Advanced materials and technologies for renewable energies - AMREN-2 (5 May 2016)

Resume : Recent years witnessed rapid cost reduction of photovoltaic (PV) technologies through innovation and volume production. The global production capacity for PV vastly exceeded market size. This period is ending, today premium PV modules are starting to be in short supply, prices are stable or even rising. This talk will discuss these developments, focussing on PV technologies expected to dominate the market. Crystalline silicon-based technologies will continue to have the largest market share. A whole portfolio of new c-Si technologies is available, allowing cell efficiencies in the 20-25% range to become mainstream, based on the use of n-Si single-crystal wafers. These include PERC-type cells with good backside passivation, hetero-junction cells combining c-Si with a-Si thin film technology, and other advanced cell concepts. Drivers of the cost curve presently are PV cells based on cast-Si with efficiencies in the 16-18% range. The use of high-perfomance, small-grain multi-Si and introduction of upgraded metallurgical Si allows further cost reductions. Highest efficiencies are possible in multijunction technology, the current world record stands at 46% for highly-concentrated systems. Currently, there is no major player in the market offering this PV technology on a cost-competitive scale. Thin-film technologies face the challenge to compete with the drastic cost-reductions of c-Si PV technology. Perovskite-based PV technology is interesting as additional layer on c-Si cells, allowing to capture high-energy photons, to develop c-Si cell efficiencies towards the 30% range.

Resume : Concentrated solar power (CSP) technologies have reached a viable economical and technical state and have been utilized worldwide for large and very large-scale applications including electric power generation and industrial heat. The dominant types of CSP systems currently in use are the parabolic trough (PT) and central receiver tower (CRT) systems. It is note worthy that CRT plants became more attractive due the high potential of further improvement of performance and operation at high temperatures (>1000 oC). The major components of CRT systems are solar field (consists of large number of mirrors tracking the sun and reflecting solar radiation on a central receiver), the receiver, and the power block. Tremendous and continuous research and technology development (R&TD) effort have been devoted to further improve the performance of all components of the CRT system. Among the issues considered for improving performance of the CRT plant are reduction of the environmental impact of the CRT operation, reduction of both initial and maintenance & operation costs, and increasing overall system’s efficiency. The focuses of such R&DT efforts have several aspects including innovations related to designs and structures of all subsystem components in addition to material’s characteristics and utilization. Development of new materials and compositions is an essential goal of the effort. This presentation reviews briefly the material’s aspects of the recent advances of all components of the CRT power plants. The contribution of the RTD work carried out within EUROSUNMED project will be also summarized.

Resume : Thermal energy storage has gained a momentum in recent years in the renewable energy field. The ceramic materials and molten salts are the current solutions to manage the intermittent nature of the renewable energy sources. The ceramic materials present a number of advantages such as thermal stability and easy use in the form of bricks. However, the ceramic materials present a lower thermal capacity than the molten salts. The purpose of this research was to improve the thermal capacity of clay ceramics using biochar resulting from thermo-chemical conversion of biomass. The materials were heated under a nitrogen atmosphere to prevent the biochar from the decomposition in the clay structure. The results showed a 91%wt conservation of the biochar after a firing up to 1100°C. The thermal capacity of the materials experiencing a 15%wt addition of biochar was improved by 12% after the firing. On the other hand, the mechanical strength was maintained due to the small particles of biochar. In fact, the mechanical strength and the thermal capacity were estimated at 11.13MPa and 1.49kJ/kg.K for a 30%wt addition. The materials have shown an efficiency comparable to that of the molten salts for thermal energy storage with an easier use as bricks. The 120kg amount of materials to cover the requirements of a low-energy house might also lead one to expect a domestic use. The valorization of biochar in thermal energy storage seems to be a promising prospect and should

Resume : Photo electrochemistry, PEC, processes have at these last years attracted large attention as an effective procedure for convert solar photon energy to chemical one. Routes for reaching efficiency higher than 10-12% of efficiency have been promoted for having a technological via more efficient that the photovoltaic conversion plus alkaline electrolyzer only in one direct step. PEC units can produce different solar fuels such as hydrogen, formic acid, methanol, methane or syngas depending on the selected catalyst and the used feed stocks of H2O and CO2. It is always produced with an improved energy balance compared with dark electro catalysis processes. Moreover, it shows a high throughput depending on the used photons absorbed material as well as on the capacity for charge separation and effective role of the used catalyst for cathode and anode electrodes. Different metal oxides with band gap in the solar spectra region without having corrosion produced by the electrolytes have been proposed as electrode materials. On the other hand, the use of more conventional photovoltaic semiconductor absorbers like Silicon, CIS, III-V,… need coating layer as protection at the same time that they must be functional compatible with the PEC processes. In this contribution, different earth abundant materials as electrode will be reviewed; examples will be presented and the potential use of feed stocks, H2 and CO2, will be discussed considering costs, life time and high yield in the solar fuel production. Special attention will be paid in the application of initially photovoltaic absorber materials like silicon, kesterite or CIS combined with protective and photo catalytic active metal oxide layers in order to scale up PEC systems in order to achieve solar refinery yields.

Resume : Since 2000 grid-connected solar photovoltaic systems have increased their world-wide cumulative capacity by three orders of magnitude to exceed 225 GW at the end of 2015. A further doubling is forecast for the next three years until the end of 2018. The question no longer is if the technology is capable to deliver, but at what prices solar photovoltaic systems can deliver electricity to the different customers. The costs of electric energy at the output of a PV module have dropped to less than 0.03 EUR/kWh (DC electricity), making it currently the lowest cost new technology for electricity generation. However, depending on the application and location, a significant cost component is added to get the power from the module to where and when it is needed. Therefore, new, innovative and cost effective overall electricity system solutions for the availability and delivery of PV electricity are essential to realise the vision of PV as a major electricity source worldwide. The massive cost reductions have been made possible by a combination of research and technology progress, manufacturing improvements and professionalization as well as market expansions. Despite the fact that the hardware costs of a PV system are more or less the same worldwide, the actual CAPEX and system prices seen in local markets can differ significantly. The main reasons for these price differences are non-technical like licensing, permitting, regulatory and financing costs, which add significant parts to the levelised costs of electricity from PV systems.

