Showing papers by "Wilhelm Warta published in 2005"

Synchrotron-based investigations of the nature and impact of iron contamination in multicrystalline silicon solar cells

Abstract: Synchrotron-based microprobe techniques were used to obtain systematic information about the size distribution, spatial distribution, shape, electrical activity, chemical states, and origins of iron-rich impurity clusters in multicrystalline silicon (mc-Si) materials used for cost-effective solar cells. Two distinct groups of iron-rich cluster have been identified in both materials: (a) the occasional large (diameter ⩾1μm) particles, either oxidized and/or present with multiple other metal species reminiscent of stainless steels or ceramics, which are believed to originate from a foreign source such as the growth surfaces, production equipment, or feedstock, and (b) the more numerous, homogeneously distributed, and smaller iron silicide precipitates (diameter ⩽800nm, often ⩽100nm), originating from a variety of possible formation mechanisms involving atomically dissolved iron in the melt or in the crystal. It was found that iron silicide nanoprecipitates account for bulk Fe concentrations as high as 1014–...

SHORT COMMUNICATION: Solar cell efficiency tables (version 25)

Abstract: Martin A. Green*y, Keith Emery, David L. King, Sanekazu Igari and Wilhelm Warta Centre for Photovoltaic Engineering, University of New South Wales, Sydney, 2052, Australia National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO, 80401, USA Sandia National Laboratories, 1515 Eubank Boulevard SE, Albuquerque, NM, 87123-0752, USA National Institute of Advanced Industrial Science and Technology (AIST), Research Center for Photovoltaics (RCPV), Central 2, Umezono 1-1-1, Tsukuba, Ibaraki, Japan Fraunhofer-Institute for Solar Energy Systems, Department: Solar Cells—Materials and Technology, Heidenhofstr. 2; D-79110 Freiburg, Germany

Solar Cell Efficiency Tables (Version 26)

Abstract: By providing guidelinesfor the inclusion of results into these tables, this not only provides an authoritative summary of the cur-rent state of the art but also encourages researchers to seek independent confirmation of results and to reportresults on a standardised basis. In the present article, new results since January 2005 are briefly reviewed.The most important criterion for inclusion of results into the tables is that they must have been measured by arecognised test centre listed in an earlier issue.

Quantifying the effect of metal-rich precipitates on minority carrier diffusion length in multicrystalline silicon using synchrotron-based spectrally resolved x-ray beam-induced current

Abstract: Synchrotron-based, spectrally resolved x-ray beam-induced current (SR-XBIC) is introduced as a technique to locally measure the minority carrier diffusion length in semiconductor devices. Equivalence with well-established diffusion length measurement techniques is demonstrated. The strength of SR-XBIC is that it can be combined in situ with other synchrotron-based analytical techniques, such as x-ray fluorescence microscopy (μ-XRF) and x-ray absorption microspectroscopy (μ-XAS), yielding information about the distribution, elemental composition, chemical nature, and effect on minority carrier diffusion length of individual transition metal species in multicrystalline silicon. SR-XBIC, μ-XRF, and μ-XAS measurements were performed on intentionally contaminated multicrystalline silicon, revealing a strong correlation between local concentrations of copper and nickel silicide precipitates and a decrease of minority carrier diffusion length. In addition, the reduction of minority carrier diffusion length due t...

Lock-in Thermography : a universal tool for local analysis of solar cells

Abstract: This contribution gives an overview about the present state of the art of Lock-in Thermography (LIT) applied in solar cell research. Originally introduced as a shunt imaging technique working without light irradiation, recently a number of new LIT techniques have been proposed using light irradiation to the cell. These techniques allow to image the lifetime distribution and Joule heat losses under illumination, and they allow to detect non- contacted regions in the cell. Moreover, shunts can be imaged already before contacts are made. All presently known LIT techniqes applied to solar cells are reviewed and their physical bases are explained. With these new techniques, LIT has become a universal tool for characterizing solar cells.

The results of the second World Photovoltaic Scale recalibration

Abstract: The World Photovoltaic Scale (WPVS) is used as a worldwide reference value for terrestrial PV performance measurements of I/sub STC/, the short-circuit current under standard test conditions. The WPVS has already been established in 1997 based on an international comparison where a set of 20 transfer/travelling standards were circulated between 11 national laboratories. After the first recalibration carried out at NREL in 1999, the PTB acted as pilot laboratory for the second recalibration, i.e. the 2003/04 intercomparison. It was performed as an international star-like comparison with 43 reference solar cells as reference standards, where 25 reference solar cells were made in accordance with the WPVS reference cell package design. Nine institutes have participated: AIST (Japan), BGNSEC (Israel), CIEMAT (Spain), ESTI (EU), Fraunhofer ISE (Germany), NREL (USA), PTB (Germany), Sandia (USA), TIPS (China). The measurements of the pilot laboratory were carried out between August 2003 and January 2004. Summarizing the main result of the comparison, the deviations of the calibration values obtained by the pilot laboratory and by the participants are, in general, within /spl plusmn/2%. In addition to the results of the comparison, typical stability and linearity test results of some reference cells as well as reproducibility of the DSR calibration facility of the pilot laboratory are described and discussed. Finally, the recommendations of a working group concerning the future development of the WPVS are presented.

