developed, for ascorbic acid (AA) and amoxicillin (AMOX) detection, which are currently used in aquaculture and persist as water contaminants. The biorecognition element of each target compound was a suitable molecularly-imprinted polymer (MIP). The AMOX MIP was developed herein for the first time and assembled by electropolymerization of eriochrome black T (EBT). It showed a wide linear response from 100 nM to 50 µM, with a sensitivity of -13.32 µA/decade. Calibration curves revealed good squared correlation coefficients (R2 > 0.99) with a limit of detection (LOD) of 11.98 nM. AA MIP was assembled according to previous work reported in the literature, displaying a linear response from 1.5 mM to 4 mM and a sensitivity of 1.356 µA/decade. The developed dual-LIG device was further tested in real samples and successfully applied to the analysis of binary mixtures prepared in environmental water samples from a well. Overall, the proposed device allows in-situ analysis of two different molecules, holds an exceptionally low-cost design when compared to competing architectures in the literature, and, the fabrication method here employed offers the possibility of easily adjusting the desired architecture on demand., The authors acknowledge funding from projects PTDC/AAGTEC/5400/2014, POCI-01-0145-FEDER-016637, and POCI01-0145-FEDER-007688, UID/CTM/50025/2019 funded by European funds, through FEDER (European Funding or Regional Development) via COMPETE2020-POCI (operational program for internationalization and competitively) and by national funding through the National Foundation for Science and Technology, I.P. (FCT). A.C.M. and A.R.C. also acknowledge funding to the National Foundation for Science and Technology, I.P., through the PhD Grants SFRH/BD/115173/2016 and SFRH/BD/130107/2017, respectively., info:eu-repo/semantics/publishedVersion

ECR/2017/000931 POCI-01-0145-FEDER-007688 PTDC/NAN-MAT/30812/2017 This paper presents a high-speed ring oscillator (RO) with amorphous Indium-Gallium-Zinc-Oxide Thin-film transistors (a-IGZO TFTs). The proposed RO reduces the delay of a single stage inverter using intermediate signals generated within the RO, hence, improving the speed. To validate the proposed idea, two conventional ROs (with diode-load load inverter and bootstrapped pseudo-CMOS inverter) and the proposed RO were fabricated at a temperature ≤ 180°C. Measured results of the proposed RO have shown a frequency and power-delay-product (PDP) of 173.2 kHz and 0.7 nJ at a supply voltage of 6V. Further, it shows approximately 155% (44%) increase in frequency and 14% (24.5%) decrease in PDP compared to diode-load inverter (bootstrapped pseudo-CMOS inverter) based ROs. Therefore, the proposed RO finds applications in low-voltage and high speed designs for timing signal generation. publishersversion published

Combining well known oxide materials with biocompatible polymers such as chitosan (Cs) and antimicrobial agents such as Ag can bring new functionalities to materials for electronics and lead to new border applications in the field of stretchable wearable bioelectronics and drug delivery systems. The paper reports on new hybrid thin films based on zinc oxide (ZnO) and Ag:ZnO nanoparticles dispersed in chitosan and incorporated in poly(methyl methacrylate) (PMMA) matrix by a modified sol-gel method. The structure, morphology, optical, electrical and antimicrobial properties of the obtained hybrid ZnO/Cs/PMMA and Ag:ZnO/Cs/PMMA thin films have been investigated. For electric characterization, current-voltage, capacitance-voltage and dielectric constant-frequency curves of the one and two-layers hybrid thin films deposed in MIS structure have been recorded. The dielectric constant values between 9.5 and 14.9 at 20 kHz, in addition with low surface roughness, optimal optical transmittance in visible and near-infrared region of about 90% and optical band gap (Eg) values between 3.543 and 3.737 eV, indicate high potential applications of the obtained hybrid films in transparent bioelectronics. The antimicrobial activity of the hybrid sols used for the film's deposition and the resulted thin films have been investigated using the paper disc method on Mueller-Hinton agar against Gram negative E. coli and Gram positive S. aureus bacteria. Ag:ZnO/Cs/PMMA films showed good antimicrobial activity against S. aureus and E. coli. authorsversion published

project PON_206_2 project PRN 2014/2020 ALTALUZ (PTDC/CTM-ENE/5125/2014 PTDC/NAN-OPT/28430/2017 PTDC/NAN-OPT/28837/2017 PTDC/EAM-PEC/29905/2017 SFRH/BPD/114833/2016 SFRH/BPD/115566/2016 One of the most promising approaches to produce industrial-compatible Transparent Conducting Materials (TCMs) with excellent characteristics is the fabrication of TCO/metal/TCO multilayers. In this article, we report on the electro-optical properties of a novel high-performing TCO/metal/TCO structure in which the intra-layer is a micro-structured metallic grid instead of a continuous thin film. The grid is obtained by evaporation of Ag through a mask of polystyrene colloidal micro-spheres deposited by the Langmuir-Blodgett method and partially dry-etched in plasma. IZO/Ag grid/IZO structures with different thicknesses and mesh dimensions have been fabricated, exhibiting excellent electrical characteristics (sheet resistance below 10 Ω/□) and particularly high optical transmittance in the near-infrared spectral region as compared to planar (unstructured) TCM multilayers. Numerical simulations were also used to highlight the role of the Ag mesh parameters on the electrical properties. preprint published