Resume : The thin film technology is taking market share from the dominant silicon wafer technology. Material, manufacturing time, and weight savings are driving the increase in thin-film cells. Among them Cu(In,Ga)Se2 based solar cells are well positioned in the field of PV technologies with present record efficiencies for small cells of 22.3 % and for production size modules of 16.5 % (www.cigs-pv.net). The preparation of a thin film solar cell is a multistage process where every step affects the resulting cell performance and the production cost. The present review discusses the concept and operation principle of thin film solar cells. Special emphasis is given for solar cells using Cu(In,Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTS) absorbers. Progress made in the field of CIGS and CZTS solar cell in recent years will be reviewed and details will be given about the advantages and limitations of these technologies.

Resume : Photovoltaic technology has made great progress during the recent years. The cost of PV systems had been decreased dramatically and today the cost of PV electricity produced in Germany is well below 10 €cent per kWh. The PV cost decrease was triggered by large volume manufacturing and improvements on technology level. The paper will address the latter aspect. Higher efficient Si solar cells had been developed using new cell architectures and improved materials. So far, the highest efficiency of 46.2 % was achieved with a multi-junction concentrator solar cell based on III-V semiconductor material. In order to achieve such a high efficiency, the selection and growth of the III-V materials is key.

Resume : First, we will highlight the unique features of the pulsed-laser deposition (PLD) technique and its latitude for the synthesis of nanomaterials and nanohybrid (NH) structures. Secondly, we will demonstrates the ability of the PLD technique to deposit high crystalline quality PbS nanoparticles (NPs) onto various substrates with the latitude to tailor their size, and hence their photoluminescence emission over the (850-1650) nm range.1 Finally, we will show that the PLD is very appropriate for the straightforward synthesis of nanohybrid materials consisting of 1D-nanostructures (SWCNTs or TiO2-NRs) controllably decorated with PbS-NPs. This will be illustrated through two examples, namely (i) the achievement of SWCNT/PbS-NPs nanohybrids based photoconductive (PC) devices exhibiting very high photoresponses (~700 % and ~1400 % at 633 and 405 nm, respectively),2 and (ii) the PLD decoration of TiO2–NRs/SWCNTs nanostructures by PbS-NPs for the fabrication of nano-heterojunction PV devices of which PCE was as high as 5.3%.3 The highly efficient charge transfer between PbS-NPs and SWCNTs is thought to be a key factor for the remarkable PC/PV properties of these PLD synthesized nanohybrid materials, where the occurrence of multi-exciton generation (MEG) has been recently pointed out.4 REFERENCES: [1] I. ka, D. Ma and M. A. El Khakani, J. Nanopart. Res., 13 (2011) 2269. [2] I. Ka, V. Le Borgne, D. Ma, and M. A. El Khakani, Adv. Mater., 24 (2012) 6289. [3] I. Ka, B. Gonfa,

Resume : The increasing energy demand in real life imposes a thoughtful research on alternative energy sources to fossil fuels. Solar thermal power plants use the sun’s energy to generate electricity on an industrial scale by concentrating the solar radiation and converting all this heat to power as in a conventional power plant. The polymer-derived ceramic route has been used to develop new silicon-based ceramic materials as possible candidates for high temperature solar volumetric receivers. Several synthetic strategies have been followed to optimize the solar absortance and chemical stability under different environments, the most promising ones consisting on the design of nanocomposites reinforced with carbide and nitride derivatives, either added as nanoparticle or grown in-situ. The absorptance strongly depends upon the chemical composition of the material but also it is strongly influenced by its porous properties. In this sense, the porosity of the material has been also tuned for a high volumetric behavior and high absorptance. Thermal shock is one of the most problematic issues concerning the actual receivers so, he have carried out thermal shock experiments either under concentrated solar radiation or simulations in an electrical furnace. The degradability of the materials was stressed out in terms of their absorptance loss and structure modification.

Resume : Energy storage possesses an important role in order to rationalize the use of both fossil and renewable energy sources. Scientists are looking for inexpensive and green energy storage systems. The development of sodium ion batteries is moving at a much faster rate and its use in the market is expected to be in near future. Very promising results have been reported in the recent past showing the performances of the sodium ion batteries very competitive for stationary energy storage [1, 2]. Energy density values of 210 Wh/kg can be obtained by using some specific electrode materials with an average cell potential of 3.3 V. A great range of compounds is being studied as possible cathode materials for Na-ion batteries. Some layered oxides, in particular Nax[FexMn1-x]O2 (where 0≤x≤1) , show high reversible capacities ( ~ 200 mA h/g), high specific energies (~ 600 mW h/g), high-rate capability and easy scale up [3]. Polyanionic materials such as phosphates Na[FexMn1-x]PO4 ,with olivine structure, and fluorophosphates Na3V2O2x(PO4)2F3-2x (0≤x≤1) show also high voltage, good thermal stability and cyclability. The sodium site occupancy and mobility are exchangeable and fluent, providing excellent properties for a cathode in a sodium-ion battery. Regarding the negative electrode, unlike the lithium ion batteries, the inability of sodium to insert into graphite is promoting the use of hard carbons, titanates, organic materials and sodium alloys composites as anode electrodes. In this talk we will present a general overview of the most interesting materials for Na-ion batteries and the relationship between the structure and the electrochemical properties of these compounds. References: [1] V. Palomares, P. Serras, I. Villaluenga, K. B. Hueso, J. Carretero-González, T. Rojo. Na-ion batteries, recent advances and present challenges to become low cost energy storage systems. Energy Environ. Sci. 2012, 5, 5884-5901. [2] V. Palomares, M. Casas-Cabanas, E. Castillo-Martinez, Man H. Han, T. Rojo. Update on Na-Based Battery Materials. A Growing Research Path. Energy Environ. Sci. 6,2312-2337(2013). [3] M. Houn Man, E.Gonzalo, G.Singh and T.Rojo. A comprehensive review of sodium layered oxides: powerful cathodes for Na-ion batteries. Energy Environ. Sci. 8, 81-102 (2015).

