Photovoltaic cells offer a clean and sustainable solution by allowing the reduction of fossil energy. In recent decades, several types of solar cells have been proposed to overcome the limitation of stiffness of common silicon-based solar cells. Due to their flexibility, thin-film solar cell technology is now of great interest to the community. Now, most of the thin-film solar cell market belongs to CdTe or CIGS based, but its implementation involves a high cost due In/Ga and safety problem to the high toxicity of Cd. Thanks to its abundance and non-toxicity [1] Sb 2 Se 3 is one of the main candidates to overcome these limitations. Furthermore, laser scribing technology, the main candidate for guaranteeing a large production volume with a high precision manufacturing, needs to support the growth of new types of absorbent material without damaging others. In this work, Sb 2 Se 3 based solar cells have been grown by the low-temperature pulsed electron deposition (LT-PED) technique [2] and the so-called P3 process has been performed by laser scribing. Photovoltaic devices were fabricated as described in [3] with the following architecture: ZnO: Al/ZnO/CdS/Sb 2 Se 3 /Mo/Glass, shown in Figure 1a . The films were deposited onto 2.5×2.5 cm 2 soda-lime glass substrates, coated with molybdenum (Mo).

The laser scribing is one of the crucial technological steps in the industrial processing of solar cells, while the mechanical scribing is generally used for practical reasons on the laboratory scale. Using a picosecond laser, preliminary results on the scribing of CuInGaSe2 thin film solar cells deposited by the low temperature pulsed electron technique, are reported. The complete comparison between laser- and mechanical-scribing is still in progress, however SEM imaging and EDX analysis confirm the excellent structural and morphological quality of the laser scribed samples.

6 aprile 2020 [3] 7 febbraio 2020 [4] 14 ottobre 2019 [5] 18 settembre 2019 [6] 9 maggio 2019 [7] 8 aprile 2019 [8] 8 febbraio 2019 13 dicembre 2018 26 settembre 2018 [9] 24 maggio 2018 10 aprile 2018 [10] 21 marzo 2018 27 febbraio 2018 [11] 20 febbraio 2018 [12] 25 gennaio 2018 [13] 4 luglio 2017 [14] 22 giugno 2017 11 gennaio 2017 [15] 12 dicembre 2016 [16] 26 settembre 2018 [17] 18 luglio 2017 [18]

An important field to improve solar cell efficiency is the optimization of the antireflection coating (ARC) to allow more light to be converted; from a theoretical point of view this could increase the solar cell efficiency of 0.5%. Different ARC designs have been investigated, the most promising approaches are based on multi layers or gradient index approaches. These approaches have been theoretically and experimentally optimized to increase the photocurrent in the spectral range 300-1880 nm. Experimental results show that the solar cell efficiency can be increased of 0.5% both on thin and standard CESI space solar cells having 30% BOL efficiency.

This chapter reports the progress on the fabrication of thin film CIGS-based solar cells by means of the low temperature pulsed electron deposition technique. The innovative and multidisciplinary approach aims to solve the main issues preventing a possible industrial scale up of the process, i.e. the need of a fast, reliable and automated process, suitable for both static and dynamic deposition of CIGS solar cells on flexible substrates. The final goal is to open new opportunities, particularly in the emerging field of the building-integrated photovoltaic.

In this paper we report on the single stage deposition of CuInxGa1-xSe2 (CIGS)-based bifacial solar cells on glass coated with Fluorine-doped Tin Oxide (FTO) or Indium Tin Oxide (ITO) by single-stage low-temperature (250 degrees C) pulsed electron deposition (LTPED).We show that the mechanism of Sodium incorporation during the low-temperature deposition of CIGS on both FTO and ITO leads to the formation of a stable n+/p+ ohmic tunnel junction and photovoltaic efficiencies exceeding 14% can be obtained without any intentional bandgap grading of CIGS.The significant degradation of the cell fill factor with decreasing CIGS thickness is found to be related to the presence of craters left behind by micro-fragments of CIGS target, which are weakly incorporated in the film during the LTPED growth and removed during the subsequent process steps. Evidence is also presented that the low-temperature deposition of CIGS on ITO leads to the formation of a Ga-rich CIGS layer at the interface and to an unintentional compositional grading propagating towards the active region of the solar cells. The defects associated with this grading may be responsible for the loss in FF and Voc with respect to the cells deposited on FTO and Mo back contacts.

