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In the last few decades, the attention of scientific community has been driven toward the research on renewable energies. In particular, the photovoltaic (PV) thin-film technology has been widely explored to provide suitable candidates as top cells for tandem architectures, with the purpose of enhancing current PV efficiencies. One of the most studied absorbers, made of earth-abundant elements, is kesterite Cu2ZnSnS4(CZTS), showing a high absorption coefficient and a band gap around 1.4-1.5 eV. In particular, thanks to the ease of band-gap tuning by partial/total substitution of one or more of its elements, the high-band-gap kesterite derivatives have drawn a lot of attention aiming to find the perfect partner as a top absorber to couple with silicon in tandem solar cells (especially in a four-terminal architecture). In this work, we report the effects of the substitution of tin with different amounts of germanium in CZTS-based solar cells produced with an extremely simple sol-gel process, demonstrating how it is possible to fine-tune the band gap of the absorber and change its chemical-physical properties in this way. The precursor solution was directly drop-cast onto the substrate and spread with the aid of a film applicator, followed by a few minutes of gelation and annealing in an inert atmosphere. The desired crystalline phase was obtained without the aid of external sulfur sources as the precursor solution contained thiourea as well as metal acetates responsible for the in situ coordination and thus the correct networking of the metal centers. The addition of KCl in dopant amounts to the precursor solution allowed the formation of well-grown compact grains and enhanced the material quality. The materials obtained with the optimized procedure were characterized in depth through different techniques, and they showed very good properties in terms of purity, compactness, and grain size. Moreover, solar-cell prototypes were produced and measured, exhibiting poor charge extraction due to heavy back-contact sulfurization as studied in depth and experimentally demonstrated through Kelvin probe force microscopy.

The use of glassceramics in photocatalysis is an attractive option for the realization of smart optical fibers and self-cleaning windows. Here we present the photocatalytic activity of germanosilicate glasses embedding Ga2O3 nanocrystals prepared by batch melting and glass heat treatment. The powdered material is used for UV-assisted degradation of rhodamine in water. The kinetics show changes after repeated experiments. In the first cycle, the apparent rate is governed by a second-order reaction with a Gaussian-like shape, whereas the second cycle follows a first-order reaction. The modification appears to be correlated with perturbations in the defect population. Photoluminescence has been used to monitor the evolution of such defects. Kinetic data on photoreactions and defect formation have been modelled in a combined frame in which the defect concentration determines the photocatalytic activity. The results prove the photocatalytic ability of the studied glassceramics. Moreover, the general validity of the kinetic model can be of interest for other systems in which the photocatalytic response depends on photoreactive species concentration.

Thin film photovoltaic devices based on CdTe and Cu(In,Ga)Se2 rely on critical raw materials, but they find an eco-friendlier alternative in Cu2ZnSn(S,Se)4-based technology. To further reduce production costs and improve sustainability, other abundant metals, such as manganese, can be tested as a potential alternative to zinc. Mn is a safe and Earth-abundant element, and it can be used in light absorber materials when it is part of quaternary chalcogenides with copper and tin. This work reports on the growth and characterization of Cu2MnSnS4 thin films produced by a two-step deposition process, to improve the fundamental understanding of this compound and to promote its application in photovoltaic. The metallic precursors have been deposited by sputtering and the stack annealed at high temperatures in sulphur atmosphere. The layers, obtained in Cu-poor Mn-poor compositional regime, have been tested in solar devices with a record efficiency of 1.13% and a high open-circuit voltage of about 445 mV delivered by the champion device after over one year from the first PV measurement. X-ray diffraction and X-ray photoelectron, Raman, photoluminescence, and admittance spectroscopies have been used to investigate the Cu2MnSnS4 defectivity, and a scenario of high defects has emerged. Therefore, to promote the development of Mn-based photovoltaics the synthesis methodology should be optimized, and the device architecture should be specifically designed for the compound.

