Over 100 mV VOC Improvement for Rear Passivated ACIGS Ultra-Thin Solar Cells

A decentralized energy system requires photovoltaic solutions to meet new aesthetic paradigms, such as lightness, flexibility, and new form factors. Notwithstanding, the materials shortage in the Green Transition is a concern gaining momentum due to their foreseen continuous demand. A fruitful strategy to shrink the absorber thickness, meeting aesthetic and shortage materials consumption targets, arises from interface passivation. However, a deep understanding of passivated systems is required to close the efficiency gap between ultra-thin and thin film devices, and to mono-Si. Herein, a (Ag,Cu)(In,Ga)Se₂ ultra-thin solar cell, with 92% passivated rear interface area, is compared with a conventional nonpassivated counterpart. A thin MoSe₂ layer, for a quasi-ohmic contact, is present in the two architectures at the contacts, despite the passivated device narrow line scheme. The devices present striking differences in charge carrier dynamics. Electrical and optoelectronic analysis combined with SCAPS modelling suggest a lower recombination rate for the passivated device, through a reduction on the rear surface recombination velocity and overall defects, comparing with the reference solar cell. The new architecture allows for a 2% efficiency improvement on a 640 nm ultra-thin device, from 11% to 13%, stemming from an open circuit voltage increase of 108 mV.     

A VLF to UHF Propagation Model for Evaluation of High-Speed Railway Electromagnetic Interference in RF Monitoring Base-Stations

Considering that recent european high-speed railway system has a traction power system of $2\times 25$  kV 50 Hz, which causes electromagnetic emission for the outside world, it is important to dimension the railway system emissions, using a frequency/distance dependent propagation model. This paper presents an enhanced theoretical model for VLF to UHF propagation, railway system oriented. It introduces the near field approach (crucial in low frequency propagation) and also considers the source characteristics and type of measuring antenna. Simulations are presented, and comparisons are set with earlier far field models. Using the developed model, a real case study was performed in partnership with Refer Telecom (portuguese telecom operator for railways). The new propagation model was used in order to predict the future high-speed railway electromagnetic emissions in the Lisbon north track. The results show the model’s prediction capabilities and also its applicability to realistic scenarios.     

Losses produced by soiling in the incoming radiation to photovoltaic modules

The accumulation of dust on the surface of a photovoltaic module decreases the radiation reaching the solar cell and produces losses in the generated power. Dust not only reduces the incoming radiation on the solar cell but also changes the dependence on the angle of incidence of such radiation. This work presents the results of a study carried out at the University of Malaga to quantify radiation losses caused by soiling on the surface of photovoltaic modules. Our results show that the mean of the daily irradiation losses in a year caused by dust deposited on the surface of a photovoltaic module is around 4%. After long periods without rain, daily irradiation losses can be higher than 20%. In addition, the irradiance losses are not constant throughout the day, and they are strongly dependent on the angle of incidence and the ratio between diffuse and direct radiations. The irradiance losses as a function of solar time are symmetric with respect to noon, where they reach the minimum value. We also propose a simple theoretical model that describes the qualitative behaviour of the irradiance losses during the day. This model takes into account the percentage of dirty surface and the diffuse/direct irradiance ratio. Copyright © 2012 John Wiley & Sons, Ltd.     

Responsive on-line gateway load-balancing for wireless mesh networks

We propose an adaptive online load-balancing protocol for multi-gateway Wireless Mesh Networks (WMNs) which, based on the current network conditions, balances load between gateways. Traffic is balanced at the TCP flow level and, as a result, the aggregate throughput, average flow throughput and fairness of flows improves. The proposed scheme (referred to as Gateway Load-Balancing, GWLB) is highly responsive, thanks to fast gateway selection and the fact that current traffic conditions are maintained up-to-date at all times without any overhead. It also effectively takes into account intra-flow and inter-flow interference when switching flows between gateway domains. We have found the performance achievable by routes used after gateway selection to be very close to the performance of optimal routes found by solving a MINLP formulation under the protocol model of interference. Through simulations, we analyze performance and compare with a number of proposed strategies, showing that GWLB outperforms them. In particular, we have observed average flow throughput gains of 128% over the nearest gateway strategy.     

