Influence of Defects on Solar Cell Characteristics

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Influence of Defects on Solar Cell Characteristics

Journal Article•DOI•

Influence of Defects on Solar Cell Characteristics

Otwin Breitenstein¹, J. Bauer¹, Pietro P. Altermatt², K. Ramspeck•Institutions (2)

Max Planck Society¹, Leibniz University of Hanover²

01 Oct 2009-Solid State Phenomena (Trans Tech Publications)-pp 1-10

TL;DR: In this article, the authors reviewed the present knowledge of the origin of non-ideal I-V characteristics of silicon solar cells and introduced new results on recombination involving coupled defect levels.

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Abstract: The current-voltage (I-V) characteristics of most industrial silicon solar cells deviate rather strongly from the exponential behavior expected from textbook knowledge. Thus, the recombination current may be orders of magnitude larger than expected for the given material quality and often shows an ideality factor larger than 2 in a wide bias-range, which cannot be explained by classical theory either. Sometimes, the cells contain ohmic shunts although the cell’s edges have been perfectly insolated. Even in the absence of such shunts, the characteristics are linear or super-linear under reverse bias, while a saturation would be classically expected. Especially in multicrystalline cells the breakdown does not tend to occur at -50 V reverse bias, as expected, but already at about -15 V or even below. These deviations are typically caused by extended defects in the cells. This paper reviews the present knowledge of the origin of such non-ideal I-V characteristics of silicon solar cells and introduces new results on recombination involving coupled defect levels.

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Journal Article•DOI•

Review of Microcrack Detection Techniques for Silicon Solar Cells

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Mahmoud Abdelhamid¹, Rajendra Singh², Mohammed Omar¹•Institutions (2)

Center for Automotive Research¹, Clemson University²

01 Jan 2014-IEEE Journal of Photovoltaics

TL;DR: This review paper addresses nondestructive testing techniques that are used to detect microfacial and subfacial cracks in bulk solar cells and uses the multi-attribute decision-making method to evaluate the different inspection tools that are available on the market.

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Abstract: Microcracks at the device level in bulk solar cells are the current subject of substantial research by the photovoltaic (PV) industry. This review paper addresses nondestructive testing techniques that are used to detect microfacial and subfacial cracks. In this paper, we mainly focused on mono- and polycrystalline silicon PV devices and the root causes of the cracks in solar cells are described. We have categorized these cracks based on size and location in the wafer. The impact of the microcracks on electrical and mechanical performance of silicon solar cells is reviewed. For the first time, we have used the multi-attribute decision-making method to evaluate the different inspection tools that are available on the market. The decision-making tool is based on the analytical hierarchy process and our approach enables the ranking of the inspection tools for PV production stages, which have conflicting objectives and multi-attribute constraints.

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101 citations

Cites background from "Influence of Defects on Solar Cell ..."

...[11], [40] reported that such cracks could act as a linear or nonlinear edge shunt, and that cracks in processed solar cells led to a...
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Journal Article•DOI•

Nondestructive local analysis of current–voltage characteristics of solar cells by lock-in thermography

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Otwin Breitenstein¹•Institutions (1)

Max Planck Society¹

01 Oct 2011-Solar Energy Materials and Solar Cells

TL;DR: By evaluating dark lock-in thermography images taken at one reverse and three forward biases, images of all two-diode-parameters J01, J02, n (ideality factor of J02), and Gp (the parallel Ohmic conductivity) of the dark current-voltage characteristic are obtained as discussed by the authors.

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96 citations

Cites background from "Influence of Defects on Solar Cell ..."

...The analysis of many global and local I-V characteristics of solar cells leads to n2 > 2 [2-4, 7], which cannot be explained by standard point defect recombination theory....
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...It had been shown previously that ideality factors larger than 2 may be caused by recombination via extended defects [7]....
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Proceedings Article•DOI•

Testing and analysis for lifetime prediction of crystalline silicon PV modules undergoing degradation by system voltage stress

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Peter Hacke¹, Ryan Smith¹, Kent Terwilliger¹, Stephen Glick¹, Dirk Jordan¹, Steve Johnston¹, Michael D. Kempe¹, Sarah Kurtz¹ - Show less +4 more•Institutions (1)

National Renewable Energy Laboratory¹

01 Jan 2013

TL;DR: In this article, a lognormal analysis is applied to the accelerated lifetime test data, considering failure at 80% of the initial module power, and the probability of module failure at an arbitrary temperature is predicted.

