The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Rolf Brendel - One of the best experts on this subject based on the ideXlab platform.
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interdigitated back contact solar cells with polycrystalline silicon on oxide passivating contacts for both polarities
Japanese Journal of Applied Physics, 2017Co-Authors: Felix Haase, Jan Krugener, Rolf Brendel, Fabian Kiefer, Soren Schafer, Christian Kruse, Robby PeibstAbstract:We demonstrate an independently confirmed 25.0%-efficient interdigitated back contact silicon solar cell with passivating polycrystalline silicon (poly-Si) on oxide (POLO) contacts that enable a high open circuit voltage of 723 mV. We use n-type POLO contacts with a measured Saturation Current Density of J 0n = 4 fA cm?2 and p-type POLO contacts with J 0p = 10 fA cm?2. The textured front side and the gaps between the POLO contacts on the rear are passivated by aluminum oxide (AlO x ) with J 0AlO x = 6 fA cm?2 as measured after deposition. We analyze the recombination characteristics of our solar cells at different process steps using spatially resolved injection-dependent carrier lifetimes measured by infrared lifetime mapping. The implied pseudo-efficiency of the unmasked cell, i.e., cell and perimeter region are illuminated during measurement, is 26.2% before contact opening, 26.0% after contact opening and 25.7% for the finished cell. This reduction is due to an increase in the Saturation Current Density of the AlO x passivation during chemical etching of the contact openings and of the rear side metallization. The difference between the implied pseudo-efficiency and the actual efficiency of 25.0% as determined by designated-area light Current?voltage (I?V) measurements is due to series resistance and diffusion of excess carriers into the non-illuminated perimeter region.
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pinhole Density and contact resistivity of carrier selective junctions with polycrystalline silicon on oxide
Applied Physics Letters, 2017Co-Authors: Tobias Wietler, Jan Krugener, Yevgeniya Larionova, Doerthe Tetzlaff, Michael Rienäcker, Felix Haase, Rolf Brendel, Robby PeibstAbstract:In the pursuit of ever higher conversion efficiencies for silicon photovoltaic cells, polycrystalline silicon (poly-Si) layers on thin silicon oxide films were shown to form excellent carrier-selective junctions on crystalline silicon substrates. Investigating the pinhole formation that is induced in the thermal processing of the poly-Si on oxide (POLO) junctions is essential for optimizing their electronic performance. We observe the pinholes in the oxide layer by selective etching of the underlying crystalline silicon. The originally nm-sized pinholes are thus readily detected using simple optical and scanning electron microscopy. The resulting pinhole densities are in the range of 6.6 × 106 cm−2 to 1.6 × 108 cm−2 for POLO junctions with selectivities close to S10 = 16, i.e., Saturation Current Density J0c below 10 fA/cm2 and contact resistivity ρc below 10 mΩcm2. The measured pinhole densities agree with values deduced by a pinhole-mediated Current transport model. Thus, we conclude pinhole-mediated cu...
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pinhole Density and contact resistivity of carrier selective junctions with polycrystalline silicon on oxide
Applied Physics Letters, 2017Co-Authors: Tobias Wietler, Jan Krugener, Yevgeniya Larionova, Doerthe Tetzlaff, Michael Rienäcker, Felix Haase, Rolf Brendel, Robby PeibstAbstract:In the pursuit of ever higher conversion efficiencies for silicon photovoltaic cells, polycrystalline silicon (poly-Si) layers on thin silicon oxide films were shown to form excellent carrier-selective junctions on crystalline silicon substrates. Investigating the pinhole formation that is induced in the thermal processing of the poly-Si on oxide (POLO) junctions is essential for optimizing their electronic performance. We observe the pinholes in the oxide layer by selective etching of the underlying crystalline silicon. The originally nm-sized pinholes are thus readily detected using simple optical and scanning electron microscopy. The resulting pinhole densities are in the range of 6.6 × 106 cm−2 to 1.6 × 108 cm−2 for POLO junctions with selectivities close to S10 = 16, i.e., Saturation Current Density J0c below 10 fA/cm2 and contact resistivity ρc below 10 mΩcm2. The measured pinhole densities agree with values deduced by a pinhole-mediated Current transport model. Thus, we conclude pinhole-mediated Current transport to be the dominating transport mechanism in the POLO junctions investigated here.In the pursuit of ever higher conversion efficiencies for silicon photovoltaic cells, polycrystalline silicon (poly-Si) layers on thin silicon oxide films were shown to form excellent carrier-selective junctions on crystalline silicon substrates. Investigating the pinhole formation that is induced in the thermal processing of the poly-Si on oxide (POLO) junctions is essential for optimizing their electronic performance. We observe the pinholes in the oxide layer by selective etching of the underlying crystalline silicon. The originally nm-sized pinholes are thus readily detected using simple optical and scanning electron microscopy. The resulting pinhole densities are in the range of 6.6 × 106 cm−2 to 1.6 × 108 cm−2 for POLO junctions with selectivities close to S10 = 16, i.e., Saturation Current Density J0c below 10 fA/cm2 and contact resistivity ρc below 10 mΩcm2. The measured pinhole densities agree with values deduced by a pinhole-mediated Current transport model. Thus, we conclude pinhole-mediated cu...
