I. Artacho - Academia.edu (original) (raw)

Papers by I. Artacho

Physical Review Applied, 2016

Solar Energy Materials and Solar Cells, 2016

IEEE Journal of Photovoltaics, 2015

2014 IEEE 40th Photovoltaic Specialist Conference (PVSC), 2014

2011 37th IEEE Photovoltaic Specialists Conference, 2011

An equivalent circuit model is applied in order to describe the operation characteristics of quan... more An equivalent circuit model is applied in order to describe the operation characteristics of quantum dot intermediate band solar cells (QD-IBSCs), which accounts for the recombination paths of the intermediate band (IB) through conduction band (CB), the valence band (VB) through IB, and the VB-CB transition. In this work, fitting of the measured dark J-V curves for QD-IBSCs (QD region being non-doped or direct Si-doped to n-type) and a reference GaAs p-i-n solar cell (no QDs) were carried out using this model in order to extract the diode parameters. The simulation was then performed using the extracted diode parameters to evaluate solar cell characteristics under concentration. In the case of QDSC with Si-doped (hence partially-filled) QDs, a fast recovery of the open-circuit voltage (V oc ) was observed in a range of low concentration due to the IB effect. Further, at around 100X concentration, Si-doped QDSC could outperform the reference GaAs p-in solar cell if the current source of IB current source were sixteen times to about 10mA/cm 2 compared to our present cell.

2012 38th IEEE Photovoltaic Specialists Conference, 2012

ABSTRACT In the last decade several prototypes of intermediate band solar cells (IBSCs) have been... more ABSTRACT In the last decade several prototypes of intermediate band solar cells (IBSCs) have been manufactured. So far, most of these prototypes have been based on InAs/GaAs quantum dots (QDs) in order to implement the IB material. The key operation principles of the IB theory are two photon sub-bandgap (SBG) photocurrent, and output voltage preservation, and both have been experimentally demonstrated at low temperature. At room temperature (RT), however, thermal escape/relaxation between the conduction band (CB) and the IB prevents voltage preservation. To improve this situation, we have produced and characterized the first reported InAs/AlGaAs QD-based IBSCs. For an Al content of 25% in the host material, we have measured an activation energy of 361 meV for the thermal carrier escape. This energy is about 250 meV higher than the energies found in the literature for InAs/GaAs QD, and almost 140 meV higher than the activation energy obtained in our previous InAs/GaAs QD-IBSC prototypes including a specifically designed QD capping layer. This high value is responsible for the suppression of the SBG quantum efficiency under monochromatic illumination at around 220 K. We suggest that, if the energy split between the CB and the IB is large enough, activation energies as high as to suppress thermal carrier escape at room temperature (RT) can be achieved. In this respect, the InAs/AlGaAs system offers new possibilities to overcome some of the problems encountered in InAs/GaAs and opens the path for QD-IBSC devices capable of achieving high efficiency at RT.

Journal of Photonics for Energy, 2013

The concept of intermediate band solar cell (IBSC) is, apparently, simple to grasp. However, sinc... more The concept of intermediate band solar cell (IBSC) is, apparently, simple to grasp. However, since the idea was proposed, our understanding has improved and some concepts can now be explained more clearly than when the concept was initially introduced. Clarifying these concepts is important, even if they are well known for the advanced researcher, so that research efforts can be driven in the right direction from the start. The six pieces of this work are: Does a miniband need to be formed when the IBSC is implemented with quantum dots? What are the problems for each of the main practical approaches that exist today? What are the simplest experimental techniques to demonstrate whether an IBSC is working as such or not? What is the issue with the absorption coefficient overlap and the Mott's transition? What would the best system be, if any?

Thin Film Solar Technology IV, 2012

ABSTRACT Cu (In1-x,Ga-x) S-2 was studied using photoreflectance spectroscopy. In this study, effo... more ABSTRACT Cu (In1-x,Ga-x) S-2 was studied using photoreflectance spectroscopy. In this study, efforts are devoted to optimizing PR set-up for measuring CIGS grown by electrodeposition: issues such as photoluminescence perturbation, high roughness and scattering are addressed. Dual frequency photoreflectance, where both probe and pump beams are modulated, is proposed here to over come the poor signal to noise ratio. Considering the low electric field regime, material parameters are extracted by employing the third derivative functional form of dielectric functions to fit data.The reliability of the technique is finally tested by measuring PR spectra on a specific 15 x 15cm(2) wafer and explanations of PR line-shape evolution on this wafer are discusse.