Investigation of series resistance losses by illuminated lock‐in thermography

Abstract: A measurement mode (JSC-ILIT) for the recently introduced Illuminated Lock-In Thermography (ILIT) method and a new interpretation of the images obtained is proposed. This mode is especially adapted for the investigation of series resistance, in particular contact resistance, in solar cells. Comparison of JSC-ILIT results to emitter potential maps obtained by Corescan demonstrate good agreement between the poorly contacted areas, proving the practical applicability of the technique. JSC-ILIT provides a quasi-contactless and fast measurement. Comparison is made with the recently introduced method of RS-ILIT. The capability of both methods to detect series resistance problems is demonstrated. Possible distortions due to inhomogeneities of bulk material quality are discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Evaluating the state of the art of photovoltaic performance modelling in Europe

Abstract: There are many models currently available which provide detailed information regarding the performance of PV modules. This paper reviews, as part of the European co-ordination action PV-Catapult, the different performance modelling approaches currently developed by European research institutions. The aim of this paper is to provide an overview of modelling approaches available and define the inputs required for each model. This will be used to investigate the accuracy of these models for different European climatic conditions in a second stage of the project. All methods are reviewed, highlighting strengths and weaknesses of each. None of the methods consider temporal variations, such as degradation in the case of amorphous silicon. This paper investigates the impact this has on the year-to-year performance translation of such devices. Furthermore there is very little consideration of the incident spectrum, which affects wide band gap devices and multi-bandgap devices disproportionately, but this effect commonly is folded into irradiance and temperature effects. The implications of these are discussed based on current sales practice of quoting straight kWh/kWp, indicating the need for a better, technology independent comparator based on realistic energy production, rather than today’s STC laboratory efficiency. The results indicate that most models can predict energy yield within 10%.

Synchrotron-based spectrally-resolved X-ray beam induced current : a technique to quantify the effect of metal-rich precipitates on minority carrier diffusion length in multicrystalline silicon

Abstract: McHugo, Thompson, et al. [1, 2] were the first to apply a suite of synchrotron-based analytical techniques to study efficiency-limiting, impurity-related defects in solar cell grade multicrystalline silicon (mc-Si). X-ray fluorescence microscopy (μ-XRF), which can be used to locate and characterize the elemental composition of metal-rich nanoprecipitates within mc-Si solar cells, and X-ray absorption microspectroscopy (μ-XAS) which allows one to identify the chemical states of these particles, were subsequently developed, with higher flux and sub-micron spot size, to detect a single iron silicide nanoprecipitate of radius 16±3 nm and to identify its chemical state [3]. However, with only μ-XRF and μ-XAS, no direct correlation between the presence of metals and device performance can be made. Recently, Hieslmair et al. [4] and Vyvenko et al. [5] demonstrated the potential of X-ray Beam Induced Current (XBIC) technique to map the recombination activity in-situ at the μXRF/XAS beamline. The physical principle of XBIC is similar to light/laser beam induced current (LBIC), in that incident photons generate minority carriers which are collected by a Schottky diode or pn junction, but X-rays are used instead of visible light. XBIC was successfully combined with μ-XRF/μ-XAS to demonstrate the recombination activity of iron and copper [3, 6, 7] related nanodefects in mc-Si. However, XBIC can give only a relative measure of recombination activity of metal clusters, and therefore it is difficult to quantitatively measure the effect of metals on the minority carrier diffusion length using this technique. This task can be achieved via the technique we propose to call spectrally-resolved X-ray beam induced current (SR-XBIC). The theory behind SR-XBIC is very similar to the spectrallyresolved laser beam induced current (SR-LBIC) technique [8]: a current collection efficiency (CCE, proportional to the fraction of photogenerated carriers collected by the pn-junction or Schottky diode) is measured using X-rays with different penetration depths (energies). X-ray photon flux is determined using a calibrated ion chamber positioned before the sample. Then, a graph is produced comparing CCE to , where α is the optical absorption coefficient, and is the attenuation (or absorption) length; for much greater than the depletion width but small enough for back surface recombination not to significantly influence CCE, an effective diffusion length L 1 − α

Spatially resolved assessment of power losses due to bulk material quality and metallization problems

Abstract: The main advantage of illuminated lock-in thermography (ILIT) over standard (dark) lock-in thermography is the ability to measure at actual operation conditions of solar cells Thus ILIT allows a quantitative and spatially resolved investigation of the sum of all power losses in a solar cell at actual operation conditions with one measurement The quantitative influence of low bulk material quality on solar cell performance is investigated Also the locations of high contact resistance of the frontside metallization and of high series resistance within the metallization were determined with ILIT The results were compared with Corescan results for the same cells and a good correlation between the locations determined with both methods was found