Search

Renewable energies are increasingly playing an important role in the world's energy supply. Society demands new solutions to solve environmental issues caused by fossil fuels. The importance of photovoltaic technology has been increasing and consequently, the necessity to have more accurate models to characterise the performance of solar cells during their entire lifetime has rose as well. Performance problems may appear during devices' lifetimes associated with factors, such as weather conditions or faulty installation. Cracking might occur, leading to abrupt reductions on the produced power, quite difficult and expensive to fix. The I–V curves of a defected or cracked solar cell might not have the shape imposed by the usual models as 1M5P. In this article, cracked c-Si solar cells are modelled using a novel model: d1MxP. This model is based on the discretisation of the diode's response on models as 1M5P. Instead of imposing a shape and compute some parameters to fit it on experimental data, the proposed model connects every two points. The results suggest a better fit using the proposed model in comparison with the 1M5P, not only in the original curves, but also modelling cracked cells. As consequence of a better fitting, the computation of important figures of merit as maximum power point or fill factor, reveals to be more precise. It is concluded that the proposed model might characterise the performance of a solar cell, even cracked, which is a huge advance aiming the possibility of simulating complex problems during the cells' operation lifetime. [ABSTRACT FROM AUTHOR]

[Display omitted] • A flexible thermoelectric device converting heat into electrical energy was performed. • Materials selection improve drastically the composites thermoelectrical properties. • Thermoelectric power factor and figure-of-merit increases up to 9 orders of magnitude. • Printable p-n thermocouples generate nW of power and charge a capacitor with 5 V. Flexible and easy processing lightweight thermoelectric materials for energy harvesting applications have shown an increasing interest. Thermoplastic polyvinylidene fluoride (PVDF) and elastomer styrene-ethylene/butylene-styrene (SEBS) polymers reinforced with thermoelectric ceramics, including bismuth sulfide (Bi 2 S 3), bismuth telluride (Bi 2 Te 3) and antimony telluride (Sb 2 Te 3), and electrically conductive carbon nanotubes (CNT) have been developed, tailoring their thermal and electrical properties for thermoelectric device applications. The Seebeck coefficient of the composites increases with thermoelectric ceramic filler content for semicrystalline PVDF composites, slightly decreasing for amorphous SEBS composite. Thermoelectric power factor and figure-of-merit in the polymer composites increases up to 9 orders of magnitude with respect to the pristine polymer, up to a maximum value of 10−3 µW/(m·K2) and 10−6, respectively, for the PVDF/CNT/Bi 2 Te 3 composite. A device composed by 2 printable p-n thermocouples based on PVDF/50Bi 2 S 3 and PVDF/50Bi 2 Te 3 can generate power in the order of the nW and charge a capacitor with 5 V. Theoretical modeling allows to evaluate different thermoelectric configurations, the effect of the number of thermocouples and the influence of the temperature gradient on device performance. [ABSTRACT FROM AUTHOR]

Flexible and stretchable materials are increasingly being investigated for future technological platforms, polymer based materials being the most suitable candidates for those emerging technologies. This work reports on polymer based scintillator composites based on the thermoplastic elastomer Styrene-Ethylene/Butadiene-Styrene (SEBS) and Gd 2 O 3 :Eu 3+ scintillator nanoparticles, to form a polymer-based flexible and stretchable material for X-ray indirect detectors. Further, visible light yield under X-ray irradiation was improved by the inclusion of 2,5 dipheniloxazol (PPO) and (1,4-bis (2-(5-phenioxazolil))-benzol (POPOP) within the polymer matrix. Together with high levels of stretchability, with deformations up to 100%, the films exhibit suitable performance with low mechanical hysteresis (less than 1.5 MJ/m 3 for cycles up to 100% of strain) and reproducibly such as a scintillator material for the conversion of X-ray radiation into visible radiation. The decrease of just ∼13% of the X-ray radiation into visible light upon stretching up to 100% is attributed to a reduction of the effective filler concentration and proves the suitability of the developed materials for large area and stretchable X-ray radiation detectors. [ABSTRACT FROM AUTHOR]

A novel approach for tissue engineering applications based on the use of magnetoelectric materials is presented. This work proves that magnetoelectric Terfenol-D/poly(vinylidene fluoride-co-trifluoroethylene) composites are able to provide mechanical and electrical stimuli to MC3T3-E1 pre-osteoblast cells and that those stimuli can be remotely triggered by an applied magnetic field. Cell proliferation is enhanced up to ≈25% when cells are cultured under mechanical (up to 110 ppm) and electrical stimulation (up to 0.115 mV), showing that magnetoelectric cell stimulation is a novel and suitable approach for tissue engineering allowing magnetic, mechanical and electrical stimuli. [ABSTRACT FROM AUTHOR]

