EUROSUNMED symposium: Advanced materials and technologies for renewable energies (AMREN-1)

Resume : Historic buildings are the trademark of many European cities, towns and villages and are a living symbol of Europe’s rich cultural heritage. However, they are also substantial contributors to CO2 emissions and rising energy bills, and often do not offer the comfort needed – comfort for users and “comfort” for heritage collections. Can these buildings be made more energy efficient while conserving their heritage value – or rather: in order to guarantee their long term structural health and preservation?

Resume : Electrical energy storage systems are more and more investigated to increase efficiency in generation systems and to support power networks highly penetrated by renewables. Different kinds of batteries, with several features and performance are available on the market or in developing phase. CNR-ITAE is involved in a number of European and Italian research projects from one hand to develop smart energy devices, from the other hand to test and evaluating performance of existing technologies. This experience is reported in this work with the aim to highlight the key role of electrochemical batteries in the future energy scenario.

Resume : REELCOOP (Renewable Electricity Cooperation) is a EU/FP7-funded project aiming to develop renewable electricity generation technologies and promoting cooperation between EU Partner Countries and Mediterranean Partner Countries. It addresses 5 areas: photovoltaics (PV), concentrated solar power (CSP), solar thermal (ST), bioenergy and grid integration. REELCOOP will develop decentralised (distributed) building integrated PV systems and ST/biomass micro-cogeneration systems, as well as centralised generation of electricity in hybrid solar/biomass power plants. This is in accordance with the EU SET-Plan approach of developing a European electricity grid able to integrate renewable and decentralised energy sources. The overall aim of REELCOOP will be to significantly enhance research cooperation and knowledge creation on renewable electricity generation, involving Mediterranean partner countries (MPC), while at the same time developing and testing new renewable electricity generation systems. The proposed systems will be developed in European organisations with collaboration of MPC partners, and tested under real-life operating conditions in the MENA region, thus establishing a cooperation network amongst partner countries.

Resume : Implementing a basic science programme for energy is one of the key roles assigned to European Energy Research Association (EERA) by the European Commission in the frame of the European Strategic Energy Technology Plan (SET-Plan). The EERA comprises 15 Joints Programmes (JP) of areas relevant to energy challenges. Basic science is often presented as crucial in generating the breakthroughs needed to bring new generations of technologies to the market. The aim of the EERA-JP AMPEA (Advanced Materials and Processes for Energy Applications) is to foster a truly multi-disciplinary approach to develop enabling tools and new concepts for future emerging energy technologies. The mission statement of AMPEA states that it has to develop new horizons for science for energy, visible in Europe at the industrial and political level. Thus, the main objective is to harness and integrate materials science and process innovation for high performance sustainable energy technologies, in order to enhance the long-term competitiveness of European Industry. AMPEA aims at working in close coordination with other EERA-JPs and with Universities to bridge fundamental and applied research fields. AMPEA presently gathers 46 public research organizations and universities from 15 European countries. The talk will present AMPEA, its organization, achievements and objectives in the context of the EERA and the European context in general.

Resume : Thermoelectric Generators (TEG) exploit the Seebeck effect in order to convert a gradient of temperature into an electrical power. As such, they offer a myriad of opportunities within the framework of the decarbonization of the energy sector and the penetration of renewable energies. TEGs appear especially pertinent for the recovery of waste heat in various environments like power plants, combustion engine vehicles, and the Internet of Things (IoT). However, the current standard efficiencies of TEGs and associated cost per watt are still prohibitive and hinder a large deployment of the technology. In this presentation, we will remind the basics of thermoelectricity, discuss the current state-of-the-art of the scientific advancement, and underline the major barriers and associated leverages than are currently investigated to enhance the performances of TE materials.

