Bringing high efficiency triple-junction solar cells developed so far to a massive electricity pr... more Bringing high efficiency triple-junction solar cells developed so far to a massive electricity production cost-competitiveness scenario requires the use of high concentrations. Moreover, the consideration of real operating conditions, for the design and optimization of the solar cell receiver — concentrator assembly, is compulsory. Such requirements involve the need for suitable modeling and simulation tools, in order to complement the
Proceedings of the 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009), 2009
... Ignacio Rey-Stolle, Carlos Algora, Ivan Garcia, Mathieu Baudrit, Pilar Espinet, Beatriz Galia... more ... Ignacio Rey-Stolle, Carlos Algora, Ivan Garcia, Mathieu Baudrit, Pilar Espinet, Beatriz Galiana and Enrique Barrig6n Instituto de Energia Solar - Universidad Politecnica de ... is the case, to model the solar cell it would be enough to divide its area into elementary units so small that ...
One of the key components of highly efficient multi-junction concentrator solar cells is the tunn... more One of the key components of highly efficient multi-junction concentrator solar cells is the tunnel junction interconnection. In this paper, an improved 3D distributed model is presented that considers real operation regimes in a tunnel junction. This advanced model is able to accurately simulate the operation of the solar cell at high concentrations at which the photogenerated current surpasses the peak current of the tunnel junction. Simulations of dual-junction solar cells were carried out with the improved model to illustrate its capabilities and the results have been correlated with experimental data reported in the literature. These simulations show that, under certain circumstances, the solar cell's short circuit current may be slightly higher than the tunnel junction peak current without showing the characteristic dip in the J-V curve. This behavior is caused by the lateral current spreading toward dark regions, which occurs through the anode/p-barrier of the tunnel junction.
This paper presents some of the results of a method to determine the main reliability functions o... more 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 valué much higher than the intended operation life time of the concentrator cells.
ABSTRACT A temperature accelerated life test on concentrator lattice mismatched Ga0.37In0.63P/Ga0... more ABSTRACT 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.
In this paper, the benefits of the ultra high concentration (¿ 1000 suns) are shown in terms of c... more 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
In this paper we intend to expand the portfolio of non-destructive techniques available for the i... more 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
The consideration of real operating conditions for the design and optimization of a multijunction... more The consideration of real operating conditions for the design and optimization of a multijunction solar cell receiverconcentrator assembly is indispensable. Such a requirement involves the need for suitable modeling and simulation tools in order to complement the experimental work and circumvent its wellknown burdens and restrictions. Three-dimensional distributed models have been demonstrated in the past to be a powerful choice for the analysis of distributed phenomena in single-and dual-junction solar cells, as well as for the design of strategies to minimize the solar cell losses when operating under high concentrations. In this paper, we present the application of these models for the analysis of triple-junction solar cells under real operating conditions. The impact of different chromatic aberration profiles on the short-circuit current of triple-junction solar cells is analyzed in detail using the developed distributed model. Current spreading conditions the impact of a given chromatic aberration profile on the solar cell I-V curve. The focus is put on determining the role of current spreading in the connection between photocurrent profile, subcell voltage and current, and semiconductor layers sheet resistance.
In this work, a compositional and morphological study of GaInP layers grown on Ge substrates is p... more In this work, a compositional and morphological study of GaInP layers grown on Ge substrates is presented. The samples have been evaluated by means of high resolution X-ray diffraction, Rutherford backscattering channeling, atomic force microscopy and scanning electron microscopy. Compositional results from HRXRD and RBS show that the quality of samples close to the lattice match are independent on the composition (Ga or In-rich), although for Ga-rich samples, the spectra from RBS channeling measurements is not equal for one 110 direction and its perpendicular, an effect that does not appear in In-rich samples. Concerning, the morphological results, two typical defects appear on GaInP nucleation layer on Ge substrate -the so called arrowhead defects and asymmetric truncated pyramids -both orientated along 110 directions. Experiments reveal that the formation of pyramids is independent on the layer composition, while the density of arrowheads increases as the layer gets more Ga-rich.
A temperature stress test was carried out on GaAs single-junction solar cells to analyze the degr... more 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 l-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.
Accelerated testing is a necessary tool in order to demonstrate the reliability of concentration ... more 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 x, 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.
On this paper we present an alternative way to analyze de electronic properties of each subcell f... more 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.
