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• Small-angle grain boundaries (SAGB) form spontaneously by dislocation aggregation during solidification of Si at a high dislocation density. • The critical density for SAGB formation was found as ca. 107 cm-2. • SAGBs tend to coalesce with other SAGBs to leave the surviving SAGBs with higher misorientation. • SAGBs are able to spontaneously increase their misorientation by absorption of individual lattice dislocations during solidification. In situ observation of the solidification process of Si combined with ex situ characterization revealed that small-angle grain boundaries (SAGBs) increase misorientation through two paths. First, coalescence with other SAGBs leads to a boost in misorientation and SAGBs tend to coalesce during solidification. Second, the absorption of individual lattice dislocations also increases the misorientation of an SAGB. Three possible mechanisms behind dislocation absorption by SAGBs have been proposed and are discussed in this paper. Among these mechanisms, the incorporation of same-sign lattice dislocations is regarded as the prominent mechanism when misorientation increases during solidification. [ABSTRACT FROM AUTHOR]

Upgraded metallurgical-grade silicon solar cells with different ranges of efficiencies have been characterized by light-beam-induced current (LBIC) measurements. The interaction between grain boundaries and metallic impurities is studied for cells fabricated on wafers from different solidification heights of the ingot. A tight relation is observed between the electrical activity of the grain boundaries and the position of the wafer in the ingot, which is related to the impurity contamination. The presence of a large amount of metallic impurities enhances the electrical activity of the grain boundaries. The main features of the LBIC images are discussed in relation to the presence of metallic impurities. [ABSTRACT FROM AUTHOR]

Small-angle grain boundary (SAGB) growth in multicrystalline Si was observed in situ during directional solidification, and the misorientation and boundary structure were analyzed by electron backscatter diffraction and high-resolution transmission electron microscopy. It was found that SAGBs change their orientation in order to reduce the number of grain boundary dislocations and thus the energy. This suggests that grain boundary dislocations have an influence on SAGB behavior during solidification. Unlabelled Image [ABSTRACT FROM AUTHOR]

The generation of a {112}Σ3 grain boundary (GB) was observed in situ from the decomposition of a Σ9 GB during directional solidification of multicrystalline Si. A faceted groove formed at the junction of the solid/melt interface and the {112}Σ3 GB. This mechanism is different from that for the growth of {111}Σ3 GBs, for which no groove formed at the interface. If the growth rates for the adjacent facets of the groove are the same, the GB can grow in a straight manner along the {112} plane. The present results suggest that kinetics can give rise to high-energy GBs during solidification. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The interaction between grain boundaries (GBs) at a silicon crystal/melt interface was studied using in situ observations during directional solidification. Two small-angle GBs (SAGBs) interact with each other to produce a new SAGB with increased misorientaion. However, the interaction between Σ3 GBs and SAGBs reveals a different phenomenon. The extending directions and misorientations of the SAGBs and Σ3 GBs show no change before and after the convergence of these two planar defects at the crystal/melt interface. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Light and elevated temperature induced degradation is observed for multicrystalline Si PERC-type solar cells, strongly limiting solar cell parameters under operation conditions. In this contribution, we investigate the effect of temperature on the degradation and regeneration kinetics of lifetime samples with different p-doping. While there is no fundamental difference visible between B- and Ga-doped materials, Ga-doped samples generally had a lower starting lifetimes and showed a slower degradation process. Ungettered Ga-doped samples did not regenerate within the applied time frame. For higher treatment temperatures (≥200°C) lifetimes after regeneration exceeded the initial values before degradation for both gettered materials. There are first indications that the degradation reaction is diffusion limited (following Arrhenius-like kinetics), while the observed regeneration kinetics might change for higher temperatures (≥150°C). [ABSTRACT FROM AUTHOR]