Communications in Computer and Information Science, 2010

This article presents one of the alternative methods developed for the early detection of ocular ... more This article presents one of the alternative methods developed for the early detection of ocular glaucoma based on the characterisation of mfERG (multifocal electroretinography) readings. The digital signal processing technique is based on Wavelets, hitherto unused in this field, for detection of advanced-stage glaucoma and the study of signal morphology by means of identity patterns for detection of glaucoma in

2012 IEEE 38th Photovoltaic Specialists Conference (PVSC) PART 2, 2013

2013 IEEE 39th Photovoltaic Specialists Conference (PVSC), 2013

International Joint Conference on Biomedical Engineering Systems and Technologies, 2009

ABSTRACT This article presents one of the alternative methods developed for the early detection o... more ABSTRACT This article presents one of the alternative methods developed for the early detection of ocular glaucoma based on the characterisation of mfERG (multifocal electroretinography) readings. The digital signal processing technique is based on Wavelets, hitherto unused in this field, for detection of advanced-stage glaucoma and the study of signal morphology by means of identity patterns for detection of glaucoma in earlier stages. Future research possibilities are also mentioned, such as the study of orientation in the development of the disease.

Solar Energy Materials and Solar Cells, 2013

ABSTRACT Intermediate band materials incorporate a collection of energy levels with special optoe... more ABSTRACT Intermediate band materials incorporate a collection of energy levels with special optoelectronic properties within the semiconductor bandgap. This feature broadens the energy range of the solar spectrum useful for photovoltaic conversion and has the potential for enabling both high-current and high-voltage photovoltaic cells. Here we present our preliminary results on a novel intermediate band solar cell based on creating an intermediate band through the incorporation of a large concentration of Ti atoms in a GaAs crystal. The characterization of the material verifies a high concentration of incorporated Ti and the absence of structural defects. The cells show below-bandgap photon absorption with a likely contribution from As antisites and Ga vacancies. The initially degraded open-circuit voltage of the cells exhibits a high voltage recovery from 0.1 V (at room temperature and one-sun irradiance conditions) to 1.4 V (at low temperature and concentrated light).

Nanotechnology, 2013

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of se... more A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude.

Materials Science and Engineering: B, 2013

Photoreflectance (PR) is a convenient characterization tool able to reveal optoelectronic propert... more Photoreflectance (PR) is a convenient characterization tool able to reveal optoelectronic properties of semiconductor materials and structures. It is a simple non-destructive and contactless technique which can be used in air at room temperature. We will present experimental results of the characterization carried out by means of PR on different types of advanced photovoltaic (PV) structures, including quantum-dot-based prototypes of intermediate band solar cells, quantum-well structures, highly mismatched alloys, and III-Vbased multi-junction devices, thereby demonstrating the suitability of PR as a powerful diagnostic tool. Examples will be given to illustrate the value of this spectroscopic technique for PV including (i) the analysis of the PR spectra in search of critical points associated to absorption onsets; (ii) distinguishing signatures related to quantum confinement from those originating from delocalized band states; (iii) determining the intensity of the electric field related to built-in potentials at interfaces according to the Franz-Keldysh (FK) theory; and (v) determining the nature of different oscillatory PR signals among those ascribed to FKoscillations, interferometric and photorefractive effects. The aim is to attract the interest of researchers in the field of PV to modulation spectroscopies, as they can be helpful in the analysis of their devices.

Las células solares de banda intermedia (IBSC) fueron propuestas en 1997 por investigadores del I... more Las células solares de banda intermedia (IBSC) fueron propuestas en 1997 por investigadores del Instituto de Energía Solar [1] como idea para sobrepasar la eficiencia de las células solares de un solo gap. Para entender esta idea es conveniente revisar primero, con la ayuda de la figura 1, algunos de los conceptos relativos al funcionamiento de una célula solar de un solo gap.