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Hameiri Z.,Solar Energy Research Institute of Singapore | Trupke T.,University of New South Wales | Trupke T.,BT Imaging Pty Ltd | Gao N.,University of New South Wales | And 2 more authors.
Progress in Photovoltaics: Research and Applications | Year: 2013

The effective doping concentration of the bulk of a silicon wafer is an important material parameter for photovoltaic applications. The techniques commonly used to measure the effective doping concentration are based on conductance or resistivity measurements and include both contacted methods, such as the four-point probe, and contactless approaches, such as eddy current measurements. Applying these techniques to diffused wafers is complicated by the fact that the total conductance is the sum of the bulk conductance and the diffused layer conductance. Without further information about the emitter properties, a clear separation of these two parameters is not possible. This paper demonstrates a contactless method for specifically measuring the effective doping concentration of the bulk without significant influence from diffused layers. Copyright © 2012 John Wiley & Sons, Ltd. A new contactless method to detrmine the bulk doping concentration is presented. The method can be used throughout the solar cell fabrication process and on a wide variety of silicon substrates, without being affected by diffused or passivation layers. An excelent agreement was demonstrated between the post-diffusion doping concentration as obtained by the new method and the pre-diffusion doping concentration from dark conductance measurements. Copyright © 2012 John Wiley & Sons, Ltd.


Bothe K.,Institute for Solar Energy Research Hamelin | Krain R.,Institute for Solar Energy Research Hamelin | Falster R.,MEMC Electronic Materials | Sinton R.,Sinton Instruments
Progress in Photovoltaics: Research and Applications | Year: 2010

The determination of the bulk lifetime of bare multicrystalline silicon wafers without the need of surface passivation is a desirable goal. The implementation of an in-line carrier lifetime analysis is only of benefit if the measurements can be done on bare unprocessed wafers and if the measured effective lifetime is clearly related to the bulk lifetime of the wafer. In this work, we present a detailed experimental study demonstrating the relationship between the effective carrier lifetime of unpassivated wafers and their bulk carrier lifetime. Numerical modelling is used to describe this relationship for different surface conditions taking into account the impact of a saw damage layers with poor electronic quality. Our results show that a prediction of the bulk lifetime from measurements on bare wafers is possible. Based on these results we suggest a simple procedure to implement the analysis for in-line inspection. Copyright © 2010 John Wiley &Sons, Ltd.


Giesecke J.A.,Fraunhofer Institute for Solar Energy Systems | Sinton R.A.,Sinton Instruments | Schubert M.C.,Fraunhofer Institute for Solar Energy Systems | Riepe S.,Fraunhofer Institute for Solar Energy Systems | Warta W.,Fraunhofer Institute for Solar Energy Systems
IEEE Journal of Photovoltaics | Year: 2013

This paper elaborates upon the theory of self-consistent minority carrier bulk lifetime measurements of silicon ingots via time-modulated photoluminescence and presents an experimental proof of concept. For silicon ingots, the solution of the continuity equation at harmonic time modulation of excess carrier generation is shown to generally reveal a remarkably pronounced contrast with respect to minority carrier bulk lifetime. We combine our dynamic self-consistent approach with an analysis of surface recombination velocity from photoluminescence intensity ratios upon irradiation with different laser wavelengths. This combined analysis enables an accurate simultaneous determination of bulk lifetime and surface recombination velocity. For sufficiently high or accurately known ingot surface recombination velocities, this approach could likewise be used for an accurate determination of the minority carrier diffusion coefficient and of minority carrier mobility in novel silicon materials. © 2011-2012 IEEE.


Sinton R.A.,Sinton Instruments | Trupke T.,BT Imaging NSW
Progress in Photovoltaics: Research and Applications | Year: 2012

Comparison of minority carrier lifetime measurements carried out in transient mode with measurements performed under steady-state conditions allows determination of the calibration constants needed in non-transient measurements. In this letter, we point out practical scenarios in which the assumptions underlying this approach break down, resulting in significant experimental errors. Specific examples for crystalline silicon wafers will be discussed to provide some guidelines on practical limitations of this calibration approach. Large errors are possible for wafers with high surface recombination velocity as might be the case for incoming wafers for a solar cell production line. Copyright © 2011 John Wiley & Sons, Ltd.


Sinton R.A.,Sinton Instruments | Haunschild J.,Fraunhofer Institute for Solar Energy Systems | Demant M.,Fraunhofer Institute for Solar Energy Systems | Rein S.,Fraunhofer Institute for Solar Energy Systems
Progress in Photovoltaics: Research and Applications | Year: 2013

Wafer quality is extremely important in determining yield and efficiency of solar cells. Ideally, this wafer quality should be determined for incoming wafers before solar cell fabrication based on the electronic quality of the wafers. Recent papers have discussed methodologies for doing this by using lifetime measurement and pattern recognition of photoluminescence (PL) images. This paper compares results from quasi-steady-state photoconductance (QSSPC) lifetime measurements with PL imaging pattern recognition of dislocations. By using a more complete analysis of the lifetime and the PL data than performed in some recent publications, a more detailed physical picture is presented here, which reconciles contradictions between previous results. In particular, the differences between PL and QSSPC lifetime measurements on as-cut wafers are discussed. The trends in voltage prediction based on measured lifetime, doping, and PL-determined dislocation densities are shown. Copyright © 2012 John Wiley & Sons, Ltd. Wafer quality is extremely important in determining yield and efficiency of solar cells. Ideally, this wafer quality should be determined for incoming wafers before solar cell fabrication based on the electronic quality of the wafers. This paper compares results from quasi-steady-state photoconductance lifetime measurements with photoluminescence (PL) imaging pattern recognition. A detailed physical picture is presented here that reconciles contradictions between previous results. The trends in voltage prediction based on measured lifetime, doping, and PL-determined dislocation densities are shown. Copyright © 2012 John Wiley & Sons, Ltd.