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junction resistivity of carrier selective polysilicon on oxide junctions and its impact on solar cell performance
IEEE Journal of Photovoltaics, 2017Co-Authors: Michael Rienäcker, Jan Krugener, Felix Haase, Rolf Brendel, Agnes Merkle, Marcel Bossmeyer, Udo Romer, Robby PeibstAbstract:We investigate the junction resistivity of high-quality carrier-selective polysilicon on oxide (POLO) junctions with the transfer length method. We demonstrate ${{n}}^{+ }$ POLO junctions with a Saturation Current Density $J_{{\rm{C,poly}}}$ of 6.2 fA/cm2 and a junction resistivity $\rho _{{\rm{c}}}$ of 0.6 mΩcm2, counterdoped ${{n}}^{+ }$ POLO junctions with 2.7 fA/cm2 and 1.3 mΩcm2, and ${{p}}^{+ }$ POLO junctions with 6.7 fA/cm2 and 0.2 mΩcm2. Such low junction resistivities and Saturation Current densities correspond to excellent selectivities $S_{{10}}$ of up to 16.2. The efficiency potential for back-junction back-contact solar cells with these POLO junctions was determined to be larger than 25 % by numerical device simulations. We demonstrate experimentally a back-junction back-contact solar cell with p -type and n -type POLO junctions with an independently confirmed efficiency of 24.25 %.
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reverse Saturation Current Density imaging of highly doped regions in silicon a photoluminescence approach
Solar Energy Materials and Solar Cells, 2012Co-Authors: Jens Muller, Karsten Bothe, Sandra Herlufsen, Helge Hannebauer, R Ferre, Rolf BrendelAbstract:Abstract We present a camera-based technique for the local determination of reverse Saturation Current densities J 0 of highly doped regions in silicon wafers utilizing photoconductance calibrated photoluminescence imaging (PC-PLI). We apply this approach to 12.5×12.5 cm² float zone silicon samples with textured surfaces and a homogeneous phosphorous diffusion with sheet resistances between 24 and 230 Ω/□. We find enhanced photoluminescence emission at metallized regions of a sample due to reflection of long-wavelength light at the rear side of the sample. Our measurement setup comprises an optical short pass filter in front of the camera effectively blocking wavelengths above 970 nm and therefore ensuring a correct calibration of the PL signal in terms of excess charge carrier Density Δ n . We analyze two sets of samples comprising metal contacts to highly doped regions prepared by Laser Transfer Doping (LTD) as well as standard tube furnace phosphorus diffusion. We find a considerably smaller J 0 value of 370 fA/cm² for the LTD approach compared to a standard diffusion process resulting in J 0 =570 fA/cm². On the basis of these results we demonstrate that J 0 imaging is a powerful analysis technique for process optimization.
A Rohatgi - One of the best experts on this subject based on the ideXlab platform.
