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32nd European Photovoltaic Solar Energy Conference and Exhibition; 1341-1342, In this work structural and electrical properties of titanium oxide thin film obtained by e-beam evaporation and annealed at different temperatures were studied using different characterization techniques, in order to evaluate its use as alternative to ITO as back contact in organic/inorganic solar cells. According to XRD analyses the obtained TiO2 films showed mainly the presence of anatase crystal structure once annealed at T> 400 °C. Electrical and optical characterization of the annealed samples shows the best results for the films annealed at T> 400 °C with a resistivity of ca.10-2 ohm cm, a mobility of 3 cm2/Vs and carrier concentration of 1019/cm3. Therefore, the observed results indicate formation of good quality titanium oxide films by using e-beam evaporation deposition technique followed by thermal annealing, with physical and electrical properties desirable for our applications.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1770-1772, Semiconductors compound as Cu2SnS3 (CTS) with cheap and more available elements are getting more and more interest. Its low bandgap makes it suitable as absorber in the long wavelength region in solar cell with heterojunction structure. In this work CTS thin films are grown by two-steps processes: precursor deposition by co-sputtering of CuS and SnS, followed by a thermal treatment in sulphur atmosphere. A first optimization of this process allowed to make a CTS based solar cell exhibiting short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) of 29.7 mA/cm2, 0.219 V as well as a total-area power-conversion efficiency of 2.37%. Furthermore the External Quantum Efficiency (EQE) curve at wavelength higher than 1200 nm has values higher than 10%.

29th European Photovoltaic Solar Energy Conference and Exhibition; 116-119, An expression for optical absorbance in Si solar cells is derived, which is a simplification of the expression for the same quantity given by Basore. Unlike the Basore expression, the simplified expression does not require the determination of the front-surface external and internal reflectance prior to be used. For a textured solar cell, it is equivalent to the Basore expression, if the average ray-path angle with respect to the surface normal is equal at all passes of light across the cell. Unlike the Basore expression, it allows fitting the measured quantum efficiency of not-textured solar cells with diffuse rear surface. The simplified expression can be easily implemented in the numerical simulation program PC1d. The measured quantum efficiency of a textured solar cell is fitted with both the new and Basore expressions. Overlapping fit-curves are obtained. The measured quantum efficiency of a not-textured solar cell with not-polished rear surface is fitted by using the new expression. Finally, with the new expression, the maximum absorbance for weakly absorbed light is estimated in solar cells with textured back surface at both flat and textured front surfaces.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3219-3221, We first define a good-quality module. Then we present the evaluating approach. We apply the approach to modules of different kind and producers. Finally, we verify the agreement of the found values of energy bandgap (Eg) with theory and published values.

26th European Photovoltaic Solar Energy Conference and Exhibition; 2911-2915, Cu2ZnSnS4 (CZTS) is considered a promising alternative to the well developed Cu(In,Ga)Se2 which contains materials such as In and Ga, expensive and with a limited availability. The best solar cell based on CZTS has recently reached a conversion efficiency of 6.8% but the material quality still needs to be improved. In this work we prepare the CZTS films by sulfurization of precursors composed by a multilayer of ZnS, Sn and Cu grown by evaporation. Precursors with different composition, order of the layers and different sulfurization temperatures are tested in order to optimize the film quality. The composition and the structural properties of the CZTS films are characterized by XRD, SEM-EDS and Raman spectroscopy. The samples are further characterized by transmittance and reflectance measurements in order to obtain an estimate of the absorption coefficient. We find that the absorption coefficient at low energies increases with increasing Zn content and with increasing sulfurization temperature. These trends are explained in term of an increase of the disorder in the material.

Catalytic aerobic oxidation of benzyl alcohol (BnOH) to benzaldehyde (PhCHO) over supported noble metal catalysts has grabbed the attention of researchers due to the critical role of PhCHO in numerous industrial syntheses. In the present study, a novel catalyst, Pd-P alloy supported on aminopropyl-functionalized mesoporous silica (NH2-SiO2), was prepared through in situ reduction and characterized by BET-BJH analysis, SEM, TEM, XRD, FTIR, TG-DTA, and XPS. Chemical properties and catalytic performance of Pd-P/NH2-SiO2 were compared with those of Pd° nanoparticles (NPs) deposited on the same support. Over Pd-P/NH2-SiO2, the BnOH conversion to PhCHO was much higher than over Pd°/NH2-SiO2, and significantly influenced by the nature of solvent, reaching 57% in toluene at 111 °C, with 63% selectivity. Using pure oxygen as an oxidant in the same conditions, the BnOH conversion increased up to 78%, with 66% selectivity. The role of phosphorous in improving the activity may consist of the strong interaction with Pd that favours metal dispersion and lowers Pd electron density.