ALTALUZ (Reference PTDC/CTM-ENE/5125/2014). SuperSolar (PTDC/NAN-OPT/28430/2017). TACIT (PTDC/NAN-OPT/28837/2017). FCT-MEC, Grant SERH/BPD/115566/2016. Combined perovskite/crystalline-silicon four-terminal tandem solar cells promise >30% efficiencies. Here we propose all-thin-film double-junction architectures where high-bandgap perovskite top cells are coupled to ultrathin c-Si bottom cells enhanced with light trapping. A complete optoelectronic model of the devices was developed and applied to determine the optimal intermediate layers, which are paramount to maximize the cells' photocurrent. It was ascertained that by replacing the transparent conductive oxides by grid-based metallic contacts in the intermediate positions, the parasitic absorption is lowered by 30%. Overall, a 29.2% efficiency is determined for ∼2 um thick tandems composed of the optimized interlayers and improved with Lambertian light trapping. authorsversion published

PD/BD/105876/2014 Our experimental outturn opens up a new vision by proposing mechano-responsive charge transfer mechanism (MRCTM) to π-conjugated polymers in the field of human-motion interactive energy harvester. Doped polyaniline (d-PANi) has been used to functionalize conducting textile fibers (f-CTFs) and integrated with our proposed design for wearable power plant. Each f-CTF generates current by patting, bending, or even soft touching. Localized force deformation at the metal/polymeric interface layer with direct visualization of charge distribution pattern has been extensively studied by atomic force microscopy. The integrated arrays of f-CTFs produce a peak power-density of ∼0.6 W m −2 with output current-density of ∼22 mA m −2 and can power at least 10 white LEDs of 2.5 W. The procured energy from f-CTFs is capable of charging a commercial 10 μF capacitor to 3 V in 80 s and powering portable electronic devices. The prototype energy harvester stably shows the same performance after more than 100 thousand times of patting, bending or twisting. proof published

The authors acknowledge the support from the FCT – Portuguese Foundation for Science and Technology through the Ph.D. scholarship SFRH/BD/125191/2016. The authors would like to acknowledge the European Commission under project NewFun (ERC‐StG‐2014, GA 640598) and BET‐EU (H2020‐TWINN‐2015, GA 692373). This work was also supported by the FEDER funds through the COMPETE 2020 Program, Portugal2020 project CelSmartSense number 17862 and the National Funds through the FCT – Portuguese Foundation for Science and Technology under the Project No. POCI‐01‐0145‐FEDER‐007688, Reference UID/CTM/50025, project FunPaper, reference EXPL/CTM‐NAN/1184/2013, project PapEl, reference PTDC/CTM‐NAN/5172/2014, project PTDC/CTM‐BIO/6178/2014 and M‐ERA‐NET2/0007/2016 (CellColor). S.N.F. acknowledges the MCTES, the European Social Funds, and the FCT for fellowships SFRH/BDP/78430/2011. D.G. acknowledges the support from the FCT – Portuguese Foundation for Science and Technology through the AdvaMTech PhD program scholarship PD/BD/52627/2014. The integration of bioinspired chiral cellulose nanocrystal (CNC) films into transistor devices with distinct sensing properties for left- and right-handed circular polarized light (LCPL and RCPL, respectively) is reported. The CNC films with a left-handed internal long-range order are infiltrated with sodium ions to yield solid-state electrolytes with photonic properties capable of LCPL reflection and RCPL transmission. They are employed as gate dielectrics in sputtered amorphous indium–gallium–zinc oxide (a-IGZO) transistors. The obtained devices operate in depletion mode at low voltages (

