Pilar Espinet
Technical University of Madrid
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Publication
Featured researches published by Pilar Espinet.
Microelectronics Reliability | 2010
Pilar Espinet; Carlos Algora; José Ramón González; Neftalí Núñez; Manuel Vázquez
A temperature stress test was carried out on GaAs single-junction solar cells to analyze the degradation suffered when working at ultra-high concentrations. The acceleration of the degradation was realized at two different temperatures: 130 °C and 150 °C. In both cases, the degradation trend was the same, and only gradual failures were observed. A fit of the dark I–V curve at 25 °C with a 3D distributed model before and after the test was done. The fit with the 3D distributed model revealed degradation at the perimeter because the recombination current in the depletion region of the perimeter increased by about fourfold after the temperature stress test. Therefore, this test did not cause any morphological change in the devices, and although the devices were isolated with silicone, the perimeter region was revealed as the most fragile component of the solar cell. Consequently, the current flowing beneath the busbar favors the progression of defects in the device in the perimeter region.
photovoltaic specialists conference | 2009
Carlos Algora; Ignacio Rey-Stolle; Iván García; Beatriz Galiana; Mathieu Baudrit; Pilar Espinet; Enrique Barrigón; José Ramón González
In this paper, the benefits of the ultra high concentration (¿ 1000 suns) are shown in terms of cost reduction and efficiency increase. Accordingly, the strategy followed at IES-UPM for more than 15 years is the development of III-V solar cells suitable for operation at 1000 suns or more. Recently, we have developed and manufactured a GaInP/GaAs dual-junction cell which results in an efficiency (measured at the Calibration Laboratory, CalLab, of Fraunhofer Institute in Freiburg) of 32.6% for a concentration range going from 499 to 1026 suns. This efficiency is the world record efficiency for a dual-junction solar cell. Besides, the efficiency is still as high as 31% at 3000 suns. The theoretical optimization of this solar cell (based on an accurate modelling) shows a potential efficiency over 36% at 1000 suns. We have extended this strategy to lattice-matched GaInP/Ga(In)As/Ge triple junction solar cells. First manufactured cells exhibit an efficiency of 31.5% at 1000 suns. The theoretical optimization of this cells show that an efficiency over 43% at 1000 suns is achievable. A roadmap has been established in order to reach this value.
Microelectronics Reliability | 2010
Neftalí Núñez; Manuel Vázquez; José Ramón González; Carlos Algora; Pilar Espinet
Accelerated testing is a necessary tool in order to demonstrate the reliability of concentration photovoltaic solar cells, devices which is expected to be working not less than 25 years. Many problems arise when implementing high temperature accelerated testing in this kind of solar cells, because the high light irradiation level, at which they work, is very difficult to achieve inside a climatic chamber. This paper presents a novel accelerated testing method for concentrator solar cells, under simulated electrical working conditions (i.e. forward biasing the solar cells at the equivalent current they would handle at 700 suns), that overcomes some of the limitations found in test these devices inside the chamber. The tracked power of the solar cells to 700×, experiences a degradation of 1.69% after 4232 h, in the 130 °C test, and of 2.20% after 2000 h in the 150 °C one. An additional test has been carried out at 150 °C, increasing the current to that equivalent to 1050 suns. This last test shows a power degradation of 4% for the same time.
photovoltaic specialists conference | 2009
Ignacio Rey-Stolle; C. Algora; Iván García; Mathieu Baudrit; Pilar Espinet; Beatriz Galiana; Enrique Barrigón
The simulation of the quantum efficiency and the I-V curves at several concentrations of a high efficiency concentrator dual-junction solar cell is presented using three different approaches: 1) analytic simulation with the one-diode model; 2) analytic simulation with distributed circuit models; and, 3) numerical simulation. The main advantages and limitations of each model are discussed and their performance is compared.