Resume : Perovskite-type oxides, half-Heusler compounds as well as their nanocomposites are prospective candidates for future solar energy conversion processes. New tailor-made compounds can enable radically better future energy technologies or improve existing devices. Herein we present our latest progress of various multifunctional materials and their implementation into solar radiation converters. The relation between sample preparation methods, microstructure, and properties are studied to design high efficiency materials. Their good performance can be explained based on e.g. their suitable band structures, adjusted charge carrier density, effective mass and - mobility, hindered phonon transport, electron filtering potentials, and strongly correlated electronic systems. These properties are tuneable by changing the composition, structure, crystallites size, interfaces and materials combinations with scalable synthesis procedures. The resulting improved materials are characterised and tested in (photo) electrocatalytic and thermoelectric conversion processes. The goal is to finally utilize the investigated materials to convert solar energy into electricity or fuels.

Resume : Overview In 2013, ASEAN accounted for about 8.5% of the world population, consumed about 4.5% of world´s primary energy, while being accountable for a remarkable 5.7% of total global energy production. As the region´s economies are steadily expanding and its main energy indicators are below global averages, demand is expected to outstrip supply unless strong measures are taken to manage the growth. This inevitably creates the challenge on energy security and sustainable development. In this context the 4th ASEAN Energy Outlook (AEO4) has been conducted and it not only aims to provide policy makers with an understanding of the energy trends and challenges being faced by the region up to the year 2035, but also to strongly involve all ASEAN Member States (AMS) in the process. The AEO4 is complementing the implementation of the ASEAN Plan of Action for Energy Cooperation (APAEC) 2016-2025, thereby deriving strategies within ASEAN to address future energy needs. The results show that in 2035, following the Business as Usual scenario, ASEAN is expected to require more than 2.7 times of its current energy to meet the targeted economic growth. Yet, the GDP increases by the factor of 3.7 indicating future energy intensity reduction. This growth indicates several challenges which have to be addressed by the energy sector also to address the new APAEC targets. Energy demand is increasing constantly in the ASEAN region. On the one hand, the demand in the electric

Resume : Layered cobalt oxide Ca3Co4O9 (CCO349) thermoelectric (TE) thin films were deposited on SrTiO3 (111) substrate by radiofrequency magnetron sputtering followed by post annealing in varying oxygen partial pressure. It was found that the as-deposited film (CaxCoO2) could transform to CCO349 phase during post annealing even when the oxygen partial pressure is as low as 1%. CCO349 film annealed in low oxygen partial pressure (P=1%) gave the highest film Seebeck coefficient (~267 µV/K at 973 K), which was comparable to the CCO349 single crystal and 16% higher than that annealed in high oxygen partial pressure (P=100%) (~230 µV/K at 973 K). However, CCO349 film annealed in 100% oxygen partial pressure shows the lowest electrical resistivity of ~4.2 mΩ cm at room temperature, leading to a highest power factor of 1.2 mW/mK2 at 973K. Our work indicates that a strong dependency of TE properties on the post-annealing oxygen partial pressure with enhanced c-oriented growth at higher O2 oxygen partial pressure.

Resume : Self-supported three-dimensional electrodes consisting of carbon paper (CP) integrated with bifunctional nickel phosphide (Ni-P) electrocatalysts have been fabricated by electrodeposition of Ni on functionalized CP, followed by a convenient one-step phosphorization treatment in phosphorus vapor at an elevated temperature. The as-fabricated CP@Ni-P electrode exhibits excellent electrocatalytic performance towards hydrogen evolution reaction (HER) in both acidic and basic solutions. The HER onset potentials (ηonset) of the electrode are -18 and -55 mV in acidic and basic solutions, respectively, and only small overpotentials of 162 and 250 mV are needed to attain a cathodic current density of 100 mA cm-2. Moreover, the CP@Ni-P electrode reveals long-term durability as cathode for water electrolysis up to ca. 160 h in 0.5 M H2SO4 and 96 h in 1.0 M KOH without noticeable degradation. Furthermore, the CP@Ni-P electrode also shows superior catalytic performance towards oxygen evolution reaction (OER). A high anodic current of 50.4 mA cm-2 is achieved at an overpotential of 0.3 V. The electrode can sustain at 10 mA cm-2 for 180 h without obvious degradation, showing outstanding durability. Given the well-defined bifunctionality, a full alkaline electrolyzer has been constructed using two identical CP@Ni-P electrodes, which is able to efficiently and stably split water. The energy efficiency of the electrolyzer is as high as 91% at 10 mA cm-2, and remains 69% at a high current density of 100 mA cm-2. The electrolyzer can split water at 10 and 20 mA cm-2 in a fairly stable manner for at least 100 h.

Resume : SnO2 and Sb-doped SnO2 (ATO) thin films were deposited on glass substrate at 400 °C by chemical spray pyrolysis. The structural, optical and electrical properties were investigated as a function of dopant concentration, which was varied between 0 and 5 at % of Antimony by using XRD, UV-visible spectrophotometry and Hall effect measurement techniques. It is found that the films are polycrystalline in nature with a tetragonal crystal structure with a preferential orientation along [110] direction. All the ATO films exhibit a transmittance between 75 and 85 % in the visible range. The ATO films were n-type degenerate semiconductor with a lowest electrical resistivity of about 6.0×10-3 Ω.cm.

Resume : Herein, we reported the fabrication of nitrogen and sulfur co-doped molybdenum carbide (NS-doped Mo2C) nanosheets (thickness: 1.0 nm) with exposed (101) facets via a two-step route. The layered NS-doped Mo2C were first prepared by carburization of layered molybdenum oxide/phenol/thioacetamide hybrid followed by solvent exfoliation of the layered Mo2C into individual nanosheets. Co-doping of N and S heteroatoms could improve the wetting properties of the Mo2C electrocatalyst in aqueous solution and co-activate the adjacent Mo centre in the doped Mo2C compound by influencing its binding strength toward hydronium cation (H3O ) and the breaking of H-O bond of H3O cation that leads to the generation of H2 molecule, and thus induce a synergetic improved reactivity toward hydrogen evolution reaction (HER). As a result, we achieve a superior HER performance at low operating potential (-61 mV at 2 mA cm-2). This value is about 4 orders of magnitude better than the commercial bulk Mo2C material.