PTDC/CTM-ENE/5125/2014. PTDC/NAN-OPT/28430/2017. TACIT (PTDC/NAN-OPT/28837/2017). SFRH/BPD/115566/2016. PD/BD/143031/2018 (via AdvaMTech PhD program). In recent years, the discovery of the excellent optical and electrical properties of perovskite solar cells (PSCs) made them a main focus of research in photovoltaics, with efficiency records increasing astonishingly fast since their inception. However, problems associated with the stability of these devices are hindering their market application. UV degradation is one of the most severe issues, chiefly caused by TiO 2 's photogenerated electrons that decompose the perovskite absorber material, coupled with the additional intrinsic degradation of this material under UV exposure. The solution presented here can minimize this effect while boosting the cells' generated photocurrent, by making use of combined light-trapping and luminescent down-shifting effects capable of changing the harmful UV radiation to higher wavelengths that do not affect the stability and can be effectively "trapped" in the cell. This work focuses in the optimization of the photocurrent gains that can be attained by emulating the changed spectrum resulting from applying down-shifting media as encapsulant in photonic-enhanced PSCs, as well as the reduction in the harmful effects of UV radiation on the devices. Such optimized photonic solution allows current enhancement while reducing the harmful UV photocarrier generation both in the TiO 2 (by 1 order of magnitude) and in the perovskite (by 80%) relative to a standard PSC without light management. authorsversion published

National Funds through FCT, Foundation for Science and Technology, under the projects ALTALUZ (PTDC/CTM-ENE/5125/2014) and SUPER SOLAR (PTDC/NAN-OPT/28430/2017). M.J.M. also acknowledges funding by FCT through the Grant SFRH/BPD/115566/2016. The control of morphology and crystallinity of solution-processed perovskite thin-films for solar cells is the key for further enhancement of the devices' power conversion efficiency and stability. Improving crystallinity and increasing grain size of perovskite films is a proven way to boost the devices' performance and operational robustness, nevertheless this has only been achieved with high-temperature processes. Here, we present an unprecedented low-temperature (

A ZnO/Cu2O-based combinatorial heterojunction device library was successfully fabricated by a simple spray pyrolysis technique using ITO-coated glass as the substrate. The combinatorial approach was introduced to analyze the impact of the ZnO and Cu2O layer thicknesses on the performance of the solar cells. The thickness of the ZnO layer was varied from ∼50 to 320 nm, and the Cu2O layer was deposited orthogonal to the ZnO thickness gradient. In the case of Cu2O, the thickness varied from ∼200 to 800 nm. The photovoltaic performance of the cells is strongly dependent on the absorber layer thickness for a particular window layer thickness and reaches a maximum short-circuit current density of 3.9 mA/cm2 when the absorber layer thickness just crosses ∼700 nm. Reducing the thicknesses of the active layers leads to a sharp decrease in the device performance. It is shown that the entire built-in bias of the heterojunction is created in the absorber layer due to low carrier density. The poor performance of the d...

Dielectric-based photonic structures, composed of a lossless but high refractive index material, are currently among the preferential solutions for light management in thin film photovoltaics, as they allow broadband manipulation of sunlight to strongly boost the absorptance in the thin solar cell layers. In this work, we present an innovative colloidal lithography nanofabrication method that allows the precise engineering of wavelength-sized features, with the materials and geometries appropriate for efficient light trapping when implemented on the front surface of the cells. The method is developed here with TiO2 nanostructures tested on amorphous-silicon absorber thin films coated on the rear side by a metallic reflector. It is a simple, low-cost and scalable approach consisting of 4 main steps: (1) deposition of periodic close-packed arrays of polystyrene colloids which act as the mask; (2) shaping the particles and increasing their spacing via dry etching; (3) infiltration of TiO2 into the inter-particle spaces and (4) removal of the polystyrene particles to leave only the structured TiO2 layer. The resultant array of wavelength-sized features acts as a nanostructured high-index anti-reflection coating, which not only suppresses the reflected light at short wavelengths but also increases the optical path length of the longer wavelengths, via light scattering, within the absorber. The optical results have been compared with numerical electromagnetic computations to provide a deeper understanding of the physical mechanisms responsible for absorptance enhancement in the cells. A notorious 27.3% enhancement in the cell photocurrent is anticipated with the fabricated structures, relative to conventional anti-reflection coatings.

Solution-processed n-type oxide semiconductors have received great interest in thin-film transistor (TFT) applications. However, solution-processed p-type oxide semiconductors are not as successful as their n-type counterparts because of the lack of material choice and their complicated fabrication procedures. In this study, a simple one-step synthetic method was employed to fabricate a p-type Cu2O thin film via in-situ reaction of a CuI film in aqueous NaOH solution at room temperature. The structure, morphology, and component variations as a function of annealing conditions (≤350 °C) were investigated. The analysis indicates that the phase evolution of Cu2O → Cu2O + CuO → CuO occurred at higher temperatures and the pure CuO phase was achieved at 250 °C. The crystallinity, average grain size, and surface morphology of the CuxO thin films were found to increase in slope as the annealing temperature increased. To explore the possible applications of the obtained CuxO films as semiconducting channel components, bottom-gated TFTs on SiO2 gate dielectrics were constructed and examined. The hole mobility of the optimized device was calculated to be 0.32 cm2 V−1 s−1, along with an on/off current ratio of 5 × 104, and a subthreshold swing of 1.1 V dec−1. The further integration of the CuxO film on an Al2O3 high-k dielectric achieves an improved device performance at 2.5 V. This work successfully demonstrates a simple method to fabricate p-type Cu-based thin films and TFTs via a solution route, which represents a great step towards the development of low-cost and all-oxide complementary metal oxide semiconductor electronics.