Pure sulfide kesterite (Cu2ZnSnS4) is one of themost promising emerging photovoltaic technologies thanks toits excellent absorption coefficient, cost-effectiveness, andenvironmental sustainability. However, record efficiencies arenot exceeding 11% due to several issues, such as absorberdefects or a nonoptimal band alignment with the toxic butconventionally used CdS buffer layer. To get rid of it, severalefforts have been made in the past few years. Among recenttheoretical works, TiO2 has been suggested as a suitable bufferlayer due to its optical and electrical properties, givingextremely promising results in device simulation. However, there are few experimental examples combining TiO2 withkesterite, and they generally show very modest performances. In this Letter, we report on the preliminary and promising results of our experimental procedure for the production of Cd-free kesterite photovoltaic devices featuring ALD-TiO2 as a buffer layer, leading to efficiencies comparable with our CZTS/CdS reference devices.

In current days, the research in the photovoltaic field aims to find and investigate cheap thin-film materials based on earth-abundant element suitable for terawatt era. To this purpose Cu2ZnSnS4 (CZTS) has been widely studied in the last decade, being structurally analogous to the well-documented Cu(In,Ga)Se2 but featuring inexpensive and abundant components. Recently we have reported a simple and straightforward sol-gel process to produce CZTS-based solar cells demonstrating how it is possible to provide a working device with an easily transferable on an industrial scale and low cost process. In this work we report important improvements to the described above methodology by growing CZTS thin films on a transparent substrate aiming to produce bifacial solar cells suitable for an incorporation into a tandem solar cell architecture. The direct droplet deposition of the precursor ink onto the FTO substrate, leads to the kesterite phase. Gelation and annealing steps, without the addition of further sulphur sources make this procedure suitable for industrial scale-up saving a considerable amount of raw materials. UV–Vis absorption, μ-Raman, Photoluminescence, X-ray diffraction and Energy Dispersive Spectroscopy measurements have been performed on the so-produced thin films. The morphology of the samples has been investigated by scanning electron microscopy, proving the extremely good quality of the material. PV devices with a FTO/Mo/CZTS/CdS/ZnO/AZO architecture were obtained showing η = 1.11% in a bifacial set up. A lower η = 0.99% has been measured by illuminating the front side of the cell only, demonstrating that the bifacial setup allows a +11% efficiency enhancement.

We investigate samples of compositionally disordered potassium-based perovskite single crystals with different composition and stoichiometry. The dielectric and Raman response is inspected over the nominal cubic-to-tetragonal long-range phase transition. The comparison between results shows that the occurrence of the phase transition is controlled by the temperature evolution of polar nanoregions (PNRs). We are able to correlate PNR order, formation, percolation, and freezing to the characteristic temperatures of each macroscopic crystal. The onset of the phase transition is found to occur when PNRs undergo a percolative ordering process, in correlation to the sudden arising of a specific high-frequency Raman mode.

The PV research is nowadays focused on finding low cost and easily processable thin-film materials, trying to move towards lighter and more versatile technologies. Among them, Cu2ZnSnS4 (CZTS) drew the attention of the scientific community thanks to its structural similarity to the already reported and well-studied Cu(In,Ga)Se2 but with the great advantage to use cheap and earth-abundant elements. In this work, we report CZTS-based solar cells produced with a simple and straightforward sol–gel process, demonstrating how further expensive and industrially non-scalable instruments are not needed in order to provide a working device. Direct drop-casting of a precursor solution onto the substrate, followed by gelation and final annealing in Ar atmosphere, generates the desired phase of the material without any further source of sulphur. The precursor solution contains metal acetate salts which play a primary role in networking the metals in the gel matrix, together with thiourea and dimethylsulfoxide. With this methodology, only the strictly necessary amount of reagents is used saving until 2–3 orders of magnitude of starting materials compared to other wet deposition techniques and working devices were obtained showing η = 1.1%. The addition of KCl as a dopant into the precursor solution was proven to be beneficial for the grain growth and material quality, so the performance of the corresponding devices rises it up to η = 1.75%. The synthesised thin films have been fully characterised by UV–Vis absorption, μ-Raman, X-ray diffraction and Energy Dispersive Spectroscopy measurements. Their morphology has been investigated by Scanning Electron Microscopy, proving the high quality of the material. The so-produced PV devices with a standard SLG/Mo/CZTS/CdS/ZnO/AZO architecture show interesting and promising results, especially in terms of short circuit current density.

