Publications

Internationally well-known through their publications, Apollon Solar's scientists bring to the company and to its partners dynamism and expertise, essential elements to succeed in their projects.

2015 - NICE - Results from extended degradation and outdoor tests NICE modules

                                                                                30th EUPVSEC, Hamburg, Germany, 2015

Apollon Solar’s NICE (New Industrial Solar Cell Encapsulation) module technology has been developed among other objectives to provide a long term stable encapsulation for solar cells against environmental impact, such as heat, humidity, UV exposure and mechanical stress. Standard state of the art modules that feature EVA (Ethylene vinyl acetate) encapsulation and a polymer backsheet often show degradation modes after long-term outdoor exposure or accelerated laboratory degradation tests according to the IEC Standard 61215 for module certification, such as the Damp heat test (exposure to 85°C and 85% rH during 1000 hours), or the UV preconditioning test. The NICE module technology overcomes these degradation modes in that it has a glass sheet on the rear instead of a polymer foil and no lamination by polymer materials such as EVA. Instead the module volume is filled by a neutral gas and the environmental protection provided by an edge seal composed of a 10mm wide polyisobuthylene (PIB) ribbon and a secondary silicone based sealing.
In this work results from a 9000 hour Damp heat test (9x the requirements of the IEC Standard) on a NICE test module with heterojunction solar cells, carried out by CEA-INES, will be shown. During 9000 hours module power and fill factor have not shown any serious degradation, fluctuations of both parameters within a margin of -2.0% to +2.0% have been observed, some of which can be attributed to test conditions (recalibration of flash tester).
Also shown are results from an outdoor installation of industrial size NICE modules on the rooftop of CEA-INES after 3-year exposure. Over this period the module power degradation including Light Induced Degradation (the modules were made from p-type multi-c Silicon solar cells) was in average from 0.4%/y to 0.5%/y.

 

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2015 - Photosil - Evaluation of the electrical properties of intentionally Al and Fe contaminated p-type Cz ingots from feedstock to solar cells

                                                                     30th EUPVSEC, Hamburg, Germany,  2015

This work presents results from different p-type Cz ingots that were grown from intentionally Iron and Aluminium contaminated Poly Silicon Feedstock that was additionally doped with Phosphorus and Boron to simulate typical compensated UMG Silicon. The objective was to investigate the impact of the metal contaminants on the material quality and the solar cells performances, as well as to provide feedback to standards for the tolerable metal content in Solar Grade Silicon feedstock.

 

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2015 - NICE - Bifacial NICE Modules from High Efficiency n-type BiSoN Solar Cells

Energy procedia Volume 77, August 2015, Pages 382–385

This paper summarizes results from bifacial glass/glass NICE modules, using n-type BiSoN solar cells with efficiencies in the 20.0% range. A first series of industrial size (Sixty 156x156mm2) modules, fabricated under non-ideal conditions, exhibit a typical power of 250Wp under front illumination at STC conditions. Two modules have been installed and monitored at the ISC-Konstanz test site in El Gouna Egypt (27°N latitude). Monitoring data from the outdoor performance of these modules between the beginning of 2014 and August 2014 are analysed and compared to the data of a standard mono-facial reference module with an STC power of 255W. The bifacial modules show an average gain in generated power of 14.3% compared to the standard mono-facial reference module. During this monitoring period instantaneous effective peak powers of 313W were observed for the bifacial modules due to reflection from the ground in addition to the front illumination of the modules. Since bifacial modules produce high currents under bifacial operation, the current rating of standard junction boxes can become a critical factor. In this paper a newly developed junction box with a maximum current of 20A and a rated current of 17A is introduced.

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2014 - NICE - NICE bifacial module technology
6th WCPEC, Kyoto, Japan, 2014

This paper presents results from bifacial NICE modules using high efficiency n-type BiSoN solar cells from ISC Konstanz. A typical industrial size (60 cells) NICE/BiSoN module exhibits a power of 248W under front illumination (STC conditions). Two modules have been installed and monitored at the ISC Konstanz´ test site in El Gouna, Egypt. A bifacial gain of 14.3% compared to a standard monofacial PV module was demonstrated.