Resume : Recently, fabrications of low-cost solar cell absorbers and buffers have drawn intensive attention. In this regard an extensive investigation on SnS and SnS2 films as absorber and buffer layers for photovoltaic applications have become one of the most highly energized research area. In the present study, the preparation and characterization of the SnS and SnS2 films grown via chemical bath deposition and sputtering is performed in addition with the study of SnS/SnS2 interface; device properties. Ionization energy and electron affinity of both SnS and SnS2 films were obtained as 5.3 eV and 4.0 eV; 6.9 eV and 4.1 eV, respectively from PYS measurements. Prototype photovoltaic cells are fabricated and the properties characterized. The quantum efficiency curve is restricted to the value ~ 950 nm corresponding to the band gap of SnS, where as in the short wavelength side, to a value of ~ 440 nm corresponding to the band gap of SnS2. The details of these results will be presented and discussed.

Resume : In the context of CPV and climate change, it is crucial to explore and master those green technologies which have the potential for the highest energy efficiency and to do so a cost that can reach grid parity over the largest possible geographic extent. One way to do so is to use materials not yet used in III-V CPV cells to better harvest high energy photons. It has only recently become feasible to explore higher band gap materials such as InGaN in order to reach that higher efficiency. At this stage, modelling has shown that efficiency is can be higher with an InGaN top cell on III-V subcells, as compared to a III-V only design with the same number of cells. In this talk we will present the advantage of increased concentration and new materials to explore and master this important CPV region.

Resume : The industrial fabrication of organic solar cells is often hampered by toxic solvents that require strong safety precautions. Whereas the use of chlorinated solvents or toxic hydrocarbons is feasible in the lab, their use in large scale printing processes would lead to enormous operational costs, which conflicts with the goal of cost effective production. In this work, we present efficient organic solar cells that were fabricated from non-halogenated solvents. To advance this concept and to enable device fabrication from non-toxic solvents, we synthesized organic solar cells entirely from aqueous and alcoholic solvents. For the absorber layer, we disperse, investigate and use P3HT:ICBA nanoparticles in environmentally friendly dispersion agents such as ethanol. In an inverted solar cell architecture with a nanoparticulate P3HT:ICBA layer the power conversion efficiency of 5% nearly matches the performance of reference devices that were fabricated from dichlorobenzene.

Resume : The purpose of this talk is to provide an overview of the most recent theoretical studies undertaken by us in the field of hydrogen storage materials research. On selected examples, the application of our computational tool of choice, density functional theory, will be illustrated to show how ab initio calculations can be of use in the effort to reach a better understanding of hydrogen storage materials and to occasionally also guide the search for new promising approaches. A deeper theoretical understanding of the catalytic mechanism involved in kinetic enhancement should be a very valuable guide in the design of new catalysts. Systems to be discussed include: Metal-organic frameworks, where we have studied hydrogen physisorption in three different types of iso-reticular MOFs, namely Zn-/Mg-/Ca-MOF16, decorated with either Li, Na, or K [1]. Lithium ion diffusion in lithium imide (Li2NH), and lithium amide (LiNH2) studied by us using both ab initio molecular dynamics simulations and the nudged elastic band method [2,3]. Finally, catalysts play an important role in many hydrogen desorption processes. We found (through a combination of experiment and theory) that carbon nanostructures, in particular nanotubes and fullerenes, can be used as catalyzing agents for hydrogen uptake and release in complex metal hydrides (such as sodium alanate, NaAlH4) and provide a model which could explain the mechanism of the catalytic effect [4]. References 1. Pornjuk Srepusharawoot, Andreas Blomqvist, C. Moysés Araújo, Ralph H. Scheicher, and Rajeev Ahuja, International Journal of Hydrogen Energy, 2011, 36, 555‒562. 2. A. Blomqvist, C. M. Araújo, R. H. Scheicher, P. Srepusharawoot, W. Li, P. Chen, and R. Ahuja, Physical Review B, 2010, 82, 024304. 3. C. Moysés Araújo, Andreas Blomqvist, Ralph H. Scheicher, Ping Chen, and Rajeev Ahuja, Physical Review B, 2009, 79, 172101. 4. P. A. Berseth, A. Harter, R. Zidan, A. Blomqvist, C. M. Araújo, R. H. Scheicher, R. Ahuja, and P. Jena, Nano Letters, 2009, 9, 1501‒1505.