Quantum dot solar cells are based on the concept of harvesting different parts of the solar light spectrum with a single, cheap semiconductor by simply changing the size of the nanoparticles. Of the many compositions explored, germanium is one of the most interesting as it has the major advantage of a large Bohr radius, which allows for the fabrication of larger particles. Moreover, germaniums possess very high optical absorption, and a small band gap give it free parameters to optimize the quantum dot solar cell. In a previous work, the germanium quantum dots were used in a Gratzel type solar cell containing an electrolyte, which is not desirable for applications. In this work instead, the n-doped germanium quantum dots were combined with a p-doped a-Si layer, making it the first all solid-state solar cell made from nanoparticles from a gas aggregation nanoparticle source. Remarkably, the effect of quantum confinement in both the germanium quantum dot assembled layer and a-Si was observed by peaks in the spectral response experiments. This work forms an important step toward realizing a germanium quantum dot based solar cell and studying quantum dot based solids.

Currently, the PV research focuses on finding low cost and easily processable materials. Here, we propose a simple chemical procedure for synthesizing Earth-abundant chalcogenide thin-films with tunable bandgap, leading to well-defined phases of Cu2XYS4 (with X = Zn, Fe; Y = Sn, Ge). The deposition process is straightforward and very cheap, based on the sol-gel technique, where the thin films are produced thanks to a direct drop-casting of the precursor solution, followed by a gelation process and heat treatment in argon atmosphere to generate the desired crystalline phase of the quaternary alloy. Metal acetate precursors were proved to have a primary role in creating a network, during the sol-gel transition, by coordinating and pre-organizing the metals in solution, together with thiourea (as the only source of Sulphur) and DMSO as solvent. Moreover, the addition of dopant amounts of KCl into the precursor solution was experimentally demonstrated to be beneficial for the grain growth and material quality, both crucial for the final solar device performance. XRD, μ-Raman, UV-Vis, and EDX spectroscopy measurements have supported the characterization of the so-synthesized layers (CZTS, Fe-substituted CZTS, Ge-substituted CZTS); their morphology was studied by SEM imaging, confirming the thin-film good quality. The bandgap, obtained from transmittance measurements, ranges from 1.4 to 2.1 eV depending on the combination of the chosen metal precursors, suggesting this class of materials as a suitable candidate as a top absorber in a tandem device architecture and promising single-junction prototypes of working solar-devices have been produced, even on semi-transparent substrate. [1 - 4] [1] V. Trifiletti et al. Chemistry Select 4 (2019) 4905. [2] V. Trifiletti et al. Materials 13 (2020) 1471. [3] G. Tseberlidis et al. Solar Energy 208 (2020) 532. [4] G. Tseberlidis et al. Solar Energy 224 (2021) 134.

Identifying new low cost and low environmental impact energy sources is becoming an imperative need of civil society. Photovoltaic (PV) is the most mature alternative renewable energy technology, led by silicon and whereas chalcogenide-based thin-film solar cells have gain market section… commercialization. Terawatt generation Here we present the synthesis and the characterization of Earth-abundant chalcogenide thin-films with tunable bandgap, leading to well-defined phases of Cu2XYS4 (with X = Zn, Fe, Mn; Y = Sn, Ge). As an alternative to the physical deposition of the metal precursor, here, we propose a straightforward and very cheap synthesis method based on the sol-gel technique. The Cu2XYS4 (with X = Zn, Fe; Y = Sn, Ge) thin films are produced thanks to a direct drop-casting of the precursor solution, followed by a gelation process and heat treatment in argon atmosphere to generate the desired crystalline phase of the quaternary alloy.3 UV-Vis, μ-Raman and XRD have characterized the so-synthesized layers, and EDX spectroscopy measurements and their morphology was studied by SEM imaging, proving the excellent quality of the material. The optical bandgaps of the presented compounds range from 1.4 to 2.1 eV, depending on the combination of the chosen metal precursors, making them suitable to be employed as stand-alone devices or as top solar cells in tandem architecture with various bottom cells. Promising single-junction prototypes of working devices have been produced, even employing semi-transparent substrates.4-6 An exciting alternative to the most studied Cu2ZnSnS4 (CZTS) is Cu2MnSnS4 (CMTS), a p-type semiconductor with Earth-abundant and low-cost elements. Manganese is cheaper (2$/kg vs 2,7$/kg) and has a higher occurrence in the Earth's crust than zinc (440ppm mean vs 65ppm mean), leading to the more economical and environmental sustainability of CMTS in respect of CZTS.1,2 Here we report the CMTS thin films, grown by a two-step deposition process (sputtering, followed by high-temperature annealing in sulphur vapours), produced in collaboration with RSE S.p.A., the industrial partner in the research project. The CMTS-based solar cells reached a record efficiency of about 1% and an open-circuit voltage exceeding 400 mV. Photoluminescence measurements allowed us to identify the detrimental defects acting in working conditions, suggesting paths to improve the photovoltaic properties. 1. S. Marchionna, A. Le Donne, M. Merlini, S. Binetti, M. Acciarri and F. Cernuschi, Journal of Alloys and Compounds, 2017, 693, 95-102. 2. A. Le Donne, S. Marchionna, M. Acciarri, F. Cernuschi and S. Binetti, Solar Energy, 2017, 149, 125-131. 3. V. Trifiletti, S. Mostoni, F. Butrichi, M. Acciarri, S. Binetti and R. Scotti., ChemistrySelect, 2019, 4, 4905-4912.