Aluminum-doped zinc oxide (AZO) transparent conductor coating has emerged as promising substitute to tin-doped indium oxide (ITO) as electrode in optoelectronic applications such as photovoltaics or light emitting diodes (LEDs). Besides its high transmission in the visible spectral region and low resistivity, AZO presents a main advantage over other candidates such as graphene, carbon nanotubes or silver nanowires; it can be deposited using the technology industrially implemented to manufacture ITO layers, the magnetron sputtering (MS). This is a productive, reliable and green manufacturing technique. But to guarantee the robustness, reproducibility and reliability of the process there are still some issues to be addressed, such as the effect and control of the target state. In this paper a thorough study of the influence of the target erosion grade in developed coatings has been performed. AZO films have been deposited from a ceramic target by RF MS. Structure, optical transmittance and electrical properties of the produced coatings have been analyzed as function of the target erosion grade. No noticeable differences have been found neither in optoelectronic properties nor in the structure of the coatings, indicating that the RF MS is a stable and consistent process through the whole life of the target.

Metal nanoparticles are of great interest for light trapping in photovoltaics. They are usually incorporated in the rear electrode of solar cells, providing strong light scattering at their surface plasmon resonances. In most cases, the nanoparticles are self-assembled by solid-state dewetting over a transparent conductive oxide (TCO) layer incorporated in the cell’s rear electrode. Up to now, this process has been optimized mainly by tuning the thermal annealing parameters responsible for dewetting, or the thickness of the precursor metallic layer; but little attention has been paid to the influence of the underlying TCO layer properties on the morphology of the nanoparticles formed, which is the focus of the present article. This work investigates Ag nanoparticles structures produced on distinct surfaces by a simple, fast and highly reproducible method employing rapid thermal annealing. The results indicate that both the thermal conductivity and surface roughness of the TCO layer play a determinant role...

Recording in vivo from the same neuron with two different methods is difficult. It requires blindly moving each probe to within ∼100 μm of one another and for this reason such “dual-recordings” are rare. However, comparing the signals measured by different techniques is necessary to understand what they measure. We developed a method to precisely align the axes of two manipulators and used it to gather a “ground truth” dataset for dense extracellular polytrodes., Cross-validating new methods for recording neural activity is necessary to accurately interpret and compare the signals they measure. Here we describe a procedure for precisely aligning two probes for in vivo “paired-recordings” such that the spiking activity of a single neuron is monitored with both a dense extracellular silicon polytrode and a juxtacellular micropipette. Our new method allows for efficient, reliable, and automated guidance of both probes to the same neural structure with micrometer resolution. We also describe a new dataset of paired-recordings, which is available online. We propose that our novel targeting system, and ever expanding cross-validation dataset, will be vital to the development of new algorithms for automatically detecting/sorting single-units, characterizing new electrode materials/designs, and resolving nagging questions regarding the origin and nature of extracellular neural signals.

The interaction of light with wavelength-sized photonic nanostructures is highly promising for light management applied to thin-film photovoltaics. Several light trapping effects come into play in the wave optics regime of such structures that crucially depend on the parameters of the photonic and absorbing elements. Thus, multi-parameter optimizations employing exact numerical models, as performed in this work, are essential to determine the maximum photocurrent enhancement that can be produced in solar cells. Generalized spheroidal geometries and high-index dielectric materials are considered here to model the design of the optical elements providing broadband absorption enhancement in planar silicon solar cells. The physical mechanisms responsible for such enhancement are schematized in a spectral diagram, providing a deeper understanding of the advantageous characteristics of the optimized geometries. The best structures, composed of TiO2 half-spheroids patterned on the cells' top surface, yield two times higher photocurrent (up to 32.5 mA/cm2 in 1.5 µm thick silicon layer) than the same devices without photonic schemes. These results set the state-of-the-art closer to the theoretical Lambertian limit. In addition, the considered light trapping designs are not affected by the traditional compromise between absorption enhancement versus current degradation by recombination, which is a key technological advantage.

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.