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Abstract: Acceleration factors are calculated for crystalline silicon photovoltaic modules under system voltage stress by comparing the module power during degradation outdoors with that in accelerated testing at three temperatures and 85% relative humidity. A lognormal analysis is applied to the accelerated lifetime test data, considering failure at 80% of the initial module power. Activation energy of 0.73 eV for the rate of failure is determined for the chamber testing at constant relative humidity, and the probability of module failure at an arbitrary temperature is predicted. To obtain statistical data for multiple modules over the course of degradation in situ of the test chamber, dark I–V measurements are obtained and transformed using superposition, which is found to be well suited for rapid and quantitative evaluation of potential-induced degradation. It is determined that shunt resistance measurements alone do not represent the extent of power degradation. This is explained with a two-diode model analysis that shows an increasing second diode recombination current and ideality factor as the degradation in module power progresses. Failure modes of the modules stressed outdoors are examined and compared with those stressed in accelerated tests.

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80 citations

Cites background or methods from "Influence of Defects on Solar Cell ..."

...density of defect states in the p-n junction [21]....
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...Rsh and all the other parameters in the model, including pre-exponentials Jo1 and Jo2 and ideality factors n1 and n2 within the first and second diode terms referred to, respectively, as the diffusion and recombination current densities [21], and the area-specific series resistance Rs , were varied to achieve fitting of the dark I–V curve....
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Journal Article•DOI•

Effects of Thermochemical Treatment on CuSbS2 Photovoltaic Absorber Quality and Solar Cell Reproducibility

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Francisco Willian de Souza Lucas¹, Francisco Willian de Souza Lucas², Adam W. Welch², Adam W. Welch³, Lauryn L. Baranowski², Lauryn L. Baranowski³, Patricia C. Dippo², Hannes Hempel⁴, Thomas Unold⁴, Rainer Eichberger⁴, Beatrix Blank⁵, Uwe Rau⁵, Lucia H. Mascaro¹, Andriy Zakutayev² - Show less +10 more•Institutions (5)

Federal University of São Carlos¹, National Renewable Energy Laboratory², Colorado School of Mines³, Helmholtz-Zentrum Berlin⁴, Forschungszentrum Jülich⁵

11 Aug 2016-Journal of Physical Chemistry C

TL;DR: In this article, a thermochemical treatment (TT) for CuSbS2 thin films was developed, which consists of annealing in Sb2S3 vapor followed by a selective KOH surface chemical etch.

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Abstract: CuSbS2 is a promising nontoxic and earth-abundant photovoltaic absorber that is chemically simpler than the widely studied Cu2ZnSnS4. However, CuSbS2 photovoltaic (PV) devices currently have relatively low efficiency and poor reproducibility, often due to suboptimal material quality and insufficient optoelectronic properties. To address these issues, here we develop a thermochemical treatment (TT) for CuSbS2 thin films, which consists of annealing in Sb2S3 vapor followed by a selective KOH surface chemical etch. The annealed CuSbS2 films show improved structural quality and optoelectronic properties, such as stronger band-edge photoluminescence and longer photoexcited carrier lifetime. These improvements also lead to more reproducible CuSbS2 PV devices, with performance currently limited by a large cliff-type interface band offset with CdS contact. Overall, these results point to the potential avenues to further increase the performance of CuSbS2 thin film solar cell, and the findings can be transferred t...

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62 citations

Journal Article•DOI•

A two-diode model regarding the distributed series resistance

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Otwin Breitenstein¹, Sven Rißland¹•Institutions (1)

Max Planck Society¹

01 Mar 2013-Solar Energy Materials and Solar Cells

TL;DR: In this paper, a two-diode model with an analytically given variable series resistance is proposed, which may describe both the dark and the illuminated characteristic up to large current densities in good approximation with one and the same physically meaningful parameter set.

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60 citations

Cites background from "Influence of Defects on Solar Cell ..."