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2013 - NICE - NICE module technology using n-type solar cells without front and rear busbars
28th EPVSEC, Paris, France, 2013

The reduction of manufacturing costs for solar panels remains the priority for all photovoltaic producers in the world. Up to today strong efforts have been made to optimize the conventional cell and module processes (p-type silicon solar cells with selective or lightly doped emitters, standard lamination with glass / EVA / cells / EVA / PVF back sheet). From now on new strategies are required to go below the current production costs. In this work, we have investigated the possibility of using the NICE module technology ("New Industrial Cell Encapsulation"), for the encapsulation of low cost n-type “PhosTop” cells. This combination with a soldering-free module technology allows removing Ag busbars from the front grid of the cells - resulting in considerable savings of this precious metal and the possibility to contact the full Al rear surface that is used to create the rear surface emitter. First full size test modules, using 60 Phostop cells, resulted in high module fill factors of > 75%.

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2013 - Photosil - P-type and n-type Cz solar cells made with 100% PHOTOSIL silicon: Impact of boron concentration
28th EPVSEC, Paris, France, 2013

This paper aims at evaluating the impact of boron concentration in PHOTOSIL Si feedstock on the performance of p- and n-type Cz mono-crystalline solar cells. By comparing solar cells made with 2 different batches of PHOTOSIL Si with different B concentration we demonstrate that reducing it from 0.3 ppmw to 0.12 ppmw leads to a small improvement of efficiency and light-induced degradation in p-type Si solar cells and to a strong improvement of efficiency in n-type bifacial solar cells. Average efficiencies of up to 18.1% in p-type solar cells and 18.5% in n-type solar cells made with 100% PHOTOSIL Si are obtained, demonstrating the very high quality of this material. Surprisingly weak light-induced degradation is measured to happen, particularly in n-type Si solar cells. The potential reasons for such a low light-induced degradation are briefly discussed.

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2013 - Photosil - PHOTOSIL UMG silicon : Industrial evaluation by multi-c p-type ingots and solar cells
28th EPVSEC, Paris, France, 2013

In order to have a market perspective as UMG Silicon for the PV industry, PHOTOSIL Silicon needs to meet quality criteria in terms of PV cell and module performance as well as production cost objectives. To address these points a 2nd generation industrial refining equipment has been made operational, with a total annual capacity of 100 MT, allowing for an industrial evaluation and qualification of PHOTOSIL Silicon. Results of two external evaluation tests of PHOTOSIL feedstock are presented in this article: (i) Using an industrial pilot line from Multi-c Silicon ingots to solar cells and (ii) by an industrial PV producer using state of the art multi-c ingot, wafering and cell processing equipment. In all cases 100% PHOTOSIL Silicon was used as feedstock for the ingot crystallization. The average cells efficiency obtained by these two routes is superior to 16% and the homogeneous material quality both on ingot and wafers is comparable to using Polysilicon as feedstock. The feedback of the industrial customer was positive, and 5 tons of PHOTOSIL Silicon has been ordered. All critical aspects regarding UMG Silicon have been carefully investigated and taken under control, like risk of SiC, SiN inclusions, resistivity control, etc.
For a final validation of the quality of PHOTOSIL Silicon, modules have been made from multi-c Si PHOTOSIL Silicon and a total capacity of 100kWp has been installed in southern France in 2012 for monitoring and power rating. The energy production has been compared to standard modules with the same efficiency; the difference of energy production over a whole year is below 2%. Under high irradiation, the performance of both module types is similar, but under low irradiation the performance of the PHOTOSIL modules is 5% lower. No specific degradation has been observed, which confirms the potential for an industrial PHOTOSIL silicon production.

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2012 - Doping - Impact of incomplete ionization on the electrical properties of compensated p-type silicon
Journal of Applied Physics 111, 043701 (2012)

This paper investigates the importance of incomplete ionization of dopants in compensated p-type Si and its impact on the majority carrier density and mobility and thus on the resistivity. Both theoretical calculations and temperature-dependent Hall-effect measurements demonstrate that the carrier density is more strongly affected by incomplete ionization in compensated Si than in uncompensated Si with the same net doping. The previously suggested existence of a compensation-specific scattering mechanism to explain the reduction of mobility in compensated Si is shown not to be consistent with the T-dependence of the measured carrier mobility. The experiment also shows that, in the vicinity of 300 K, the resistivity of compensated Si has a much weaker dependence on temperature than that of uncompensated silicon.

