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335 results on '"Bertomeu J"'

1. Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

Author

Kail, F., Farjas, J., Roura, P., Secouard, C., Nos, O., Bertomeu, J., Alzina, F., and Cabarrocas, P. Roca i

Subjects
Condensed Matter - Materials Science
Abstract

The structural relaxation of pure amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) materials, that occurs during thermal annealing experiments, has been analysed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain, but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si and crystalline silicon., Comment: 15 pages, 3 figures, 1 table to be published in Applied Physics Letters

Published
2010
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2. Effects of Deposition Temperature and Working Pressure on the Thermal and Nanomechanical Performances of Stoichiometric Cu3N: An Adaptable Material for Photovoltaic Applications

Author

Rodríguez-Tapiador, M. I., primary, Jiménez-Suárez, A., additional, Lama, A., additional, Gordillo, N., additional, Asensi, J. M., additional, del Rosario, G., additional, Merino, J., additional, Bertomeu, J., additional, Agarwal, A., additional, and Fernández, S., additional

Published
2023
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6. Effects of Deposition Temperature and Working Pressure on the Thermal and Nanomechanical Performances of Stoichiometric Cu 3 N: An Adaptable Material for Photovoltaic Applications.

Author

Rodríguez-Tapiador, M. I., Jiménez-Suárez, A., Lama, A., Gordillo, N., Asensi, J. M., del Rosario, G., Merino, J., Bertomeu, J., Agarwal, A., and Fernández, S.

Subjects
COPPER, RUTHERFORD backscattering spectrometry, TEMPERATURE effect, MAGNETRON sputtering, RAMAN microscopy, DIAMOND-like carbon
Abstract

The pursuit of efficient, profitable, and ecofriendly materials has defined solar cell research from its inception to today. Some materials, such as copper nitride (Cu3N), show great promise for promoting sustainable solar technologies. This study employed reactive radio-frequency magnetron sputtering using a pure nitrogen environment to fabricate quality Cu3N thin films to evaluate how both temperature and gas working pressure affect their solar absorption capabilities. Several characterization techniques, including X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), Raman spectroscopy, scanning electron microscopy (SEM), nanoindentation, and photothermal deflection spectroscopy (PDS), were used to determine the main properties of the thin films. The results indicated that, at room temperature, it is possible to obtain a material that is close to stoichiometric Cu3N material (Cu/N ratio ≈ 3) with (100) preferred orientation, which was lost as the substrate temperature increases, demonstrating a clear influence of this parameter on the film structure attributed to nitrogen re-emission at higher temperatures. Raman microscopy confirmed the formation of Cu-N bonds within the 628–637 cm−1 range. In addition, the temperature and the working pressure significantly also influence the film hardness and the grain size, affecting the elastic modulus. Finally, the optical properties revealed suitable properties at lower temperatures, including bandgap values, refractive index, and Urbach energy. These findings underscore the potential of Cu3N thin films in solar energy due to their advantageous properties and resilience against defects. This research paves the way for future advancements in efficient and sustainable solar technologies. [ABSTRACT FROM AUTHOR]

Published
2023
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16. Copper Nitride: A Versatile Semiconductor with Great Potential for Next-Generation Photovoltaics.

Author

Rodríguez-Tapiador, M. I., Asensi, J. M., Roldán, M., Merino, J., Bertomeu, J., and Fernández, S.

Subjects
SOLAR energy conversion, PHOTOTHERMAL spectroscopy, MAGNETRON sputtering, THIN films, SEMICONDUCTORS, BAND gaps, POLYCRYSTALLINE semiconductors
Abstract

Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on glass substrates and silicon wafers via radio-frequency magnetron sputtering at different nitrogen flow ratios with total pressures ranging from 1.0 to 5.0 Pa. The thin films' structural, morphology, and chemical properties were determined using XRD, Raman, AFM, and SEM/EDS techniques. The results revealed that the Cu3N films exhibited a polycrystalline structure, with the preferred orientation varying from 100 to 111 depending on the working pressure employed. Raman spectroscopy confirmed the presence of Cu-N bonds in characteristic peaks observed in the 618–627 cm−1 range, while SEM and AFM images confirmed the presence of uniform and smooth surface morphologies. The optical properties of the films were investigated using UV-VIS-NIR spectroscopy and photothermal deflection spectroscopy (PDS). The obtained band gap, refractive index, and Urbach energy values demonstrated promising optical properties for Cu3N films, indicating their potential as solar absorbers in photovoltaic technology. This study highlights the favourable properties of Cu3N films deposited using the RF sputtering method, paving the way for their implementation in thin-film photovoltaic technologies. These findings contribute to the progress and optimisation of Cu3N-based materials for efficient solar energy conversion. [ABSTRACT FROM AUTHOR]

Published
2023
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17. High – Mobility Flourine Doped Indium Oxide Films For high Efficiency Silicon Solar Cells

Author

Tom, T., Tutsch, L., Hermle, M., Asensi, J.M., López-Vidrier, J., Bertomeu, J., and Bivour, M.

Subjects
Low Temperature Route for Si Cells, Silicon Materials and Cells
Abstract

8th World Conference on Photovoltaic Energy Conversion; 128-132, Transparent conducting oxides with high infrared transparency and high mobility are crucial for further enhancing the efficiency of crystalline silicon solar cells. Numerous hydrogen-doped or cation-doped indium oxide films have been intensively studied, while anion doping in indium oxide films is still under development. Here we investigate the fluorine doped indium oxide films deposited by industrial DC sputtering by varying the oxygen and hydrogen percentages. To gain a holistic understanding on the role of hydrogen and oxygen we performed a very wide parameter variation of these gases. The films were processed at room temperature and were annealed at 220 °C on a hot plate in ambient conditions. Electrical, optical, and structural properties of the films were investigated and highest mobility of 87 cm2/Vs at a carrier density of 2.5×1020 cm−3 was achieved when depositing under 2.3% O2 and 2.0% H2 flow. The strong correlation between the defined figure of merit and the electron mobility of the films is observed. The solid phase crystallization of the annealed films was identified by X-ray diffraction. The highest mobility films achieved an efficiency of 21.8% in silicon heterojunction solar cells..

Published
2022
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18. Elimination of Interface Energy Barriers Using Dendrimer Polyelectrolytes with Fractal Geometry

Author

Ros, E., Tom, T., Ortega, P., Martin, I., Maggi, E., Asensi, J. M., López-Vidrier, J., Saucedo, E., Bertomeu, J., Puigdollers, J., and Voz, C.

Abstract

In this work we study conjugated polyelectrolyte (CPE) films based on polyamidoamine (PAMAM) dendrimers of generations G1 and G3. These fractal macromolecules are compared to branched polyethylenimine (b-PEI) polymer using methanol as the solvent. All of these materials present a high density of amino groups, which protonated by methoxide counter-anions create strong dipolar interfaces. The vacuum level shift associated to these films on n-type silicon was 0.93 eV for b-PEI, 0.72 eV for PAMAM G1 and 1.07 eV for PAMAM G3. These surface potentials were enough to overcome Fermi level pinning, which is a typical limitation of aluminium contacts on n-type silicon. A specific contact resistance as low as 20 mΩ·cm2was achieved with PAMAM G3, in agreement with the higher surface potential of this material. Good electron transport properties were also obtained for the other materials. Proof-of-concept silicon solar cells combining vanadium oxide as a hole-selective contact with these new electron transport layers have been fabricated and compared. The solar cell with PAMAM G3 surpassed 15% conversion efficiency with an overall increase of all the photovoltaic parameters. The performance of these devices correlates with compositional and nanostructural studies of the different CPE films. Particularly, a figure-of-merit (Vσ) for CPE films that considers the number of protonated amino groups per macromolecule has been introduced. The fractal geometry of dendrimers leads to a geometric increase in the number of amino groups per generation. Thus, investigation of dendrimer macromolecules seems a very good strategy to design CPE films with enhanced charge-carrier selectivity.

Published
2023
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