En este trabajo se describen dos compresores que codifican las senales de voz utilizando un bit p... more En este trabajo se describen dos compresores que codifican las senales de voz utilizando un bit por muestra;ambos codecs se caracterizan por: 1o) la escasa potencia de calculo que precisan para codificar las senales de audio, y 2o) la sencillez del circuito
The lifetime of ultraviolet high-power light-emitting diodes (UV HP-LEDs) is an open issue due to... more The lifetime of ultraviolet high-power light-emitting diodes (UV HP-LEDs) is an open issue due to their high current density, high temperature, and UV radiation. This work presents a reliability study and failure analysis of three high-temperature accelerated life tests (ALTs) for 13,500 h with 3 W commercial UV LEDs of 365 nm at a nominal current in two working conditions: continuous mode and cycled mode (30 s on/30 s off). Arrhenius–Weibull parameters were evaluated, and an equation to evaluate the lifetime (B50) at any junction temperature and other relevant lifetime functions is presented. The Arrhenius activation energy was 0.13 eV for the continuous mode and 0.20 eV for the cycled mode. The lifetime at 50% survival and 30% loss of optical power as a failure definition, working at Ta = 40 °C with a multi-fin heat sink in natural convection, was over 4480 h for the continuous mode and 19,814 h for the cycled mode. The need to add forced convection for HP-LED arrays to achieve th...
Development of contaminant detection systems in various natural and industrial environments has b... more Development of contaminant detection systems in various natural and industrial environments has been favored in recent years thanks to the evolution of processors and sensors. Our group works specifically on contaminant detection systems in inland waters: immediate and continuous detection is a fundamental requirement in this type of sensing. Regarding the sensors, the proposed system is based on fluorescence, since it offers a method in which there is no contact with water, which means less wear on the components and a great saving in cleaning and maintenance. On the other hand, the spectrum processing is of great importance, since it is used both in the generation of a library of fluorescence spectra taken in the laboratory and in the continuous analysis of the samples and in the comparison algorithm for identification. The validity of the system is based on the last process that is carried out in a very short time. This article describes a system to process spectra in a more acce...
Abstract Qualification standards are on the base of the high endurance and resilience of space so... more Abstract Qualification standards are on the base of the high endurance and resilience of space solar cells. In these standards, such as the European ECSS-E-ST-20-08C or the American AIAA S-111A counterpart, life tests related with high temperature accelerated tests (among many others) are included. There are several issues that make it difficult to assess the multijunction solar cell life from temperature tests in these standards. For example, in the European standard, an activation energy of 0.7 eV determined many years ago for silicon devices is assumed. On the other hand, the American standard proposes temperature accelerated tests at the temperatures of 50 °C, 80 °C and 110 °C which are clearly low to really accelerate the life tests of solar cells. Accordingly, in this paper we present the resulting reliability figures (reliability function, failure probability and MTTF) derived of an innovative temperature ALT which allows the proper estimation of the activation energy of commercial lattice matched GaInP/Ga(In)As/Ge triple junction solar cells. The main conclusions are: a) an activation energy of 0.97 eV has been estimated. This value results in significantly higher lifetime values for the tested cells. b) the shape parameter obtained from Weibull failure density function, β, is 1.67; c) the tested solar cells perform as robust devices showing high reliability values in the temperature range of 80 °C–130 °C; d) for higher temperatures, especially beyond 150 °C, the reliability decays significantly; f) reliability functions and parameters can be assessed for any operation temperature and failure criterion.
Progress in Photovoltaics: Research and Applications, 2019
A temperature accelerated life test on Upright Metamorphic Ga0.37In0.63P/Ga0.83In0.17As/Ge triple... more A temperature accelerated life test on Upright Metamorphic Ga0.37In0.63P/Ga0.83In0.17As/Ge triple‐junction solar cells has been carried out. The acceleration has been accomplished by subjecting the solar cells to temperatures (125, 145 and 165°C) significantly higher than the nominal working temperature inside a concentrator (90°C), while the nominal photo‐current (500×) has been emulated by injecting current in darkness. The failure distributions have been fitted to an Arrhenius–Weibull model resulting in an activation energy of 1.39 eV. Accordingly, a 72 years warranty time for those solar cells for a place like Tucson (AZ, USA), was determined. After the ALT, an intense characterization campaign has been carried out in order to determine the failure origin. We have detected that temperature soak alone is enough to degrade the cell performance by increasing the leakage currents, the series resistance, and the recombination currents. When solar cells were also forward biased an inc...
