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The present invention relates to novel molecules suitable to the use in the separation/removal of carbon dioxide from gaseous mixtures as liquid-phase carbon dioxide absorbers and suitable to allow the subsequent release of the absorbed carbon dioxide in form of different ionic liquids, preferentially a glycine salt with choline hexanoate, ester between glycine and hexanoic alcohol (hexyl glycinate) and glycerol ester with glycine and hexanoic acid. The present invention also relates to a method and a plant for the capture of carbon dioxide from gaseous mixtures by using an absorber for carbon dioxide in liquid phase with a heating jacket.

We report preliminary results on InGaP/InGaAs/Ge photovoltaic cells for concentrated terrestrial applications, monolithically integrated on engineered Si(001) substrates. Cells deposited on planar Ge/Si(001) epilayers, grown by plasma-enhanced chemical vapor deposition, provide good efficiency and spectral response, despite the small thickness of the Ge epilayers and a threading dislocation density as large as 107/cm2. The presence of microcracks generated by the thermal misfit is compensated by a dense collection grid that avoids insulated areas. In order to avoid the excessive shadowing introduced by the use of a dense grid, the crack density needs to be lowered. Here, we show that deep patterning of the Si substrate in blocks can be an option, provided that a continuous Ge layer is formed at the top, and it is suitably planarized before the metalorganic chemical vapor deposition. The crack density is effectively decreased, despite that the efficiency is also lowered with respect to unpatterned devices. The reasons of this efficiency reduction are discussed, and a strategy for improvement is proposed and explored. Full morphological analysis of the coalesced Ge blocks is reported, and the final devices are tested under concentrated AM1.5D spectrum. Copyright © 2016 John Wiley & Sons, Ltd.

We investigate the effect of surface Ga accumulation on the growth of In0.5Ga0.5N by PAMBE at low temperatures (T= 440 °C). We find that the control of the surface metal condition is very important because the crystallization process strongly depends on the metal flux impinging on the surface. The growth rate rapidly decreases when the supply of metal flux exceeds certain amount. Such phenomenon can be explained by the model taking into account droplet effects on the incorporation of metals adatom into the crystal.

La presente invenzione riguarda nuove molecole adatte all’utilizzo nella separazione/rimozione di anidride carbonica da miscele gassose in qualità di assorbenti in fase liquida dell’anidride carbonica e atte a consentire il successivo rilascio dell’anidride carbonica assorbita. La presente invenzione riguarda altresì un metodo ed un impianto per la cattura di anidride carbonica da miscele gassose mediante l’utilizzo di un assorbente per l’anidride carbonica in fase liquida. The present invention relates to novel molecules suitable to the use in the separation/removal of carbon dioxide from gaseous mixtures as liquid-phase carbon dioxide absorbers and suitable to allow the subsequent release of the absorbed carbon dioxide. The present invention also relates to a method and a plant for the capture of carbon dioxide from gaseous mixtures by using an absorber for carbon dioxide in liquid phase.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1837-1839, Nowadays there are two main approaches to produce CIGS solar cells: sputtering followed by selenization evaporation and coevaporation process. High efficiency solar cells are obtained by the sequential threestage co-evaporation process. On the other hand sputtering system is more suitable for an industrial application but the efficiencies are systematically lower. In our laboratory we have developed a new hybrid sputtering and evaporation system to obtain a scalable process combining the advantages of both techniques. This technique has been already applied to deposition on glass and stainless steel substrates. Quite good results were obtained reaching an efficiency of 15% on glass and 13% on stainless steel substrates respectively. In this paper we report the results obtained on polyimide and thin boron silicate glass (100um) films.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1730-1732, Thin film solar cells based on Cu(In,Ga)Se2 (CIGS) yield, up to now, a maximum photovoltaic conversion efficiency if CdS deposited by chemical bath deposition is used as buffer layer. However, due to the disadvantages of CdS (like the toxicity classification of Cd, the non-vacuum nature of the chemical bath deposition and the absorption of blue light) an extensive research was employed in the last years on finding new alternative buffer layers. Thereby, the aim of this work follows the technical progress of the research which focuses on the development of Cd-free buffer layers for chalcogenide photovoltaics. Zinc tin oxide, (Zn2SnO4) and indium sulfide (InxSy) thin films were evaluated as alternative buffer layer for chalcogenide-based PV. The investigated thin films buffer layer have been deposited both on soda lime glass substrates and on Cu(In,Ga)(Se,S)2, in order to prepare the solar cells, by using r.f. sputtering. Some of the technological problems of the Cd-free buffer layers like the influence of the growth conditions, homogeneity, short deposition times, and post thermal treatments are investigated. The performances of the CIGS-based solar cells fabricated using ZTO and InxSy as buffer layers were compared to the standard CdS solar cells deposited by chemical bath deposition (CBD). Since the alternative buffer layers allowed more or less half of the efficiency reached using CBD-CdS further optimizations of the investigated buffer layers are currently in progress.