Resume : Leaf vascular patterns are the mechanisms and mechanical support for the transportation of fluidics for photosynthesis and leaf development properties. The spatial relationship of vascular networks in leafs are important functions in optimal transport efficiency of fluidics. Embedding leaf vein hierarchical order into an optical clear material, ocm, will enable mechanisms to highly regulate material temperature regions. The research is not focused on thermal conductivity but the adsorption of solar radiation (non-thermal) IR. Heat conductivity of the ocm will be regulated by leaf morphogenesis set by understanding of leaf veneration patterns that can be defined as a fluidic resistor network. Fluidic resistance by microvascular networks of continuous circulating fluid into, through and out of the matrix can be optimized by fluidic resistance flow patterns. The embedment of vascular pattern formations into a material will enable thermal switching selectivity in response to IR. Thermal switching selectivity is thermal interface flow targeting using volume filled vascular fluidic conduits for thermal exchange. Circuit resistance optimization of transport fluidic flow resistance within a closed loop network, determines this thermal exchange as a cyclic flow within a material domain. Nature’s biological systems are living multifunctional mechanical information systems of chemical composition. They have the ability to learn and adapt to changing climatic conditions by self-regulation of solar radiation. Leaf veneration networks enable conduit circuit flow for nutrient fluidic delivery. Hence leaf spatial vasculature pattern formations, perform functional significant regulatory roles in leaf morphogenesis by structured vein branching order. Leaf vein veneration are influenced by fluidic resistance and flow in the transportation of functional fluids within leaf blade regions. This biological engineering function of (primary, secondary and tertiary veins) hierarchy will advance fluidic embedded networks in a ocm device, by fluidic flow target resistance optimization in vascular pattern conduits, will be investigated in this paper. Key words: veneration, resistance, fluidics, thermal switching. Mark Alston, Programme director | School of the Built Environment University of Salford, Salford, Manchester. e: m.e.alston@salford.ac.uk

Resume : We have investigated the electronic and magnetic properties of the cubic praseodymium oxides perovskites PrMnO3 were calculated using the density functional theory (DFT) with both generalized gradient approximation (GGA) and GGA+U approaches, where U is on-site Coulomb interaction correction. The results show a half-metallic ferromagnetic ground state for PrMnO3 in GGA+U approach, while semi-metallic ferromagnetic character is observed in GGA. The results obtained, make the cubic PrMnO3 a promising candidate for application in spintronics.

Resume : CZTS thin films have been successfully deposited onto Mo-glass substrates by ultrasonic spray technique, followed by a sulfurization process at 560 °C under Argon atmosphere. The effect of the Cu/(Sn+Zn) in the starting solution on the properties was studied. The X-ray diffraction and Raman spectroscopy studies revealed the formation of CZTS kesterite structure with (112) preferential orientation. Morphological, optical and electrical properties of CZTS films have been also investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), photoluminescence and Hall effect measurements.

Resume : Profound knowledge of the morphological and chemical structure is essential in the case of electrochemical conversion devices such as Solid Oxide Fuel Cells (SOFC). This is due to the fact that the design of these sandwich systems is mainly based on ceramics whose elemental composition and dimensions have to be well controlled in order to maximize the efficiency of electronic and ionic transport. Moreover, the high operating temperatures impose strict chemical stability requirements on the components. Therefore, detailed studies at the micro- and nano-scale have to be provided to validate the conditions of the manufacture process and verify the microstructural quality of SOFCs. Correlative three-dimensional studies of the morphological and chemical structure of the SOFC were performed by combining X-ray Nano-Computed Tomography (CNT) and Focused Ion Beam Time-Of-Flight Secondary Ion Mass Spectrometry (FIB-ToF-SIMS). The application of these techniques allowed relatively large samples with dimensions of several tens of microns to be analyzed with high spatial resolution of the order of 100 nm. The studies were mainly targeted on the distribution and interlayer migration of elemental components inside a cell. Particularly, a great emphasis was placed on strontium diffusion from the oxygen electrode, i.e. Lanthanum Strontium Cobalt Ferrite (LSCF), towards the electrolyte of Yttria-Stabilized Zirconia (YSZ). Moreover, the influence of the fabrication process on the contamination of the SOFC with chromium and aluminum was investigated. As the geometry of cells strongly affects the capability of a system in terms of fuel flow, the studies of grain formation as well as porosity of different SOFC layers were studied in this work. This work has demonstrated how a novel combination of 3-D analytical techniques is able to provide morphological and compositional information of SOFC structures, but may also be applied to other micron sized structures with high porosity and/or heterogeneity.

Resume : A comparative study is performed to obtain the energy performance of different photovoltaic module technologies, when they are exposed to the same atmospheric conditions in a temperate climate. Three commercial PV module technologies are studied: crystalline silicon (c-Si), heterojunction with intrinsic thin-layer (HIT) and micromorphous silicon (a-Si/mc-Si). At least 6 month of data is available for each technology and more than 1 year for c-Si. The experimental platform is installed at the SIRTA observatory located in Palaiseau, near Paris. SIRTA is a reference meteorological and climate science observatory: the site is part of the Baseline Surface Radiation Network (BSRN) since 2003. During the 16-month study period (August 2014 to November 2015), the average daily sun irradiance was 3 443 Wh/m²/day and the mean air temperature was about 15°C. The I-V curve of each PV module, as well as the backside temperature and the in-plane solar irradiance, were measured every minute from sunrise to sunset throughout their respective measuring periods. All other atmospheric parameters, such as air temperature, were measured continuously with a frequency of 1 Hz, 24 hours per day. The comparison shows that the performance of a-Si/mc-Si is better than that of c-Si and HIT modules for this location, with higher daily yield values and higher performance ratio. However, c-Si and HIT modules achieve a better performance during the winter months while a-Si/mc-Si modules perform better in summer.