Resume : In this study, Iron-doped tin dioxide thin films were deposited on glass substrate at 350 °C by spray pyrolysis technique. Structural, optical and electrical properties of the films were investigated as a function of dopant concentration, which was varied between 0 and 5 at % of Iron. X-ray diffraction analysis showed polycrystalline structure with clear characteristic peak of SnO2 cassiterite phases in all films. Atomic Force Microscopy (AFM) reveals that film roughness is not affected by iron doping. All films present a high transmittance in the visible range. From the electrical measurements, it was found that the resistivity increased with Fe2+-doping levels. Hall Effect measurements showed an n-type conductivity

Resume : We have investigated the influence of chromium (Cr) doping on the magneto-electrical properties of polycrystalline samples La0.75Sr0.25Mn1-xCrxO3 (0.15≤x≤0.25), prepared by sol-gel method. Comparison of experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behavior of three samples is quite well described by a theory based on electron-electron, electron-phonon and electron-magnon scattering and Kondo-like spin dependent scattering. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping (SPH) model is found to fit well the experimental curves.

Resume : Transparent conducting Al-In co-doped ZnO thin films were successfully synthesized onto glass substrates by spray pyrolysis technique. The influence of doping on the structural, optical and electrical properties was investigated. X-ray diffraction results showed that the samples have the hexagonal wurtzite structure with a preferred orientation toward the c-axis. No peaks belonging to In and Al or their oxides is observed in the limit of XRD technique detection. The surface morphology of the co-doped films showed well-defined hexagonal grains. A high transmittance above 75% and electrical resistivity around 10-1Ω.cm were reached.

Resume : Neodymium and thulium codoped ZnO (NTZO) thin films were deposited on glass substrates by chemical spray pyrolysis method. The influence of doping on structural, optical and electrical properties was characterized by various techniques. X-ray diffraction (XRD) patterns revealed that all the films have a polycrystalline nature fitting with the expected hexagonal wurtzite structure. Rare earth doping has no sensitive effects on the structure and does not lead to any secondary phase. Transmittance measurements showed that the addition of Tm reduces the optical transmittance from 80% down to about 50% in the visible region. Photoluminescence spectra at room temperature were dominated by an emission band due to the excitonic emission, which decreased and shifted toward lower wavelength region after Tm doping. Hall Effect measurements showed low resistivities and interesting carrier mobilities which makes these films promising for photovoltaic devices.

Resume : Photovoltaic cells based on CdS/CdTe heterojunction have important advantages like ordinary preparation techniques which conduct to small product prices, good chemical and physical stability, and reduced masses which recommend them for both terrestrial and spatial applications. Our study is related with the changes induced on the physical properties of CdS/CdTe heterojunction based photovoltaic cells by the protons and alpha particles irradiation with 500 keV energy and 1011 and 1013 particles/cm2 fluencies. The samples were prepared in “superstrate” configuration by magnetron sputtering technique onto optical glass substrates covered with a thin ITO layer. To complete the photovoltaic cells a Cu/Au back electrode was deposited by thermal vacuum evaporation. The irradiation procedures were performed using a Cockcroft-Walton Tandetron accelerator, 3 MV. In order to evaluate the induced changes of the protons and alpha particles irradiation on the physical properties of the prepared samples, optical, electrical and photoelectrical investigations were made at room temperature and the results were discussed. Specific parameters like band gap, series and shunt resistances, fill factor and EQE values were calculated and compared for as grown and irradiated prepared samples. Keywords: CdS, CdTe, protons, alpha particles, irradiation Acknowledgements: This work was partially financially supported by the projects: CDI-STAR No. 64/2013 and CDI-POPAS, No. 1/2012, respectively.