Quantum dot intermediate band (IB) solar cells have been proposed in order to increase the efficiency of traditional solar cells and immediately attracted a lot of attention and research since the time they were first proposed [1]. The IB introduces an extension of the absorption coefficient of the semiconductor to lower energies, allowing a more thorough collection of the solar spectrum, via a two-step absorption of low-energy photons. Quantum dot (QD) structures are good candidates for IB solar cells, because their confined energy levels can overlap and form a miniband in dense arrays and the position of these levels and bands can be tuned varying the size and spacing of the QDs. The IB working mechanisms have been demonstrated for InAs QDs in GaAs [2], and a lot of research is devoted to reduce the problems due to strain, and defect nucleation increasing carrier escape [3]. Droplet epitaxy (DE) [4] is a molecular beam epitaxy technique that allows for the growth of quantum dots of materials lattice matched to the barrier and the removal of the wetting layer. DE makes possible to indipendently control density, size and shape of the nanostructures. Densities as high as some 1011 cm-2 per layer have been reported [5] and potentially a large number of layers can be stacked because the system is strain-free, leading to a much higher density of states in the IB than the more conventional Stranski-Krastanov techniques. Since it is a strain-free technique, there are virtually no defects in DE-grown materials, and this is fundamental to have high performance devices. Moreover, DE nanostructures can be grown without the presence of a wetting layer [6], that would introduce unwanted quantum-well-like states in the system. By tuning the size of the QDs it is obviously possible to change the position of the IB, and by tuning their aspect ratio the high energy states of the QDs can also be tuned in order to have a small electron-phonon coupling with the barrier. The lack of defect and wetting layer states can greatly reduce thermal escape of carriers from the IB, leaving photon-induced transitions the dominant ones, as requested by IB theory [1]. For these reasons DE is a good candidate for the realization of QD-IB solar cells. We demonstrate the key working principle of IB materials, that is the production of sub-gap two-photon photocurrent, with Al0.3Ga0.7As solar cells containing GaAs QDs grown by DE (figure 1a). The devices were illuminated at 15K by continuous monochromatic light and chopped broadband IR light (1.5 – 20 m), and the signal was demodulated by a lock-in amplifier. The continuous light pumps electrons into the QDs and the chopped IR promotes them to the CB where they can be collected generating an electric signal. As a control, a reference sample without QDs was grown and measured in the same conditions, but no two-photon signal was detected (see figure 2b). Measurements show that the shape of the two-photon photocurrent signal is different from the VB-CB photoresponse, indicating clearly that a two-photon process involving the QD levels is taking place. The two-photon signal response is in good agreement with the PL spectrum of the QD samples (figure 1b), that lets us easily understand the position of the energy levels of the system. [1] A. Luque, A. Martì, Physical Review Letters, 78, 5014 (1997). [2] A. Martì, E. Antolìn, C. R. Stanley, C. D. Farmer, N. Lòpez, P. Dìaz, E. Cànovas, P. G. Linares and A. Luque, Physical Review Letters 97, 247701 (2006). [3] A. Luque and A. Martì, Prog. Photovolt: Res. Appl. 9, 73-86 (2001) [4] N. Koguchi and K. Ishige, Japanese Journal of Applied Physics 32, 2052–2058 (1993). [5] M. Jo, T. Mano, Y. Sakuma and K. Sakoda, Applied Physics Letters 100, 212113 (2012) [6] S. Sanguinetti, K. Watanabe, T. Tateno, M. Wakaki, N. Koguchi, T. Kuroda, F. Minami, and M. Gurioli, Applied Physics Letters 81, 613 (2002)