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screen printed large area bifacial n type back junction silicon solar cells with selective phosphorus front surface field and boron doped poly si siox passivated rear emitter
Applied Physics Letters, 2018Co-Authors: Andrew M Tam, Vijay Yelundur, Adam M. Payne, Ajay Upadhyaya, Vinodh Chandrasekaran, Arnab Das, Yingyuan Huang, Aditi Jain, A RohatgiAbstract:This paper reports on the effect of screen printed metallization on the passivation quality of a boron doped poly-Si/SiOx passivated contact (PC) structure composed of a very thin Si oxide (∼15 A) capped with boron doped poly-Si. Our boron doped poly-Si/SiOx passivated contact (p-Poly Si/SiOx PC) with a SiNx capping layer gave excellent surface passivation with a very low Saturation Current Density of ∼5 fA/cm2. After screen printed metallization on poly-Si with a metal coverage of ∼10%, this value increased to ∼17 fA/cm2. This paper also demonstrates the fabrication of screen printed, large area (239 cm2), high efficiency (∼21%) n-base bifacial back junction Si solar cells with p-Poly-Si/SiOx PC on the rear and a phosphorus implanted n++-n+ selective front surface field. Detailed analysis is performed to quantify recombination and extract the Saturation Current Density contributions (J0) from each layer of the cell including the metallized front surface field and the tunnel oxide passivated contact. Finally, 2D device modeling of this back junction cell is performed by implementing a simple approach which replaces the p-Poly-Si/SiOx PC by an equivalent p-n junction with the same J0 and gives a good match between the measured and simulated cell parameters using the extracted J0 and recombination velocity values.This paper reports on the effect of screen printed metallization on the passivation quality of a boron doped poly-Si/SiOx passivated contact (PC) structure composed of a very thin Si oxide (∼15 A) capped with boron doped poly-Si. Our boron doped poly-Si/SiOx passivated contact (p-Poly Si/SiOx PC) with a SiNx capping layer gave excellent surface passivation with a very low Saturation Current Density of ∼5 fA/cm2. After screen printed metallization on poly-Si with a metal coverage of ∼10%, this value increased to ∼17 fA/cm2. This paper also demonstrates the fabrication of screen printed, large area (239 cm2), high efficiency (∼21%) n-base bifacial back junction Si solar cells with p-Poly-Si/SiOx PC on the rear and a phosphorus implanted n++-n+ selective front surface field. Detailed analysis is performed to quantify recombination and extract the Saturation Current Density contributions (J0) from each layer of the cell including the metallized front surface field and the tunnel oxide passivated contact. Fina...
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screen printed large area bifacial n type back junction silicon solar cells with selective phosphorus front surface field and boron doped poly si siox passivated rear emitter
Applied Physics Letters, 2018Co-Authors: Andrew M Tam, Vijay Yelundur, Adam M. Payne, Ajay D. Upadhyaya, Vinodh Chandrasekaran, Arnab Das, Yingyuan Huang, Aditi Jain, A RohatgiAbstract:This paper reports on the effect of screen printed metallization on the passivation quality of a boron doped poly-Si/SiOx passivated contact (PC) structure composed of a very thin Si oxide (∼15 A) capped with boron doped poly-Si. Our boron doped poly-Si/SiOx passivated contact (p-Poly Si/SiOx PC) with a SiNx capping layer gave excellent surface passivation with a very low Saturation Current Density of ∼5 fA/cm2. After screen printed metallization on poly-Si with a metal coverage of ∼10%, this value increased to ∼17 fA/cm2. This paper also demonstrates the fabrication of screen printed, large area (239 cm2), high efficiency (∼21%) n-base bifacial back junction Si solar cells with p-Poly-Si/SiOx PC on the rear and a phosphorus implanted n++-n+ selective front surface field. Detailed analysis is performed to quantify recombination and extract the Saturation Current Density contributions (J0) from each layer of the cell including the metallized front surface field and the tunnel oxide passivated contact. Finally, 2D device modeling of this back junction cell is performed by implementing a simple approach which replaces the p-Poly-Si/SiOx PC by an equivalent p-n junction with the same J0 and gives a good match between the measured and simulated cell parameters using the extracted J0 and recombination velocity values.