Bringing high efficiency triple-junction solar cells developed so far to a massive electricity pr... more Bringing high efficiency triple-junction solar cells developed so far to a massive electricity production cost-competitiveness scenario requires the use of high concentrations. Moreover, the consideration of real operating conditions, for the design and optimization of the solar cell receiver — concentrator assembly, is compulsory. Such requirements involve the need for suitable modeling and simulation tools, in order to complement the
Proceedings of the 2009 34th IEEE Photovoltaic Specialists Conference (PVSC 2009), 2009
... Ignacio Rey-Stolle, Carlos Algora, Ivan Garcia, Mathieu Baudrit, Pilar Espinet, Beatriz Galia... more ... Ignacio Rey-Stolle, Carlos Algora, Ivan Garcia, Mathieu Baudrit, Pilar Espinet, Beatriz Galiana and Enrique Barrig6n Instituto de Energia Solar - Universidad Politecnica de ... is the case, to model the solar cell it would be enough to divide its area into elementary units so small that ...
One of the key components of highly efficient multi-junction concentrator solar cells is the tunn... more One of the key components of highly efficient multi-junction concentrator solar cells is the tunnel junction interconnection. In this paper, an improved 3D distributed model is presented that considers real operation regimes in a tunnel junction. This advanced model is able to accurately simulate the operation of the solar cell at high concentrations at which the photogenerated current surpasses the peak current of the tunnel junction. Simulations of dual-junction solar cells were carried out with the improved model to illustrate its capabilities and the results have been correlated with experimental data reported in the literature. These simulations show that, under certain circumstances, the solar cell's short circuit current may be slightly higher than the tunnel junction peak current without showing the characteristic dip in the J-V curve. This behavior is caused by the lateral current spreading toward dark regions, which occurs through the anode/p-barrier of the tunnel junction.
This paper presents some of the results of a method to determine the main reliability functions o... more 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 valué much higher than the intended operation life time of the concentrator cells.
ABSTRACT A temperature accelerated life test on concentrator lattice mismatched Ga0.37In0.63P/Ga0... more ABSTRACT 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.
In this paper, the benefits of the ultra high concentration (¿ 1000 suns) are shown in terms of c... more 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
In this paper we intend to expand the portfolio of non-destructive techniques available for the i... more 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
The consideration of real operating conditions for the design and optimization of a multijunction... more The consideration of real operating conditions for the design and optimization of a multijunction solar cell receiverconcentrator assembly is indispensable. Such a requirement involves the need for suitable modeling and simulation tools in order to complement the experimental work and circumvent its wellknown burdens and restrictions. Three-dimensional distributed models have been demonstrated in the past to be a powerful choice for the analysis of distributed phenomena in single-and dual-junction solar cells, as well as for the design of strategies to minimize the solar cell losses when operating under high concentrations. In this paper, we present the application of these models for the analysis of triple-junction solar cells under real operating conditions. The impact of different chromatic aberration profiles on the short-circuit current of triple-junction solar cells is analyzed in detail using the developed distributed model. Current spreading conditions the impact of a given chromatic aberration profile on the solar cell I-V curve. The focus is put on determining the role of current spreading in the connection between photocurrent profile, subcell voltage and current, and semiconductor layers sheet resistance.
In this work, a compositional and morphological study of GaInP layers grown on Ge substrates is p... more In this work, a compositional and morphological study of GaInP layers grown on Ge substrates is presented. The samples have been evaluated by means of high resolution X-ray diffraction, Rutherford backscattering channeling, atomic force microscopy and scanning electron microscopy. Compositional results from HRXRD and RBS show that the quality of samples close to the lattice match are independent on the composition (Ga or In-rich), although for Ga-rich samples, the spectra from RBS channeling measurements is not equal for one 110 direction and its perpendicular, an effect that does not appear in In-rich samples. Concerning, the morphological results, two typical defects appear on GaInP nucleation layer on Ge substrate -the so called arrowhead defects and asymmetric truncated pyramids -both orientated along 110 directions. Experiments reveal that the formation of pyramids is independent on the layer composition, while the density of arrowheads increases as the layer gets more Ga-rich.
A temperature stress test was carried out on GaAs single-junction solar cells to analyze the degr... more 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 l-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.
Accelerated testing is a necessary tool in order to demonstrate the reliability of concentration ... more 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 x, 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.
On this paper we present an alternative way to analyze de electronic properties of each subcell f... more 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.
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