...In contrast to this strong material-induced influence on J01, the recombination current density, which is described by J02 and n2 in the dark I–V curve, is essentially process-related, since it is mostly caused by extended defects crossing the p–n junction as cracks or badly passivated cell edges [21]....
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...As already mentioned before, the different parameters obtained from the I–V curves characterizes effects with different physical origins [21]....
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Journal Article•DOI•

Correlation of pre‐breakdown sites and bulk defects in multicrystalline silicon solar cells

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Dominik Lausch¹, Kai Petter, Holger von Wenckstern¹, Marius Grundmann¹•Institutions (1)

Leipzig University¹

01 Mar 2009-Physica Status Solidi-rapid Research Letters

TL;DR: In this paper, a strong correlation between the pre-breakdown sites visible in dark lock-in thermography due to local heating and the intensity of spatially resolved electroluminescence of reverse-biased solar cells was observed.

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Abstract: Strong correlation between the pre-breakdown sites visible in dark lock-in thermography due to local heating and the intensity of spatially resolved electroluminescence of reverse-biased solar cells was observed. By comparing differently texturised solar cells we could show that the pre-breakdown sites are not correlated to the surface morphology, e.g. etch pits resulting in local field enhancement. The positions of the pre-breakdown sites are identical for acidic and alkaline texturised solar cells and therefore are directly related to bulk defects in the wafer. Nevertheless, the breakdown voltage is lower for acidic texturised solar cells; the parameters of breakdown are influenced by the texture in contrast to the position. Also pre-breakdown sites are observed in areas without specific surface features for alkaline texturised solar cells. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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67 citations

The Origin of Ideality Factors n > 2 of Shunts and Surfaces in the Dark I-V Curves of Si 625 Solar Cells

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O. Breitenstein, P. P. Altermatt, K. Ramspeck, A. Schenk

01 Jan 2006

TL;DR: In this paper, the edge recombination current and other non-linear shunts can be described as regions that are highly disturbed, even amorphous, crossing the pn-junction.

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Abstract: So far, a general model for the explanation of non-linear shunts and edge currents, often showing ideality factors n > 2, has been missing. Non-linear shunts like scratches and edge currents are the major source of the recombination current of industrial crystalline silicon solar cells. Moreover, the reverse current of such cells behaves always linear or even superlinear instead of saturation-type, as expected. We propose that the edge recombination current and other non-linear shunts can be described as regions that are highly disturbed, even amorphous, crossing the pn-junction. The recombination within such regions needs model descriptions that go beyond the SRH approximation, because the density of defects is so high that carriers recombine via more than one defect (so-called multi-level recombination). Two variants of coupled defect level recombination, both leading to idealiy factors larger than 2, are realistically modelled by Sentaurus simulations. Under reverse bias, the high local density of states in the defective material enables hopping conduction, which explains the linear reverse characteristics.

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60 citations

"Influence of Defects on Solar Cell ..." refers background or result in this paper

...By comparing the I-V characteristics of scratches made with different loads it had been found that the ideality factor increases with increasing load, hence with increasing local concentration of defect states [13]....
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...By performing scratches of different load in previously ideally behaving solar cells, it has been found that the ohmic reverse conductivity, just as the recombination current, drastically increases with increasing load of the scratches [13]....
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...It was shown in [13] that indeed the series resistance increases the ideality factor of the recombination current, but it is not the primary reason for a large ideality factor....
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...The treatment in [13] was only qualitative....
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...in the edge region or in other regions of non-linear (recombination-induced) shunts [13]....
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Journal Article•DOI•

Imaging physical parameters of pre‐breakdown Sites by lock‐in thermography techniques

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Otwin Breitenstein¹, J. Bauer¹, Jan-Martin Wagner¹, Andriy Lotnyk¹•Institutions (1)

Max Planck Society¹

01 Dec 2008-Progress in Photovoltaics

TL;DR: In this paper, lock-in thermography (LIT) was used to study the local temperature coefficient of pre-breakdown sites in solar cells and the normalized local slope of the I-V characteristics.