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evaluating the impact of Current generation screen printed ag paste on si solar cell emitter Saturation Current Density
Photovoltaic Specialists Conference, 2016Co-Authors: I B Cooper, Keenan Jones, Keith Tate, A RohatgiAbstract:Current-generation screen-printed (SP) Ag pastes have shown capability to contact lightly doped Si solar cell emitters displaying low Saturation Current Density (J 0e ) with high fill factor (FF). However, we have observed that higher firing temperatures are needed to achieve low resistance Ag contact, which may degrade J 0e and result in lower open circuit voltage (V OC ). Higher firing temperatures have also resulted in rear SP Al film blistering. In order to decouple the effects of front and rear contact formation on cell performance, we present data on the impact of SP Ag contacts on n+ phosphorus (P) emitter J 0e for a range of doping densities and firing temperatures. Using a range of Ag coverage areas (A metal ) we extract the J 0e under SP Ag (Joe, me ta i)· We observe that the change in J 0e as a function of A metal (dJ 0 JdA meta j) increases as firing temperature increases, indicating increasing J 0e , metal . Calculated V OC loss at A metal = 7%, a typical coverage for SP Ag contacts, cannot fully account for experimental V OC loss, and Al back surface field (Al-BSF) degradation due to high temperature firing was found to dominate V OC losses.
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high implied voc 715 mv and low emitter Saturation Current Density 10fa cm2 from a lightly b doped implanted emitter
Photovoltaic Specialists Conference, 2015Co-Authors: Ajay Upadhyaya, B Rounsaville, Keeya Madini, Keenan Jones, Kyungsun Ryu, Vinodh Chandrasekaran, Arnab Das, Bruce Mcpherson, Atul Gupta, A RohatgiAbstract:In this paper, we demonstrate a very low emitter Saturation Current Density (J0e) of ∼10 fA/cm2 from an implanted lightly doped B emitter (>150 ohm/□) passivated with Al2O3/SiNx stack. The test cell structure with lightly B doped emitter passivated with Al2O3/SiNx on front and tunnel oxide/n+ poly silicon passivated back gave a high implied Voc of 715∼722 mV on ∼5 Ω-cm n-type Cz wafers. It is also shown that Ti/Pd/Ag contact resistance on the lightly doped B emitter was ∼2 mΩ-cm2, but screen printed Ag/Al contact gave a high contact resistance of 25 mΩ-cm2. Therefore, a selective B emitter was used in this study, which gave ∼21.0% efficiency with Voc of 689 mV.
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low resistance screen printed ag contacts to pocl 3 emitters with low Saturation Current Density for high efficiency si solar cells
Photovoltaic Specialists Conference, 2012Co-Authors: I B Cooper, Keith Tate, A F Carroll, Kurt Richard Mikeska, R C Reedy, A RohatgiAbstract:The silicon (Si) PV industry recognizes the value of phosphorus (P) emitters with low Saturation Current Density (J 0e ) for ability to produce high final cell open circuit voltage (V OC ). However, emitters of such quality, which usually display low surface phosphorus concentration ([P surface ]) are notoriously difficult to contact using traditional screen-printed silver (Ag) thick film pastes. Here, we tailored P emitter profiles via POCl 3 diffusion to create solar cell emitters displaying low J 0e values of 67 – 148 fA/cm2 and variable electrically active [Psurface] of 0.5E20 – 2.0E20 atoms/cm3 in order to study the conditions necessary for low resistance contact to such emitters without appreciably deviating from industrial process conditions. Using a screen-printable Ag conductor paste tailored to contact low [P surface ] emitters, we show fill factor (FF) as high as 80% while maintaining V OC as high as 637 mV on tailored emitters with low J 0e . This results in average solar cell efficiencies of 18.6% with a best efficiency of 18.8%. Series resistance (R SERIES ) analysis revealed that contact resistance was the major resistive component dictating final R SERIES and FF. Finally, microstructural SEM analysis of the Ag/Si contact interface suggested that thin interfacial glass films and extensive Ag precipitate/crystallite surface coverage may explain how such high FF can be attained on emitters with low J 0e and low [P surface ].
Stefan W. Glunz - One of the best experts on this subject based on the ideXlab platform.