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2012 - Doping - Incomplete ionization and carrier mobility in compensated p-type and n-type silicon
IEEE Journal of Photovoltaics 3, 108 (2013)

In this paper, we show through both calculations and Hall effect measurements that incomplete ionization of dopants has a greater influence on the majority-carrier density in p-type and n-type compensated Si than in uncompensated Si with the same net doping. The factors influencing incomplete ionization at room temperature are shown to be the majority-dopant concentration, its ionization energy and type, and the compensation level. We show that both the majority- and the minority-carrier mobilities are lower in compensated Si than expected by Klaassen’s model and that the discrepancy increases with the compensation level at room temperature. The study of the temperature dependence of themajority-carrier mobility shows that there is no compensationspecific mechanism and that the reduction of the screening in compensated Si cannot explain alone the observed gap between experimental and theoretical mobility.

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2012 - Doping - Compensation engineering for silicon solar cells
Energy Procedia 15, 67 (2012)

This paper discusses the role of compensation engineering as a means to allow higher concentrations of dopants in
silicon than would otherwise be acceptable for solar cell fabrication. Special attention is given to tri-doping, a technique consisting on the addition of gallium to boron and phosphorus doped UMG-Si (upgraded metallurgical grade silicon) feedstock to better control the net dopant density. Firstly, we review the current understanding of compensated silicon, focusing on the fundamental electronic properties of charge carriers: their density, mobility and lifetime. Based on those parameters, we then model solar cell efficiency in order to identify the advantages and limitations of compensation engineering. Given the current uncertainty of the majority and minority carrier mobilities, we study the possible impact of different levels of mobility reduction on solar cell efficiency. This modelling indicates that it is possible to achieve reasonable solar cell efficiencies, around 18%, even in cases of strong dopant compensation and mobility reduction. Lastly, the alternative of using n-type compensated silicon is briefly discussed, taking into account recent evidence that such material can degrade significantly upon illumination.

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2012 - Photosil - World class solar cell efficiency on n-type CZ UMG silicon wafers by heterojunction technology
27th EPVSEC, Frankfurt, Germany, 2012

Highly purified n-type UMG (“Upgraded Metallurgical”) Silicon shows a strong potential for high efficiency low cost solar cells. Compared to p-type Silicon, n-type Silicon is in general less susceptible to lifetime degradation due to residual metal impurities or to light induced degradation due to the Boron-Oxygen complex. In this work a 15kg 6 inch mono-c Cz Silicon ingot has been grown from 100% highly purified UMG Silicon obtained with the PHOTOSIL process. In this feedstock the Boron and Phosphorus concentrations measured by GDMS were found to be 0.3 ppmw and 2 ppmw respectively. The resulting ingot is n-type, fully mono-crystalline and has a resistivity from 0.2 to 1 ohm.cm. Other impurities, especially metals were not detectable with the analysis techniques applied (GDMS, ICP OES). The ingot was cut into 125x125 mm2 pseudo square wafers of 180 micron thickness. A first series of solar cells were processed on these wafers using an industrial hetero-junction process of Roth & Rau. The best solar cell had an energy conversion efficiency of 19.0% (average: 18.6%) under standard testing conditions with a very high Voc of 725mV. According to the knowledge of authors this is the highest efficiency ever reported on industrial type solar cells fabricated on 100% UMG Silicon.

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2012 - Photosil - Dopant specifications for p-type UMG silicon, mono-c vs multi-c
27th EPVSEC, Frankfurt, Germany, 2012

This work demonstrates the potential for high efficiency solar cells on wafers from 100% PHOTOSIL silicon. Multicrystalline and CZ p-type solar cells have been investigated using the same feedstock quality with actual dopant concentrations : B=0.3 ppmw and P=0.8 ppmw. Multicrystalline Photosil solar cells have the same efficiency like standard Multicrystalline solar cells. PHOTOSIL feedstock is directly usable to pull CZ ingot. The interest for a highly compensated p-type UMG silicon ingot has been revealed in regards to the cell efficiency distribution along the ingot height. High efficiency solar cells have been obtained on CZ wafers with an 18.0% maximum efficiency, but the LID was too high due to a higher oxygen concentration in CZ. The impurities responsible for LID need to be reduced. For CZ ingots we suggest a Boron concentration below 0.2 ppmw in the feedstock. These results demonstrated that feedstock specification need to be adjust according to the final product (CZ or multi-c).