Inorganic materials dominated the PV market from the beginning. PV devices based on silicon are the most common solar cells currently being produced and it is mainly due to silicon technology that the PV has been growing by 40% per year over the last decade. Cost, sustainability and environmental issues are at the core of the PV silicon based industry activities. An additional step in the silicon solar cell development is on-going and it is related to a further efficiency improvement through defect control, device optimization, surface modification, nanotechnology approaches. Inorganic thin film PV technologies have been under development in the last decades as a low cost alternative to bulk c-Si. Incidentally, this technology is the most suitable for Building Integrated Photovoltaics (BIPV) and for large-scale production since the module is the final stage of an in-line process that does not require the assembly of discrete smaller cells. In the frame of inorganic thin film Cu(In,Ga)Se2 (CIGS) solar cells is one of the most promising in terms of the efficiency record (20.3 %), nearly reaches the one of Si solar cell [1] and of stability. Despite the promise of CIGS thin-film and also of CdTe photovoltaic technologies with respect to reducing cost per watt of solar energy conversion, these approaches rely on elements that are either costly and/or rare in the earth's crust (e.g. In, Ga, Te) or that present toxicity issues (e.g., Cd), thereby potentially limiting these technologies in terms of future cost reduction and production growth. The new material Cu2ZnSnS4 (CZTS), in which indium and gallium are replaced by the readily available elements zinc and tin, is very promising in terms of reduced cost and sustainability but an intense research activities to optimize the growth process and the material quality are still necessary before transferring the device on the market. In the MIB-SOLAR center of UNIMIB, a new method for chalcogenide thin film (CIGS) deposition on glass and flexible substrates has recently been developed, in collaboration with a small enterprise [2, 3]. Up to now the process has been optimized for CIGS films with a thickness of around 2 micron, obtaining a cell efficiency of 14% on glass and 8.3% on stainless steel substrate, respectively, in less than 3 years of activity. In the last year we started a new activity regarding CZTS thin film [4]. Two main growth deposition methods are under investigation and testing: 1) Sputtering process and 2) Sol gel method This article points out the most important advances and current technologies related to inorganic PV devices. In the meantime the most challenging and promising strategies acting to increase the ratio between the efficiency and the cost of inorganic solar cells in our laboratory will be described. Some novel concepts under development in MIBSOLAR centers, which could have an important role in the future of PV will be also described. NOTE BIBLIOGRAFICHE [1] P.Jackson, D. Hariskos, E. Lotter, S. Paetel, R. Wuerz, R. Menner, W.Wischmann, M.l Powalla Prog. Photovolt: Res. Appl. 19:894–897 (2011) [2] Acciarri, M. Binetti S., Le Donne A., Lorenzi B., Caccamo L., Miglio L., Moneta R. Marchionna S., Meschia M. Cryst. Res. Technol. 46, No. 8, 871–876 (2011) [3] European Patent 2013 n° EP 13425019.0

