Influence of Defects on Solar Cell Characteristics
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.
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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TL;DR: In this article, a variety of microstructural defects in crystalline silicon solar cells which appear during the cell processing steps are investigated and localized using visible light emission under reversed bias voltage.
19 citations
TL;DR: In this paper, the authors used high-throughput metrology methods for detailed performance loss analysis of approximately 400 industrial crystalline silicon solar cells, all coming from the same production line.
Abstract: Novel, high-throughput metrology methods are used in this paper for detailed performance loss analysis of approximately 400 industrial crystalline silicon solar cells, all coming from the same production line. The characterization sequence combines traditional global cell measurements (e.g., current–voltage, Suns- ${V}_{\text{OC}}$ ) with camera-based cell imaging of voltage distribution and power dissipation from photoluminescence and lock-in thermography, respectively. Spatial variations in current collection are visualized using a high-speed external quantum efficiency and reflectance measurement technique. A nondestructive transfer length method (TLM) measurement technique is also implemented, featuring circular TLM structures hidden within the busbars of the cells. The variance of individual loss parameters and their impact on cell performance are quantified for this large group of cells. Based on correlations performed across parameters, recombination losses in the bulk and rear surface of the cell are shown to be the primary limiting factor for the cell efficiency. The nature of these distributions and correlations provide important insights about loss mechanisms in industrial solar cells, helping to prioritize efforts for optimizing the performance of the production line. Additionally, many of the parameters extracted from these techniques can be tied back to incoming material quality issues (e.g., poor bulk carrier lifetime, nonuniform wafer doping) and to individual unit processes (e.g., texturing, phosphorus diffusion, silicon nitride deposition, metallization), allowing the data to be used directly for process control in manufacturing. All of the datasets are made available for download.
19 citations
Cites background from "Influence of Defects on Solar Cell ..."
...at grain boundaries or dislocations [33]) and poor field effect passivation at the silicon surface [34], all of which are dependent on the manufacturing materials and processes used to produce...
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01 Jan 2012
17 citations
TL;DR: Results show that using the proposed strategy, micro cracks visibility is much more prominent than its counterparts present in literature and the Internet of Things accreditation is done using Arduino and WiFi module.
Abstract: Micro-cracks in solar Photo-Voltaic Cells (PVCs) can be formed in the vicinity of PVC/wafer manufacturing process or by thermal stress produced in transportation/handling or by inclement weather condition. Its insight is must as it reduces the efficiency of PVCs, enfeeble the cell constitution as well as affect the net manufactured production yield resulting in increase in production cost. The detection of these micro-cracks is strenuous owing to wafer’s heterogeneous textured base and involves two steps; first visualization of micro-cracks to imaging device, second efficient image processing technique to extract these micro-cracks from the captured image. In this paper Mamdani Fuzzy logic is proposed for extracting micro-cracks from solar PVCs images and comparison of performance analysis is done using MATLAB. The results show that using the proposed strategy, micro cracks visibility is much more prominent than its counterparts present in literature. To access local and remote output current data of solar panel the Internet of Things accreditation is done using Arduino and WiFi module.
16 citations
TL;DR: In this paper, the authors focus on the impact of crack morphology measured by photoluminescence imaging in the as-cut stage on the electrical solar cell parameters and derive a sorting criterion for microcracks concerning their electrical impact, which depends on wafer thickness and material type.
Abstract: Microcracks that are induced in early processing stages, especially before emitter diffusion, strongly influence the current–voltage $(I-V)$ characteristics of the solar cell. We focus on the impact of crack morphology measured by photoluminescence imaging in the as-cut stage on the electrical solar cell parameters. To provide a sufficient statistical base, microcracks are intentionally induced in a well-defined way in multi- (mc-Si) and mono- (Cz-Si) crystalline silicon wafers in the as-cut stage, the damaged wafers being processed to solar cells afterwards. From the dataset, a sorting criterion for microcracks concerning their electrical impact is derived, which depends on wafer thickness and material type. It is shown that cracks above 4 mm2 lead with high probability to severe shunts and, thus, need to be sorted out. Investigations by means of scanning electron microscopy (SEM) and electron-beam induced current (EBIC) measurements reveal that shunts with very low parallel resistance in Cz-Si solar cells can be attributed to metal-to-metal contacts between front and rear sides of the solar cell. Moreover, it is shown that the reduced robustness of Cz-Si compared with mc-Si concerning the formation of shunts at microcracks originates from a widening of the crack channels above 10 μm in alkaline texturing, which facilitates the formation of metal-to-metal contacts.