Resume : Flexible thin film solar cells have attracted a great deal of attention as mobile power sources and key components for building-integrated photovoltaics, due to their light-weight and flexible features in addition to compatibility with low cost roll-to-roll fabrication processes. Among many thin film materials, organic-inorganic perovskite materials are emerging as highly promising candidates for high efficiency thin film photovoltaics however there is a large room to improve the performance, scalability and reliability of the flexible perovskite solar cells. Herein, we report an efficient, flexible perovskite solar cell fabricated on ultra-thin flexible glasses using a two-step evaporation process. In such a device structure, the flexible glass substrate is highly transparent, robust with low thermal expansion coefficient, and perovskite thin film was deposited with thermal evaporation method which showed large scale uniformity. In addition, a nanocone array antireflection film was attached to the front side of the glass substrate in order to improve the optical transmittance and achieve water repelling effect at the same time. It was found that the fabricated solar cells have reasonable bendability, remaining 96% of the initial value after 200 bending cycles, and the power conversion efficiency was improved from 12.06% to 13.14% by using the anti-reflection film which also demonstrated excellent superhydrophobicity.

Resume : The passivated emitter and rear cell (PERC) design has remained one of the most efficient monocrystalline-silicon photovoltaic cell designs in the lab and in production through the use of point contacts. The use of point contacts, however, is not at all widespread in thin-film technologies, as forming the openings with a nanometer scale on thin-film solar cells would be very expensive if done with existing techniques. In this work, we explore an alternative, low-cost technique to forming point contacts on thin-film silicon solar cells. The technique presented here is nano-scale contacting by using nanoparticles (NPs) of polystyrene as a sacrificial mask. Nanoparticles (NP's) with diameters of 100nm are dispersed by spin coating onto a substrate of ITO deposited on metallic layers (Al and Ag), which will eventually act as a back reflector. Room-temperature deposition of SiO2 and SiN was performed by a high density plasma technique. After removing the NP’s by dissolving them in toluene, the samples are characterized by using SEM, and by local resistance mapping using an AFM. Homogenously distributed nano-contacts were obtained, with an average distance to a contact around 200nm, which is close to the diffusion length of holes in hydrogenated amorphous silicon (a-Si:H). A set of NIP a-Si:H solar cells have been deposited on these structures (with and without nano-contacts in the back reflectors), and their opto-electrical characteristics will be presented.

Resume : Recently First Solar has reported a per peak watt manufacturing cost of less than $1 for their CdTe solar panels, achieving a major milestone in the quest for grid-parity [1]. Improving cell efficiency and reducing the processing costs will further reduce the cost of solar panels, making them viable and accessible for all. However, it has been predicted that the record efficiency to date (16.5%[2]) may be close to the practical efficiency limit for CdS/CdTe hetero-junction solar cell (~17.5%[3]) in contrast to old theoretical prediction of ~30% for ideal homo-junction CdTe solar cell. Thus, inevitably, low-cost processing techniques have to be employed in order to reduce the cost of the fabrication of solar cells any further. The eelectrodeposition technique is an attractive low cost technique that has been successfully used in the solar cell industry. Therefore in this work, CdTe heterojunction solar cells were fabricated by electrodeposition in a three electrode setup in an aqueous medium. The optimum cathodic deposition potential applied was 695 mV vs SCE ( 0.24 V vs. Normal Hydrogen Electrode) and the annealing conditions were 350ºC for 20 minutes in air. Pre-annealed chloride treatment evidently improved the material, optical and device characteristics. The best efficiency obtained to date for 2 mm x 2 mm devices was 8.4% with the open ciruit voltage (VOC), current density ( JSC) and fill factor (FF) being 640 mV, 31 mA/cm2 and 0.42 References [1]. http://www.firstsolar.com/en/index.php [2]. Wu, X., Keane, J.C., Dhere, R.G., DeHart, C., Albin, D.S., Duda, A., Gessert, T.A., Asher, S., Levi, D.H., Sheldon, P. 2001. Solar Energy Conf., Munich, Germany, II, p. 995. [3]. Arturo Morales-Acevedo, Solar Energy Materials & Solar Cells 90 (2006) 2213.

Resume : The interfacial charge carrier dynamics of three-component TiO2-CdSe-graphene quantum dots composite nanostructures were investigated. The samples were prepared by coupling TiO2 nanowires with cysteine-modified CdSe nanoparticles. Subsequently, chitosan-modified graphene quantum dots (GQDs) were attached to the surface of CdSe, resulting in the formation of TiO2-CdSe-GQDs composite structures. For TiO2-CdSe nanowires, due to the relative band alignment, the photoexcited electrons will transfer from CdSe to TiO2 and the photogenerated holes are transported in the opposite direction. This feature improved charge separation but caused severe photocorrosion at CdSe. GQDs possess well-defined HOMO-LUMO band structure and can mediate charge carrier transfer when combined with semiconductor nanostructures. With the introduction of GQDs on CdSe, the photoexcited electrons transferred from graphene quantum dots to CdSe and then to TiO2, while the photogenerated holes were transported from TiO2 to CdSe and finally to graphene. This vectorial charge transfer not only enhanced the carrier utilization efficiency but also improved the long-term stability for photocatalytic applications. Time-resolved photoluminescence and electrochemical impedance spectra were measured to quantitatively analyze the charge transfer events across the interface. The samples were further employed as the photocatalyst for water splitting. Through systematic understanding of charge dynamics and their correlation with photocatalytic properties, insights into the advantages of GQDs introduction in terms of interfacial charge transfer and chemical stability were acquired.

Resume : Energy storage is a key element in energy conservation and efficiency of thermal energy utilization. Among different methods of storing energy as heat, latent heat storage (LHS) using phase change materials (PCMs) has been widely used. In this work, three types of nanostructure materials (graphene, single wall carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs)) were mixed with a NaNO3- KNO3 binary salt (60:40 ratio). Composites prepared at four different weight fractions (0.1, 0.5, 1.0, and 1.5 wt. %) were investigated. Composites prepared in water were sonicated for 3 hours and dried in a muffle furnace for one hour. The structure and morphology of the Nano-materials, composites, and fabricated PCMs were determined by Raman spectroscopy and scanning electron microscope. The melting enthalpy, melting point, specific heat, thermal conductivity and thermal diffusivity were characterized using differential scanning calorimetry and hot disk thermal constants analyzer. The graphene additives enhanced the thermal energy storage capacity, while carbon nanotubes improved the thermal conductivity.