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Abstract: Local pre-breakdown sites in solar cells can be studied by lock-in thermography (LIT). Three new LIT techniques are proposed and demonstrated here, which are TC-DLIT for studying the local temperature coefficient of pre-breakdown sites, Slope-DLIT for measuring the normalized local slope of the I–V characteristics, and MF-ILIT for imaging the local carrier multiplication factor. First results on multicrystalline silicon cells show that the pre-breakdown mechanism cannot completely be described by the conventional impact ionization and internal field emission models. Copyright # 2008 John Wiley & Sons, Ltd.

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59 citations

"Influence of Defects on Solar Cell ..." refers background or methods in this paper

...Thermal measurements of the temperature coefficient (TC) and the slope of such sites have shown that the edge leakage shows a positive TC and a low slope, sites "I" and "II" show a clearly negative TC, and type "II" shows an only slightly negative ore close to zero TC and a medium slope [22]....
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...By performing DLIT under various reverse biases and special LIT techniques for imaging the local temperature coefficient, slope, and avalanche multiplication factor [22], the following observations about breakdown in acidically etched industrial MC solar cells were made: Breakdown occurs only locally at certain breakdown 6 Gettering and Defect Engineering in Semiconductor Technology XIII...
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...It has also been found that only breakdown sites of type "III" show significant avalanche multiplication of photo-generated carriers and a high slope [22]....
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Journal Article•DOI•

Electronic activity of SiC precipitates in multicrystalline solar silicon

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J. Bauer¹, Otwin Breitenstein¹, Jean-Patrice Rakotoniaina•Institutions (1)

Max Planck Society¹

01 Jul 2007-Physica Status Solidi (a)

TL;DR: In this paper, the electrical properties of the silicon carbide particles were investigated and it was concluded that the shunt current flows inside of the filaments of the solar cells and that the carbide precipitates are highly conductive.

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Abstract: In the upper part of block-cast multicrystalline silicon one often finds silicon carbide and silicon nitride precipitates and inclusions. These contaminants can cause severe ohmic shunts in solar cells and thus decrease the efficiency of the solar cells very strongly. It is well known that the silicon carbide precipitates cause the ohmic shunts. However, the electrical properties of the silicon carbide was unknown so far. To study the electrical properties of these silicon carbide particles we isolated them from the silicon bulk material and performed different electrical measurements on them. The measurements show that the silicon carbide precipitates are highly conductive. An investigation of the heterojunction silicon – silicon carbide was also performed and a simulation of this heterojunction leads to a new model of the ohmic shunt mechanism. It is concluded that the shunt current flows inside of the filaments.

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59 citations

"Influence of Defects on Solar Cell ..." refers background in this paper

...Due to the incorporation of N, which is the dominant shallow donor in SiC, these filaments are nconducting and are in direct contact to the emitter [26]....
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Proceedings Article•DOI•

Interpretation of the Commonly Observed I-V Characteristics of C-SI Cells Having Ideality Factor Larger Than Two

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Otwin Breitenstein¹, Pietro P. Altermatt², K. Ramspeck, Martin A. Green³, J. Zhao³, Andreas Schenk⁴ - Show less +2 more•Institutions (4)

Max Planck Society¹, Leibniz University of Hanover², University of New South Wales³, ETH Zurich⁴

07 May 2006

TL;DR: In this article, a coupled defect recombination via two shallow (or one shallow and one deep) level was applied to explain the observed high ideality factors due to trap-assisted tunneling.

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Abstract: The dark I-V characteristics of crystalline silicon solar cells usually deviate from that expected by classical diode theory by an unusually high ideality factor and magnitude at biases smaller than about 0.5 V. It had been shown that the recombination current is flowing preferentially in certain local extended defect positions like the edge or local shunts. There, the local density of recombination centers in the pn-junction is higher than in the bulk by orders of magnitude. In this work, we go beyond the SRH theory to explain the recombination effects occurring in such heavily damaged pn-junction regions. Firstly, we apply the coupled defect recombination via two shallow (or one shallow and one deep) level, which explains the observed high ideality factors due to trap-assisted tunneling. Secondly, we apply the coupling of two defects to recombination via deep donor-acceptor pairs, which cause the high ideality factors due to saturation of the recombination rate between the two defects. Thirdly, the local extension of the recombination region across the edge of the cell (due to electrostatic charging) is an other explanation of very high recombination currents.

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51 citations