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2012 - NICE - Secured intrinsic under-pressure in the NICE modules - The oxygen gettering approach
27th EPVSEC, Frankfurt, Germany, 2012

APOLLON SOLAR’s NICE (New Industrial Solar Cell Encapsulation) module technology is an innovative technology to encapsulate and electrically interconnect solar cells without neither soldering nor full area EVA-type encapsulant. An organic edge sealing delimits the internal volume in which an under-pressure is created, allowing to establish the electrical contact between solar cells and interconnectors by pressure. The under-pressure is kept inside thanks to a Poly-IsoButhylen (PIB) material, used as organic sealing for more than 40 years in the insulating glazing industry allowing us to expect more than a 30-years lifetime for the NICE modules. Being a new technology, no long term performance information from the field is available from NICE modules working for several decades. In order to be confident on the 30-years lifetime, the module is able to support a slight increase of pressure without any problem of efficiency. Moreover, an additional security can be obtained by controlling the variation of gas inside the module. In particular we will show how the oxygen can be partly removed by the module elements themselves. After an introduction on the partial pressure concept, this paper will present a recent results on oxygen segregation inside the module. It was found that the cells and the copper inside the module are able to capture the incoming oxygen with a potential of 100 time the initial oxygen quantity present in the module. The NICE module is then intrinsically protected from oxygen diffusion through the PIB sealing during its lifetime.

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2012 - Photosil - 19% Efficiency Heterojunction Solar Cells on Cz Wafers from Non-Blended Upgraded Metallurgical Silicon
38th IEEE, Austin, Texas, USA, 2012

 

Highly purified n-type UMG (“Upgraded Metallurgical”) Silicon is a material with a strong potential for high efficiency low cost solar cells. Compared to p-type Silicon, n-type Silicon is in general less susceptible to lifetime degradation due to residual metal impurities or to light induced degradation due to the Boron-Oxygen complex.


In this work a 15kg 6 inch mono-c Cz Silicon ingot has been grown from 100% highly purified UMG Silicon obtained with the PHOTOSIL process. In this feedstock the Boron and Phosphorus concentrations measured by GDMS were found to be 0.3 ppmw
and 2 ppmw, respectively. The resulting ingot is n-type, fully mono crystalline and has a resistivity range from 0.2 to 1 ohm.cm. Other impurities, especially metals, were not detectable with the analysis techniques applied (GDMS, ICP-OES). The ingot was cut into 125x125 mm2 pseudo square wafers of 180 micron thickness. A first series of solar cells were processed on these wafers using an industrial hetero-junction process by Roth & Rau. The best solar cell from a batch of 14 had an energy conversion efficiency of 19.0% (compared to an average: 18.6%) under standard testing conditions with a very high Voc of 725mV. An independent confirmation of these results is pending.

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2012 - NICE - NICE module technology- from the concept to the mass production - a 10 years review
38th IEEE, Austin, Texas, USA, 2012

Apollon Solar’s NICE (New Industrial Solar Cell Encapsulation) module technology is an innovative technology to encapsulate and electrically interconnect solar. The electrical series connection is made using an under-pressure in the module allowing the front and back glasses to press the copper ribbons directly onto the cell busbars. Contrary to standard modules, NICE modules do not use EVA-like encapsulants. Instead a PIB (Poly-Isobutylene) edge sealing is used to provide a barrier for moisture ingress. This paper proposes a full overview of this technology from its concept to the final 60-cells module product.