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comparison of emitter Saturation Current densities determined by injection dependent lifetime spectroscopy in high and low injection regimes
Progress in Photovoltaics, 2012Co-Authors: Christian Reichel, Jan Benick, Filip Granek, Oliver Schultzwittmann, Stefan W. GlunzAbstract:The determination of the emitter Saturation Current Density J0e of symmetrical test structures, analyzed by injection-dependent lifetime spectroscopy (IDLS), in high as well as in low injection regimes is compared. A detailed investigation of the influence of different models for the Auger recombination on the evaluation of the measured minority carrier lifetime is performed. It can be concluded that a good agreement for the extraction of J0e under high and low injection conditions for lightly and highly doped emitters on textured and untextured surfaces was obtained if the Auger parameterization of Kerr et al. is applied. For deep-diffused emitter profiles on textured surfaces a significant increase of J0e well above the geometrical surface area ratio of untextured and textured surfaces of 1.7 was observed. A verification of the experimentally determined values for J0e is performed by numerical device simulations. The simulated surface recombination velocity for the investigated emitter doping profiles is in good agreement to analytical calculations. Copyright © 2010 John Wiley & Sons, Ltd.
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Thermal stability of the Al2O3 passivation on p-type silicon surfaces for solar cell applications
Physica Status Solidi - Rapid Research Letters, 2009Co-Authors: Jan Benick, Armin Richter, Martin Hermle, Stefan W. GlunzAbstract:Al2O3 has been shown to provide an outstanding passivation quality on p-type surfaces after annealing at moderate temperatures (∼425 °C). However, most industrial silicon solar cells are based on printing technologies for metallization, including a high temperature firing step for the contact formation. To investigate the thermal stability of the Al2O3 passivation, symmetrical p and p+ np + lifetime samples were coated with Al2O3 and exposed to typical firing processes at temperatures between 700 °C and 850 °C. Up to a firing temperature of 825 °C the Al2O3 passivation is shown to be stable on highly boron-doped surfaces. An emitter Saturation Current Density of ∼60 fA/cm2 could be measured for the p+ np+ samples, allowing a maximum open circuit voltage (Voc) >695 mV. The firing stability of the Al 2O3 is an important step for the realization of an industrial n-type silicon solar cell. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Karsten Bothe - One of the best experts on this subject based on the ideXlab platform.
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effective diffusion length and bulk Saturation Current Density imaging in solar cells by spectrally filtered luminescence imaging
IEEE Journal of Photovoltaics, 2016Co-Authors: O Breitenstein, David Hinken, Felix Frühauf, Karsten BotheAbstract:Most methods for interpreting electroluminescence (EL) or photoluminescence (PL) images of solar cells evaluate the local diode voltages but not the local luminescence intensity itself. One exception is the Fuyuki approximation, which assumes that the local value of the luminescence signal is proportional to the local effective diffusion length. This dependence has been derived for infinitely thick solar cells and neglects self-absorption of the luminescence photons. However, for real solar cells and imaging conditions, with increasing diffusion length, the luminescence signal approaches a limiting value; hence, the Fuyuki approximation no longer holds. In this paper, we compare EL and PL images of multicrystalline solar cells using different kinds of light filtering and find that gentle shortpass filtering is useful for avoiding optical artifacts. Based on earlier calculations, a physically founded formula for the dependence of the gently shortpass-filtered luminescence signal on the bulk diffusion length, for a given rear surface recombination velocity, is presented. Since this formula only barely allows us to calculate the diffusion length from the luminescence signal, a simplified approximate formula is proposed, and its accuracy is checked. This method is tested on EL and ${V_{{{\rm oc}}}}$ PL images of solar cells. We find that for a typical industrial multicrystalline Al-backside solar cell, the obtained effective diffusion length images correlate well with such images obtained by spectral LBIC image evaluation. In addition, the Saturation Current Density images correlate well with such images obtained by dark lock-in thermography, which show a much lower spatial resolution. The main limitation of the proposed method is that it is basically approximate and needs some fitting parameters.