Resume : Cu2ZnSnS4 (CZTS) quaternary semiconductor nanocrystals were synthesized by controling the kesterite and wurtzite phases. The kesterite phase of CZTS nanocrystlas was obrained using Oleylamine as solvent and as capping agent, and two kinds of metal precursors; e.g. metal chlorides and metal acetate, for Cu, Zn and Sn, and elemental sulfur as a Sulfur source. The wurtzite CZTS phase was obtained when the dodecanethiol and oleic acid were replaced with Oleylamine. The as-synthesized (CZTS) nanocrystals were characterized by X-ray diffraction (XRD), Raman spectroscopy, UV?Vis absorption spectroscopy and Transmission electron microscopy (TEM).

Resume : We have prepared and characterized thin films of amorphous silicon (s-Si) by the electron beam deposition on different substrates (glass, aluminum and three types of silicon: monocrystalline silicon, multicrystalline silicon and compact powder silicon). The prepared Si-films were annealed at different temperatures ranging from 620?C up to 1000?C, for different durations. Raman measurements, of the annealed samples, show the existence of amorphous silicon on glass substrate and crystalline silicon on other substrates. The silicon crystallization was proved by Raman spectroscopy and scanning electron microscope images (SEM), the X-ray diffraction measurements reveal a polycrystalline structure of deposited silicon. Results obtained from silicon thin films deposited on substrates sintered from silicon powder reveal that this kind of substrates is promising for photovoltaic devices.

Resume : GaAs nanowires (NWs) have a great potential for application in solar cells due to lower costs and higher energy conversion efficiency, when compared to their conventional thin film based counterparts. With the view to the device applications, the influence of the growth substrate’s nature on the physical properties of the NWs is central interest. In this work, we present a structural and optical study of Mg doped GaAs NWs with the same nominal concentration, grown by MBE on GaAs(111)B and Si(111) substrates. Concerning the structural investigation, scanning electron microscopy images reveal a clear influence of the substrate on the orientation of NWs, being the vertical orientation the dominant one for the GaAs(111)B substrate. Additionally, X-ray diffraction is used to investigate the crystalline phase of the NWs. The electronic levels’ structure of both samples was studied by photoluminescence (PL). The low temperature PL spectra show clear differences in the observed radiative transitions and relative intensities. Also, the signal to noise ratio in the PL spectra is higher for the GaAs(111)B substrate which is attributed to a lower density of defects in comparison with the growth in the Si(111) substrate. The nature of the radiative and non-radiative recombination channels is discussed based on the dependence of the PL on the excitation power and temperature, and correlated with the crystalline structure of the NWs.

Resume : Cu2ZnSnS4 (CZTS) has recently been presented as a promising absorber layer in photovoltaic technology. The electrical performance of CZTS based solar cells has increased but is far behind the current values for Cu(In,Ga)Se2, or even silicon. The identification of the radiative transitions in the complete solar cell structure as well as the influence of the growth parameters on the electronic levels structure is crucial for the improvement of the devices. In this work we compare the electronic properties of solar cells with CZTS absorbers prepared in two different ways. In the first set, metallic precursors were sulphurized in a tubular furnace directly exposed to a sulphur vapour. In the second set, the precursors were sulphurized in graphite box where sulphur pellets have been evaporated. From a structural point of view, Scanning electron microscopy revealed higher grain sizes for the sample sulphurized in the tube furnace although X-ray diffraction and Raman spectroscopy have shown that the dominant phase in both samples is the CZTS. The photoluminescence (PL) of the sample sulphurized in the tube furnace corresponds to a single, broad and asymmetric band whereas for the other set of samples, a second component is identified at a higher energy. The influence of fluctuating potentials in the CZTS absorber layer and of the CdS buffer layer on the PL is clearly observed. In addition, the measurement temperature influence in the optical properties is discussed.