Performance of Fade Mitigation Techniques in a Fixed 48 GHz HAPS Network

The 48 GHz band has been allocated world-wide for fixed service with HAPS. High-capacity broadband access networks can be implemented in this band. The main drawback is the troposphere effects on the propagation, particularly rain attenuation, that may limit the link availability. In this paper, the performance of HAPS-ground links working in this band is analysed by means of simulation. Experimental slant-path propagation data, gathered at 49.5 GHz, are used in the simulations, so that attenuation levels and their temporal evolution may be considered realistic. The simulated system is defined in ITU-R Rec. F-1500. Only urban coverage links are simulated, as the propagation data correspond to a 40° elevation link. The use of Fade Mitigation Techniques (FMT) is shown to be useful to improve the link performance. The improvement is evaluated for two different FMTs: Power control and adaptive coding. Results are presented regarding link availability and other parameters related to the particular FMT, as well as outage dynamics.     

Pyrite decomposition in fresh Blacksville No. 2 coal: Effect of additives

The Mössbauer effect has been used to study, under liquefaction conditions, the effect of additives (S, FeS₂, Fe₇S₈ and Fe) on the transformation of pyrite in fresh Blacksville No. 2 coal. It was observed that the addition of iron sulphides enhanced the conversion of the inherent pyrite in coal, an effect attributed to a combined cracking activity of the pyrrhotites and H₂S on the less reactive organic covering of some of the inherent coal pyrite. The addition of sulphur produced a higher partial pressure of H₂S; total conversion of pyrite to pyrrhotite was not observed. The stoichiometry of the pyrrhotites present in the residue of the experiment with sulphur showed a smaller atomic percentage of iron than in the experiment without additives, this change in stoichiometry being attributed to the higher partial pressure of H₂S in the reactor. When metallic iron was added, the partial pressure of H₂S in the reactor decreased (iron acts as a scavenger) and troilite was also formed.     

Thermodynamic studies of phosphate adsorption on Pt(1 1 1) electrode surfaces in perchloric acid solutions

The thermodynamics of the so-called perfectly polarizable electrode was employed to analyze the total charge densities for a nearly defect-free Pt(1 1 1) electrode in a series of NaH₂PO₄ solutions with an excess of inert electrolyte (0.1 M HClO₄) at constant ionic strength and pH. Thermodynamic analysis using both electrode potential and charge density as independent electrical variables is described. The Gibbs excess, Gibbs energy of adsorption and charge numbers both at constant electrode potential and constant chemical potential for anion adsorption at the Pt(1 1 1) surface have been determined. The calculated electrosorption valencies and charge numbers at constant chemical potential are close to two electrons per adsorbed anion, suggesting that in the absence of co-adsorbed species, HPO₄²⁻ is the predominant adsorbed species. The maximum Gibbs excess of adsorbed hydrogenphosphate attains a value of ≈3.2 × 10¹⁴ ions cm⁻² which corresponds to a coverage of ≈0.22 ML.     

Poly(vinyl chloride) and wood flour press mould composites: New bonding strategies

In this work, different strategies for improving the association between hydrophilic wood flour surfaces and poly(vinyl chloride) (PVC) hydrophobic surfaces were tested. Three new coupling agents, based on living radical polymerisation (LRP), involving PVC were synthesised and tested in formulations with PVC and wood flour. The melt mixing behaviour was analysed in terms of the torque exerted by the mixing blades and related to the structural properties of the mixture. These products were ground and sheets were produced by press moulding. The composites were characterised by dynamic mechanical analysis. It was found that the use of a new block copolymer poly(vinyl chloride)‐b‐poly(hydroxypropyl acrylate)‐b‐poly(vinyl chloride), prepared by LRP, increases the elastic modulus of the composite, under controlled conditions, involving the use of specific amounts of the copolymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Cleaner water using bimetallic nanoparticle catalysts

Groundwater contaminated by hazardous chlorinated compounds, especially chlorinated ethenes, continues to be a significant environmental problem in industrialized nations. The conventional treatment methods of activated carbon adsorption and air‐stripping successfully remove these compounds by way of transferring them from the water phase into the solid or gas phase. Catalysis is a promising approach to remove chlorinated compounds completely from the environment, by converting them into safer, non‐chlorinated compounds. Palladium‐based materials have been shown to be very effective as hydrodechlorination catalysts for the removal of chlorinated ethenes and other related compounds. However, relatively low catalytic activity and a propensity for deactivation are significant issues that prevent their widespread use in groundwater remediation. Palladium‐on‐gold bimetallic nanoparticles, in contrast, were recently discovered to exhibit superior catalyst activity and improved deactivation resistance. This new type of material is a significant next‐step in the development of a viable hydrodechlorination catalysis technology. Copyright © 2008 Society of Chemical Industry