NEW APPROCH TO DETERMINE THE ACCURATE MINORITY CARRIER LIFETIME

In the recent years, considerable research has been done on multijunction (MJ) solar cell. A monolithic MJ solar cell is composed of several junctions connected in series, all of which should be closely current matched for efficient photovoltaic device operation. The most successful implementation of this device is the InGaP/GaAs/Ge triple junction cell, attaining efficiencies in excess of 29 % AM0. The degradation of the cell characteristics under the high energy electron and proton irradiation depends on the semiconductor material and the specific solar cell structure. High energy particles lead to displacement damage and deep recombination centres reducing the minority carrier lifetime. In the present work, we present a new method, which allows to get exact value of the minority carrier lifetime and to apply this to p+/n InGaP solar cell material.In the recent years, considerable research has been done on multijunction (MJ) solar cell. A monolithic MJ solar cell is composed of several junctions connected in series, all of which should be closely current matched for efficient photovoltaic device operation. The most successful implementation of this device is the InGaP/GaAs/Ge triple junction cell, attaining efficiencies in excess of 29 % AM0. The degradation of the cell characteristics under the high energy electron and proton irradiation depends on the semiconductor material and the specific solar cell structure. High energy particles lead to displacement damage and deep recombination centres reducing the minority carrier lifetime. In the present work, we present a new method, which allows to get exact value of the minority carrier lifetime and to apply this to p+/n InGaP solar cell material

Extracting Double Diode Model Parameters Based on Cross Entropy Optimization Algorithm

A Cross Entropy (CE) optimization technique is suggested in this study in order to extract the optimal parameters of solar cell model. The solar cell model namely Double diode model, is used in this paper in the purpose to verify the proposed method. The seven unknown parameters of double diode model are: the photo-generated current, the diffusion current, saturation current, the series resistance, the shunt resistance, the diffusion ideality factor and recombination diode ideality factor. These parameters were used to determine the corresponding maximum power point (MPP) from the illuminated current–voltage (I–V) characteristic. The metaheuristic algorithms have created a center of attention due to the non-linearity of the solar cell models and the incapability of traditional optimization methods to precisely extract the parameters. Different cases and studies have been done to identify the unknown parameters of the solar cell double model. The efficiency of CE algorithm is investigated by comparing this method with various and different other techniques. This comparison is done using statistical indicators and analysis such as: mean absolute bias error, root mean square error and coefficient of determination. The results show that CE is a very efficient technique to identify the electrical parameters of the PV solar cells and modules

High efficiency of two solar cells CIGS/CIS stacked mechanically

In our work, we have simulated and optimized solar cells based on the mechanically stacked system using the Analysis of Microelectronic and Photonic Structures (AMPS-1D) simulator in respect to overall performance. The structures of solar cells are based on the top cell Copper- Indium-Gallium- diselenide, CuIn1-xGaxSe2, referred to as CIGS, and the bottom cell Copper- Indium-Gallium, CIS. We have simulated each cell individually and extrapolated their optimal parameters (thickness, concentration of absorber). In the case of tandem, we calculated the efficiency of each cell optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The current-matching limitation imposed by series connection reduces efficiency relative to independently-connected cells

Analysis of Multijunction solar cells: Electroluminescence study

This paper describes the principle of the study which is based on electroluminescence to extract the parameters characterizing the recombination centers induced by irradiation in a solar cell. This technique is able to provide direct information on each individual junction constituting the multijonctions. The results are compared with those obtained by electrical methods.This paper describes the principle of the study which is based on electroluminescence to extract the parameters characterizing the recombination centers induced by irradiation in a solar cell. This technique is able to provide direct information on each individual junction constituting the multijonctions. The results are compared with those obtained by electrical methods