Progress in Photovoltaics: Research and Applications, 2016
Accelerated life tests are frequently used to provide reliability information in a moderate perio... more Accelerated life tests are frequently used to provide reliability information in a moderate period of time (weeks or months), and after that, a failure analysis is compulsory to detect the failure origins. In this paper, a failure analysis has been carried out after a temperature accelerated life test on lattice matched GaInP/Ga(In)As/Ge triple junction commercial solar cells. Solar cells were forward biased in darkness inside three climatic chambers in order to emulate the photo‐generated current under nominal working conditions (a concentration level of 820 suns). After the accelerated aging test, a characterization of the resulting cells by means of quantum efficiency, dark and illumination I–V curves, electroluminescence, scanning electron microscope, energy dispersive X‐ray, scanning transmission electron microscope and X‐ray photoelectron spectroscopy has been carried out.Current is identified as the cause of degradation while temperature just dominates the accelerating factor...
Progress in Photovoltaics: Research and Applications, 2017
This paper proposes a methodology for assessing the concentrator solar cell reliability in a real... more This paper proposes a methodology for assessing the concentrator solar cell reliability in a real application for a given location provided the results from accelerated life tests. We have applied this methodology for the evaluation of warranty times of commercial triple junction solar cells operating inside real concentrator modules in Golden (Colorado, USA), Madrid (Spain) and Tucson (Arizona, USA) for the period 2012–2015. Warranty times in Golden and Madrid, namely, 68 and 31 years, respectively, for the analysed period, indicate the robustness of commercial triple junction solar cells. Nevertheless, the warranty time of 15 years for Tucson suggests the need of improvement in the heat extraction of the solar cell within the concentrator module. Therefore, the influence of the location on the reliability of concentrator solar cells is huge, and it has no sense to supply general reliability values for a given concentrator product. The influence of these warranty times for the thre...
Space solar cells have been subjected to an innovative temperature Accelerated Life Test (ALT) to... more Space solar cells have been subjected to an innovative temperature Accelerated Life Test (ALT) to get information on their degradation and their activation energy. Our procedure emulates the thermal stress that solar cells suffer working under space conditions. Solar cells were kept in a climatic chamber under nitrogen atmosphere at three different temperatures for few months. After degradation, results have been fitted to a temperature Arrhenius model, in order to obtain the activation energy and acceleration factor of space GaInP/Ga(In)As/Ge triple junction solar cells.
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
In order to get a cost competitive commercial product based in III-V solar cells, a complete asse... more In order to get a cost competitive commercial product based in III-V solar cells, a complete assessment of their reliability must be done. A full strategy of tests has been designed to tackle this matter. Real time and homologated accelerated tests are ongoing, as well as a complete statistical analysis which will establish the main reliability parameters and the failure
En este trabajo se describen dos compresores que codifican las senales de voz utilizando un bit p... more En este trabajo se describen dos compresores que codifican las senales de voz utilizando un bit por muestra;ambos codecs se caracterizan por: 1o) la escasa potencia de calculo que precisan para codificar las senales de audio, y 2o) la sencillez del circuito
The lifetime of ultraviolet high-power light-emitting diodes (UV HP-LEDs) is an open issue due to... more The lifetime of ultraviolet high-power light-emitting diodes (UV HP-LEDs) is an open issue due to their high current density, high temperature, and UV radiation. This work presents a reliability study and failure analysis of three high-temperature accelerated life tests (ALTs) for 13,500 h with 3 W commercial UV LEDs of 365 nm at a nominal current in two working conditions: continuous mode and cycled mode (30 s on/30 s off). Arrhenius–Weibull parameters were evaluated, and an equation to evaluate the lifetime (B50) at any junction temperature and other relevant lifetime functions is presented. The Arrhenius activation energy was 0.13 eV for the continuous mode and 0.20 eV for the cycled mode. The lifetime at 50% survival and 30% loss of optical power as a failure definition, working at Ta = 40 °C with a multi-fin heat sink in natural convection, was over 4480 h for the continuous mode and 19,814 h for the cycled mode. The need to add forced convection for HP-LED arrays to achieve th...
Development of contaminant detection systems in various natural and industrial environments has b... more Development of contaminant detection systems in various natural and industrial environments has been favored in recent years thanks to the evolution of processors and sensors. Our group works specifically on contaminant detection systems in inland waters: immediate and continuous detection is a fundamental requirement in this type of sensing. Regarding the sensors, the proposed system is based on fluorescence, since it offers a method in which there is no contact with water, which means less wear on the components and a great saving in cleaning and maintenance. On the other hand, the spectrum processing is of great importance, since it is used both in the generation of a library of fluorescence spectra taken in the laboratory and in the continuous analysis of the samples and in the comparison algorithm for identification. The validity of the system is based on the last process that is carried out in a very short time. This article describes a system to process spectra in a more acce...