Resume : Integration of thermal energy storage (TES) with concentrated solar power plants improves performance and availability of the plant. Utilization of latent heat storage (LHS) using phase change materials (PCMs) facilitates heat transfer at constant temperature. Composites of graphite derivatives (expanded graphite (EG), Graphene and exfoliated graphite Nano-platelets) imbedded in octadecane matrix were prepared, with four different weight fractions (0.5, 1.0, 1.5 and 2 wt.%), and characterized. EG was prepared by mixing natural graphite with concentrated sulfuric and nitric acid then heat treated. The microstructures of the composites were measured by scanning electron microscope and Raman spectroscopy. Melting point and melting enthalpy of the composite were measured using differential scanning calorimetry and hot disk thermal conductivity analyzer measured the specific heat, thermal conductivity and thermal diffusivity. Although graphite derivatives have little effect on energy storage capacity, the impact of EG on thermal conductivity of PCM is pronounced and more important for TES application.

Resume : Typical power block of CSP is combined cycles (CC) consists of a gas turbine (GT) and a steam turbine (ST). Development of operating scheme of CC in a decoupled mode using 100% solar energy in a concentrated receiver tower (CRT) is one of the objectives of EUROSUNMED project. In this case receiver provides thermal energy to two storage tanks at the required temperature to operate the turbines. The heat rejected from the GT is also transferred to the tank connected to the ST. In this scheme the two turbines are working independently and receiving thermal energy from each respective tank. This paper presents the results of numerical analysis using Matlab software programming system and Simulink package to calculate the efficiency of CC in both operating schemes. Furthermore, the energy losses and the energy flow in each component of the system are calculated to evaluate efficiency improvement resulted from decoupled operation. The option of transferring thermal energy to the two tanks at the required temperature from two receivers on the same tower was also analyzed. The results indicated improvement in the thermal efficiency and provided guidance for design improvement of the CRT plant.

Resume : Among the normalized and scaled performance metrics, the module performance ratio (PR) calculated using the maximum power values measured outdoor, is a better indicator of the technology’s performance, when several PV modules are compared. It implies however an experimental set-up and a waiting time of months or even years to have relevant data to access the real module performances. In this study, the artificial neural networks (ANNs) have been used to model the performance ratio of four photovoltaic modules including one monocrystalline, two polycrystalline and one micromorph (a-Si/µc-Si) module. The ANN architecture adopted, is a multilayer perceptron (MLP). The inputs of the MLP models are the solar irradiance and air ambient temperature while the output is the module performance ratio. It is shown that a three layer MLP with five hidden neurons, accurately models the performance ratio regardless of PV module technology. The results obtained from the MLP model are compared with those of the five parameters electrical model (L5P). The model comparison is done through two widely used forecasting errors: the root mean square error (RMSE) and the mean absolute percentage of error (MAPE). The values of both RMSE and MAPE are less than 0.02 for MLP based models and are about three to nine times lower than those obtained from the electrical model. It is also shown that the poor fit of the L5P model is due to a bad estimation of series and shunt resistances.

Resume : In this paper, the studied organic thin films were prepared with different solutions based on poly (3-hexylthiophene) (P3HT) and on (6,6)-phenyl C61-butyric acid methyl ester fullerene (PCBM) dissolved in different solvents: chlorobenzene (CB), di-chlorobenzene (DB) and bromobenzene (BB) separately. The prepared solutions were stirred for at least 2 hour to get a homogenous solution. After cleaning process of glass substrates in an ultrasonic bath, organic thin films were deposited on glass and on silver/glass substrates (for SPR characterization), by the spin coater at 1000 r.p.m. for 30 seconds and then placed on a hotplate at 110°C for 5 to 10 minutes to remove residue solvent. The effect of solvents on surface morphology and on optical properties was examined by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), UV–visible spectrophotometer and surface plasmon resonance.

Resume : The presence of partial shadings on photovoltaic (PV) systems, can originate irreversible damages on the PV panels. To understand how partial shading at the cell level affects module normal operation, a standard monocrystalline silicon PV module, divided in three equivalent cell strings by bypass diodes, was submitted to several shading fractions ranging between 10% and 100% of a solar cell area and characterized by thermal imaging using a thermal camera; I-V curves were also obtained. For all the shadings tested, a significant and non-uniform increase of temperature of the shaded cell was detected. A loss in the current produced in the string containing the shaded cell was also verified, such loss increases as the shaded area is larger, plummeting the electrical power produced by the module. Such loss can represent one third of the module power for complete shading of one solar cell. For equal shading fractions, the power loss is higher when the shaded area is on the center of the cell than on its edge. The module temperature distribution is also affected by the position of the shaded area. For a shading fraction of 50% of the cell area, placed at the cell edge, the temperature of the two strings connected to the same bypass diode is higher than in the rest of the module. If the same shaded area is placed at the cell center, only the shaded cell temperature is affected. For shaded fractions higher than 50%, an increase in the temperature of the diode isolated string was always observed.

Resume : Thermal Energy Storage (TES) technology is a very effective tool for energy conservation and improvement of energy utilization and management. Integration of TES system with concentrated Solar Power Plants (CSP) improves the plant availability and its economics. Millions of Tons of Electric Arc Furnace (EAF) slag are wasted from steel manufacturing worldwide and could be utilized as TES material. This paper presents the data resulted from characterization of the thermo-physical properties, crystalline structure, and chemical composition of four different slag samples, collected from a major steel production company located in Alexandria, Egypt, to evaluate their potential use as TES. A complete analysis was done before and after exposing the samples to specific heat treatment. Thermal Stability was also examined at a wide range of temperatures from ambient up to 800 C under nitrogen, inert gas and air. Appreciable improvement in the thermal conductivity, diffusivity, volumetric heat capacity, and structure of the EAF slag was observed as a result of heat treatments.