Universities are today seen as living labs for the creation of knowledge with the aim of transferring it to society. The integration of sustainability is a critical point in this context, as solutions for problems experienced in society can be experimented with regarding physical aspects, such as Solid Waste Management (SWM), and efficiency in energy and water use, but also social aspects such as accessibility, equality, and inclusion. This paper explores the implementation of similar SWM projects in two European universities, Milan-Bicocca University and Instituto Superior Técnico from Lisbon University. Milan-Bicocca was the pioneer project that followed an ambitious model that demanded the removal of all isolated waste bins from inside the offices and rooms, replacing them with waste collection islands in the public spaces. This meant a very coordinated procedure and communication plan, and inspired the pilot project in Instituto Superior Técnico, currently in the expansion phase. This paper describes the implementation of each model and their specificities, and a roadmap is proposed that resulted from the interactions, meetings, and discussions between the two teams, Italian and Portuguese.

The demand for new responsive materials is continuously growing in several areas as a result of approaching the physical limits of technologies, which now calls for a drastic change of strategy. Here, we report on memory responsive oxide-in-oxide nanostructured films obtained by radio-frequency sputtering of a 7.5Li2O–2.5Na2O–20Ga2O3–45GeO2–25SiO2 (mol%) glass target produced by melt quenching. Atomic force microscopy and scanning electron microscopy show that as-deposited oxide layers exhibit native nanophase separation, with the occurrence of Ga-rich oxide nanostructures – about 15 nm thick and 100 nm in diameter – incorporated in oxide layers about 70 nm thick. Interestingly, despite the wide band gap (above 4 eV), the nanostructured oxide films reveal the formation of unconventional electric field dependent charge transport paths across the material. The frequency and temperature dependence of electric conductivity and dielectric function highlights n-type conduction sustained by charge percolation through the oxide layer. Importantly, the results demonstrate the occurrence of conductivity changes by more than an order of magnitude in a few volts, and trapped charge values up to 1016 electrons per cm3.

The purpose of the study was to investigate the presence of mascara deposits on polymeric siloxane-hydrogel contact lenses (CLs) after in vivo 8 h of wear and to compare the affinity to mascara of two siloxane-hydrogels through in vitro contamination tests. The siloxane-hydrogel CLs were the Filcon V monthly replacement OPEN30 and the Delefilcon A daily disposable DAILIES TOTAL1 showing a water gradient from the core to the outermost hydrophilic surface layer. The investigated cosmetic was a blue mascara. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were carried out on new CLs, CLs exposed in vitro to mascara, and CLs worn for 8 h by mascara wearers (after rinsing the CLs in sodium chloride solution). Images by an optical microscope were acquired and processed on new CLs and CLs treated in vitro. EDX analyses on mascara allowed to characterize its elemental composition including aluminum (Al), which is neither a tear nor a CL component, thus being a marker of the presence of mascara deposits on polymeric siloxane-hydrogels. Adsorbed deposits containing Al were observed by SEM/EDX on all worn CLs of both materials, which showed a special affinity for the mascara components, more marked than for the tear components. By processing the images taken by optical microscopy after in vitro tests, the presence of mascara deposits was found to be more than two times higher in Delefilcon A compared to Filcon V CLs.