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2011 - Photosil - UMG Silicon from the PHOTOSIL project – a status overview in 2011 on the way towards industrial production
26th EPVSEC, Hamburg, Germany, 2011


This paper gives an overview on the latest progress of the French PHOTOSIL project towards an industrial production. The PHOTOSIL consortium has been working for 6 years on a new innovative refining approach to produce Upgraded Metallurgical Silicon (UMG) with a purity compatible with the specifications of the PV industry. The involved refinement processes are based on physical techniques and run on an industrial pilot level with batch sizes of 100kg. Two major directions for the evaluation of the quality of the PHOTOSIL UMG Silicon were pursued:

(i) a large quantity 1.3 tons of UMG Si was produced on the pilot facility using the standard PHOTOSIL purification process to demonstrate the process stability in a continuous operation and its compatibility with the specifications required by the PV industry. This UMG Silicon was used to demonstrate an installed module capacity of 100 kW using multi-c Silicon solar cells from 100% PHOTOSIL UMG Silicon, which is currently under outdoor evaluation for energy rating.

(ii) high quality UMG Silicon was purified with an improved process, to evaluate the ultimate performance potential in terms of solar cell efficiencies compared to the performance of high purity polysilicon from the Siemens route. The results of both evaluation routes as well as an economic evaluation allowed to start the next phase of the PHOTOSIL project that will install by 2014 an improved and simplified 500 t/y industrial purification equipment.

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2011 - NICE - Cell-ribbon contacts interface study in NICE modules
26th EPVSEC, Hamburg, Germany, 2011

Apollon Solar’s NICE (New Industrial Solar Cell Encapsulation) module technology is an innovative technology to encapsulate and electrically interconnect solar cells using pressure contacts instead of soldering. This paper shows results from a study of the characteristics of the pressure contacts in the NICE modules. The impact of the rubbing between the interconnector ribbons and cell busbars, the busbars design itself and the glass flatness have been investigated. It is shown that these three parameters must be carefully controlled to avoid any problem during the NICE module lifetime in order to maintain a high long term performance and reliability

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2011 - Crystallisation - Influence of high growth velocity for multi crystalline Silicon ingots on solar cells efficiencies
26th EPVSEC, Hamburg, Germany, 2011

In order to further reduce the costs of multi-crystalline ingots this work aims at increasing the ingot growth velocities well above the typical values of 1.5 cm/h or less, that are found in most industrial multicrystalline Silicon ingot growth processes. A reduced cycle time for the growth of multi-c Silicon ingots directly transfers to reduced direct costs of this important production step in the PV value chain. The impact of the growth velocity on the crystalline quality has been investigated. The objective is to obtain similar solar cell efficiencies on multi-crystalline wafer from ingots grown at higher velocities compared to the standard conditions . Solar cells from ingots crystallized at 1 cm/h and 2 cm/h have been processed and characterized. An additional ingot has been crystallized at an even higher growth velocity of 3 cm/h but the macroscopic crystal structures were not satisfying and indicated already a low quality of the ingot, so no solar cells were processed from this high velocity ingot.

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2011 - Doping - Influence of net doping, excess carrier density and annealing on the boron oxygen related defect density in compensated n-type silicon
Journal of Applied Physics 110, 063708 (2011)

In this study, we present experimental data regarding the concentration of the boron-oxygen complex in compensated n-type silicon when subjected to illumination. We find that the defect density is independent of the net dopant concentration and is strongly dependent on the minority carrier concentration during illumination. We show that annealing at temperatures in the range 500°C to 700°C permanently reduces the defect density possibly via a decrease in the oxygen dimer concentration.

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2011 - Doping - Recombination Activity and Impact of the Boron–Oxygen-Related Defect in Compensated n-Type Silicon
IEEE Journal of Photovoltaics, Vol.1, N°1, July 2011

In this paper, we present experimental data regarding the recombination activity and concentration of the boron–oxygen complex in compensated n-type silicon, doped with phosphorus and boron, when subjected to illumination. Unlike the data of Bothe et al. in n-type silicon compensated with thermal donors, our results suggest the dominant defect level in our doping range to be a shallow level (EC–ET = 0.15 eV), with a capture cross-section ratio σn/σp of around 0.006, suggesting a negatively charged center. We also confirm previous results showing an increasing defect density with bias light intensity. Due to the strong lifetime reduction observed, we suggest that this material might not be suited to make high-efficiency n-type solar cells, unless practical strategies to reduce the defect concentration can be developed.