In this paper a technique based on the analysis of forward bias capacitance for interface characterization in Schottky structure is proposed. In particular, the occurrence of multiple peaks in the capacitance-voltage curve was related to non-uniform properties of the interfaces, for instance undesired localized interface defects. A graphene/silicon solar cell is considered as case of study. Experimental forward bias capacitance-voltage curve exhibits multiple peaks, thus suggesting the occurrence of interface defects. A numerical model of the solar cell was implemented in TCAD environment considering non-uniform interface properties. The model was calibrated to describe the experimental behavior and allowing to extract the defects distribution. HNO3 doping in graphene was exploited to reduce defects. The effectiveness of this approach was proved comparing experimental capacitance before and after doping.

Silicon heterojunction solar cells have largely demonstrated their suitability to reach high efficiencies. We have here focused on p-type c-Si wafers as absorber, considering that they share more than 90% of the solar cell market. To overcome some of the issues encountered in the conventional (n)a-Si:H/(p)c-Si configuration, we have implemented a mixed phase n-type silicon oxide (n-SiOx) emitter in order to gain from the wider bandgap and lower activation energy of this material with respect to (n)a-Si:H. The workfunction of the transparent conductive oxide layer (WTCO) plays also a key role, as it may induce an unfavourable band bending at the interface with the emitter. We have here focused on AZO, a promising alternative to ITO. Different layers with varying WTCO were prepared, by changing relevant deposition parameters, and were tested into solar cells. The experimental results have been explained with the aid of numerical simulations. Finally, for the n-SiOx/(p)c-Si heterojunction with optimized WTCO a potential conversion efficiency well over 23% has been estimated. © 2015 Published by Elsevier Ltd.

Cycling high temperature CO2 capture using CaO&ndash, based solid sorbents, known as the calcium looping (CaL) process, is gaining considerable scientific and industrial interest due to the high theoretical sorbent capacity (0.78 gCO2/gCaO), the low specific cost, and the negligible environmental impact of the employed materials. In this work, we investigated the self&ndash, combustion synthesis of CaO&ndash, CaZrO3 sorbents with different CaO contents (40, 60, and 80 wt%) for use in the CaL process. CaZrO3 was used as a spacer to avoid CaO grains sintering at high temperature and to reduce the diffusional resistances of CO2 migrating towards the inner grains of the synthetic sorbent. Samples were characterized by X&ndash, ray diffraction (XRD), Brunauer&ndash, Emmett&ndash, Teller (BET), and scanning electron microscopy (SEM) analyses. The reaction between CO2 and CaO (i.e., carbonation) was carried out in 20 vol% CO2 at 650 &deg, C and calcination (i.e., decomposition of CaCO3 to CaO and CO2) at 900 &deg, C in pure Ar or with 85 vol% CO2 using a thermogravimetric analyzer (thermogravimetric/differential thermal analysis (TG&ndash, DTA)). The most stable sorbent was with 40 wt% of CaO showing a CO2 uptake of up to 0.31 g CO2/gsorbent and 0.26 g CO2/gsorbent operating under mild and severe conditions, respectively. The experimental data corroborated the prediction of the shrinking core spherical model in the first phase of the carbonation. A maximum reaction rate of 0.12&ndash, 0.13 min-1 was evaluated in the first cycle under mild and severe conditions of regeneration.

The considerable spread of Cu2ZnSnS4 (CZTS) optical properties reported in the literature is discussed in terms of material stoichiometry. To this purpose, kesterite thin films were prepared by sulfurization of multilayered precursors of ZnS, Cu and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy were used for structural and compositional analysis. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric and Photothermal Deflection Spectroscopy (PDS) measurements to assess the absorption coefficient of samples with different compositions. The PDS data show an increase of the sub-band absorption as the Sn content decreases. The results are interpreted assuming the formation of additional defects as the tin content is reduced. Those defects can also be responsible for the decrease of the band gap energy value as the Sn/Cu ratio is decreased. © 2013 Elsevier B.V. All rights reserved.

Cu2SnS3 is an earth abundant material suitable for photovoltaic applications. Unfortunately, the material still suffers of a low diffusion length of the carriers due to the presence of spurious phases, voids, defects and small grain size. In order to improve the quality of our samples, the influence of the deposition parameters on its structural properties has been studied. The solar cell obtained with the optimized Cu2SnS3 has shown an external quantum yield larger than 80% around 500 nm a conversion efficiency in the order of 3%, a Jsc of 26 mA and a Voc of 240 mV, one of the world best result obtained with a Cu2SnS3 based solar cell. Furthermore the external quantum yield at wavelength larger than 1200 nm is still around 30% making this material interesting for IR detectors also. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Non-stoichiometric nickel oxide (NiOx) is attracting growing attention due to its characteristics of p-type transparent conductive layer and to the possibility to tailor its optical and electrical properties. NiOx could also be employed as the electron blocking layer in silicon-based heterojunction solar cells. However, at present not much work has been done in this direction. In this paper we investigate the optoelectronic characteristics of NiOx thin films and demonstrate the usability of NiOx as emitter layer in silicon based heterostructure solar cells due to its hole collection selectivity. Test heterojunctions show a rectifying behaviour, even if their characteristics are still limited by the density of defects at the c-Si/NiOx interface, as deduced by comparing the experimental results with numerical simulations. This suggests that the quality of the interface between NiOx and c-Si needs to be improved, either by optimizing the deposition process of NiOx or by depositing a buffer layer able to carefully passivate the silicon surface and helpfully allow the growth of oxide layer. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