Resume : Thin film silicon solar cells on low cost foreign and flexible substrates could be attractive for low cost production of photovoltaic electricity. This work aims at the synthesis of high-quality continuous polycrystalline silicon (pc-Si) layers on cheap Aluminium substrates using the aluminium induced crystallization (AIC) process of amorphous silicon. To avoid uncontrolled exchange of Al/Si, an Al-doped ZnO diffusion barrier layer against impurities but still conducting has been used. For the AIC process, a 200 nm thick Al-layer acting as a source of Al, was first electron beam evaporated over the substrates. Amorphous silicon films with thicknesses ranging from 200 nm were deposited by ECR-PECVD on the substrates. The annealing temperature and time were the key parameters of the Al/Si exchange process. Here, the direct crystallization using a conventional furnace was carried out at T=480 degree C and for a duration of 10h. After the removal of the aggregated impurities (Al and a-Si) and defects (grain boundaries) on the surface by selective etching. The resulting crystallized layers were characterized by Raman spectroscopy. The as-grown AIC polysilicon films were found to be continuous and densely packed without amorphous phase. The AIC process was followed by (1) 10 μm thick a-Si deposition by ECR-PECVD and (2) by n-type a-Si deposition using PVD. These layers were crystallized using solid phase epitaxy. Properties of the crystallized layers for different thermal budgets (1h, 2h, 5h, 10h and 12h at 600 degree C) are further studied with Raman spectroscopy and X-ray ray diffraction technique. Additional experiments will be carried out to assess the quality of the fabricated p-i-n diode in terms of Voc and leakage current. The research leading to these results has received funding from the European Union Seventh Framework programme (FP7/2007-2013) – Project EUROSUNMED- under grant agreement n°608593

Resume : The realization of thin films of polycrystalline silicon on foreign substrates is an attractive alternative to the ingot casting which allows a reduction in costs. The purpose of this work is to form polycrystalline silicon films from the crystallization of amorphous silicon deposited on aluminum substrate. This kind of substrate will then be used as conductive support but also as a reflector on the rear face of the photovoltaic cell. However, because of their miscibility, silicon and aluminum can strongly react during heating leading to an Al-Si alloy rather than to separated materials. In this work, 2 to 5 microns thick amorphous silicon films were deposited by ECR-PECVD on various type of aluminium substrate. Such substrates were non, partially or totally anodized meaning that an alumina layer is formed on top surface. Crystallization of the amorphous silicon was carried out using a temperature of 550 ? C and varied times from 10 to 80 min. The as-crystallized Silicon films are then characterized by Raman spectroscopy, scanning electron microscopy and by electron backscatter diffraction. The results show the feasibility of amorphous silicon crystallization using both a low temperature of 550 ? C and a short duration of 80 min. The analysis shows the formation of two separate layers during the process: a silicon / aluminum alloy as the upper layer and a polysilicon film at the bottom and in contact with the aluminum substrate. We also found that the crystallization process is strongly dependent on the degree of anodization of the Al substrate. Silicon layers with few micrometers grains are thus obtained and can potentially be used as nucleation sites for the fabrication of the absorbing silicon films for photovoltaic applications.

Resume : Photovoltaic solar cells are mainly made of expensive crystalline silicon which is used in excess. While a 50µm-thick c-Si layer would be enough to capture de vast majority of incident photons, 180µm-thick layers are commonly used. The goal of this work is to produce low-cost silicon thin films using low-energy, low-dose hydrogen implantation, which results in formation of blisters, as an initial technological step. This step is used for the formation of crystalline silicon seeds on low-cost substrates. Deposition, followed by crystallization of a thin Si layer on such substrate with Si seeds, can be considered as a low-cost method for the formation of a base for thin Si based solar cells. In this work the first step of the proposed approach, the formation of hydrogen initiated blisters and subsequent use as crystalline silicon seed, is studied in detail. Evolution of blister size as a function of hydrogen energy (20 KeV, 100 keV) and fluences (1015 - 5-7.1016 H+/cm²) has been studied. An aluminum layer has been deposited on hydrogen implanted samples by magnetron sputtering. Si seeds were bonded to this layer which was glued to a substrate with melted solder glass at elevated temperatures and transferred onto this substrate upon cooling. Micro-Raman measurements were used to prove that exfoliated and transferred Si seeds are crystalline. Perspectives as well as problems of the proposed approach are discussed.