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2011 - Doping - Electrical properties of boron, phosphorus and gallium co-doped silicon
Energy Procedia, Vol.8, p. 349, 2011

A number of ingots were grown from solar grade poly Silicon, to which Boron, Phosphorous and Gallium were added as dopants. The introduction of Gallium as a third dopant allowed for a better control of the resistivity and the doping type during ingot growth. Measured resistivity in this material is shown to be systematically higher than that calculated using Scheil’s law for the dopants distribution and Klaassen’s model for the majority carrier mobility. This resistivity underestimation is shown to be, at least partially, due to a reduction of the majority carrier mobility in highly compensated Si compared to Klaassen’s model. A similar reduction is observed for the minority carrier mobility. We propose a correction term in the mobility calculation, to allow a greater accuracy in the prediction of the resistivity and mobility of compensated solar grade silicon.

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2011 - Doping - Ga co-doping in Cz-grown silicon ingots to overcome limitations of B and P compensated silicon feedstock for PV applications
Phys. Status Solidi C 8, No. 3, 678–681 (2011)

 In this paper, we investigate gallium co-doping during CZ crystallization of boron and phosphorus compensated Si. It is shown that the addition of gallium yields a fully p-type ingot with high resistivity despite high B and P contents in the silicon. Segregation of doping impurities is consistent with theory. Minority carrier lifetime and majority carrier mobility measurements indicate that this material is suitable for the realization of solar cells with comparable efficiencies to standard material. Significant light-induced degradation of minority carrier lifetime is however revealed to occur in this material.

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2010 - Photosil - High performance purified UMG silicon via the PHOTOSIL process
CSSC4, Taipei, Taiwan, 2010

This paper gives an overview on major results obtained by the French PHOTOSIL project on the purification of metallurgical grade silicon. A detailed description of the different purification steps of the PHOTOSIL process is presented, focusing on improvements of the process effectiveness that have been achieved during the last years. As a quality indicator chemical analysis results of the purified Silicon are given, followed by the evolution of solar cell efficiencies that reflect the improved quality of the purified Silicon. In order to show the ultimate quality potential of the PHOTOSIL Silicon, as a representative of the metallurgical Silicon route, a special highly purified Silicon batch has been prepared by using an optimized version of the PHOTOSIL process. The results obtained, in terms of purity of the Silicon and solar cell efficiencies, indicate a strongly reduced gap to classical electronic grade Silicon.
2010 - Photosil - Silicon feedstock for solar cells – Availability, quality criteria and future
CSSC4, Taipei, Taiwan, 2010

Over the past decade, the availability, quality and associated cost of silicon feedstock have been some of the most important and debated issues in the silicon-based solar cell industry. In the current paper, a status for some of the currently operating metallurgical SoG-Si feedstock routes and producers in Norway, France and China, is given. Factors such as energy requirements and emissions/waste products, as well as product purity, are examined. In addition, a summary of the demands on subsequent solar cell processing for different types of feedstock is given. An outlook for the future demand on solar grade silicon feedstock is presented.
2010 - Photosil - Segregation and crystallization of purified metallurgical grade silicon: influence of process parameters on yield and solar cell efficiency
25th EPVSEC, Valencia, Spain, 2010

This work has been performed in the frame of the PHOTOSIL project dedicated to the purification and crystallization of metallurgical grade silicon [1]. Compared to electronic grade, purified metallurgical grade presents high levels of metallic impurities, light elements and dopants. The purpose of the work is to optimize the process parameters of the segregation and crystallization stages for this particular feedstock, with the aim of obtaining solar cell conversion efficiencies higher than 15%. We particularly focus on the segregation of impurities, among which metals, dopants (B and P) and light elements, carbon and oxygen being known to lead to unwanted structures such as small equiaxed grains (“grits”) and precipitates acting as recombination centers.

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2010 - Photosil - Status of the Photosil project for the production of solar grade silicon from metallurgical grade silicon
25th EPVSEC, Valencia, Spain, 2010

This article gives an up-date on the progress of the French PHOTOSIL project from a technical and an economical point of view. During the last 5 years, the French PHOTOSIL consortium formed by FerroPEM, CEAINES, CNRS SiMAP and APOLLON SOLAR has been working on a combination of new, innovative up-grading and purification techniques for MG Silicon on an industrial pilot level, to arrive at UMG Silicon that is compatible with the purity and economical requirements of the PV industry. The objectives of this project are production costs <15€/kg, average photovoltaic performances of >15% solar cell efficiencies on multi-crystalline wafers from ingots
made of 100% UMG Silicon and a material yield of >85% after crystallisation.

