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Journal ArticleDOI

Influence of Defects on Solar Cell Characteristics

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

AbstractThe 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.

Topics: Theory of solar cells (56%)

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Citations
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Journal ArticleDOI
Abstract: 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. A local series resistance is explicitly considered and may be provided as a series resistance image, e.g. resulting from luminescence imaging. The results enable a separate investigation of factors influencing the depletion region recombination current and the diffusion current, which is governed by the bulk lifetime. Local I–V characteristics of special sites may be simulated.

93 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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Journal ArticleDOI
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.
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.

87 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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Proceedings ArticleDOI
01 Jan 2013
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.

77 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 ArticleDOI
Abstract: The two-diode model is widespread for interpreting dark and illuminated current–voltage characteristics of solar cells, though it does not hold correctly for high current densities due to the distributed character of the series resistance. This is one reason for the fact that fitting the dark and the illuminated characteristic leads to two different sets of two-diode parameters. After locally analyzing a typical multicrystalline solar cell, it is found that here the grid conductivity represents the most significant contribution to the distributed series resistance. A simplified equivalent circuit implying a 1-dimensional current distribution is used for simulating current-dependent effective (lumped) series resistances in the dark and under illumination. It is found that the influence of the distributed series resistance on both characteristics can be described empirically by introducing a series resistance being variable for high currents. Moreover, well-known departures from the superposition principle often cannot be neglected. Therefore the second diode contribution is generally stronger under illumination than in the dark, and also the parallel resistance may be affected. We introduce only one additional series resistance parameter and consider that the second diode parameters and the parallel resistance may be different under illumination and in the dark. In this way, the current dependence of both the dark and the illuminated series resistance can be described with the same consistent set of first diode and series resistance parameters. Based on these findings, 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.

55 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 ArticleDOI
Abstract: Owing to its high carrier mobility and thickness-tunable direct band gap, black phosphorus emerges as a promising component of optoelectronic devices. Here, we evaluate the device characteristics of p-n heterojunction diodes wherein thin black phosphorus layers are interfaced with an underlying, highly n-doped GaAs substrate. The p-n heterojunctions exhibit close-to-ideal diode behavior at low bias, while under illumination they display a photoresponse that is evenly distributed over the entire junction area, with an external quantum efficiency of up to 10% at zero bias. Moreover, the observed maximum open circuit voltage of 0.6 V is consistent with the band gap estimated for a black phosphorus sheet with a thickness on the order of 10 nm. Further analysis reveals that the device performance is limited by the structural quality of the black phosphorus surface.

54 citations


References
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Book
01 Jan 1974
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.

2,108 citations


Journal ArticleDOI
01 Sep 1957
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.

1,852 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
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

1,709 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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Journal ArticleDOI

841 citations


Book
01 Oct 1991
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.

279 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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