In this study, a method for determining the intrinsic recombination velocity at the junction of a silicon solar cell is presented. The expression of intrinsic recombination velocity at the junction was established under irradiation in frequency modulation. Based on this expression, an electrical model of the intrinsic recombination velocity at the junction is presented.
A three-dimensional study is made to improve the theoretical approach of spectral response of bifacial polycrystalline silicon solar cells. This study has allowed taking into account new parameters like grain size and grain boundaries recombination velocity, which reduce the cell efficiency. Losses in emitter region and external magnetic field are also being taken into account in order to perfect the description of measured spectral response. Then the new analytical expressions of carrier, photocurrent and short circuit densities are produced for front side and rear side illuminations. Homemade software based on the new analytical expressions of internal quantum efficiency is used to fit the experimental data. PACS:73.50.Pz KEYWORDS: 1-Spectral response; 2-Polycrystalline; 3-Solar cell; 4-Magnetic field. INTRODUCTIONThe spectral response (SR) data are useful to determine the quality of solar cells. From the SR, one can determine fundamental parameters of solar cells like: effective diffusion length (L eff ), effective lifetime (τ eff ), back surface recombination velocity (S B ), which are used in the characterization above. There exists a lot of techniques of characterization using SR data, but each of them uses its own theoretical approach of SR. We can cite the linear fit method (Warta, 1992.), (Werner, et al., 1993), (Basu and Singh, 1994, pp.317-329), (Spiegel, et al., 2000), (Tool et al., 2002); its application leads to L eff directly and is suitable for solar cells where L eff is much smaller than the base region thickness.The theoretical approach of SR is better in producing accurate values of fundamental parameters. Thereby, the other parameters must be taken into account to describe SR especially for the polycrystalline silicon solar cells (Lu, et al., 2003) (Fedorov, et al., 2002, pp.49-55), which are mainly used in terrestrial applications. The grain size and the grain boundaries recombination velocity (S g ) (Lu, et al., 2003) (Ba, et al., 2003, pp.143-154) in polycrystalline silicon solar cells are important parameters which affect its efficiency.During the SR measurement (Spiegel, et al., 2000), the influences of external conditions like the temperature and the magnetic field intensity are not outdone.In this paper we make a new theoretical approach of the spectral response through a three dimensional study. In order to improve the SR, we are taking into account the contribution of emitter region, grain size, grain boundaries (GBs) recombination velocity, and an external magnetic field. We also apply a new technique to determine the recombination parameters based on new expressions of spectral response by fitting experimental data. This work is split into three parts: in the first part we have the theory that leads to the internal quantum efficiency, then in the second part we investigate the influence of magnetic field and GBs recombination and in the last part we present the new method and the results of its application. MODELLING Model and assumptionsIn this study, we use a sampl...
An n + -p-p + bifacial solar cell under constant magnetic field is placed in a fast-switch-interrupted circuit and submitted to a constant multi-spectral illumination. The transient decay occurs between two steady states through operating points depending on two variable resistors; this allows us to obtain a transient decay at any operating point of the I-V curve of the solar cell, from the short circuit to the open one. The influence of magnetic field on the transient photocurrent has been studied using Matlab Simulink simulations. These simulations lead to an equivalent circuit of the bifacial cell in transient state assuming that the photocurrent is the diffused. PACS: 73.50.Pz
The use of the back surface field BSF within the thin film cells isn't elaborated in a current state of research. In this article we try to adapt it to the Cu(In,Ga)Se 2 thin film solar cells. The theoretical study is based on the resolution in one dimension of the equations which govern the behaviour of a photovoltaic cell. The spectrum used is the AM 1.5. The experimental method takes into account all physical phenomena which happen in the solar cell. The comparison of the macroscopic electric parameters of the two cells with BSF and without BSF enabled us to obtain a conversion efficiency of 21.95% for the cell with BSF whereas it is equal to 20.78% for the cell without BSF. The use of the BSF presents a broad maximum absorption band which extends from 0.4µm to 1µm through the study of the quantum efficiency of the cell. The spectral response of the layer reaches a value of 0.7A.W -1 for an incidental wavelength of approximately 1000nm which corresponds to the gap of the absorber of the solar cell of 1.2eV. The improvement of the thickness of the p+ CIGS up-doped, indicates an optimal thickness of 0.5.µm.We find for this thickness an open circuit voltage of 0.71V, a short-circuit current density of 37.409mA.cm -2 and a conversion efficiency of 21.95%. The optimization of the doping concentration acceptors of the p+ CIGS, shows that the optimal concentration corresponds to 10E18cm -3. We find with this acceptors density an open circuit voltage of 0.69V, a short circuit current density of 37.40mA.cm -2 and a conversion efficiency of 21.74%.
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