Zinc oxide (ZnO) is a widely studied wide band gap semiconductor with applications in several fields, namely to enhance solar cells efficiency. Its ability to be grown in a wide variety of nanostructured morphologies, allowing the designing of the surface area architecture constitutes an important advantage over other semiconductors. Laser assisted flow deposition (LAFD) is a recently developed growth method, based on a vapour-solid mechanism, which proved to be a powerful approach in the production of ZnO micro/nanostructures with different morphologies as well as high crystallinity and optical quality. In the present work we report the use of the LAFD technique to grow functional ZnO nanostructures (nanoparticles and tetrapods) working as nano templates to improve the dye-sensitized solar cells (DSSCs) efficiency. The structural and morphological characterization of the as-grown ZnO crystals were performed by X-ray diffraction and electron microscopy, respectively, and the optical quality was assessed by photoluminescence spectroscopy. DSSCs were produced using a combination of these nanostructures, which were subsequently sensitized with N719 dye. An efficiency of ∼3% was achieved under simulated AM 1.5 illumination conditions for a dye loading time of 1 h.

The charge transfer dynamics at interfaces are fundamental to know the mechanism of photovoltaic processes. The internal potential in solar cell devices depends on the basic processes of photovoltaic effect such as charge carrier generation, separation, transport, recombination, etc. Here we report the direct observation of the surface potential depth profile over the cross-section of the ZnO nanorods/Cu2O based solar cell for two different layer thicknesses at different wavelengths of light using Kelvin probe force microscopy. The topography and phase images across the cross-section of the solar cell are also observed, where the interfaces are well-defined on the nanoscale. The potential profiling results demonstrate that under white light illumination, the photoinduced electrons in Cu2O inject into ZnO due to the interfacial electric field, which results in the large difference in surface potential between two active layers. However, under a single wavelength illumination, the charge carrier generation, separation, and transport processes between two active layers are limited, which affect the surface potential images and corresponding potential depth profile. Because of changes in the active layer thicknesses, small variations have been observed in the charge carrier transport mechanism inside the device. These results provide the clear idea about the charge carrier distribution inside the solar cell in different conditions and show the perfect illumination condition for large carrier transport in a high performance solar cell.

The capability to control in an smart way the infrared reflectance to environmental temperature variations can be achieved with thermochromic materials like VO2. In this paper, we report the application of VO2 on ceramic tiles aiming to control the reflected infrared radiation on smart roofs and thus improving the energy efficiency, which is associated to the reduction of the carbon dioxide emissions. The VO2 nanoparticles have been produced by hydrothermal synthesis assisted by microwave irradiation, providing a new, quicker and cleaner production route. Afterwards, the VO2 nanoparticles were transferred to the surface of ceramic glassy tiles, which were prepared through dispersing the nanopowders in water and followed by spray coating with posterior annealing treatments in order to promote the surface adhesion as well as the stabilization of the material monoclinic phase. The VO2 transition temperature was controlled by doping with tungsten and a reduction from 69 °C to 49 °C was achieved. The superior thermochromic characteristics of VO2 nanoparticles in conjunction with this new application to a smart roof offers a great potential to regulate the energy in an intelligent way.

The present work shows the effect of magnesium doping on structural, optoelectrical and electrical properties of Cu2O thin films prepared by spray pyrolysis. The variation in the concentration of Mg shows significant impact on the final thin film properties, whereas the film doped with 0.5 at% of Mg exhibited major property improvements in comparison with the undoped thin film and among the other concentrations tested. This condition was further applied for the deposition of an absorber layer in a heterojunction solar cell array with a gradient in thicknesses of active layers to investigate the impact of changing thicknesses on the PV parameters of the solar cell. TiO2 was used as a window layer and the 0.5 at% Cu2O doped film as an absorber layer. The produced heterojunction solar cell array was further exposed to a rapid thermal annealing treatment. The I–V measurements show an open circuit voltage of up to 365 mV and a short circuit current density, which is dependent on absorber layer thickness, and reaches to a maximum value of 0.9 mA/cm2.

In this work, suspended 4-mm-wide graphene membranes are obtained through a sublimation-assisted transfer process, using few-layer films grown by microwave plasma chemical vapor deposition. This result is achieved by a new approach involving the removal of the graphene-transfer supporting layer in vacuum. The membranes produced by this procedure show the largest area-to-thickness ratio described in the literature with a 2-fold improvement when compared to the best results using the conventional PMMA-assisted transfer, and a five orders of magnitude increase when compared to previous sublimation-assisted processes. This breakthrough allows the implementation of a wide variety of technological applications where 2D materials with atomic thickness and large areas are required. As large-area free-standing membranes are difficult to obtain, a new figure of merit is defined to benchmark the various methods of suspending graphene. A high transfer yield is achieved, and the mechanical and optical properties of the 3.7 nm thick membranes are evaluated. Finally, a prototype condenser microphone is built and tested, and found to exhibit an enhanced specific response.