Abstract Qualification standards are on the base of the high endurance and resilience of space so... more Abstract Qualification standards are on the base of the high endurance and resilience of space solar cells. In these standards, such as the European ECSS-E-ST-20-08C or the American AIAA S-111A counterpart, life tests related with high temperature accelerated tests (among many others) are included. There are several issues that make it difficult to assess the multijunction solar cell life from temperature tests in these standards. For example, in the European standard, an activation energy of 0.7 eV determined many years ago for silicon devices is assumed. On the other hand, the American standard proposes temperature accelerated tests at the temperatures of 50 °C, 80 °C and 110 °C which are clearly low to really accelerate the life tests of solar cells. Accordingly, in this paper we present the resulting reliability figures (reliability function, failure probability and MTTF) derived of an innovative temperature ALT which allows the proper estimation of the activation energy of commercial lattice matched GaInP/Ga(In)As/Ge triple junction solar cells. The main conclusions are: a) an activation energy of 0.97 eV has been estimated. This value results in significantly higher lifetime values for the tested cells. b) the shape parameter obtained from Weibull failure density function, β, is 1.67; c) the tested solar cells perform as robust devices showing high reliability values in the temperature range of 80 °C–130 °C; d) for higher temperatures, especially beyond 150 °C, the reliability decays significantly; f) reliability functions and parameters can be assessed for any operation temperature and failure criterion.
Progress in Photovoltaics: Research and Applications, 2019
A temperature accelerated life test on Upright Metamorphic Ga0.37In0.63P/Ga0.83In0.17As/Ge triple... more A temperature accelerated life test on Upright Metamorphic Ga0.37In0.63P/Ga0.83In0.17As/Ge triple‐junction solar cells has been carried out. The acceleration has been accomplished by subjecting the solar cells to temperatures (125, 145 and 165°C) significantly higher than the nominal working temperature inside a concentrator (90°C), while the nominal photo‐current (500×) has been emulated by injecting current in darkness. The failure distributions have been fitted to an Arrhenius–Weibull model resulting in an activation energy of 1.39 eV. Accordingly, a 72 years warranty time for those solar cells for a place like Tucson (AZ, USA), was determined. After the ALT, an intense characterization campaign has been carried out in order to determine the failure origin. We have detected that temperature soak alone is enough to degrade the cell performance by increasing the leakage currents, the series resistance, and the recombination currents. When solar cells were also forward biased an inc...
Progress in Photovoltaics: Research and Applications, 2016
Accelerated life tests are frequently used to provide reliability information in a moderate perio... more Accelerated life tests are frequently used to provide reliability information in a moderate period of time (weeks or months), and after that, a failure analysis is compulsory to detect the failure origins. In this paper, a failure analysis has been carried out after a temperature accelerated life test on lattice matched GaInP/Ga(In)As/Ge triple junction commercial solar cells. Solar cells were forward biased in darkness inside three climatic chambers in order to emulate the photo‐generated current under nominal working conditions (a concentration level of 820 suns). After the accelerated aging test, a characterization of the resulting cells by means of quantum efficiency, dark and illumination I–V curves, electroluminescence, scanning electron microscope, energy dispersive X‐ray, scanning transmission electron microscope and X‐ray photoelectron spectroscopy has been carried out.Current is identified as the cause of degradation while temperature just dominates the accelerating factor...
Progress in Photovoltaics: Research and Applications, 2017
This paper proposes a methodology for assessing the concentrator solar cell reliability in a real... more This paper proposes a methodology for assessing the concentrator solar cell reliability in a real application for a given location provided the results from accelerated life tests. We have applied this methodology for the evaluation of warranty times of commercial triple junction solar cells operating inside real concentrator modules in Golden (Colorado, USA), Madrid (Spain) and Tucson (Arizona, USA) for the period 2012–2015. Warranty times in Golden and Madrid, namely, 68 and 31 years, respectively, for the analysed period, indicate the robustness of commercial triple junction solar cells. Nevertheless, the warranty time of 15 years for Tucson suggests the need of improvement in the heat extraction of the solar cell within the concentrator module. Therefore, the influence of the location on the reliability of concentrator solar cells is huge, and it has no sense to supply general reliability values for a given concentrator product. The influence of these warranty times for the thre...
Space solar cells have been subjected to an innovative temperature Accelerated Life Test (ALT) to... more Space solar cells have been subjected to an innovative temperature Accelerated Life Test (ALT) to get information on their degradation and their activation energy. Our procedure emulates the thermal stress that solar cells suffer working under space conditions. Solar cells were kept in a climatic chamber under nitrogen atmosphere at three different temperatures for few months. After degradation, results have been fitted to a temperature Arrhenius model, in order to obtain the activation energy and acceleration factor of space GaInP/Ga(In)As/Ge triple junction solar cells.
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
In order to get a cost competitive commercial product based in III-V solar cells, a complete asse... more In order to get a cost competitive commercial product based in III-V solar cells, a complete assessment of their reliability must be done. A full strategy of tests has been designed to tackle this matter. Real time and homologated accelerated tests are ongoing, as well as a complete statistical analysis which will establish the main reliability parameters and the failure
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