TiO2 is a n-type oxide semiconductor used in many fields of chemistry and engineering, included dye sensitized and organic solar cells. Different methods have been investigated to prepare TiO2 films, nevertheless its poor electrical and optical characteristics hampers its use as a transparent conductor oxide. In this work thin TiO2 film obtained by e-beam evaporation and thermally annealed at different temperatures were studied using different characterization techniques, in order to evaluate its use as emitter layer or back contact in silicon based heterojunction solar cells. By Raman analysis we found the TiO2 films showed mainly the presence of anatase crystal structure once thermally annealed at T > 400 °C. Electrical and optical characterization of the thermally annealed samples showed that the best results consisted in a resistivity of around 10-2 Ωcm, a mobility of 3 cm2/Vs and carrier concentration of 1019/cm3. From capacitance-voltage characteristics of TiO2 /p-c-Si, the built-in potential has been evaluated in order to assess the band alignment with crystalline silicon. Good quality titanium oxide films by using e-beam evaporation deposition technique followed by thermal annealing have been obtained with physical and electrical properties desirable for photovoltaic applications. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

The valence band offset (VBO) at the interface CdS/Cu2ZnSnS 4 was investigated by x-ray photoelectron spectroscopy (XPS). The VBO was measured by two different procedures: an indirect method involving the measurements of the core levels together with the XPS bulk valence band (VB) spectra and a direct method involving the analysis of XPS VB spectra at the interface. The indirect method resulted in a VBO value of (-1.20 ± 0.14) eV while the direct method returned a similar value of (-1.24 ± 0.06) eV but affected by a lower uncertainty. The conduction band offset (CBO) was calculated from the measured VBO values. These two measured values of the VBO allowed us to calculate the CBO, giving (-0.30 ± 0.14) eV and (-0.34 ± 0.06) eV, respectively. These values show that the CBO has a cliff-like behaviour which could be one of the reasons for the Voc limitation in the CdS/CZTS solar cells. © 2013 IOP Publishing Ltd.

In this paper we investigate the p-type a-Si:H/ia-Si:H/p-type c-Si structure, commonly used as base contact in amorphous/crystalline silicon heterojunction solar cell when fabricated on p-type c-Si wafer. Even though the most effective amorphous silicon/crystalline silicon heterostructure is based on n-type c-Si due to higher bulk lifetime, the p-type c-Si still remains the most common and cheaper substrate for silicon based solar cell. In particular we study the effect of localized 532 nm pulsed laser treatment at different laser conditions in order to reduce the cell series resistance due to the base contact. In this approach the p-type a-Si:H layer is used as a source of boron dopant. Depending on the thickness of the p-type a-Si:H film, when the laser beam is focused on p-type a-Si:H layer the boron can be transferred into the c-Si base to form an overdoped region and then an effective local Back Surface Field, able to enhance the hole collection at the metal of the base electrode in the p-type c-Si based heterojunction solar cell. The application of a thin Aluminum layer on top of the amorphous silicon to be treated by laser is also concerned. Series resistance of a transverse structure composed by the laser treated p-type a-Si:H/c-Si/opposite surface contacted by InGa is considered to optimize the laser procedure. Values as low as 0.5 Ωcm2 are obtained when the aluminum layer is adopted. © 2015 The Authors.

Al doped zinc oxide (ZnO:Al) is a transparent and conductive oxide used as contact and antireflection layer in solar cell based on Si or chalcogenide. Generally it is grown by magnetron sputtering but the resistivity of our films grown with this technique are still in the order of 10 -3 Ωcm for layers grown at the temperatures used to produce the solar cells. The doping property of Hydrogen for Al:ZnO grown with two different sputtering techniques, DC magnetron sputtering and Pulsed magnetron sputtering at different growth parameters have been studied and the sample characterized optically, electrically and structurally. The best resistivity is 6.7*10 -4 Ωcm was obtained using Pulsed magnetron sputtering.

High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high Voc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si-H2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H+ ions accumulated during the plasma exposure, leading to a more stable configuration.