PD/BD/143031/2018 PTDC/EAM-PEC/29905/2017 PTDC/NAN-OPT/28430/2017 PTDC/NAN-OPT/28837/2017 UID/CTM/50025/2019 Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (2015/21455-1); Engineering and Physical SciencesResearch Council (EP/P02324X/1). Solar cells can strongly benefit from optical strategies capable of providing the desired broadband absorption of sunlight and consequent high conversion efficiency. While many diffractive light-trapping structures prove high absorption enhancements, their industrial application rather depends on simplicity concerning the integration to the solar cell concept and the process technology. Here, we show how simple grating lines can perform as well as advanced light-trapping designs. We use a shallow and periodic grating as the basic element of a quasi-random structure, which is highly suitable for industrial mass production. Its checkerboard arrangement breaks the mirror symmetry and is shown, for instance, to enhance the bulk current of a 1 µm slab of crystalline silicon by 125%. We explain its excellent performance by drawing a direct link between a structure's Fourier series and the implied photocurrent, derived from a large and diverse set of structures. Our design rule thus meets all relevant aspects of light-trapping for solar cells, clearing the way for simple, practical, and yet outstanding diffractive structures, with a potential impact beyond photonic applications. publishersversion published

A novel Photovoltaic-Electrochemical (PV-EC) integrated system is designed, capable of converting CO2 into carbon-based fuels, in which “smart” synergetic effects between the two technologies are explored, such as thermal coupling (TC) and electronic regulation (DC-DC), that can strongly improve the energetic performance. We show that, when thermally-coupled, the PV and EC cells exhibit a symbiotic behaviour: the solar-to-fuel efficiency stays almost temperature-independent due to improved reaction kinetics, which compensates for photovoltaic thermal losses. The electronic regulation is equally important, because it guarantees that all power provided by PV generation is channelled to the EC load. When conjugated with TC, the DC-DC converter can boost production up to 50% beyond the TC improvement. For operating temperatures in the 40–90 °C range, combined TC and DC-DC can boost production by up to 586% and 42.9% for Perovskite/Si double-junction and mono-crystalline Si solar cells, respectively. These solutions are tested in two PV-powered pathways for methane production: 1-step, CO2→CH4, and 2-step, CO2→Syngas→CH4; where in the latter the intermediate syngas is converted to methane through catalytic hydrogenation. Despite the advantageous simplicity of the direct production (1-step) of methane, the comparison between the two paths showed that the second route achieves close to 20% higher annual yield.

The authors also acknowledge funding from the European Commission through the projects 1D-NEON (H2020-NMP-2015, grant 685758-21D). The work was also partially funded by the Nanomark collaborative project between INCM (Imprensa Nacional-Casa da Moeda) and CENIMAT/i3N. P.A. Carvalho acknowledges support from the Research Council of Norway through grants 275752 and 197405/F50. The present study reports the production of upconverter nanostructures composed by a yttrium oxide host matrix co-doped with ytterbium and europium, i.e., Y2O3:Yb3+/Eu3+. These nanostructures were formed through the dissociation of yttrium, ytterbium and europium oxides using acetic, hydrochloric and nitric acids, followed by a fast hydrothermal method assisted by microwave irradiation and subsequent calcination process. Structural characterization has been carried out by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM) both coupled with energy dispersive X-ray spectroscopy (EDS). The acid used for dissociation of the primary oxides played a crucial role on the morphology of the nanostructures. The acetic-based nanostructures resulted in nanosheets in the micrometer range, with thickness of around 50 nm, while hydrochloric and nitric resulted in sphere-shaped nanostructures. The produced nanostructures revealed a homogeneous distribution of the doping elements. The thermal behaviour of the materials has been investigated with in situ X-Ray diffraction and differential scanning calorimetry (DSC) experiments. Moreover, the optical band gaps of all materials were determined from diffuse reflectance spectroscopy, and their photoluminescence behaviour has been accessed showing significant differences depending on the acid used, which can directly influence their upconversion performance. publishersversion published