Resume : The sawing technique commonly used to cut silicon wafers used in the PV industry generates a lot of material losses, which has a significant impact on the silicon-based cells cost. Moreover, it is probable that it will not be possible to extend this technique to very low wafers thicknesses like those expected by PV roadmaps (i.e 50 µm by 2035). MeV energy hydrogen implantation in silicon and subsequent thermal annealing is a kerf-free process that allows reducing the consumption of silicon and hence the costs. We have shown that this process can be used to detach entire (111)Si layers with thickness from 10 to 100 µm for energies up to 3 MeV. However, results about (100)Si was less efficient: higher fluence was required to achieve detachments, and the obtention of large size layers was an issue. The goal of this work is to understand the poor transfer record with detachment in (100)Si, and then, to improve (100)Si detachments in the MeV range hydrogen implantation. Hydrogen was implanted in (100)Si at fluences varying from 5x1016 to 1x1017 H/cm² with energies from 1 to 2 MeV. Subsequent thermal treatments (300-800°C) were applied. TEM results revealed that fracture precursor defects (platelets) have an unfavorable orientation to promote fracture propagation in (100)Si. Nevertheless, in this work, we show that an optimization of the thermal treatment allows reducing the required fluence to achieve detachment in (100)Si and improve the size of transferred (100)Si layers.

Resume : According to the advances in thin film processes, electronic chips now integrate a lot of electronic functions on the same area, especially in portable equipment, wireless sensor networks, and other microsystems. As a result, microenergy sources need to be developed in order to drive such integrated electronic devices, or to provide power during the temporary failure of the primary power sources. Supercapacitors, until now consisting of liquid-state electrolytes, have been widely regarded as energy storage devices for several electronic systems. Although solid electrolytes have a lower ionic conductivity compared to liquids, we can overcome this drawback by decreasing the thickness of solid electrolytes in order to reduce the diffusion path of charged defects or by increasing the effective surface area by using porous electrodes. Therefore, with solid-state electrolytes, supercapacitors have advantages such as negligible leakage current and a wide operational temperature range. Here we incorporated protons in BaTiO3 films during a low-temperature deposition process and studied electrical defects resulting from the hydrogen incorporation. We emphasize that drastic changes occur on both chemical and electrical properties of the films when hydrogen is added to the sputtering gas. The double-layer capacitance can reach values up to several µF/cm2. Finally, attempts were made to explain the effect of the double layer on the electrical properties of the hydrogenated films.

Resume : Perovskite solar cells have experienced unprecedented advancements with power conversion efficiencies soaring up to the current record of 20.1% within the past 5 years.[1] The high effi-ciency coupled with the large bandgap (tunable up to 2.3 eV) of perovskites make them ideal candidates as top cells in a tandem device with CIGS. The development of high performance perovskite solar cells with high transparency in the near infrared (NIR) region is decisive for realizing efficient tandem devices. Here, we present our latest results on the NIR transparent perovskite solar cells and integrate them in 4-terminal perovskite-CIGS tandem devices. Par-ticularly, we first introduce a novel concept that employs a porous nanostructured PbI2 layer consisting of nanoplates to rapidly prepare single phase perovskite with a compact and flat morphology at room temperature. The high quality perovskite film allows us to fabricate planar perovskite devices with a power conversion efficiency of 14.2% under reverse J-V meas-urements. The novel process is applied for the development of NIR transparent devices, and above 10% perovskite solar cell with high transmission in NIR was achieved. The design, fab-rication and performance of perovskite-CIGS tandem devices will be discussed in detail. This work represents a further step forward towards high performance perovskite-CIGS tandem devices. [1] NREL, efficiency chart, http://www.nrel.gov/ncpv/images/efficiency_chart.jpg., accessed: December, 2014.