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The reliability of thermography- and luminescence-based series resistance and Saturation Current Density imaging
Solar Energy Materials and Solar Cells, 2015Co-Authors: Otwin Breitenstein, David Hinken, Jan Bauer, Karsten BotheAbstract:The conventional quantitative evaluation of dark lock-in thermography (DLIT), electroluminescence (EL), and photoluminescence (PL) images of solar cells is based on the model of independent diodes, where each image pixel is assumed to be connected with the terminals by an independent series resistance. In reality, however, the solar cell represents a 2-dimensional resistance-diode network. In this work solar cells containing well-defined spatial distributions of the Saturation Current Density J01 and also containing J02-type and ohmic shunts are modeled for various externally applied biases and illumination conditions realistically as a 2-dimensional resistance-diode network. The resulting local diode voltage distributions are converted into DLIT, EL and PL images, which are further processed by conventional evaluation methods, which rely on the simple model of independent diodes. These are the so-called “Local-IV” method for the DLIT analysis, which may be supported by EL results to obtain series resistance images, and “C-DCR” for the PL analysis. This leads to calculated images of the local effective series resistance Rs and of J01. Regarding the resulting Rs images, PL shows the expected series resistance distribution and is not affected by the shunt regions. The DLIT–EL Rs images instead yield expected values only in the homogeneous regions, which are not affected by the assumed shunts. DLIT–EL determines higher values of Rs in local shunt regions and lower values around these regions and in spatially extended shunt regions. Regarding the J01 images both methods again give the expected results if J01 is distributed homogeneously. However, in the shunted regions, PL suffers from balancing Currents within the emitter and DLIT from optical blurring. By comparing local and extended regions of increased J01 we find that DLIT approximates the expected J01 value better than PL, which clearly underestimates even extended local maxima of J01. For a local Current analysis of silicon solar cells we recommend the use of DLIT for the determination of J01 images and PL for the determination of Rs images.
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Towards more accurate imaging of the local Saturation Current Density in solar cells by using alternative PL evaluation methods
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015Co-Authors: Otwin Breitenstein, David Hinken, Jan Bauer, Karsten BotheAbstract:We have performed 2-dimensional inhomogeneous solar cell simulations using the circuit-simulation program Spice and obtained photoluminescence (PL), electroluminescence (EL), and dark lock-in thermography (DLIT) images for various illumination and biasing conditions. These images were evaluated by established methods for retrieving images of the Saturation Current Density J01. We found that DLIT delivers blurred but quantitatively correct J01 images, but PL generally delivers too weak local maxima of J01. This is due to the used model of independent diodes, which is too simple to describe the local diode voltage in inhomogeneous cells precisely. In reality lateral balancing Currents exist, which are not regarded in established PL evaluation methods. For solving this problem we have checked two alternative PL evaluation methods, which are already published but not established yet. Especially the Laplacian-based method has the potential to overcome this problem. For our simulated images the method yields correct results. However, in spite of some improvements for the determination of the calibration image, our first experimental results obtained by using this method do not agree yet with lock-in thermography based J01 results.
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dynamic infrared lifetime mapping for the measurement of the Saturation Current Density of highly doped regions in silicon
IEEE Journal of Photovoltaics, 2014Co-Authors: Jens Muller, Felix Haase, Helge Hannebauer, Christoph Mader, Karsten BotheAbstract:Previously, the dynamic infrared lifetime mapping (ILM) approach was used for a spatially resolved determination of the reverse Saturation Current Density J0 of local highly doped regions in silicon. However, possible restrictions of the method have not been considered yet. We show that 1) injection dependent lifetimes, 2) a nonlinearity between camera signal and excess charge-carrier Density, as well as 3) an additional signal due to a modulated sample temperature may affect the lifetime measurement and thus the correct determination of J0. Moreover, we consider the impact of injection dependent lifetimes and the modulated sample temperature under high-level injection. We apply our approach to symmetrically phosphorous diffused and textured samples with sheet resistances between 23 and 150 Ω/sq. Using the adopted evaluation algorithm of the dynamic ILM technique, we obtain an agreement in J0 evaluated by dynamic ILM and photo-conductance decay measurements of 8%.