Quantum dot intermediate band (IB) solar cells have been proposed in order to increase the efficiency of traditional solar cells and immediately attracted a lot of attention and research since the time they were first proposed. The IB introduces an extension of the absorption coefficient of the semiconductor to lower energies, allowing a more thorough collection of the solar spectrum, via a two-step absorption of low-energy photons. Quantum dot (QD) structures are good candidates for IB solar cells, because their confined energy levels can overlap and form a miniband in dense arrays and the position of these levels and bands can be tuned varying the size and spacing of the QDs. The IB working mechanisms have been demonstrated for InAs QDs in GaAs, and many efforts are devoted to reduce the problems due to strain, and defect nucleation increasing carrier escape. Droplet epitaxy (DE) is a molecular beam epitaxy technique that allows for the growth of quantum dots of materials lattice matched to the barrier and the removal of the wetting layer. DE makes possible to indipendently control density, size and shape of the nanostructures. Densities as high as some 1011 cm-2 per layer have been reported and potentially a large number of layers can be stacked because the system is strain-free. Being a strain-free technique, there are virtually no defects in DE-grown materials. By tuning the size of the QDs it is obviously possible to change the position of the IB, and by tuning their aspect ratio the high energy states of the QDs can also be tuned in order to have a small electron-phonon coupling with the barrier. The lack of defect and wetting layer states can greatly reduce thermal escape of carriers from the IB, leaving photon-induced transitions the dominant ones, as requested by IB theory. For these reasons DE is a good candidate for the realization of QD-IB solar cells. We demonstrate the key working principle of IB materials, that is the production of sub-gap two-photon photocurrent, with Al0.3Ga0.7As solar cells containing GaAs QDs grown by DE. Measurements show that the shape of the two-photon photocurrent signal is different from the VB-CB photoresponse, indicating clearly that a two-photon process involving the QD levels is taking place. The two-photon signal response is in good agreement with the PL spectrum of the QD samples, that lets us easily understand the position of the energy levels of the system.

In this study, we have investigated the Hall majority carrier mobility of p-type, compensated multicrystalline solar grade silicon (SoG-Si) wafers for solar cells in the temperature range 70–373 K. At low temperature (~70 K) the difference in the mobilities measured for the compensated and the uncompensated reference samples is the highest, and the measured mobility shows dependence on the compensation ratio. Mobilities decrease with increasing temperature, and towards room temperature, the mobilities of the different samples are in the same range. The measurements show that, for these samples, the contribution from lattice scattering is dominating over ionized impurity scattering at room temperature. In the range of interest for silicon solar cells (above room temperature), the trend in carrier mobility is similar for all the samples, and the measured value for the sample with low compensation ratio and low doping density is comparable to the uncompensated references. A comparison of resistivity and majority carrier density measured by the Hall setup at room temperature and by four-point probe and glow discharge mass spectroscopy, respectively, is reported as well

We report the fabrication procedure and the characterization of an Al0.3Ga0.7As solar cell containing high-density GaAs strain-free quantum dots grown by droplet epitaxy. The production of photocurrent when two sub-bandgap energy photons are absorbed simultaneously is demonstrated. The high quality of the quantum dot/barrier pair, allowed by the high quality of nanostructured strain-free materials, opens new opportunities for quantum dot based solar cells. Left: Scheme of the fabricated quantum dot solar cell. Right: 1 × 1 μm2 image of the dot layer. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The research in thin film solar cells has been dominated by light absorber materials based on chalcogenides CdTe and Cu(In,Ga)Se2 in the last decades. Both the toxicity of cadmium and the scarce availability of indium lead towards the development of a material which constituents are earth-abundant and relatively harmless. Polycrystalline Cu2ZnSnS4 (CZTS) is a semiconductor with a bandgap between 1,40 and 1,50 eV and an absorption coefficient higher than 104 cm-1, thus suitable for being employed as a thin film light absorber. Kesterite-type CZTS material showing the highest energy conversion efficiency (η) is synthesized mostly via vacuum-based methods such as sputtering or evaporation of metals (or metal sulphides) onto the suitable substrate. These techniques have the advantage of easily controlling the chemical composition and phase profile in the thin films and normally have good reproducibility. However, the real low-cost potential of kesterites could be more efficiently exploited if combined with a scalable, non-vacuum deposition method. Starting from a sol-gel recipe proposed by Tanaka et al. [1] this work aims at fabricating CZTS using less expensive metallic precursors spin-coated on a rigid substrate. The annealing step was conducted using elemental sulphur rather than hydrogen sulphide, in order to develop a safer sulphurization method.