The quest for single-stage deposition of CuInGaSe2 (CIGS) is an open race to replace very effective but capital intensive thin film solar cell manufacturing processes like multiple-stage coevaporation or sputtering combined with high pressure selenisation treatments. In this paper the most recent achievements of Low Temperature Pulsed Electron Deposition (LTPED), a novel single stage deposition process by which CIGS can be deposited at 250 °C, are presented and discussed. We show that selenium loss during the film deposition is not a problem with LTPED as good crystalline films are formed very close to the melting temperature of selenium. The mechanism of formation of good ohmic contacts between CIGS and Mo in the absence of any MoSe2 transition layers is also illustrated, followed by a brief summary of the measured characteristics of test solar cells grown by LTPED. The 17% efficiency target achieved by lab-scale CIGS devices without bandgap modulation, antireflection coating or K-doping is considered to be a crucial milestone along the path to the industrial scale-up of LTPED. The paper ends with a brief review of the open scientific and technological issues related to the scale-up and the possible future applications of the new technology.

In this study, a comparison between Al-doped ZnO (AZO) as Transparent Conductive Oxide for Cu(In,Ga)Se2-based solar cells grown by Pulsed Electron Deposition (PED) and Radio Frequency Magnetron Sputtering (RFMS) was performed. PED yielded polycrystalline [002] mono-oriented thin films with low electrical resistivity and high optical transparency with heater temperatures ranging from room temperature (RT) to 250°C. The electrical resistivity of these films can be tuned by varying the heater temperature, reaching a minimum value of 3.5×10−4Ωcm at 150°C and an average transmittance over 90% in the visible range. An AZO film grown at RT was deposited by PED on an actual Cu(In,Ga)Se2-based solar cell, resulting to an efficiency value of 15.2% on the best device. This result clearly shows that PED is a suitable technique for growing ZnO-based thin films for devices/applications where low deposition temperature is required. On the other hand, an optimized AZO thin film front contact for thin film solar cells was studied and fabricated via RFMS. The parameters of this technique were tweaked to obtain highly conductive and transparent AZO thin films. The lowest resistivity value of 3.7×10−4Ωcm and an average transmittance of 86% in the 400–1100nm wavelength range was obtained with a heater temperature of 250°C. A thick sputtered AZO film was deposited at RT onto an identical cell used for PED-grown AZO, reaching the highest conversion efficiency value of 14.7%. In both cases, neither antireflection coatings nor pure ZnO layer was used.

Solution‐free and catalyst‐free vertically aligned ZnO nanorods have been synthesized by thermal CVD reactor at relatively low temperature (<500°C) to produce high‐surface 3D photoanode on glass substrate. Different TCOs films such as Al doped ZnO films deposited by PED, RF‐sputtering techniques and ITO were considered for the growth as starting seeding layer for the nanorods. The aim of the paper is mainly focused to control the thickness and length of these nanostructures by varying not only the growth parameters, such as amount of Zn evaporation, but also substrate characteristics, such as grain size of Al doped ZnO and ITO seeding films. The morphology of the different TCO substrates and also the grown ZnO nanorods have been analyzed with the help of atomic force microscopy and scanning electron microscopy. The study revealed that size and orientation of ZnO nanorods are mainly related to TCO's grain morphology and crystallinity, while their length can be controlled by varying Zn evaporation parameters.

The evaporation mechanisms from a solid target in pulsed electron deposition (PED) technique have been investigated by analysing the chemical composition and the thickness distribution of CuGaSe2 (CGS) films grown at different discharge voltages on glass substrates. The behaviour of the plasma plume generated from the target can be described by a linear combination of two coexisting processes: incongruent thermal evaporation and congruent ablation, which exhibit different weights depending on the PED voltage. The first component arises from the thermodynamic liquid-to-vapour transition involving the very first layers of the target surface, while the second one is due to the subsurface target penetration of the pulsed e-beam. The chemical composition of the thermally evaporated cloud, according to the CuGaSe2 phase diagram, exhibits an incongruent Cu depletion during the solid-to-gas phase transition with respect to the target, thus forming the ordered vacancy compound CuGa3Se5, while the sublimation of ablated species is perfectly stoichiometric. The thermally evaporated plasma follows a typical surface source spatial distribution, while the expansion of the ablation products exhibit a forward-peaked angular behaviour proportional to cos(p) theta (4 < p < 7). The incongruent component becomes negligible by enhancing the discharge voltage, where the e-beam is able to more deeply penetrate the target, and the electron power density exceeds the threshold ablation value of 1 x 10(8) W cm(-2). The proposed mechanism for PED process is compared to other models describing the plume generation in pulsed high-energy-induced growth technique. This study represents a remarkable result to better understand and control the PED process.