We investigated the effect of the grain boundary (GB) character of multicrystalline Si (mc-Si) on the efficiency of external and internal gettering of impurities during phosphorus diffusion gettering (PDG). We utilized seed crystals with an artificially designed GB configuration to grow mc-Si ingots with different artificial GB characters. PDG combined with an originally developed multiple-cycle gettering technique at low temperature was introduced on intentionally Fe-contaminated mc-Si samples to enhance external and internal gettering. A significant positive PDG effect was observed after PDG combined with the multiple-cycle technique, as evidenced by the increase in lifetimes after PDG. A bright cloud-like photoluminescence signal around contaminated GBs was observed for artificial Σ5-GBs and tilt-GBs after PDG, suggesting the enhancement of the internal gettering efficiency by leaving a cleaner area around the GBs. This result suggests the importance of the control of crystal defect character as well as impurities in mc-Si ingots, which could strongly affect the PDG efficiency. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A rear side PECVD passivation stack and an aluminum firing-through paste for the rear side metallization of p-type bifacial multicrystalline solar cells were developed. Both passivation stack and Al paste were adapted to each other to reach best cell efficiencies. The refractive index of the rear side PECVD passivation stack is optimized to be etched effectively by the firing-through Al paste. Our experiments have shown that the boron doping underneath the passivation stack is helpful to reach a good passivation quality and contact formation. The paste was improved in the way to reach a low contact resistivity without impeding the V OC resulting in a compromise of these two parameters. We found out that the glass frit composition and mixture in the paste are the crucial factors for this kind of application. The so far highest cell efficiency of 17.8% with a V OC of 633 mV was reached with our Al firing-through paste on a PECVD SiN X layer. [ABSTRACT FROM AUTHOR]

High-efficiency Si solar cells have attracted great attention from researchers, scientists, engineers of photovoltaic (PV) industry for the past few decades. Many researchers, scientists, and engineers in both academia and industry seek solutions to improve the cell efficiency and reduce the cost. This desire has drawn stronger support from major funding agencies and industry and stimulated a growing number of major research and research infrastructure programs, and a rapidly increasing number of publications in this filed. This article reviews materials, devices, and physics of high-efficiency Si solar cells developed over the last 20 years and presents representative examples of superior performances and competitive advantages. In this paper there is a fair number of topics, not only from the material viewpoint, introducing various materials that are required for high-efficiency Si solar cells, such as base materials (FZ-Si, CZ-Si, MCZ-Si, and multi-Si), emitter materials (diffused emitter and deposited emitter), passivation materials (Al-BSF, high-low junction, SiO2, SiOx, SiNx, Al2O3and a-Si:H), and other functional materials (antireflective layer, transparent conductive oxide and metal electrode), but also from the device and physics point of view, elaborating on physics, cell concept, development, and status of most types of high-efficiency Si solar cells, including passivated emitter and rear contact (PERC), passivated emitter and rear locally diffused (PERL), passivated emitter and rear totally-diffused (PERT), Pluto, PANDA, interdigitated back-contacted (IBC), emitter-wrap-through (EWT), metallization-wrap-through (MWT), heterojunction with intrinsic thin-layer (HIT), and so on. Finally, the technical data of these high-efficiency Si solar cells has been tabulated. [ABSTRACT FROM AUTHOR]

The effect of iron and copper contamination on the recombination properties of extended defects in multicrystalline Si is investigated by the Electron Beam Induced Current (EBIC) method. Plastically deformed Si samples containing dislocations and dislocation trails are also studied for a comparison. It is shown that Fe contamination leads to an essential increase of the EBIC contrast of electrically active grain boundaries and dislocation trails. The EBIC contrast of deformation induced dislocations also increases after iron diffusion while the recombination activity of grown-in dislocations in multicrystalline Si does not practically change after such treatment. Cu contamination also leads to an essential increase of the EBIC contrast of electrically active grain boundaries and dislocation trails. But dislocation contrast in both plastically deformed Si and multicrystalline Si does not practically increase after Cu contamination. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this work a novel passivation technique is proposed for multicrystalline silicon wafers for the purpose of solar cell application. The new method combines the use of double treatment based on porous Si and TiO2 passivation. Porous silicon (PS) was prepared by electrochemical anodization of multi crystalline substrates (mc-Si) under different conditions of current density (The current density used is between 3 and 50 mA/cm2). It was demonstrated that the porosity increases with increasing current density from 27, 66% to 81%. TiO2 nanoparticles with different nanometric sizes were incorporated inside pores by the way of the pulsed laser deposition (PLD) technique. The deposited layers have been characterized by spectrophotometry, Fourier transform infrared spectroscopy (FTIR) analysis. It was found that the binary structure of TiO2/PS minimizes the average reflectivity of the mc-Si substrates from 36% for bare multi crystalline silicon to around 14% for treated substrate. The TiO2/porous Si treated samples present high photoluminescence intensity and an enhancement of the optoelectronic properties. As a result the effective minority carrier lifetime shows a strong improvement after the combined treatment (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this work, the gettering process in the multicrystalline Si wafers by the combined getter structures of the porous Si and Al layers during annealings at temperatures 600 up to 750 •C has been theoretically studied. A kinetic model based on the diffusion equation has been developed, and the characteristics of increase in the minority charge carrier diffusion length as a result of gettering annealings have been determined. The obtained results are useful for technology of multicrystalline Si solar cells to improve their properties. [ABSTRACT FROM AUTHOR]