26th European Photovoltaic Solar Energy Conference and Exhibition; 676-680, In this paper we report the experimental results obtained from the manufacturing and characterization of III-V solar cells based on single junction, dual junction and triple junction structures. The main solar cell materials are GaAs and (Al)InGaP compounds. A test plan for qualification of “bare” solar cells for concentration systems is presented with its results. The test plan was derived from the space experience and it is based on the European Standards ECSS-E ST20-08, modified keeping into account the terrestrial standard for CPV modules (IEC 62108). The solar cells performances and their reliability is discussed with emphasis to the particular operation conditions induced by the CPV approach. These solar cells were then used and tested in two different CPV approaches: one based on standard concentrators and the other based on spectrum splitting concentrators. The systems, designed for standard concentration, need very high efficiency solar cells, therefore triple junction solar cells InGaP/GaAs/Ge are preferable. HCPV (High Concentration Photovoltaic) systems, based on this approach, have demonstrated efficiencies as high as 29%. The limit of this approach is that the multi junction solar cell structure is optimised for a specified incident spectrum (generally AM1.5D). During the day the spectrum is changing and the efficiency cannot be maintained, especially in the early morning and in the late afternoon. Spectrum splitting systems divide the light in several wavelength regions and use single or dual junction solar cells, optimised on each wavelength region. In this case a very high efficient system can be obtained that is less affected by spectrum variation. The use of standard concentrator and spectrum splitting systems is compared from a theoretical, experimental and economical point of view. The first results of outdoor performances are presented and discussed.

Thanks to the rapid growth of the photovoltaic market the silicon demand is continuously increasing. The shortage of purified silicon between 2004 and 2008 induced a strong price increase and trigged a capacity expansion as well as the introduction in ingot production of the so called “upgraded metallurgic grade silicon” (UMG-Si) as a feedstock. However, new solar grade silicon might contain significant higher fractions of impurities. It is well known their impact on the final cell quality but the debate is open about what are the acceptable contamination levels within the purified silicon feedstock also because it is well known that during the growth process and cell manufactory the material quality improves. In the recent period in the market there is an increasing availability of silicon feedstock at lower cost but its quality is not always guaranteed. In this paper we report a new fast in line characterization tools for feedstock analysis based on the Laserinduced breakdown spectroscopy. We applied this technique to the characterization of metallurgic grade silicon feedstock with the aim of valuate the applicability of this technique in the photovoltaic industry as in-line portable characterization tool. Different silicon grade feedstock were analyzed and selectivity and detection limit for the main impurities present in the silicon feedstock were determined

This paper reports the electrical characterization of commercially available crystalline silicon solar cells encapsulated with poly-vinylacetate doped with different Eu3R organic complexes. The inclusion of these complexes in the encapsulating matrix allows down-shifting of the solar spectrum components below 420 nm toward the maximum quantum efficiency of the solar cells. This effect has been proven under Air Mass 1 5 conditions (simulating terrestrial applications) where an increase of the total power delivered by the encapsulated cells has been observed. Moreover, this enhancement has been obtained using very low percentage by weight of organolanthanide dopants, allowing a reduction in the Watt peak price. At higher concentrations a strong quenching of the energy transfer from the organic antenna to the lanthanide ion has been observed.

The nucleation process of oxygen precipitates in silicon at 650 degreesC was investigated using photoluminescence (PL) measurements, which are demonstrated to provide a highly sensitive tool for the characterization of precipitates differing in structure and shape. The results of this study were first analyzed from a thermodynamic and kinetic point of view in order to explain the effect of minute differences in oxygen concentration on the PL spectra, which indicates that two kinds of nanometric oxides coexist in dynamic equilibrium. Then a hypothesis is advanced about the origin of the oxygen-induced PL bands, which is explained in terms of carrier confinement effects induced by the strain at oxide precipitates. (C) 2004 The Electrochemical Society.