Recombination via point defects and their complexes in solar silicon (original) (raw)
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Recombination in compensated crystalline silicon for solar cells
Journal of Applied Physics, 2011
Deliberate compensation of crystalline silicon results in a decrease in the equilibrium carrier concentration, which leads to an increased carrier lifetime for the intrinsic recombination processes of Auger and radiative recombination. We present modeling which reveals that compensation also often leads to a significant increase in lifetime for recombination through defects via the Shockley-Read-Hall mechanism, a conclusion which is confirmed experimentally for the case of interstitial iron in p-type silicon. We show that the increased Shockley-Read-Hall lifetime can result from either an injection-level effect for deep levels, or from a Fermi-level effect for shallower levels. For cases where the defect exhibits no injection dependence of the carrier lifetime, compensation does not lead to an increased lifetime. Further modeling demonstrates that in certain cases, the lifetime increase can be expected to significantly outweigh the competing reductions in carrier mobilities and net doping, resulting in an improved short-circuit current, open-circuit voltage, and solar cell efficiency. V
Performance Degradation of Silicon Solar Cells Triggered by Carrier Recombination
The formation process of the metastable boron-oxygen-related defect complex is analysed by investigating the degradation of the open-circuit voltage of Cz-Si solar cells in the dark as a function of an applied voltage at temperatures ranging from 298 to 373 K. We provide clear experimental evidence of the defect formation not only occurring as a consequence of illumination or the injection of minority carriers via a pn-junction but also under apparent equilibrium conditions at elevated temperatures in the dark. By applying a reverse voltage a partial suppression of the defect formation can be achieved. All results can consistently be explained by a recombination-enhanced defect formation mechanism correlated with the total recombination rate. Combining the experimental results with calculations of the minority carrier densities corresponding to the applied voltages, we are able to show that 50% of the maximum defect concentration is already being formed at minority carrier concentrations as low as 5×10 9 cm -3 .
Role of surface recombination in multi-crystalline silicon solar cells
Multi-crystalline silicon solar cell was fabricated using crystalline p-substrates with emitter front contact of n-type crystalline silicon. This paper reviews that an efficiency of the Multi-crystalline silicon solar cell which was analysed to demonstrate the surface recombination of the substrate that affects the performance of the solar cell, was investigated in detail by computer simulation using PC1D software. The surface recombination was found to be a key factor to affect the performance of the solar cell. A detailed simulation studies were analysed. Accordingly, the optimization of the multi-crystalline silicon solar cell on c-Si substrates was provided.
Recombination centers in electron-irradiated Czochralski silicon solar cells
Journal of Applied Physics, 1994
The defect responsible for the minority-carrier lifetime in p-type Czochralski silicon introduced by electron irradiation has been detected and characterized by deep-level transient spectroscopy and spin-dependent recombination. From the isotropic g value (2.00.55), the defect is tentatively identified as a Si dangling bond originating from a vacancy cluster. Its energetic location in the gap is at 630 meV below the conduction band. The electron and hole cross sections and their variation with temperature have been determined, and found to account for the tninority-carrier lifetime of the material.
Lifetime limiting recombination pathway in thin-film polycrystalline silicon on glass solar cells
Journal of Applied Physics, 2010
The minority carrier lifetimes of a variety of polycrystalline silicon solar cells are estimated from temperature-dependent quantum efficiency data. In most cases the lifetimes have Arrhenius temperature dependences with activation energies of 0.17-0.21 eV near room temperature. There is also a rough inverse relationship between lifetime and the base dopant concentration. Judging by this inverse law, the activation energies of the lifetimes, and the absence of plateau behavior in the lifetimes of the higher doped cells at low temperatures, it is inferred that the dominant recombination pathway involves the electronic transition between shallow states which are 0.05 -0.07 eV below the conduction band and 0.06-0.09 eV above the valence band, respectively, consistent with the shallow bands in silicon dislocations. The modeled recombination behavior implies that deep levels do not significantly affect the lifetimes for most of the cells at and below room temperature.
Progress in Photovoltaics: Research and Applications, 2012
The recombination current in polycrystalline silicon on glass solar cells can be modeled by the superposition of two processes, one which involves only shallow electronic levels and another which occurs via deep levels at charged extended defects. The former process is most likely linked to clean dislocations, whereas the latter may originate either from charged dislocations or grain boundaries. The consideration of both kinds of processes is necessary for an accurate description of the device behaviors of poly-Si on glass solar cells over a wide range of dopant densities. The effects of varying the impurity and dislocation densities are also briefly discussed.
Solar Energy Materials and Solar Cells, 2008
Impedance spectroscopy (at forward bias and under illumination) of solar cells comprised thin hydrogenated amorphous silicon (a-Si:H) films deposited on crystalline silicon (c-Si) wafers was analyzed in terms of ac equivalent circuits. Shockley-Read-Hall recombination at states on the device interfaces governs the cell dynamic response. Recombination process was modeled by means of simple RC circuits which allow to determine the capture rate of electrons and holes. Carrier lifetime is found to be stated by the electron capture time t SRH Et n , and it results in the range of 300 ms. The Al-annealed back contact was regarded as the dominating recombination interface. r
Solar Energy Materials and Solar Cells, 2011
Solar grade, p-type multicrystalline silicon wafers with large grains from different parts of silicon ingots produced by the metallurgical route (SoG-Si) at ELKEM Solar were studied using a number of complementary methods such as microwave photoconductivity decay, deep level transient spectroscopy, transmission and scanning electron microscopy, X-ray fluorescence, and secondary ion mass spectroscopy. Wafers from the top of the ingots have uniform spatial distributions of both minority carrier lifetime (average lifetime t¼3.2 ms) and concentrations of illumination-sensitive recombination centers (N rc ¼ 3 Â 10 10 À 2 Â 10 11 cm À 3) over the whole wafers. Wafers from the bottom of the ingots have regions of very low lifetimes (t ¼ 0.3 ms) and high concentrations of illumination-sensitive recombination centers (N rc ¼2 Â 10 12 cm À 3). In the top part of the ingots the observed DLTS peaks can be attributed to copper-related extended defects, and the DLTS results from grains and grain boundaries are not significantly different. The main factors limiting the lifetime in the high lifetime regions are concluded to be illumination-sensitive recombination centers such as Fe-B pairs, B-O complexes, and Cu-related extended defects. The low lifetimes in the bottom part of the ingots are explained by a combination of several factors including high concentrations of illumination-sensitive recombination centers and of some deleterious elements (S, Na and Al), and a large amount of structural defects.
Base doping and recombination activity of impurities in crystalline silicon solar cells
Progress in Photovoltaics: Research and Applications, 2004
The optimisation of base doping for industrial crystalline silicon solar cells is examined with model calculations. Focus is on the relation between base doping and carrier recombination through the important impurities interstitial iron (Fe i) and the metastable boron-oxygen (BO) complex. In p-type silicon, the optimum base resistivity is strongly dependent on defect concentration. In n-type silicon, recombination due to Fe i is much lower and nearly independent of resistivity. Fe i is likely representative for other transition metal impurities. In many real cells a balance between Fe i or similar defects, and BO will occur.