In the present study, an ethylene glycol-based electrolyte is used to electrodeposit copper onto zinc for the synthesis of the Zn/Cu/Sn stack, precursor of Cu2ZnSnS4. The employed solution contains diethanolamine (DEA) which supports the formation of amine-complexes, whose features are studied by UV–vis absorption, ESI-MS, and FTIR measurements, providing insight on the optimal concentration of DEA for copper complexation. Cyclic voltammetries (CVs) are carried out at increasing [DEA]/[Cu2+] ratios, highlighting the amine effect on the reduction potential of the copper species. The displacement reaction between copper and zinc is investigated by immersion potential measurements, showing a direct correlation to the voltammetric data. The optimized copper solution resulted in a negligible displacement contribution, allowing the electrochemical synthesis of Mo(sub)/Zn/Cu/Sn stack on a relatively large area (4 cm2). The metallic precursor is analyzed by SEM/EDS, AFM, XRD, and GDOES techniques. Finally, the kesterite CZTS phase is obtained through reactive annealing with elemental sulfur and it is characterized by SEM/EDS, XRD, and Raman spectroscopy. Photoelectrochemical water splitting on CZTS/CdS/Pt heterostructure is carried out in an aqueous solution at pH 6.85, showing a photocurrent of -5.05 mA/cm2 at 0 V vs RHE. A maximum applied bias photon-to-current efficiency (ABPE) value of 2.15% was found at 0.84 V bias.

A round-robin proficiency test (RR PT) on thin-film multi-junction (MJ) photovoltaic (PV) cells was run between 13 laboratories within the European project CHEETAH. Five encapsulated PV cells were circulated to participants for being tested at Standard Test Conditions (STC). Three cells were a-Si/μc-Si tandem PV devices, each of which had a different short-circuit current ratio between the top junction and the bottom one; the remaining two cells were single-junction PV devices made with material representative of the individual junctions in the MJ cells. The RR PT's main purpose was to assess the capability of the participating laboratories, in terms of employed facilities and procedures, to test MJ PV devices. Therefore, participants were requested to perform STC measurements of all cells according to their own procedure, which might not include external quantum efficiency measurements. The European Solar Test Installation (ESTI) of the Joint Research Centre (JRC) provided the reference calibrations against which the participants' results are compared. ESTI made also a verification of the cells performance at STC at the end of the RR PT, in order to allow a comparison between the initial stable state at which the cells were calibrated (just before circulation) and the one they had reached at the end of the RR PT. The overall results of the RR PT are here presented and discussed together with some aspects of MJ PV testing that emerged as not adequately applied or largely missing. Their full implementation is expected to improve the consistency of future results.

Gallium incorporation in silicate glasses gives rise to compounds in which the nucleation and growth of Ga-oxide nanostructures can be designer controlled so as to obtain a number of functional properties for photonic applications. However, despite planar geometry pertains to a large part of modern technology, no information is available yet on the scalability of Ga-oxide segregation mechanisms in oxide thin films. In fact, incorporated Ga-oxide nanostructures have only been obtained in bulk materials. Here we show that deposition of Ga-alkali-germanosilicate thin films by radiofrequency-plasma sputtering gives rise to Ga-oxide nanostructures incorporated in an amorphous matrix. X-ray diffraction, X-ray reflectivity, small-angle X-ray scattering, and atomic force microscopy data unveil the formation of lenticular nanoaggregates, only a few nm thick, even in as-deposited materials as a result of two-dimensional aggregation of spinel-like Ga2O3 nanoparticles. Importantly, the aggregate size distribution is controlled not only by the temperature but also by the film thickness when it is reduced from 102 nm to only a few nm. The results open the way to the design of oxide-in-oxide thin films with incorporated networks of nanostructures which can act as percolation paths for unconventional electric responses in neuromorphic functional systems.