Abstract: 57Fe Mössbauer absorber experiments are performed at 1273 and 300K on two different samples of multicrystalline Si (mc-Si), whose minority carrier lifetimes are 41 and 1.5μs, respectively. The samples are deposited with 1.5nm 57Fe, and are annealed and measured simultaneously at 1273K for 1 week. The spectra consist of four singlets at 1273K, and of three singlets at 300K. Comparing the present results with those from 57Fe-deposited CZ-Si single crystal, the 57Fe atoms are found to exist in the mc-Si matrix dominantly as substitutional Fe atoms and different Fe-defect clusters, but not as FeSi2 precipitates. One of the components at 1273K, which yields an isomer shift of 1.1mms−1, appears to be due to interstitial Fe atoms trapped on defects. The fraction depends clearly on the minority carrier lifetime, and therefore, on the quality of the mc-Si samples. [Copyright &y& Elsevier]

An industrial sol–gel process to coat solar glass with a porous SiO2 antireflection (AR) layer has been recently developed. This paper presents the first detailed study obtained on sets of commercial multicrystalline silicon solar cells encapsulated with patterned low-iron glasses, with or without this AR coating. Measurements under standard test conditions (STC) show a current gain of 2.65% with the AR glass, whereas an additional current gain is obtained at high light incidence angle. Based on the mini-module results and on the outdoor monitoring of test modules to evaluate temperature effects, simulations were performed to asses the yearly photovoltaic energy yield gain at different locations. A significant energy yield increase of 3.4–3.7% is expected with the new AR glass. [Copyright &y& Elsevier]

In this study we have investigated inclusions present in certain areas of a multicrystalline silicon ingot cast in industry. The inclusions were retrieved from the matrix by dissolution in HF:HNO3, followed by filtration. We identified the inclusions as β-SiC and β-Si3N4 by using Electron Probe Microanalyzer and Electron Backscatter Diffraction. These inclusions appear to a great extent as large clusters consisting of both types of particles. We also obtained a particle size distribution giving the following diameter range; 75 μm< 80 mass%<385 μm. As the carbide particles tend to grow on the nitrides, the latter seem to act as nucleating centers for carbide precipitation. Several of the analyzed parts resulted in no measurable content by this method, indicating an inhomogeneous distribution. [Copyright &y& Elsevier]

Surface photovoltage (SPV) method for the characterization of multicrystalline silicon material for photovoltaic applications has been investigated, in view of its application as in-line characterization tool in photovoltaic industry. Minority carrier diffusion lengths have been measured by SPV on as-grown multicrystalline Si wafers as well as on emitter diffused multicrystalline Si wafers, showing the capability and the flexibility of the method. The usual assumptions for SPV data analyses have been critically discussed. The SPV values of diffusion length have been related with material characteristics and process control. [Copyright &y& Elsevier]

The performance of photovoltaic devices is greatly influenced by the surface characteristics such as surface roughness and presence of organic contaminants; therefore, their measurement is of great importance for photovoltaic industry. Moreover, these parameters should be measured by non-contact, fast methods capable of application as in-line techniques in photovoltaic industry. Surface roughness measurements and detection of organic contaminants by work-function measurements are the subject of this contribution. Monocrystalline and multicrystalline silicon wafers have been analyzed by Scanning Kelvin Probe (SKP ) in order to obtain work-function maps. These presented regions of higher work-function values correspond to organic contaminants, which are deliberately deposited on the wafer surface. In this way we have demonstrated the capability of work-function measurements for the detection of the contaminants. Moreover, unintentional organic contamination has been detected on multicrystalline Si wafers by SKP analyses. At the same time, the surface roughness has been obtained from surface topography maps. [Copyright &y& Elsevier]