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reverse Saturation Current Density imaging of highly doped regions in silicon a photoluminescence approach
Solar Energy Materials and Solar Cells, 2012Co-Authors: Jens Muller, Karsten Bothe, Sandra Herlufsen, Helge Hannebauer, R Ferre, Rolf BrendelAbstract:Abstract We present a camera-based technique for the local determination of reverse Saturation Current densities J 0 of highly doped regions in silicon wafers utilizing photoconductance calibrated photoluminescence imaging (PC-PLI). We apply this approach to 12.5×12.5 cm² float zone silicon samples with textured surfaces and a homogeneous phosphorous diffusion with sheet resistances between 24 and 230 Ω/□. We find enhanced photoluminescence emission at metallized regions of a sample due to reflection of long-wavelength light at the rear side of the sample. Our measurement setup comprises an optical short pass filter in front of the camera effectively blocking wavelengths above 970 nm and therefore ensuring a correct calibration of the PL signal in terms of excess charge carrier Density Δ n . We analyze two sets of samples comprising metal contacts to highly doped regions prepared by Laser Transfer Doping (LTD) as well as standard tube furnace phosphorus diffusion. We find a considerably smaller J 0 value of 370 fA/cm² for the LTD approach compared to a standard diffusion process resulting in J 0 =570 fA/cm². On the basis of these results we demonstrate that J 0 imaging is a powerful analysis technique for process optimization.
Robert Bock - One of the best experts on this subject based on the ideXlab platform.
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the bf alu concept n type silicon solar cells with surface passivated screen printed aluminum alloyed rear emitter
IEEE Transactions on Electron Devices, 2010Co-Authors: Robert Bock, Jan Schmidt, Bram Hoex, Susanne Mau, Rolf BrendelAbstract:Aluminum-doped p-type (Al-p+) silicon emitters fabricated by means of screen-printing and firing are effectively passivated by plasma-enhanced chemical-vapor deposited (PECVD) amorphous silicon (a-Si) and atomic-layer-deposited (ALD) aluminum oxide (Al2O3) as well as Al2O3/SiNx stacks, where the silicon nitride (SiNx) layer is deposited by PECVD. While the a-Si passivation of the Al-p+ emitter results in an emitter Saturation Current Density J0e of 246 fA/cm2, the Al2O3/SiNx double layers result in emitter Saturation Current densities as low as 160 fA/cm2, which is the lowest J0e reported so far for screen-printed Al-doped p+ emitters. Moreover, the Al2O3 as well as the Al2 O3/SiNx stacks show an excellent stability during firing in a conveyor belt furnace at 900°C. We implement our newly developed passivated Al-p+ emitter into an n+np+ solar cell structure, the so-called ALU+ cell. An independently confirmed conversion efficiency of 20% is achieved on an aperture cell area of 4 cm2 , clearly demonstrating the high-efficiency potential of our ALU+ cell concept.
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n type silicon solar cells with surface passivated screen printed aluminium alloyed rear emitter
Physica Status Solidi-rapid Research Letters, 2008Co-Authors: Robert Bock, Jan Schmidt, Rolf BrendelAbstract:Aluminium-doped p-type (Al-p+) silicon emitters fabricated by means of a simple screen-printing process are effectively passivated by plasma-enhanced chemical-vapour deposited amorphous silicon (a-Si). We measure an emitter Saturation Current Density of only 246 fA/cm2, which is the lowest value achieved so far for a simple screen-printed Al-p+ emitter on silicon. In order to demonstrate the applicability of this easy-to-fabricate p+ emitter to high-efficiency silicon solar cells, we implement our passivated p+ emitter into an n+np+ solar cell structure. An independently confirmed conversion efficiency of 19.7% is achieved using n-type phosphorus-doped Czochralski-grown silicon as bulk material, clearly demonstrating the high-efficiency potential of the newly developed a-Si passivated Al-p+ emitter. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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excellent passivation of highly doped p type si surfaces by the negative charge dielectric al2o3
Applied Physics Letters, 2007Co-Authors: Bram Hoex, Pietro P. Altermatt, Jan Schmidt, Robert Bock, Van De Mcm Richard Sanden, Wmm Erwin KesselsAbstract:From lifetime measurements, including a direct experimental comparison with thermal SiO2, a-Si:H, and as-deposited a-SiNx:H, it is demonstrated that Al2O3 provides an excellent level of surface passivation on highly B-doped c-Si with doping concentrations around 1019cm−3. The Al2O3 films, synthesized by plasma-assisted atomic layer deposition and with a high fixed negative charge Density, limit the emitter Saturation Current Density of B-diffused p+-emitters to ∼10 and ∼30fA∕cm2 on >100 and 54Ω∕sq sheet resistance p+-emitters, respectively. These results demonstrate that highly doped p-type Si surfaces can be passivated as effectively as highly doped n-type surfaces.