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2010 - NICE - IEC Certification and Extended Ageing Test of NICE Module
25th PVSEC, Valencia, 2010

ABSTRACT: Apollon Solar’s NICE (New Industrial Solar Cell Encapsulation) module technology is an innovative technology to encapsulate and electrically interconnect solar cells without neither soldering nor encapsulant. An organic edge sealing delimits the internal volume in which an underpressure is created, allowing to establish the electrical contact between solar cells and interconnectors by pressure. This technology represents a completely new approach for the solar cell encapsulation: besides industrial and cost advantages, a better long term module performance stability and an improved lifetime are expected.

The IEC certification of this technology represents a major step in its development, in order to prove the product robustness. This article present the results of the first certification process according to IEC of NICE modules manufactured with our prototype production line designed by Vincent Industrie and installed at INES. The certification is carried out by the TÜV Rheinland in Cologne, and shows a very high performance stability, with a maximal power degradation of 2 % (while IEC norms require a degradation lower than 5%).

In addition to the IEC tests, we also present results of several largely extended mechanical and ageing tests carried out at INES and TÜV Rheinland. We notably obtained remarkable results, with a power degradation after 1000 thermal cycling lower than 2%.

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2010 - Doping - Doping engineering to increase the material yield during crystallization of B and P compensated silicon
25th EPVSEC, Valencia, Spain, 2010

 

In this paper, we investigate gallium co-doping during crystallization of boron and phosphorus
compensated Si. It is shown that the addition of gallium yields a fully p-type ingot with high resistivity despite high B
and P contents in the silicon melt. Segregation of doping impurities is consistent with theory. Minority carrier lifetime
and majority carrier mobility measurements indicate that this material is suitable for the realization of solar cells with
comparable efficiencies to standard material. Significant light-induced degradation of minority carrier lifetime is
however revealed to occur in this material as in standard boron-doped silicon.

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2010 - Photosil - High Performance Solar Cells made from 100% UMG-Silicon Obtained via the Photosil Process
35th IEEE PVSEC, Hawai, 2010

The presented work is part of the French PHOTOSIL project which deals with the purification of metallurgical grade (MG) silicon to obtain Solar Grade (SoG) silicon by a combination of innovative refinement/up grading techniques such as segregation and plasma purification. The main objectives of this project are production costs <15€/kg, a photovoltaic performance of >15% solar cell efficiencies, and material yields >85% after crystallization. In this paper we present the latest results obtained with a highly purified metallurgical silicon via a modified PHOTOSIL process.

Solar cells have been processed on 12.5x12.5 cm² wafers from both ingots using industrial type standard screen printed processes at the CEA-INES. Solar cells from the PHOTOSIL ingot were fabricated with an industrial process optimized for SoG silicon directly purified from MG Silicon. In case of the EG ingot the average efficiency was 16.3% with a maximum of 17%. In case of the ingot from PHOTOSIL silicon, solar cells from the p-type region have reached an average efficiency of 15.7 % including a best cell with 16.2 %.

In addition, a 6” Cz ingot was crystallized from the same purified silicon feedstock. The fabricated cells showed a high average efficiency of 17,4% was reached with a maximum efficiency of 17,6%, which is one of the highest efficiency reported so far if not the highest on purified metallurgical silicon. These results clearly demonstrate the potential of the metallurgical silicon route for application in PV and the possibility to reach high efficiencies.

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2009 - NICE - Evaluation of Gas and Humidity Tight Sealing of Apollon Solar’s NICE Modules
24th PVSEC, Hamburg, 2009

ABSTRACT: APOLLON SOLAR’s NICE (New Industrial Solar Cell Encapsulation) technology aims at drastically reducing the manufacturing costs of PV modules, while at the same time increasing the total module lifetime. It makes use of a sealing technology which is well established in the insulating glass industry to replace the state-of-the-art lamination technology for PV modules.

An additional feature is the soldering free electrical series connection of the solar cell busbars with the metal interconnectors, thanks to an under-pressure inside the module. Thanks to these features, the NICE process is completely inline and easy to automate.