Zinc oxide (ZnO) is one of the most promising materials for realizing three-dimensional (3D) nanostructured transparent conducting oxides (TCOs) on large scale, because it is cheap, it can be modified with large concentrations of trivalent elements (such Al, Ga or In) and it is characterized by good electron mobility, wide bandgap and visible-range transparency. But, above all, it can be easily obtained in the form of different nanostructures with a large number of growth techniques. A solution-free and catalyst-free approach has been explored here by the vapor phase synthesis of vertically aligned ZnO nanorods on ZnO:Al (AZO) films grown by pulsed electron deposition (PED). The obtained nanostructured TCOs resulted to be homogeneous on large areas and easily patternable by means of mechanical masks. The morphology, crystalline structure, electrical and optical properties of the obtained samples have been characterized in depth. The possible use of such a nanostructured TCO in excitonic (e.g. DSSC) or low-reflectivity traditional solar cells is discussed.

An approach to low-cost production of Cu(In,Ga)Se2 (CIGS) solar cells based on pulsed electron deposition (PED) has achieved a crucial milestone. Lab-scale solar cells with efficiencies exceeding 15% were obtained by depositing CIGS from a stoichiometric quaternary target at 270 °C and without any post-growth treatment. An effective control of the p-doping level in CIGS was achieved by starting the PED deposition with a layer of NaF tailored to generate the optimum Na diffusion. These results show that PED is a promising technology for the development of a competitive low-cost production process for CIGS solar cells.

Zinc Sulphide films were grown by pulsed electron deposition (PED) from room temperature to 350 degrees C to investigate the possibility of its application in solar cells, in particular as an alternative buffer layer deposited at low temperature. The films were characterized by X-ray diffraction, TEM, AFM, optical absorption and electrical measurements. ZnS films display crystalline structure and columnar growth at room temperature on amorphous substrate; the crystallization improves with the substrate temperature and is predominantly related to the cubic (111) orientation, while the thicker films show coexistence of hexagonal and cubic structures. All the samples have transparencies exceeding 70% in the range 400-1000 nm, energy band gap between 3.25 and 3.65 eV increasing with temperature and resistivity in the range of 10(4)-10(6) Omega cm. The optimization of the growth rate as a function of the growth parameters (substrate temperature and electron gun voltage) is also discussed. The reported results indicate that ZnS might be a suitable material for photovoltaic applications, specifically in process requiring low deposition temperature. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ABSTRACT We report a novel route for growing Cu(In,Ga)Se 2 (CIGS) thin films, based upon the Pulsed Electron Deposition (PED) technique. Unlike other well‐known deposition techniques, PED process allows the stoichiometric deposition of CIGS layers in a single stage, without requiring any further treatments for Cu/(In + Ga) ratio adjustment nor selenization. The structural properties of polycrystalline CIGS films strongly depend on the growth temperature, whereas post‐deposition annealing enhances the grain size and the <112> out‐of‐plane preferred orientation of the chalcopyrite structure, without affecting the film composition. Preliminary measurements of the performances of solar cells based on these films confirm the great potentiality of PED‐grown CIGS as absorber layers. Copyright © 2011 John Wiley & Sons, Ltd.

We investigate the high-temperature magnetic and transport properties of LaMn7O12, which displays a similar perovskitelike structure and the same single-valent Mn3+ properties of LaMnO3 but a much simpler Jahn-Teller (JT) distortion at T-JT = 650 K. We find that the magnetic response of LaMn7O12 is similar to that of LaMnO3 below T-JT, but strikingly different in the undistorted phase above T-JT, where the Curie-Weiss susceptibility is strongly suppressed. Electrical resistivity and thermopower measurements unveil a concomitant crossover from nonadiabatic to adiabatic small polaron regime. This suggests that the above suppression is due to low-spin electron-hole dimers formed by the e(g) charge transfer between Mn sites and stabilized by the slow JT dynamics above T-JT.