Resume : To limit the consumption of fossil fuels, hot water production by using photothermal solar receptors is growing in importance. An efficient photothermal receptor have to display a high solar absorptance (α>0.9), in the UV-VIS and near-IR regions (0.5-2µm) with a low thermal emittance (ε<0.1), in the mid-far infrared region (2-20µm) [1-3]. Here we report for the first time the formation of the solar selective CuO layer by the electrophoretic deposition (EPD) of CuO nanoparticles. A tandem absorber-reflector system is formed of CuO thin film and a highly IR reflecting metallic substrate, respectively. CuO suspensions are characterized by Dynamic light scattering (DLS) and Small angle X-Ray diffraction (SAXS) where they show to be stable during the time of the experiment. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis-NIR spectra and Fourier transform (FTIR) spectra are used to characterize the composition, microstructure and the final optical properties of the films obtained. These CuO tandem systems obtained by EPD exhibits the required optical properties in comparison to traditional processing techniques usually used. [1] Bogaerts WF, Lampert CM. Materials for Photothermal Energy Conversion. Journal of Materials Science. 1983;18:2847-75. [2] Charlot A, Bruguier O, Toquer G, Grandjean A, Deschanels X. Nanocomposites derived from silica and carbon for low temperature photothermal conversion. Thin Solid Films. 2014;553:157-60. [3] Charlot A, Deschanels X, Toquer G. Submicron coating of SiO2 nanoparticles from electrophoretic deposition. Thin Solid Films. 2014;553:148-52.

Resume : An electroluminescence measuring system was developed based on a low cost Complementary Metal Oxide Semiconductor (CMOS) sensor digital camera. Electroluminescence (EL) and Reverse Bias Electroluminescence (ReBEL) imaging were performed on both monocrystalline and multicrystalline silicon solar cells. EL measurements were performed with a bias voltage Vb near Voc and ReBEL measurements performed with Vb between 4 V to 18 V. The imaging obtained in this range of biases allows for the identification of different defect types. Defects such as metal contamination and cracks were induced in the solar cells and their effects were again characterized by EL and ReBEL. The imaging performed permitted the identification of defects such as metal contaminations, shunts, metal contact failures or cracks. Furthermore, luminescence measurements were performed at different temperatures which permitted the differentiation between intrinsic and extrinsic defects. The newly developed system was validated by comparing EL and ReBEL images obtained with a similar setup employing a high sensitivity scientific grade Charge Coupled Device sensor camera specifically developed for luminescence imaging. Such comparison demonstrated the feasibility of the new system, validating its use for solar cell characterization. To further analyse the influence of defects and confirm defect type (induced or not), the solar cells were also characterized by Suns-Voc, one sun iV and dark iV and localised external quantum efficiency.

Resume : Third generation hot carrier solar cells could achieve very high conversion yield at reasonable cost. Different theoretical approaches have been used to model these devices and to determine the maximal achievable efficiency, by taking into account different working conditions as well as different losses. However, the uncertainty about the kind of the carrier which heats has led to consider in the different models that both electrons and holes were at a same hot temperature. Here we revisit the theoretical work about hot carriers in order to take into account two different hot temperatures, one for each type of carrier (electron or hole). Then we use this theoretical approach to model the hot carrier solar cell performance with different electron and hole thermodynamical properties. Hot carrier solar cells are classically considered to have an absorbing material, converting light into electron-hole pairs at a same hot temperature, and two energy selective contacts. These energy selective contacts enables to convert the excess of kinetic energy of each type of carrier into potential electrical energy, represented by an energy increase by converting carriers from the hot to the ambient cold temperature. These contacts also avoid the cooling of hot carriers in the absorbing material by scattering with the colder ones coming from the electrical circuit. In the different developed models of the hot carrier solar cell, the carriers are considered to be at a same hot temperature and their respective absolute electrochemical potentials are considered to be the half of the quasi-Fermi level splitting: the system is totally symmetric. The previously developed models of the hot carrier solar cell consider two balance equations to solve the system: the particle current density balance and the internal energy current density balance. The current densities through the contacts are described by a Landauer Büttiker formalism. The different electron and hole thermodynamical properties (temperature and electro-chemical potentials) are taken into account by considering energy and particle current densities accounting for different electron and hole temperatures and electrochemical potentials, and their detailed balance. In our work we show that this model gives an insight into the carrier thermodynamical properties and the efficiency of the hot carrier solar cell. We emphasize the coupling between the carriers dynamics, since an increased thermalization rate for the holes decreases both electron and hole temperatures. Moreover, this model can work with externally ab initio computed transmissions of each contact. This work enables to have a more accurate investigation of the electron and hole dynamics and is a valuable tool to design hot carrier solar cell architectures as well as energy selective contacts. Ross, Nozik, J. Appl. Phys, 53, 1982 Le Bris, Appl. Phys. Lett, 97, 2010 Hirst, Sol. Energ. Mat. 120, 2014

Resume : A novel and non-vacuum Electrostatic Spray Assisted Vapour Deposition (ESAVD) process has been developed to deposit CIGS/CZTS absorber layers [1-3]. With the efficiency improvement of solar cells, there is an increasing demand for the storage of solar energy. Photoelectrochemical(PEC) water splitting is a clean, renewable and very promising method for the storage of intermittent solar energy in the form of H2. In this work, we studied the application of ESAVD deposited CIGS absorber as photoanode in the PEC solar water splitting system. Similar device structure (Mo glass/CIGS/CdS/i-ZnO:AZO) to CIGS solar cells was used for water splitting. A thin layer of platinum was electrodeposited on top of AZO layer in order to improve the PEC water splitting efficiency. PEC measurements was proceeded from 0∼ -1.5V vs Ag/AgCl in 0.25M Na2SO4 (pH=7), scanning from positive to negative with scan rate of 10mV/s. The Pt catalyst improved the photocurrent by four folds and CIGS demonstrated good stability under continuous illumination. References: [1] Mingqing Wang, Xianghui Hou, Junpeng Liu, KwangLeong Choy*, Paul Gibson, Elhamali Salem,Demosthenes Koutsogeorgis, and Wayne Cranton, Phys. Status Solidi A 212(1), 2015, 72–75 [2] Md. Anower Hossain,‡ Mingqing Wang,‡ and Kwang-Leong Choy*, ACS Appl. Mater. Interfaces, 7 (40) ,2015, 22497–22503 [3] Giovanni Altamura, Mingqing Wang, Kwang-Leong Choy,Thin Solid Films, 597,2015,19-24 Acknowledgements: This work has been funded by British Council DST-UKERI thematic partnership project. This work has also been funded by the European Union’s Seventh Framework Programme Scalenano, FP7/2007-2013 under grant agreement nº 28448

