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Room temperature photo-response of titanium supersaturated silicon at energies over the bandgap

  • Olea Ariza, Javier
  • López Estrada, Esther
  • Antolín Fernández, Elisa
  • Martí Vega, Antonio
  • Luque López, Antonio
  • García-Hemme, E.
  • Pastor Pastor, David
  • García-Hernansanz, R.
  • Prado, Agustín del
  • González-Díaz, G.
Silicon samples were implanted with high Ti doses and subsequently processed with the pulsed-laser melting technique. The electronic transport properties in the 15-300 K range and the room temperature spectral photoresponse at energies over the bandgap were measured. Samples with Ti concentration below the insulator-metal (I-M) transition limit showed a progressive reduction of the carrier lifetime in the implanted layer as Ti dose is increased. However, when the Ti concentration exceeded this limit, an extraordinary recovery of the photoresponse was measured. This result supports the theory of intermediate band materials and is of utmost relevance for photovoltaic cells and Si-based detectors.
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Lateral absorption measurements of InAs/GaAs quantum dots stacks: Potential as intermediate band material for high efficiency solar cells

  • Cánovas Díaz, Enrique
  • Martí Vega, Antonio
  • Luque López, Antonio
  • Farmer, C.D.
  • Stanley, Colin
  • Sanchez, A.M.
  • Ben, T.
  • Molina Rubio, Sergio Ignacio
Prototypes based on InAs/GaAs QDs have been manufactured in order to realize the theoretically predicted high efficiency intermediate band solar cells (IBSCs). Unfortunately, until now, these prototypes have not yet demonstrated the expected increase in efficiency when compared with reference samples without IB material. One of the main arguments explaining this performance is the weak photon absorption in the QD-IB material, arising from a low density of QDs. In this work, we have analyzed the absorption coefficient of the IB material by developing a sample in an optical wave-guided configuration. This configuration allows us to illuminate the QDs laterally, increasing the path length for photon absorption. Using a multi-section metal contact device design, we were able to measure an absorption coefficient of ∼100 cm−1 around the band edge (∼1 eV ) defined by the transition in InAs/GaAs QD-IB materials. This figure, and its influence on the IBSC concept, is analyzed for this system.
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Inx(GayAl1-y)1-xAs quaternary alloys for quantum dot intermediate band solar cells

  • García-Linares Fontes, Pablo
  • Farmer, C.D.
  • Antolín Fernández, Elisa
  • Chakrabarti, S.
  • Sanchez, A.M.
  • Ben, T.
  • Molina Rubio, Sergio Ignacio
  • Stanley, Colin
  • Martí Vega, Antonio
  • Luque López, Antonio
Within the context of quantum dot Intermediate Band Solar Cells (QD-IBSC), it is of interest to investigate the maximum value that can be achieved for the smaller of the transitions (EL), since values larger than 0.3 eV are required for improved performance. This work provides both theoretical and experimental arguments to verify the shift of the IB position to deeper energies by using an Inx(GayAl1−y)1−xAs capping layer, fulfilling the double function of increasing the QD size and eliminating the discontinuity in the conduction band between the quaternary cap and the GaAs barrier.
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Advances in Intermediate Band Solar Cell Research

  • Luque López, Antonio
  • Martí Vega, Antonio
• Introduction • Deep level IB materials – IB and SRH recombination – Proven bulk IB materials and cells • QD implementation – Current enhancement – Voltage preservation – Experimental proof of concept and some implications • Proof of concept • The need of two photons – The way to go • Conclusions
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Experimental advances in the next generation of solar cells

  • Martí Vega, Antonio
  • Luque López, Antonio
We consider next generation solar cells concepts those that have the potential to exceed the limiting efficiency calculated by Shockley and Queisser for single gap solar cells (40.7 %) and still have not been commercialized. Among these concepts, this paper deals with the multiple exciton generation (or impact ionization or multiple carrier generation) solar cell, the intermediate band solar cell and the hot carrier solar cell. These concepts were proposed theoretically more than ten years ago. In the last years, the number of experiments supporting the theories behind and paving the way towards their practical implementation has leaped forward. This work reviews these experimental advances
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Light trapping properties of cylindrical well diffraction gratings in solar cells: Computational calculations