ALTALUZ (Reference PTDC/CTM-ENE/5125/2014). SUPERSOLAR (PTDC/NAN-OPT/28430/2017. SFRH/BPD/115566/2016. SFRH/BPD/114833/2016. PD/BD/143031/2018. Optical solutions are promising for Perovskite solar cell (PSC) technology, not only to increase efficiency, but also to allow thinner absorber layers (higher flexibility) and improve stability. This work optimized the combined anti-reflection and scattering properties of two types of light trapping (LT) structures, based on TiO 2 semi-spheroidal geometries with honeycomb periodicity, for application in PSCs with substrate configuration and different perovskite layer thicknesses. Their optically lossless material (TiO 2 ) allows the structures to be patterned in the final processing steps, integrated in the cells’ top n contact, therefore not increasing the surface area of the PV layers and not degrading the electric performance via recombination. Therefore, this strategy circumvents the typical compromise of state-of-the-art LT approaches between optical improvements and electrical deterioration, which is particularly relevant for PSCs since their main recombination is caused by surface defects. When patterned on the cells’ front, the wave-optical micro-features composing the LT structures yield up to 21% and 27% photocurrent enhancement in PSCs with conventional (500 nm thick) and ultra-thin (250 nm) perovskite layers, respectively; which are improvements close to those predicted by theoretical Lambertian limits. In addition, such features are shown to provide an important encapsulation role, preventing the cells’ degradation from UV penetration. authorsversion published

In this work, zinc oxide (ZnO) and titanium dioxide (TiO2) nanostructures were grown on different cellulose paper substrates, namely, Whatman, office, and commercial hospital papers, using a hydrothermal method assisted by microwave irradiation. Pure ZnO and TiO2 nanostructures were synthesized; however, the growth of TiO2 above ZnO was also investigated to produce a uniform heterostructure. Continuous ZnO nanorod arrays were grown on Whatman and hospital papers; however, on office paper, the formation of nanoplates originating nanoflower structures could be observed. TiO2 nanoparticles homogeneously covered all the substrates, in some conditions forming uniform TiO2 films. Structural characterization was carried out by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The optical characterization of all the materials was carried out. The produced materials were investigated for multifunctional applications, like photocatalyst agents, bacterial inactivators, and ultraviolet (UV) sensors. To evaluate the photocatalytic activity under UV and solar radiations, rhodamine B was the model-test contaminant indicator and the best photocatalytic activity was achieved with Whatman paper. Hospital paper with TiO2 nanoparticles showed significant antibacterial properties against Staphylococcus aureus. ZnO-based UV sensors demonstrated a responsivity of 0.61 μA W-1.

Materials are addressed as possible enablers for solutions to many global societal challenges. A foresight exercise has been conducted to identify research paths to design, with a new approach, a generation of materials which can provide multi-functionalities. These material systems have been named “stem”, in analogy to living cells where a base of primitive units can be designed and assembled for self-reacting to external inputs. These materials will embed a concept of “internet in things”, where their processing capacity will enable the systems to interact with the environment and express diverse functionalities. Stem materials do not exist yet, but many clues from different theoretical and experimental results suggest they can be developed, and because living organisms exist. This article aims at launching this new approach and promoting the structuring of a multi-disciplinary community to fill the research gaps.

The optical and electrical properties of a nanostructured metal oxide have a great deal of dependence on their morphology. Therefore it is of great importance to fully understand how to control the growth and morphology of different metal oxide nanostructures, depending on the synthesis method used and the synthesis parameters (such as time, temperature, reactants, solvents, and additives). This chapter presents a review of the synthesis methods (top down and bottom up) used to produce nanostructured metal oxides as well as the studies performed to better understand how to control the morphology (and structure) of nanostructures.

Biowaste, derived from cooking-oven-produced carbon nanoparticles (WCP), are incorporated into polyaniline (PANI) via in-situ chemical oxidative polymerization to achieve excellent electrochemical properties for application in supercapacitors. The WCP-PANI composite electrodes have shown high-performance charge storage, due to combinatorial effect of electrical double layer capacitance from WCP and pseudocapacitance from PANI. With increase in the WCP percolation, work function of PANI is increased, which improves the charge-trapping capabilities of composites. For such distinct charge-trapping mechanism, areal capacitance of the composite microelectrode remains near-constant with increase in scan rate or current density. This indicates the suppression of diffusion limitations at higher scan rates to considerably enhance the rate capability. Also, with increasing polymerization time, strong interaction in this conjugated system greatly improves the charge-transfer reaction between PANI and WCP. The areal capacitance of the composite electrode is found to increase more than 600 times over pure PANI electrode. Moreover, energy-power performance of the microelectrode reveals almost 550% increment in the power density with a mere 1% decrement in energy density. Such rationally synthesized WCP-PANI composite electrodes using biowaste carbon nanomaterials, provide opportunities for the development of next-generation green-supercapacitors with improved energy storage performance. proof published