Nowadays, optical systems play an important role in communications. Dual depletion PIN photodiodes are common devices that can operate in different optical bands, depending on the chosen semiconductors. However, since semiconductor properties vary with the surrounding conditions, some optical devices/systems can act as sensors. In this research work, a numerical model is implemented to analyze the frequency response of this kind of structure. It considers both transit time and capacitive effects, and can be applied to compute photodiode frequency response under nonuniform illumination. The InP-In 0.53 Ga 0.47 As photodiode is usually used to convert optical into electrical power at wavelengths around 1300 nm (O-band). This model is implemented considering an input frequency variation of up to 100 GHz. The focus of this research work was essentially the determination of the device's bandwidth from the computed spectra. This was performed at three different temperatures: 275 K, 300 K, and 325 K. The aim of this research work was to analyze if a InP-In 0.53 Ga 0.47 As photodiode can act as a temperature sensor, to detect temperature variations. Furthermore, the device dimensions were optimized, to obtain a temperature sensor. The optimized device, for a 6 V applied voltage and an active area of 500 μ m 2 , had a total length of 2.536 μ m , in which 53.95% corresponded to the absorption region. In these conditions, if the temperature increases 25 K from the room temperature, one should expect a bandwidth increase of 8.374 GHz, and if it decreases 25 K from that reference, the bandwidth should reduce by 3.620 GHz. This temperature sensor could be incorporated in common InP photonic integrated circuits, which are commonly used in telecommunications. [ABSTRACT FROM AUTHOR]

Solar cell equivalent circuit modelling is usually based on continuous I-V models, with a set of data obtained by analytical expressions. This work proposes an almost discrete novel mathematical method and correspondent electrical model, based on the I-V curve adjustment at every two adjacent points. It is based on the discretisation of any diode model behaviour, such as the 1M5P (also known as 1D5P) or the 1M7P (also known as 2D7P). For this reason, the model is named d1MxP, meaning that it is a discrete (d) model (1M) with x parameters (xP). The modelling methodology validation process uses experimental data already published in the literature. According to the presented results, the proposed method shows increased accuracy when compared to the 1M5P or 1M7P equivalent models. The accuracy on the maximum power point and fill factor determination is relevant, resulting in an improvement of up to 3.34% in the maximum power, up to 5.70% in its voltage and up to 8.20% in its current, for the analysed data. Furthermore, Fill Factor values, have variation from up to 35.98%. The temperature influence on the silicon solar cell is also analysed, to validate the results. The proposed method allows highly accurate curve fitting to the (experimental) points and consequently, to obtain a more accurate model to analyse the performance of solar cells under different conditions. [ABSTRACT FROM AUTHOR]

Environmentally-friendly materials are being pursued world-wide for applications across a wide range of technologies. For application in spray-printed radiation detectors, water-based scintillator inks have been produced by combining a thermoplastic elastomer poly (vinyl) alcohol (PVA) and Gd 2 O 3 :Eu 3+ scintillator nanoparticles. Formulations of these green inks with different concentrations of scintillator nanoparticles have been assessed in terms of their rheological properties: the optimal concentration of scintillator nanoparticles in the water-based ink for spray-printing was 0.75 wt%. This optimized ink formulation exhibits Newtonian behavior with a viscosity around 100 cps and performance characteristics suitable for spray-printing scintillators for indirect X-ray detectors. [ABSTRACT FROM AUTHOR]

The energy harvesting efficiency of poly(vinylidene fluoride–trifluoroethylene) spin coated films and its nanocomposites with piezoelectric BaTiO 3 have been investigated as a function of ceramic filler size and content. It is found that the best energy harvesting performance of ∼0.28 μW is obtained for the nanocomposite samples with 20% filler content of 10 nm size particles and for 5% filler content for the 100 and 500 nm size fillers. For the larger filler average sizes, the power decreases for filler contents above 5% due to increase of the mechanical stiffness of the samples. Due to the similar dielectric characteristics of the samples, the performance is mainly governed by the mechanical response. The obtained power values, easy processing and the low cost and robustness of the polymer, allow the implementation of the material for micro and nanogenerator applications. [ABSTRACT FROM AUTHOR]

Polymer based smart materials and, in particular, piezoresistive ones, are increasingly being used in a wide variety of applications ranging from automotive components to medical devices. This work reports on water-based piezoresistive polymer composites developed from thermoplastic poly (vinyl alcohol) (PVA) filled with carbon nanotubes (MWCNT) for the fabrication of high performance piezoresistive materials and sensors. PVA is a water-soluble synthetic polymer with suitable mechanical properties for the development of large strain sensors. MWCNT/PVA nanocomposites with good linearity between deformation and electrical resistance variation and with gauge factors up to 3 were achieved. Further, the materials were formulated in the form of inks for spray and screen printing of the sensors, which demonstrated a good performance for strain sensing both under laboratory tests conditions and when connected to a readout and communication system. Therefore, polymer based piezoresistive sensors were developed by a green approach and capable to be implemented by scalable printing technologies. [ABSTRACT FROM AUTHOR]

Polymer based scintillator composites have been produced by combining poly(vinylidene fluoride), PVDF, and Gd 2 O 3 :Eu 3+ scintillator nanoparticles. Additionally, 2,5 dipheniloxazol (PPO) and (1,4-bis (2-(5-phenioxazolil))-benzol (POPOP) were introduced in the polymer matrix in order to improve visible light yield under x-ray irradiation. It is shown that addition of PPO and POPOP has no influence on the polymer structure, increases dielectric constant from ∼7 to ∼14, which is suitable for improving energy resolution, and increases in 40% the overall transduction performance of the composite without sacrificing its homogeneity and transparency. Thus, the developed Gd 2 O 3 :Eu 3+ /PPO/POPOP/PVDF composites are appropriate for large area X-ray radiation detectors. [ABSTRACT FROM AUTHOR]