Swirhun J.S.,Sinton Instruments | Sinton R.A.,Sinton Instruments | Forsyth M.K.,Sinton Instruments | Mankad T.,Sinton Instruments
Progress in Photovoltaics: Research and Applications | Year: 2011

Measuring the bulk lifetime of unpassivated blocks and ingots is of great interest to the solar cell industry. The eddy-current photoconductance method is a common choice for such measurements, employing the quasi-steady-state (QSS) mode for lower lifetime samples, and the transient photoconductance decay (PCD) mode for higher lifetime samples. Due to the high surface recombination velocity in unpassivated bulk samples, the lifetime measured with this method consists of components of recombination at both the surface and in the bulk. In order to determine the bulk lifetime from the measurement data, simulations of both transient and QSS mode measurements were conducted. © 2010 John Wiley & Sons, Ltd.


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 600.49K | Year: 2014

The goal of this project is to develop new manufacturing equipment for use in the fabrication of solar panels. The engineering innovations demonstrated in the Phase I of this SBIR will be incorporated into manufacturing equipment for the solar module industry enabling a reduction in the cost of solar electricity.


A solar cell or module is illuminated at one sun intensity and is placed into short circuit. Current and voltage measurements are taken. Control circuitry commands a second, higher terminal voltage of the solar cell such as a maximum power voltage. A higher intensity light pulse (for example, three suns) is applied to the solar cell or module when the second voltage is commanded. Voltage ramps more quickly because of the high-intensity light pulse. When the second terminal voltage is reached the light pulse terminates and measurements are taken while the solar cell remains illuminated at one sun intensity. The solar cell is placed into open circuit conditions and in conjunction with that action another high-intensity light pulse is applied. When the steady-state open circuit voltage for one sun is reached the pulse terminates. Characteristics are measured including current and voltage at the terminals of the solar cell or module.


Short-circuit current, maximum power, and open circuit voltage during a single flash are determined by varying intensity, voltage, and current. An apparatus determines the substrate doping and the series resistance of the solar cell. The series resistance of the cell is determined from a voltage step from the maximum power voltage operating point to the open-circuit condition. Methods are described for determining the substrate doping from stepping or sweeping the voltage. The first uses a voltage step and finds the change in charge that results. This determines a unique doping if the series resistance is known. The second uses data for a case of varying current, voltage, and light intensity, and compares this data to the case of varying voltage and intensity with no current. By transposing both cases into the steady state, agreement between the two data sets is found for unique doping and series resistance values.


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 174.69K | Year: 2013

Industrial cell and module tester for silicon solar cells have converged on a conventional model in which an IV curve is swept during a constant-intensity flashlamp pulse. This scheme has many technical and cost drawbacks. Sinton Instruments has invented techniques that could radically change next- generation cell and module testers in order to lower the cost while simultaneously enabling sophisticated process control based on detailed characterization of the electronic properties of the devices. These instruments would incorporate: The Suns-Voc technique: A full IV curve is constructed during a single flash at open circuit voltage. This curve gives critical device physics information on the quality of the wafer, surface passivations, as well as enabling a full energy-loss analysis including resistance and recombination effects; The constant-charge mode of multi-flash testing. This Sinton-patented technique enables fast- throughput, error-free measurement of the new generations of high-efficiency, high- capacitance solar cells with a cost effective instrument; Advanced diagnostics techniques for cell or module test that measures detailed device physics parameters of the solar cells or modules, in order to optimize the cell fabrication, module fabrication, and subsequent reliability studies. The would permit data mining with detail sufficient for cause and effect studies relating starting silicon material, process control at each step, cell performance, module performance, and reliability studies; Innovations for incorporating these measurements into testing sequences with much higher throughput than existing cell and module-test instruments, targeting 2 to 4 times conventional tools; The existing Sinton industrial systems were designed specifically for the high-efficiency niche market that makes up less than 2% of manufacturing capacity for silicon modules. The early adopters jumped to this radical new technology because conventional instruments did not work for these modules. The ability to apply this completely novel approach to measuring solar cells and modules relies on the expertise developed at Sinton Instruments in controlling the light source characteristics as well as having active electronic loads that can optimize for the specific device-physics characteristics of the target technology. The result enables process optimization reporting both the conventional nameplate characteristics simultaneously with R & amp;D-quality characterization that relates cause and effect. An enormous opportunity exists to bring these advances to the rest of the industry. The use of a common methodology at cell and module test permits precise loss analysis comparing cell to module production data. The project will have 2 parts. Reoptimize the production module testers for general applicability to all types of modules. Three generations of silicon modules made at present, with distinct characteristics. A successful implementation will enable superior device-physics tracking, throughput up to 12 modules per minute, and a capital cost less than of conventional module testers. Users would also know that this capital investment would migrate with the technology into high-efficiency, since this is proven. Production cell testers require very-high throughput. A successful implementation of this unconventional test instrument into cell test could cut testing costs by a factor of 2-4, simultaneously enabling vastly more sophisticated analysis and process control and a seamless migration to high-efficiency cells.

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