16 citations
References
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Book•
01 Jan 1974
TL;DR: In this article, a discussion is given of some aspects of the metal insulator transition and the status of the "minimum metallic conductivity" is discussed, and the concept is valid for liquids and in some, but not all, solid systems.
Abstract: A discussion is given of some aspects of the metal insulator transition. Particular attention is paid to the status of the “minimum metallic conductivity”. The concept is valid for liquids, and in some, but not all, solid systems.
2,109 citations
01 Sep 1957
TL;DR: In this article, the authors show that the current due to generation and recombination of carriers from generation-recombination centers in the space charge region of a p-n junction accounts for the observed characteristics.
Abstract: For certain p-n junctions, it has been observed that the measured current-voltage characteristics deviate from the ideal case of the diffusion model. It is the purpose of this paper to show that the current due to generation and recombination of carriers from generation-recombination centers in the space charge region of a p-n junction accounts for the observed characteristics. This phenomenon dominates in semiconductors with large energy gap, low lifetimes, and low resistivity. This model not only accounts for the nonsaturable reverse current, but also predicts an apparent exp (qV/nkT) dependence of the forward current in a p-n junction. The relative importance of the diffusion current outside the space charge layer and the recombination current inside the space charge layer also explains the increase of the emitter efficiency of silicon transistors with emitter current. A correlation of the theory with experiment indicates that the energy level of the centers is a few kT from the intrinsic Fermi level.
1,934 citations
"Influence of Defects on Solar Cell ..." refers background or methods in this paper
...It will be shown below that the characteristics of real solar cells behave very differently to the predictions of [2] because recombination in the depletion region contributes significantly to the cell’s total external current....
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...This large ideality factor cannot be explained with classical diode theory, and also the J02 is about 3 orders of magnitude larger than expected by [2]....
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...The classical theory of p-n junction diodes was established by Shockley [1] and was later extended by recombination in the p-n junction depletion region by Sah, Noyce, and Shockley [2]....
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...According to [2] and also to recent, more realistic numerical simulations [3], J02 should be in the order of 10 A/cm(2) for relatively poor material with a excess carrier lifetime of = 10 μs, and the ideality factor should be maximally n = 2....
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Book•
01 Oct 1981
TL;DR: In this paper, the solar source of light energy is described and quantified, along with a review of semiconductor properties and the generation, recombination, and the basic equations of photovoltaic device physics.
Abstract: Solar cell theory, materials, fabrication, design, modules, and systems are discussed. The solar source of light energy is described and quantified, along with a review of semiconductor properties and the generation, recombination, and the basic equations of photovoltaic device physics. Particular attention is given to p-n junction diodes, including efficiency limits, losses, and measurements. Si solar cell technology is described for the production of solar-quality crystals and wafers, and design, improvements, and device structures are examined. Consideration is given to alternate semiconductor materials and applications in concentrating systems, storage, and the design and construction of standalone systems and systems for residential and centralized power generation. Bibtex entry for this abstract Preferred format for this abstract
1,773 citations
"Influence of Defects on Solar Cell ..." refers methods in this paper
...It is common practice to include also these entities in a one- or two-diode model via an equivalent circuit [5]:...
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...a one-diode model, for the approximation of the I-V characteristics [5]....
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842 citations
Book•
01 Oct 1991
TL;DR: In this article, a homogeneous semiconductor at equilibrium drift, diffusion, generation, recombination, trapping and tunneling metaloxide-semiconductor capacitor P/N and other junction diodes metal-oxide semiconductor and other field effect transistors bipolar junction transistor and other bipolar transistor devices.
Abstract: Electrons, bonds, bands and holes homogeneous semiconductor at equilibrium drift, diffusion, generation, recombination, trapping and tunneling metal-oxide-semiconductor capacitor P/N and other junction diodes metal-oxide-semiconductor and other field-effect transistors bipolar junction transistor and other bipolar transistor devices.
286 citations
"Influence of Defects on Solar Cell ..." refers background in this paper
...Also modern textbooks such as Sah [4] describe the current-voltage (I-V) characteristic of solar cells on these theoretical grounds, which predicts that the reverse current-density saturates for a reverse bias below -100 mV to a constant value of -(J01 + J02)....
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...The classical theory of p-n junction diodes was established by Shockley [1] and was later extended by recombination in the p-n junction depletion region by Sah, Noyce, and Shockley [2]....
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...Also, the breakdown behavior of real (especially of MC) solar cells under reverse bias deviates significantly from the predictions in [4]....
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...According to established theory, solar cells with a base doping concentration of 10(16) cm should break down by avalanche at a reverse bias above -50 V [4]....
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...Advanced theory predicts avalanche breakdown above a certain reverse bias, which is below -50 V for typical solar cells having a base doping concentration of 10(16) cm [4]....
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