The mechanical properties of CeO2 layers that are undoped or doped with other elements (e.g. Zr and Ta) are a topic of special interest specially in the manufacturing of superconductor buffer layers by pulsed electron deposition. Nowadays, the trend is to produce small devices (i.e. coated conductors), and the correct mechanical characterization is critical. In this sense, nanoindentation is a powerful technique widely employed to determine the mechanical properties of small volumes. In this study, the nanoindentation technique allow us determine the hardness (H) and Young's modulus (E) by sharp indentation of different buffer layers to explore the deposition process of CeO2 that is undoped or doped with Zr and Ta, and deposited on Ni–5%W at room temperature. This study was carried out on various samples at different ranges of applied loads (from 0.5 to 500mN). Scanning electron microscopy images show no cracking for CeO2 doped with Zr, as the doping agent increases the toughness fracture of the CeO2 layer. This system, presents better mechanical stability than the other studied systems. Thus, the H for Zr–CeO2 is around 2.75·106Pa, and the elastic modulus calculated using the Bec et al. and Rar et al. models equals 249·106Pa and 235·106Pa respectively.

We have deposited SiC thin films using two different deposition techniques, Pulsed Electron Deposition (PED) and Pulsed Laser Deposition (PLD). The PED technique is a relatively new technique where a pulsed electron flux with high energy directly hits the target surface producing a plasma in a very similar way to PLD, where, instead, a pulsed laser beam is used. These two techniques can give very dense thin films with stoichiometry much closer to the target one’s compared to others physical vapour deposition techniques (sputtering, e-beam). The major drawback of PED is that the thin film surface is affected by the presence of particulate, due to the impact of the high energy electron beam with the target. In the PLD system we used a magnetic field to curve the plasma path in the vacuum and we placed the substrate at 90 ○ with respect to the target allowing the deposition of particulate-free samples. The characterization of the films has been made by measuring the optical reflectance vs angle of incidence in the EUV region (from 121.6 nm down to 40.7 nm), taking measurements at different time from deposition. X-ray photoemission measurements have been also carried out to show stoichiometry and the presence of contaminants. Other measurements such as X-ray diffraction, atomic force microscopy and profiling were also carried out to check crystalline domains and surface roughness.

We report the synthesis and the characterization of PrMn7O12, a new manganite with multiple (quadruple) perovskite structure of general chemical formula: AA(3)(')B(4)O(12). This family of manganites is extremely interesting and is attracting a great attention; thanks to its structural peculiarity (and complexity), it might help the comprehension of the ordering phenomena (charge, orbital, spin), which is one of the most challenging issues in the strongly electron correlated rare-earth oxides. Like the majority of the materials having similar structure, PrMn7O12 is a metastable compound, requiring high pressure synthesis. Contrary to other reported isostructural compounds, PrMn7O12 crystallizes in two different forms with rhombohedral (R-3) and monoclinic (I2/m) symmetry, the latter characterized by a distortion of the perovskite structure lattice that depends on the synthesis conditions. The approximate stability fields of the two PrMn7O12 phases have been defined in the P/T space, allowing the synthesis of almost single phase samples functional to physical characterization. For the monoclinic phase we succeeded in the growth of crystals sufficiently large to perform structural refinement by single crystal x-ray diffraction data; the rhombohedral structure was instead refined by Rietveld method applied to powder x-ray diffraction data. Although the two phases differ slightly from the crystallographic point of view, physical characterizations reveal surprisingly different properties, in particular for what concerns the magnetic behavior. The differences of the two structures might be explained with a different electronic configuration of Mn, implying the partial occupation of Mn3+ in low spin state on the B site of the rhombohedral polymorph.

A first order structural Jahn-Teller transition at T_{JT} = 650 K has been recently reported for the quadruple perovskite LaMn7O12 . We have carried out magnetization and transport measurements below and above T_{JT} in order to investigate the effect of the transition. Electrical conduction turns out to be polaronic, changing from non-adiabatic to adiabatic through the transition. Magnetic behavior can be described by non-interacting Mn3+ ions below T_{JT}, while above T_{JT} it is of questionable interpretation. The effect of thermal cycling on as grown samples of different purity degree also allowed us to clarify the intrinsic magnetic response of LaMn7O12 at lower temperatures.