Over the last decades, zinc oxide nanostructures (NSs) have been studied due to outstanding chemical and physical properties, able to serve a plethora of applications. The growth of NSs on different substrates coated with ITO film allow their direct implementation in various micro-/nano-devices. The microwave-assisted hydrothermal method is a new hybrid approach used for synthesis of oxide NSs due to unique advantages in energy efficiency/high reaction rate and possibility of obtaining different morphologies with size and shape-controlled, which are relevant for some applications. In this paper, we present a simple one step synthesis of ZnO 1D and 2D NSs with homogeneous distribution and orientation perpendicular to substrates covered with ITO film, using a microwave-assisted hydrothermal method. The effect of seed layer treatment on the structure, morphology and optical properties of the obtained NSs have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV/VIS/NIR and photoluminescence spectroscopy. The obtained ZnO NSs with 1D and 2D morphologies show high visible transmittance between 80–90 % and band gap energy values between 3.27 and 3.22 eV. The I-V curves and photoluminescence spectra indicate good ohmic contacts on both sides (ITO and Au-top electrodes) and highlight the effect of the thermal treatment of seed layer on the photoluminescence emission and electrical conductivity of the obtained NSs.

This work reports on the role of structure and composition on the determination of the performances of p-type SnOx TFTs with a bottom gate configuration deposited by rf magnetron sputtering at room temperature, followed by a post-annealed step up to 200 &deg, C at different oxygen partial pressures (Opp) between 0% and 20% but where the p-type conduction was only observed between in a narrow window, from 2.8% to 3.8%. The role of structure and composition were evaluated by XRD and M&ouml, ssbauer spectroscopic studies that allows to identify the best phases/compositions and thicknesses (around 12 nm) to be used to produce p-type TFTs with saturation mobility of 4.6 cm2 V&minus, 1 s&minus, 1 and on-off ratio above 7 &times, 104, operating at the enhancement mode with a saturation voltage of &minus, 10 V. Moreover, a brief overview is also presented concerning the present state of the existing developments in processing SnOx TFTs with different methods and using different device configurations.

Many diseases have their treatment options narrowed and end up being fatal if detected during later stages. As a consequence, point-of-care devices have an increasing importance for routine screening applications in the health sector due to their portability, fast analyses and decreased cost. For that purpose, a multifunctional chip was developed and tested using gold nanoprobes to perform RNA optical detection inside a microfluidic chip without the need of molecular amplification steps. As a proof-of-concept, this device was used for the rapid detection of chronic myeloid leukemia, a hemato-oncological disease that would benefit from early stage diagnostics and screening tests. The chip passively mixed target RNA from samples, gold nanoprobes and saline solution to infer a result from their final colorimetric properties. An optical fiber network was used to evaluate its transmitted spectra inside the chip. Trials provided accurate output results within 3 min, yielding signal-to-noise ratios up to 9 dB. When compared to actual state-of-art screening techniques of chronic myeloid leukemia, these results were, at microscale, at least 10 times faster than the reported detection methods for chronic myeloid leukemia. Concerning point-of-care applications, this work paves the way for other new and more complex versions of optical based genosensors. Funding Agencies|FEDER funds through the COMPETE Programme; FCT - Portuguese Foundation for Science and Technology [POCI-01-0145-FEDER-007688, UID/CTM/50025/2013]; project DISERTOX [PTDC/CTM-NAN/2912/2014]; Unidade de Ciencias Biomoleculares Aplicadas - UCIBIO - FCT/MCTES [UID/Multi/04378/2013]; ERDF [POCI-01-0145-FEDER-007728, PD/BD/52211/2013]

To address the challenges of the next generation of smart windows for energy-efficient buildings, new electrochromic devices (ECDs) are introduced. These include indium molybdenum oxide (IMO), a conducting oxide transparent in the near-infrared (NIR) region, and a NIR-emitting electrolyte. The novel electrolytes are based on a sol-gel-derived di-urethane cross-linked siloxane-based host structure, including short chains of poly (&epsilon, caprolactone) (PCL(530) (where 530 represents the average molecular weight in g mol&minus, 1). This hybrid framework was doped with a combination of either, lithium triflate (LiTrif) and erbium triflate (ErTrif3), or LiTrif and bisaquatris (thenoyltrifluoroacetonate) erbium (III) ([Er(tta)3(H2O)2]). The ECD@LiTrif-[Er(tta)3(H2O)2] device presents a typical Er3+ NIR emission around 1550 nm. The figures of merit of these devices are high cycling stability, good reversibility, and unusually high coloration efficiency (CE = &Delta, OD/&Delta, Q, where Q is the inserted/de-inserted charge density). CE values of &minus, 8824/+6569 cm2 C&minus, 1 and &minus, 8243/+5200 cm2 C&minus, 1 were achieved at 555 nm on the 400th cycle, for ECD@LiTrif-ErTrif3 and ECD@LiTrif-[Er(tta)3(H2O)2], respectively.