Modelling and Optimization of GaAs used in mechanically stacked solar cells

Different approaches have been made in order to reach higher efficiencies. Concepts for multilayer solar cells have been developed. This can be realised if multiple individual single junction solar cells with different, suitably chosen band gaps are connected in series in multi-junction solar cells. In our work, we have simulated and optimized solar cells based on the system mechanically stacked using computer modelling and predict their maximum performance. The structures of solar cells are based on the single junction Si, Ge and GaAs cells. We have simulated each cell individually and extracted their optimal parameters (thickness, concentration, the recombination velocity…..), also, we calculated the efficiency of each cells optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The optimal values of physical parameters giving the best current of short-circuit and voltages of open circuit as well high conversion efficiency have obtained for the two solar materials and tandem.Different approaches have been made in order to reach higher efficiencies. Concepts for multilayer solar cells have been developed. This can be realised if multiple individual single junction solar cells with different, suitably chosen band gaps are connected in series in multi-junction solar cells. In our work, we have simulated and optimized solar cells based on the system mechanically stacked using computer modelling and predict their maximum performance. The structures of solar cells are based on the single junction Si, Ge and GaAs cells. We have simulated each cell individually and extracted their optimal parameters (thickness, concentration, the recombination velocity…..), also, we calculated the efficiency of each cells optimized by separation of the solar spectrum in bands where the cell is sensible for the absorption. The optimal values of physical parameters giving the best current of short-circuit and voltages of open circuit as well high conversion efficiency have obtained for the two solar materials and tandem

Properties of Cd1-xZnx Te crystals grown by High Pressure Bridgman (HPB)

In this paper we present results of a modelling of the current-voltage characteristics of metal/ultra-thin oxide/semiconductor structures with negatively biased metal gate (V<0), when the oxide thickness varies from 45Å to 80Å. We analyze the theoretical influence of the temperature and Schottky effect on the Fowler-Nordheim (FN) conduction. The results obtained show that these influences depend on the electric field in the oxide and on the potential barrier at the metal/oxide interface. At the ambient temperature, the influence on this potential barrier is lower than 1.5%. However, it can reach 45% on the pre-exponential coefficient of the FN current. It is therefore necessary to consider in the FN classical conduction expression a correction term that takes account the temperature and Schottky effects. These results are validated experimentally by modelling the current-voltage characteristics of the realized structures at high field.In this paper we present results of a modelling of the current-voltage characteristics of metal/ultra-thin oxide/semiconductor structures with negatively biased metal gate (V<0), when the oxide thickness varies from 45Å to 80Å. We analyze the theoretical influence of the temperature and Schottky effect on the Fowler-Nordheim (FN) conduction. The results obtained show that these influences depend on the electric field in the oxide and on the potential barrier at the metal/oxide interface. At the ambient temperature, the influence on this potential barrier is lower than 1.5%. However, it can reach 45% on the pre-exponential coefficient of the FN current. It is therefore necessary to consider in the FN classical conduction expression a correction term that takes account the temperature and Schottky effects. These results are validated experimentally by modelling the current-voltage characteristics of the realized structures at high field

Extraction of equivalent circuit parameters of solar cell: influence of temperature

A new method to evaluate the five parameters of illuminated solar cells is described. The method is based on nonlinear least squares approach. On calculating the lsqcurvefit-function with constraints, between the experimental current-voltage I(V) characteristic and a theoretical arbitrary characteristic based on Lambert W-function. The used model is implemented as a MATLAB® script which yields the I(V) characteristics of the LILT under test. The model has been validated against by applying it to experimental I(V) characteristics. Some parameters of the model have been measured directly whereas others have been evaluated by means of direct computation on the data sheet or by means of best-fit on the measured data. The results have been compared and an analysis of the errors is presented

Analysis of Multijunction solar cells: Electroluminescence study

This paper describes the principle of the study which is based on electroluminescence to extract the parameters characterizing the recombination centers induced by irradiation in a solar cell. This technique is able to provide direct information on each individual junction constituting the multijonctions. The results are compared with those obtained by electrical methods. I

The Metastability of Deep Donor Defects in Semiconductor Compounds

There is a whole class of deep donor defects which exhibit a metastable character, i.e. transform into a metastable state after a specific photo-excitation. Typical examples are the EL2 defect in GaAs and the DX center in several ternary III-V compounds. We shall present other defects which behave similarly, demonstrating that this metastable character is not specific of a defect but is a common behaviour of a class of defects. We shall also demonstrate that for all these defects the thermal excitation of electrons takes place in the $L$ conduction band and that the metastable chaxacter is a direct consequence of this. This leads to a new concept of a metastable state, a result of an electronic metastability due to a band structure effect and not to a strong electron-phonon interaction.