Resume : High-efficiency thermoelectric (TE) materials are important for power-generation devices that are designed to convert waste heat into electrical energy or to use in solid-state refrigeration. These applications require innovativematerials which not only possess high conversion efficiency (related to high dimensionless number called figure of merit, "ZT" which is a combination of three material properties: Seebeck coefficient (S), electrical conductivity ( and thermal conductivity ( : ZT = S2T/, but should also be no toxic and have high chemical stability in air, over a wide temperature range such as oxide materials. From last decade, a major breakthrough in the field of TE came bydesigning nanostructures that scatter phonons more effectively than electrons, so that the thermal conductivity is reduced more than the electrical conductivity.Herein we present a cheap and thermodynamically driven process to produce intra-granular nanostructures in bulk materials: the spinodal decomposition in the Nb5+-doped SnO2-TiO2 system via an innovative molecular approach. Such in-situ partitioning takes advantage to produce nanostructuration with coherent interfaces. While classical approach based on SnO2 (nano)powders mixing faces trouble to sinter dense ceramics, our bottom-up approach,trough synthesisof mixed TixSn1-xO2 (x = 0.25; 0.5; 0.75) rutile nanoparticles, suppress pure SnO2 grains and allow full densification at low temperature by SPS process. Impact of the pressure, heating rate and soaking time of SPS process onto the densification, the nano-structuration and the dopant distribution will be addressed towards the thermoelectric properties.

Resume : An innovative approach to improve the performance of thin film photovoltaic (PV) cells is based on light capture enlargement due to the introduction of energy down-shifting (DS) layer that are supposed to convert high-energy photons (UV light) into low-energy ones (visible light), which are more efficient in the PV conversion process . For this purpose, ZnOnanoparticles (NPs) have aroused an increasing interest since they possess a variety of intrinsic defects that provide light emission in the visible range without the introduction of any additional impurity. However, high photoluminescentquantum yield (PLQY), green/yellow emission, stable dispersion and easy scale–up process are expected for industrial photovoltaic applications. Li-doping and polymer surface modifications of ZnO nanoparticles are mainly used in order to reach high PLQY (>30%) but PLQY decay over few days, uses of sophisticated polymers or multi-step reactions are the main issues for industrial implementation.Herein, we present a quick and convenient chemical solution approach to get unique mesospheric self-assembly hybrid ZnOsystem with intense (PLQY = 40-75%) and stable visible emissions. We also demonstrate that the use of mixture of commercial polyacrylic acid-based polymers can provide scalable amounts of ZnO NPs clear water suspensions that can be dried and dispersed again in water without compromising the functional performance (e.g. transparency and PLQY) of the final DS layer. We will then address the effects of the ZnO NPs surface functionalization - such as nature, molecular weight, concentration, ratio of the PAA-based polymers - on the enhancement of the efficiency of DS layers in solar cells technology.

Resume : Cuprous oxide (Cu2O) is an attractive absorber for thin film photovoltaics (PV) due to its direct bandgap of 2 eV, high absorption coefficient, earth-abundance, non-toxicity and low-cost fabrication possibility. The theoretical maximum conversion efficiency from a single junction Cu2O cell is approx. 20%. Cu2O is natively p-doped. The inability to produce n-type Cu2O imposes the use of heterojunction solar cells, commonly employing n-type ZnO. From the non-vacuum fabrication routes for Cu2O, thermal oxidation of Cu sheets and electrochemical deposition (ECD) are predominantly used. Whereas the former gives rise to highest efficiencies, the latter has the advantage of minimum material and energy consumption, which are of paramount importance for industrial production. Here we focus on two aspects of the Cu2O/ZnO cell development. Firstly on the optimization of the potentiostatic electrodeposition, in order to produce Cu2O films of pure chemical composition, large crystallite sizes, free of voids and structural defects. Particularly, we investigate the role of the conductive substrate (TCO- or metal-coated glass) and of the deposition potential on the nucleation and growth of Cu2O crystals, which determine the absorber film properties. The second aspect in our study is the combination of ECD-Cu2O with ALD (atomic layer deposition)-grown ZnO, focusing on the quality of the heterojunction interface. Optimized heterojunction solar cells present short circuit current densities in excess of 8 mA/cm2 and open circuit voltage close to 500 mV. These results show the potential of all-oxide PV for low-cost energy harvesting.