Earth abundant Cu2MnSnS4(CMTS) absorbers for thin film solar cells were grown for the first time by a two-step vacuum approach. Metal precursors deposited on Mo-coated soda lime glass by thermal evaporation were annealed in sulfur vapors. Two series of CMTS samples were prepared to evaluate the effect of both the precursor stack (thickness and order of the metal layers) and the annealing procedure on the thin film quality. Several techniques, including Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Raman, X-ray Diffraction and Photoluminescence were used to test the CMTS layers and to study any possible secondary phase. Large grain size, high absorption coefficient and direct band suitable for PV applications have been obtained for Cu-poor/Mn-rich samples grown by sulfurization at 500°C&nbsp

Kesterite compound Cu2ZnSnS4 is the most promising next leader in the chalcogenide thin films technology as it is based on earth-abundant elements. In this work, kesterite thin films were prepared with a wet chemistry method by using a DMSO solution containing thiourea and acetylacetone, without further addition of vapour sulfur compounds to obtain the Cu2ZnSnS4 phase. The composition and stability of the molecular precursor-ink were investigated by EPR, IR and Raman spectroscopy. Acetate precursors were proved to have a primary role in creating a network in the sol-gel transition by bridging the metals in solution, together with thiourea and DMSO coordination. The high-quality of the thin films, obtained by spin coating deposition and thermal treatment at 500°C, was assessed by XRD, Raman, Energy-Dispersive spectroscopy and optical analysis, which revealed a direct band gap of 1.5 eV. Therefore, the precursor-ink and the deposition process developed in this work are very well suitable for solar cell application.

A chloride-free solution based on ethylene glycol was shown to be suitable for the electrodeposition of copper onto zinc, allowing the fabrication of a Mo/Zn/Cu/Sn metallic precursor stack. The addition of diethanolamine (DEA) played an essential role in minimizing displacement reactions by shifting copper reduction towards a more negative potential. The electrochemical behavior of copper species with and without DEA was studied by cyclic voltammetry, and subsequently confirmed by displacement reaction assessment (OCV and ICP-OES measurements). The metallic stack was characterized by SEM and AFM, showing the effectiveness of the copper plating solution. Reactive annealing was carried out in a tubular furnace to obtain the CZTS kesterite semiconductor, as confirmed by XRD and Raman spectroscopy. Keywords: Organic solution, Ethylene glycol, Diethanolamine, Chloride-free, CZTS

In recent years, multi-crystalline solar grade silicon (mc-SoG-Si), instead of expensive electronic-grade Si, is being considered in photovoltaic industry for production of solar modules. These materials usually contain a comparable amount of acceptors (e.g. boron) and donors (e.g. phosphorus) and are therefore called compensated mc-SoG-Si. The electrical parameters, e.g. majority carrier mobility (μ), majority carrier density (p) and resistivity (ρ), of compensated mc-SoG-Si which affect performance of the solar cells vary non-linearly with temperature due to several complex mechanisms. In this study, the authors propose artificial neural network (ANN)-based models to predict the three electrical parameters of mc-SoG-Si material. Using a limited amount of measurement data, the authors have shown that the ANN-based models can predict the three electrical parameters of a given sample over a wide temperature range of 70-400 K and a specific range of compensation ratio. The authors have shown with extensive simulated results that these models can predict the three parameters with a maximum error of ±10%.

It is well known that the major constrain to the efficiency of photovoltaic (PV) devices comes from the generation of unused heat. In this context, thermoelectric generators have been proposed as a viable heat recovery solution, leading to an increase of the overall efficiency. Within this kind of hybrid solutions, the PV and TEG parts can be either electrically separated or connected in the same circuit. In the second case, the presence of the TEG in series to the PV cell can lead to electrical losses. In this work we analyze the effect of various parameters on the output power of electrically hybridized HTEPV systems by means of both electrical measurements and simulations. The results reveal that while electrical lossless condition exists (as also reported in previous work) it not always corresponds to significant power gains respect with the sole PV case. In addition, the strong temperature sensitivity of the lossless condition makes the electrical hybridization hardly practically implementable. This sensitivity in the framework of an actual application scenario, where the solar radiation is variable over time, would make the system working often in a suboptimal regime. The present study gives a new understanding on the actual applicability of electrically hybridized HTEPV devices.