AIP Conference Proceedings | 10th Internacional Conference on Concentrator Photovoltaic: CPV-10 | 07/04/2014 - 09/04/2014 | Albuquerque, New Mexico, EE.UU | 2014
Vincenzo Orlando; Pilar Espinet; Neftalí Núñez; Fabian Eltermann; Yedileth Contreras; Jesús Bautista; M. Vázquez; Andreas W. Bett; Carlos Algora
A temperature accelerated life test on concentrator lattice mismatched Ga0.37In0.63P/Ga0.83In0.17As/Ge triple-junction solar cells-on-carrier is being carried out. The solar cells have been tested at three different temperatures: 125, 145 and 165°C and the nominal photo-current condition (500X) is emulated by injecting current in darkness. The final objective of these tests is to evaluate the reliability, warranty period, and failure mechanism of these solar cells in a moderate period of time. Up to now only the test at 165°C has finished. Therefore, we cannot provide complete reliability information, but we have carried out preliminary data and failure analysis with the current results.
photovoltaic specialists conference | 2008
Pilar Espinet; Carlos Algora; Ignacio Rey-Stolle; Iván García; Mathieu Baudrit
Characterization is a key process in attaining high efficiency in the state-of-the-art multi-junction solar cells. This work will summarize our efforts in using eletroluminescence for characterising multijunction solar cells. This study will present the possibilities of electroluminescence (EL) spectroscopy as a fast and simple characterization technique which is able to provide extensive information about the solar cells performance. Finally, four of the applications of this technique will be presented: band gap estimation, barrier effect for minority carriers, information on the thermal performance of encapsulated devices and determination of the shunt resistance of each cell in a dual junction device.
photovoltaic specialists conference | 2011
Neftalí Núñez; José Ramón González; Manuel Vázquez; Pilar Espinet; Carlos Algora
This paper presents some of the results of a method to determine the main reliability functions of concentrator solar cells. High concentrator GaAs single junction solar cells have been tested in an Accelerated Life Test. The method can be directly applied to multi-junction solar cells. The main conclusions of this test carried out show that these solar cells are robust devices with a very low probability of failure caused by degradation during their operation life (more than 30 years). The evaluation of the probability operation function (i.e. the reliability function R(t)) is obtained for two nominal operation conditions of these cells, namely simulated concentration ratios of 700 and 1050 suns. Preliminary determination of the Mean Time to Failure indicates a value much higher than the intended operation life time of the concentrator cells.
photovoltaic specialists conference | 2010
Carmen M. Ruiz; Ignacio Rey-Stolle; Iván García; Enrique Barrigón; Pilar Espinet; V. Bermúdez; Carlos Algora
On this paper we present an alternative way to analyze de electronic properties of each subcell from the complete device. By illuminating the cell with light sources which energy is near one of the subcell bandgaps, it is possible to “erase” the presence of such subcell on the CV curve. The main advantages of this technique are that it is not destructive, it can be measured on the complete cell so can be easily implemented as a diagnostic technique for controlling electronic deviations.
spanish conference on electron devices | 2009
Pilar Espinet; Ignacio Rey-Stolle; Carlos Algora
Characterization is a key process in attaining high efficiency in state-of-the-art multijunction solar cells. However, the characterization of these devices using methods involving optical excitation and measurements of optical response is challenging and time consuming. For instance the experimental access to information about individual subcells is difficult to attain with common methods. This work will present how the characterization of these devices benefits from the use of electroluminescence spectroscopy (EL). In this study we use a low cost EL set-up -which could be easily integrated in any in-line characterization tool at a manufacturing site-to derive the individual performance of each subcell in the multijunction stack. Using electroluminescence measurements, the external quantum efficiency of each subcell, the current-voltage curve of each subcell and the individual quality factors of each subcell are calculated.
photovoltaic specialists conference | 2009
Carmen M. Ruiz; Ignacio Rey-Stolle; Iván García; Enrique Barrigón; Pilar Espinet; E. Saucedo; V. Bermúdez; Carlos Algora
In this paper we intend to expand the portfolio of non-destructive techniques available for the individual characterization of the subcells in a monolithic multijunction stack. The goal is to explore the use of low-temperature, variable frequency, capacitance-based techniques to extract information of the minority carrier parameters, presence of traps and electronic defects in each subcell in the device. Despite this technique has been extensively applied for the characterization of thin-film materials and devices it has deserved little attention in the field of III-V multijunction solar cells.