Resume : Recently solar energy receives a great attention as an important source of renewable energy. Solar energy is converted to electrical energy directly through photovoltaic (PV) or indirectly through concentrated solar power (CSP) system which converts solar energy to heat energy which in turn can be used by thermal power station to generate electricity. This paper present a comparative study between the two types of solar power (PV&CSP). This study includes types, components, initial and running costs, efficiency, advantages and disadvantages and storage systems.

Resume : Using rocks as cheap material storage in solar power plants can be considered as a promising alternative to molten salt, as it improves the dispatchability of the power plants at lower costs. The present work discusses the suitability of rocks in order to be used in a packed bed configuration with air as a heat transfer fluid. Thus, required characteristics of rocks have been specified, and several rocks have been identified as potential candidates for the storage application (such as: Basalt, Quartzite and cipolin…). In the other hand, an initial characterization has been conducted in order to study the thermophysical and mechanical properties of the first batch of rocks. Another variety of rocks will be subjected to characterization (peridotite and gneiss). A study of rock durability will be required in order to make a final decision concerning the most potential rocks for this application.

Resume : One of the main difficulties when modeling cavity receivers is determining convection heat losses and, specifically, natural convection processes. In this work, a CFD simulation of a cavity receiver similar to those used in large scale solar thermal power plant has been carried out. The ultimate goal of this work is to validate the various approaches proposed by several authors to estimate through much simpler correlations the convection heat losses in such cavity receivers and summarized in [1]. In this work, the modeling of the receiver and first results of the CFD simulation regarding natural convection inside a cavity are shown, while the actual validation of the existing correlations is still ongoing.

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Resume : Four junction cell is the state-of-the-art solar cell technology for future CPV applications. The materials used are GaInP/GaAs//InGaAsP/InGaAs with bandgap energies of 1.88/1.44//1.11/0.70 eV. This multi-junction cell assembled with wafer bonding of two lattice matched tandem cells has already demonstrated world record efficiencies. The bandgaps are chosen to be optimal for conversion under sunlight concentration of around 500x. Most used in CPV applications is still the triple-junction cell with typical record efficiency around 41% under concentration [1 - 4]. This paper presents the improvements made since the achievement of the efficiency world record using the wafer bonded four junction technology [5 - 7]. Wafer bonding is powerful technology to combine lattice-mismatched materials without creating dislocations. Two lattice matched crystal structures are brought together forming covalent bonds at the interface [8]. The requirements on surface roughness, defectivity and preparation of the materials are very high, but this method offers on the other hand the opportunity to combine optimized and nearly defect free materials in a multi-junction solar cell device. Wafer bonding has been described by several authors in the past [9 – 13] but the present work, for the first time, resulted in a cell efficiency which outperforms all triple-junction cell devices under concentration. The ideal band gap combination of the four junctions enable an excellent material quality across al

Resume : The ETRERA_2020 is conducted by a team of twelve organisations from nine different countries in Europe, Africa and Middle East. The ETRERA_2020 idea is to improve S&T and entrepreneurial relationship between European Member States and the neighbouring Mediterranean countries in the strategic field of renewable energy production, distribution and storage by a range of activities targeted to bridging the existing gap between research and innovation.

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Resume : Testing for performance: the requirements to reduce the difficulty of rating PV devices: mature technologies and new developments

Resume : SCALENANO: Towards a competitive full solution & high efficiency CIGS industrial technology

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