The growth dynamics of Ga(In)N semiconductors by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) at low temperatures (T = 450 °C) is here investigated. The presence of droplets at the growth surface strongly affects the adatom incorporation dynamics, making the growth rate a decreasing function of the metal flux impinging on the surface. We explain this phenomenon via a model that considers droplet effects on the incorporation of metal adatoms into the crystal. A relevant role is played by the vapor-liquid-solid growth mode that takes place under the droplets due to nitrogen molecules directly impinging on the droplets. The role of droplets in the growth dynamics here observed and modeled in the case of Nitride semiconductors is general and it can be extended to describe the growth of the material class of binary compounds when droplets are present on the surface.

Exploitation of solar energy conversion has become a fundamental aspect of satisfying a growing demand for energy. Thus, improvement of the efficiency of conversion in photovoltaic (PV) devices is highly desirable to further promote this source. Because it is well known that the most relevant efficiency constraint, especially for single-junction solar cells, is unused heat within the device, hybrid thermo-photovoltaic systems seem promising . Among several hybrid solutions proposed in the literature, coupling of thermoelectric and PV devices seems one of the most interesting. Taking full advantage of this technology requires proper definition and analysis of the thermal losses occurring in PV cells. In this communication we propose a novel analysis of such losses, decoupling source-dependent and absorber-dependent losses. This analysis enables an evaluation of the actual recoverable amount of energy, depending on the absorber used in the PV cell. It shows that for incoming solar irradiation of $$1000\,\hbox {W}/\hbox {m}^{2}$$ , and depending on the choice of material, the maximum available thermal power ranges from $$380\,\hbox {W}/\hbox {m}^{2}$$ (for single-crystal silicon) to $$130\,\hbox {W}/\hbox {m}^{2}$$ (for amorphous silicon).

Cu2ZnSnS4 (CZTS) thin films and solar cells were successfully prepared using a new process based on spray pyrolysis technique. The main advantage of the proposed process is the avoiding of sulphurisation process at high temperature and in toxic gases like H2S. X-ray diffraction studies and Raman spectroscopy confirmed the formation of good-quality microcrystalline CZTS films in a tetragonal structure. Optical measurements showed that CZTS films have a direct band gap and high absorption coefficient (4 × 104 cm−1) as requested for solar cell application. CZTS solar cell prototypes deposited on low-cost flexible plastic substrates were prepared and tested.

Objectives: This article compares the optical performance of soft contact lenses (CLs) treated with multipurpose or hydrogen peroxide care systems. Methods: The investigated care systems were (1) 3% hydrogen peroxide solution Oxysept (Abbot Medical Optics, Abbott Park, IL) and (2) multipurpose solution Regard (Vita Research, Ariccia, Italy). Three types of silicone hydrogel CLs were studied (comfilcon A, lotrafilcon B, and balafilcon A), unworn and exposed for 30 times to the solutions, which were replaced every 8 hr. The optical performance of the CLs was evaluated through the on-eye transmitted light wavefront patterns by considering new CLs as references. The surface morphology of the CLs was investigated by scanning electron microscopy. Results: Statistically significant modifications in the range 0.1 to 0.3 μm of Zernicke coefficients and modifications of the root mean square of the wavefront aberration function were found for CLs treated with multipurpose solution, in agreement with the observed modifications of the surface morphology. Statistically significant changes were also found after exposure to the hydrogen peroxide solution, but the variation of the Zernicke coefficients was found lower than 0.1 μm, thus being negligible in CL optical performances. Conclusions: In addition to disinfection ability and ocular surface reactions, CL care systems are different in solution-related CL optical performance. Multipurpose solutions may affect the CL surface morphology with significant modifications of the transmitted light wavefront pattern.

Earth abundant and low cost Cu2MnSnS4 (CMTS) thin films were grown by a two-step vacuum approach: metal precursor stacks grown by thermal evaporation were heat treated in elemental sulfur vapors. Cu-poor/Mn-rich CMTS samples with large grain size and good layer compactness were obtained by sulfurization at 585°C with an initial step at 115°C to enhance the metal intermixing. They were primarily tested by Energy Dispersive Spectroscopy, micro-Raman and Photoluminescence. Then, solar cells based on them were realized and tested, showing enhanced performance with respect to a previous study (efficiency 0.5%, open-circuit voltage 302mV, short-circuit current density 4.6mA/cm2, fill factor 36%). A 40min post-deposition annealing in air at 225°C significantly improved the performance of these emerging PV devices (efficiency 0.83%, open-circuit voltage 354mV, short-circuit current density 5.8mA/cm2, fill factor 40%). The beneficial effects of the low temperature annealing were investigated, in terms both of material properties and PV device performance modification