  • Martí Vega, Antonio
  • Luque López, Antonio
  • Tobías Galicia, Ignacio
  • Mellor Null, Alexander Virgil
Light trapping using diffraction gratings is a promising approach to increasing absorption in solar cells. In this paper, the computationally calculated absorption enhancement expected from a diffraction grating consisting of a triangular array of cylindrical wells is presented. Angle-extended polychromatic illumination is considered, and special attention is paid to absorption of sub-bandgap photons in an intermediate band solar cell. Results are compared to the absorption enhancement expected from an ideal Lambertian (randomizing) scatterer, which is considered as a baseline. It is found that for cells which absorb very weakly, the diffraction grating provides absorption enhancement above that of the ideal Lambertian scatterer over a wide wavelength range. For cells which absorb more strongly, the grating underperforms the ideal Lambertian scatterer over almost all wavelengths. Finally, the grating period, well height and well radius are optimised. Keywords: Light Trapping, Diffraction Grating, Intermediate Band Solar Cell
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Embedment of metal nanoparticles in GaAs and Si for plasmonic absorption enhancement in intermediate band solar cells

  • Moura Dias Mendes, Manuel Joao de
  • Hernández Martín, Estela
  • Tobías Galicia, Ignacio
  • Martí Vega, Antonio
  • Luque López, Antonio
The high near-field enhancement occurring in the vicinity of metallic nanoparticles (MNPs) sustaining surface plasmons can only be fully exploited in photovoltaic devices if the MNPs are placed inside their semiconducting material, in the photoactive region. In this work an experimental procedure is studied to embed MNPs in gallium arsenide (GaAs) and silicon (Si), which can be applied to other semiconductor host materials. The approach consists in spin-coating colloidal MNPs dispersed in solution onto the substrate surface. Then a capping layer of the same material as the substrate is deposited on top to embed the MNPs in the semiconductor. The extinction spectra of silver (Ag) and gold (Au) MNPs embedded in GaAs and Si is modeled with Mie theory for comparison with optical measurements. This contribution constitutes the initial step towards the realization of quantum-dot intermediate band solar cells (QD-IBSC) with MNP
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Improving up-conversion with PBS quantum dots

  • Pan, Aline Cristiane
  • Cañizo Nadal, Carlos del
  • Luque López, Antonio
This paper evaluates the enhancement of the up-conversion phenomena by combining rare-earth doped phosphors with PbS quantum dots (QDs). We present results on the characterization of two different ways of adhering the up-converter with this fluorescent material to bifacial solar cells: by dissolving the powder in a spin-on oxide and by dissolving it in a silicone gel. The improvement in photocurrent detected for both the oxide and silicone alternatives when including the QDs is 60% better than without them. It is shown that the absorption and emission characteristics of the PbS QDs embedded in oxide and silicone can be tuned into to the desired spectral region. Keywords: quantum dots, up-converter, solar cell
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Study of GaAs(Ti) thin films as candidates for IB solar cells manufacturing

  • Silvestre, S.
  • Boronat, A.
  • Castaner, L.
  • Fuertes Marrón, David
  • Martí Vega, Antonio
  • Luque López, Antonio
Thin films of GaAs(Ti) have been deposited by sputtering on glass and n_GaAs substrates under different process conditions. Optical characteristics of these samples have been analyzed to study the potential of this material in intermediate Band solar cell manufacturing
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Characterization of the manufacturing processes to grow triple-junction solar cells

  • Kalyuzhnyy, Nikolay A.
  • Evstropov, V. V.
  • Lantratov, Vladimir M.
  • Mintairov, Sergey A.
  • Mintairov, M. A.
  • Gudovskikh, Alexander S.
  • Luque López, Antonio
  • Andreev, V. M.
A number of important but little-investigated problems connected with III-V/Ge heterostructure in the GaInP/GaInAs/Ge multijunction solar cells grown by MOVPE are considered in the paper. The opportunity for successfully applying the combination of reflectance and reflectance anisotropy spectroscopy in situ methods for investigating III-V structure growth on a Ge substrate has been demonstrated. Photovoltaic properties of the III-V/Ge narrow-band subcell of the triple-junction solar cells have been investigated. It has been shown that there are excess currents in the Ge photovoltaic p-n junctions, and they have the tunneling or thermotunneling character. The values of the diode parameters for these current flow mechanisms have been determined. The potential barrier at the III-V/Ge interface was determined and the origin of this barrier formation during MOVPE heterogrowth was suggested.
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