Observation of metal precipitates at prebreakdown sites in multicrystalline silicon solar cells

Kwapil, Wolfram; Gundel, Paul; Schubert, Martin C.; Heinz, Friedemann D.; Warta, Wilhelm; Weber, E. R.; Goetzberger, A.; Martı́nez-Criado, G.

doi:10.1063/1.3272682

Cited by 55 publications

(41 citation statements)

References 22 publications

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“…Hence, it can be expected that iron may play a decisive role in forming these breakdown sites. Indeed, it had been shown in micro X−ray fluorescence investigations by Kwapil et al [59] that iron−containing precipitates may exist in type−2 breakdown sites. By performing TEM investigations in these sites, nee− dle−shaped FeSi 2 precipitates have recently been found in grain boundaries, which may stick through the p−n junction [60].…”

Section: The Reverse Currentmentioning

confidence: 99%

Understanding the current-voltage characteristics of industrial crystalline silicon solar cells by considering inhomogeneous current distributions

Breitenstein

2013

Opto-Electronics Review

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Solar cells made from multi- or mono-crystalline silicon wafers are the base of today’s photovoltaics industry. These devices are essentially large-area semiconductor p-n junctions. Technically, solar cells have a relatively simple structure, and the theory of p-n junctions was established already decades ago. The generally accepted model for describing them is the so-called two-diode model. However, the current-voltage characteristics of industrial solar cells, particularly of that made from multi-crystalline silicon material, show significant deviations from established diode theory. These deviations regard the forward and the reverse dark characteristics as well as the relation between the illuminated characteristics to the dark ones. In the recent years it has been found that the characteristics of industrial solar cells can only be understood by taking into account local inhomogeneities of the dark current flow. Such inhomogeneities can be investigated by applying lock-in thermography techniques. Based on these and other investigations, meanwhile the basic properties of industrial silicon solar cells are well understood. This contribution reviews the most important experimental results leading to the present state of physical understanding of the dark and illuminated characteristics of multi-crystalline industrial solar cells. This analysis should be helpful for the continuing process of optimizing such cells for further increasing their energy conversion efficiency.

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Section: The Reverse Currentmentioning

confidence: 99%

Understanding the current-voltage characteristics of industrial crystalline silicon solar cells by considering inhomogeneous current distributions

Breitenstein

2013

Opto-Electronics Review

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“…Direct evidence of Fe precipitation was found recently by micro-x-ray fluorescence (l-XRF) investigations at breakdown sites. 30 Figure 6(b) shows a SEM image of a position containing two breakdown sites in grain boundaries (see insets) together with l-XRF mappings of iron in these two sites (c). Obviously, the type-2 breakdown originates from iron-containing precipitates lying within Fe-contaminated grain boundaries.…”

Section: B Defect-induced Breakdownmentioning

confidence: 99%

Understanding junction breakdown in multicrystalline solar cells

Breitenstein

Bauer

Bothe

et al. 2011

Journal of Applied Physics

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122

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Extensive investigations on industrial multicrystalline silicon solar cells have shown that, for standard 1 X cm material, acid-etched texturization, and in absence of strong ohmic shunts, there are three different types of breakdown appearing in different reverse bias ranges. Between À4 and À9 V there is early breakdown (type 1), which is due to Al contamination of the surface. Between À9 and À13 V defect-induced breakdown (type 2) dominates, which is due to metal-containing precipitates lying within recombination-active grain boundaries. Beyond À13 V we may find in addition avalanche breakdown (type 3) at etch pits, which is characterized by a steep slope of the I-V characteristic, avalanche carrier multiplication by impact ionization, and a negative temperature coefficient of the reverse current. If instead of acid-etching alkaline-etching is used, all these breakdown classes also appear, but their onset voltage is enlarged by several volts. Also for cells made from upgraded metallurgical grade material these classes can be distinguished. However, due to the higher net doping concentration of this material, their onset voltage is considerably reduced here.

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“…of the reverse voltage regime-2 [9,33] which is dominated by the so-called type-2 prebreakdown sites [20] and defined by an exponential increased reverse -characteristic from about −7 V to −12 V. With increasing number of Type-A defects the reverse current is increasing too. Therefore, Type-A defects are dominating the prebreakdown behavior in reverse voltage regime-2.…”

Section: Influence Of Type-a Defects On the Prebreakdown Behavior In mentioning

confidence: 99%

“…In summary, already on a macroscopic level (6 solar cell) we can clearly distinguish two types of recombination active defects denoted as Type-A (purple) and Type-B (orange). Type-A defects are determined by low intensity of the indirect band-to-band luminescence at 1.1 eV, missing defect luminescence between 0.75 and 0.82 eV and their so called type-2 prebreakdown behavior [20]. Type-A defects are most likely caused by metal contaminations in form of precipitates and atomic decorations as reported in Lausch et al [21].…”

Section: Short Review Of Defect Classificationmentioning

confidence: 99%

Influence of Different Types of Recombination Active Defects on the Integral Electrical Properties of Multicrystalline Silicon Solar Cells

Lausch

Hagendorf

2015

Journal of Solar Energy

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In this contribution the influence of different types of recombination-active defects on the integral electrical properties of multicrystalline Si solar cells is investigated. Based on a previous classification scheme related to the luminescence behavior of crystal defects, Type-A and Type-B defects are locally distinguished. It is shown that Type-A defects, correlated to iron contaminations, are dominating the efficiency by more than 20% relative through their impact on the short circuit current I SC and open circuit voltage V OC in standard Si material (only limited by recombination active crystal defects). Contrarily, Type-B defects show low influence on the efficiency of 3% relative. The impact of the detrimental Type-A defects on the electrical parameters is studied as a function of the block height. A clear correlation between the area fraction of Type-A defects and both the global Isc and the prebreakdown behavior (reverse current) in voltage regime-2 (−11 V) is observed. An outlier having an increased fullarea recombination activity is traced back to dense inter-and intragrain nucleation of Fe precipitates. Based on these results it is concluded that Type-A defects are the most detrimental defects in Si solar cells (having efficiencies > 15%) and have to be prevented by optimized Si material quality and solar cell process conditions.

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Observation of metal precipitates at prebreakdown sites in multicrystalline silicon solar cells

Cited by 55 publications

References 22 publications

Understanding the current-voltage characteristics of industrial crystalline silicon solar cells by considering inhomogeneous current distributions

Understanding the current-voltage characteristics of industrial crystalline silicon solar cells by considering inhomogeneous current distributions

Understanding junction breakdown in multicrystalline solar cells

Influence of Different Types of Recombination Active Defects on the Integral Electrical Properties of Multicrystalline Silicon Solar Cells

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