Today, after more than 70 years of continued progress on silicon technology, about 85% of cumulative installed photovolatic (PV) modules are based on crystalline silicon (c-Si). 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 grown by 40% per year over the last decade. An additional step in the silicon solar cell development is ongoing, and it is related to a further efficiency improvement through defect control, device optimization, surface modification, and nanotechnology approaches. This paper attempts to briefly review the most important advances and current technologies used to produce crystalline silicon solar devices and in the meantime the most challenging and promising strategies acting to increase the efficiency to cost/ratio of silicon solar cells. Eventually, the impact and the potentiality of using a nanotechnology approach in a silicon-based solar cell are also described.

This paper reports the electrical characterization of commercially available crystalline silicon solar cells encapsulated with poly-vinylacetate doped with different Eu3+ 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. Copyright © 2009 John Wiley & Sons, Ltd.

Aim of this work is to study the electrical properties and the minority charge carrier recombination behaviour of extended defects in multicrystalline silicon (mc-Si) ingots grown from solar grade silicon (SoG-Si) feedstock. The pure metallurgical SoG-Si feedstock has been produced directly by carbothermic reduction of very pure quartz and carbon without subsequent purification processes.This mc SoG-Si is studied by temperature-dependent Electron Beam Induced Current measurements and PhotoLuminescence spectroscopy and the potentiality of the combination of these two techniques in the identification of the defects which limit the quality of the base material is shown. The EBIC mapping technique shows the presence of electrically active grain boundaries at room temperature while dislocations result inactive. Dislocations become active only at temperatures lower than 250K, indicating a moderate level of metal decoration. The most detrimental defects in this material seem to be the grain boundaries and impurities dissolved in the matrix. Furthermore, the PL spectra reveal the presence of oxygen and carbon related complexes. In this work we show that the knowledge about the defect related recombination processes acquired by a combined application of EBIC measurements and PL-spectroscopy is of particular importance to tune the proper solar cell process step to be applied on such material.

Because of economic and energy-consumption considerations, multicrystalline solar grade silicon (mc-SoG-Si), instead of expensive electronic-grade Si, is being considered in photovoltaic (PV) industry for production of solar modules. These materials usually contain a comparable amount of acceptors (e.g., Boron) and donors (e.g., Phosphorus) and are therefore called compensated mc-SoG-Si. The three main electronic parameters, e.g., majority carrier mobility (μ), majority carrier density (p) and resistivity (ρ), of compensated mc-SoG-Si vary nonlinearly with temperature due to several complex mechanisms. In this paper, we propose two artificial neural network (ANN)-based models to predict these electronic parameters of mc-SoG-Si material. Using a limited amount of measurement data, we have shown that the first ANN-based model can predict the three electronic parameters of a given sample without accounting for the compensation ratio over a wide temperature range of 70-400 K. Whereas, the second ANN model can predict these electronic parameters of a given sample with unknown compensation ratio over the same temperature range. With extensive simulation results we have shown that these models can predict the three parameters with a maximum error of ±10%.

Cu2ZnSnS4(CZTS) absorber layers grown by sputtering were investigated by photoluminescence before and after the chemical bath deposition of CdS in order to evaluate the possible passivation of point defects by Cd atoms at the absorber/buffer layer interface. According to the literature, a broad emission around 1.21 eV was observed at low temperature under above bandgap excitation of the as-grown CZTS samples. Broad bands at 1.075 eV and 0.85 eV were detected for the first time under below bandgap excitation of the as-grown CZTS samples at low temperature, which were explained in terms of radiative transitions involving point defect-related levels determined in the literature by first-principles calculations. The emissions observed in the as-grown samples were monitored by both above and below bandgap excitations also in standard CZTS solar cells produced on the same layers. The obtained results suggest that, as in the case of Cu(In, Ga)Se2, Cd atoms passivate point defects at the absorber/buffer layer interface also in CZTS.