Resume : The optical and thermal properties of the solar receiver are crucial issues in the efficiency of concentrating solar power plants and therefore also in central receiver (tower) technologies. Tube-based central receivers are commonly painted with a selective coating posing high solar absorptance and low thermal emittance to increase the absorbed power and decrease thermal losses respectively. These characteristics should always be considered in simulation software to accurately estimate the receiver behavior. For the sake of simplicity and computational effectiveness, usually average single values from measurements are used for the absorptance and temperature dependent regressions are used for the surface emittance. While this approach seems to be good enough for the emittance, severe incidence angle dependence is found in the coating absorptance measurements, but its impact has been seldom analyzed. This work presents a study on the influence of the incidence angle dependence of the coating’s absorptance in a tube-based central receiver. For this, detailed optical simulations of real-like receiver and solar field geometries have been carried out using Tonatiuh, a Monte Carlo-based ray tracing software specifically focused in high concentrating optical systems. To assess the influence of the incidence angle in the finally absorbed power, the same geometry has been simulated with two different coating models, one implementing the angular dependency and the other one neglecting it. A silicon-based high-temperature commercial coating, PyroMark 2500, commonly used in central receiver systems and well characterized in the literature has been used as a reference. Results show that, even though angular dependency seems to be relevant in laboratory measurements, its impact on real systems performance can be generally neglected in simulations.

Resume : In order to reduce Si consumption in the industry, kerf-free wafering of thinner Si layers is largely investigated. In this work, the combination of two commonly used processes is presented in order to exfoliate silicon seeds in a simple way. H+ implantation, used in Ion-Cut processes, is a way to transfer precise and homogeneous layers of Si at depths – so-called Rp – determined by implantation energy. On the other hand, stress-induced spalling is easy and cheap: a stress-inducing layer is deposited on an Si substrate which is then cooled, inducing the cracking of layers from about 25 to 200µm thick. Yet these layers are rough and their thickness is difficult to control. This work uses low-energy H+ implantation as a guide for stress-induced cleavage. This process allows the exfoliation of 700nm-thick seeds and of tunable 50 to 120µm-thick c-Si layers. The process is carried out as follows: mono c-Si wafers are implanted with H+ at low energy, thermally treated to activate hydrogen diffusion, and then glued on a cheap metal layer with stress-inducing glue. Upon cooling, Si cracks at a depth depending on Rp and on the thermal treatment. Using such process, high quality mono c-Si 700nm-thick seeds as well as 50 to 120µm-thick layers were successfully detached from low-energy implanted silicon wafers. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 608593.

Resume : The photovoltaic solar cell industry is putting a lot of effort to reduce silicon cell thickness as a way to achieve cost reductions while taking advantage of expected high conversion efficiencies for such thicknesses. Indeed there are two positive points in this trend, i) material gains could be obtained and ii) thickness decrease allows some relaxation in terms of silicon bulk quality. Moreover, the classic process of ingot sawing cannot be a conceivable solution to produce thin silicon wafers, since more than 50 % of the silicon material will be lost during this step. In this work, we present solar cells made of thin silicon films formed at room temperature by the SLIM-cut technique using an epoxy layer. SLIMcut method consists in detaching thin monocrystalline silicon layers from a film inducing stress. In our case, a layer of epoxy is manually distributed on the surface of a monocrystalline silicon sample and annealed at 150 °C for 1h. The propagation of crack is activated by cooling the sample on an aluminum plate which is cooled by liquid Nitrogen. A relationship between the thickness of the epoxy layer and the foil has been determinated experimentally. Different structures of solar cells adapted to the silicon thin films have been performed. As an example, using silicon film of around 100 µm thick, conversion efficiencies of 14% and 16.7% were measured respectively using a conventional solar simulator and the "suns-Voc" system. Acknowledgments: The research leading to these results has received funding from the European Union Seventh Frame work programme (FP7/2007-2013) under grant agreement n°608593

Resume : MeV energy hydrogen implantation in silicon followed by thermal annealing is an economical kerf-less approach, that can be used to produce high quality ultra-thin silicon substrates for PV applications. By using this process, the successful delamination of ultra-thin (111)Si substrates with thicknesses in the range of 20 to 150 µm have been reported. However, results reported about (100)Si was less efficient. Indeed, unlike (111)Si, thin substrates obtained with (100)Si break in small pieces during the delamination process. That underlines that the delamination efficiency strongly depends on the silicon crystal orientation. This work focuses on the understanding of this difference of efficiency. Hydrogen was implanted in both (111) and (100) mono-Si with fluence from 7x1016 to 2x1017cm-2 and at energies up to 2.5MeV. A complete investigation of the thermal evolution of fracture precursors defects (platelets) was performed. We found that platelets orientation is at the origin of the difference of the delamination efficiency. Indeed, TEM results revealed that in (111)Si most of platelets are parallel to the surface whatever the hydrogen fluence. While in (100)Si, we found that platelets are parallel to the surface only for hydrogen fluences higher than 1x1017H/cm². As a consequence, we obtained full delamination in (111)Si with low hydrogen fluence (around 5x1016H/cm²), while in (100)Si full delamination occurs with high hydrogen fluences (around 2x1017H/cm²).

Resume : We investigated the formation of microcrystalline silicon (μc-Si :H) epitaxially grown on polysilicon seed layer on aluminium substrate using Electron cyclotron resonance plasma enhanced chemical vapor deposition method (ECR-PECVD). The μc-Si :H film serves as an active intrinsic absorber layer for a PIN configuration solar cell. A seed polysilicon (P+) layer was created by depositing amorphous silicon by ECR-PECVD method (using SiH4/Ar gases) directly on Al substrate followed by thermal annealing at 5500C resulting in a layer exchange. The μc-Si:H films was then deposited using a SiH4/H2 gas mix employing the same reactor. The optimization of deposition parameters was carried out on Cz Si wafers. The parameters which allowed to reach the highest crystalline fraction of ~ 65% are obtained for SiH4=4 sccm, H2=40 sccm and a deposition temperature 4800C. The Raman spectroscopy was carried out on the deposited films to determine the crystalline fraction while the spectroscopic ellipsometry measurements were applied to get insight on the optical constants of the deposited layers as well as on their the thickness. X-ray diffraction (XRD) measurements were taken to identify the crystalline phase of the deposited film and surface morphologies of films were observed by scanning electron microscopy (SEM).