Modules with 36 silicon solar cells have been produced with the NICE technology and evaluated, including by tests according to the IEC 61215 standard. Although the power degradation of the tested modules remained largely in the acceptable range, the evaluation revealed two areas onto which additional work was necessary to increase the overall performance and reliability of the NICE modules: (i) mechanical aspects concerning the stability of cells and migration of cells and interconnectors during thermo-cycling tests, (ii) performance losses due to a lack of optical continuity between front glass and solar cell. This work reports on solutions to overcome both performance limiting factors.

Keywords: Module Manufacturing, Cost Reduction, Encapsulation

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2009 - Crystallisation - New method for grain size characterisation of a Multi-Crystalline Silicon Ingot
Poster Presentation at the 24th PVSEC, September 2009, Hamburg, Germany

In order to estimate the quality of the crystallisation process of multi-crystalline Silicon ingots, we have developed a new optical method for the determination of grain sizes on as-cut wafers that were taken from different height positions of the ingot. This fast method is based on image analysis and allows in a simple way to get numerical data which represent the crystallographic quality of silicon wafers. The obtained data were used to calculate a grain size distribution over the analysed wafer area as well as an average grain size by using two different algorithms. It was thus possible to represent the average grain size as a function of ingot height, which indicates ingot regions of lower crystalline quality, for example regions of equiaxed growth of very small grains (“grit”).

This technique was used for the characterisation of different multi-crystalline Silicon ingots, using Silicon feedstock of different quality (electronic, upgraded metallurgical or solar grade), and also to monitor the impact of modifications of the crystallisation process parameters on the grain sizes distribution. It was found that this method is able to give a first qualitative impression of the multi-crystalline ingots and wafers which in the end are used to produce solar cells.

Keywords: crystallization, silicon, grain.

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2009 - Doping - Doping engineering as a Method to Increase the Performance of Purified MG Silicon During Ingot Crystallisation
34th IEEE Conference, in June 2009, Philadelphia, USA

This paper presents an overview of significant crystallisation results obtained with purified metallurgical grade silicon in the framework of the French Photosil project.

Especially we show that in case of a high Boron concentration in the feedstock (>2.1017 cm-3), the higher the compensation level is, the higher the solar cells efficiency will be. Several ingots were crystallised with different concentrations of boron and phosphorus and the best solar cell efficiency (15.2%) was obtained with the highest compensated ingot.

Moreover we show that this performance improvement is due to an increase of carrier lifetime which largely counterbalances the decrease of carrier mobilities, likely caused by scattering effect of ionized dopants.

However, due to the different segregation coefficients of the major dopant atoms, Boron and Phosphorus, compensated multi-c Silicon ingots often show n-type regions, decreasing the overall material yield. Based on these findings, we suggest a novel concept of doping engineering, allowing a control of the compensation level through the entire ingot height, by introducing a well defined mix of dopant atoms (B, P and Ga) to the silicon before crystallisation. This can lead at the same time to a higher electrical performance and a higher material yield of the crystallised Silicon. As a further perspective the use of lower grade and less expensive Silicon with a high electrical performance and material yield can be expected.

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2008 - NICE - Industrialisation of NICE technology
Poster Presentation at the 23rd PVSEC, September 2008, Valencia, Spain

APOLLONSOLAR’s NICE (New Industrial Solar Cell Encapsulation) technology makes use of an air and humidity tight sealing technology known from the insulating glass industry and based on the application of an organic sealing material from the family of poly-isobutylene (PIB).

Important features of the NICE technology are the absence of EVA lamination and the use of an underpressure inside the module to provide the electrical series connexion between solar cell contact lines and metal interconnectors, thus suppressing the soldering of metal interconnectors to the solar cell busbars, which is the most widely used technology today. Other important features include a specially developed metal foil that is used as for the metal rear surface and new external connector which is integrated in the edge-sealing of the module. From a production point of view, the NICE module technology presents a largely simplify module assembling technology since it allows for a complete inline operation which can be fully automated.

This paper presents first results obtained with the new NICE pilot production line, realised by VINCENT INDUSTRIES. The pilot line incorporates all necessary automated production stations without the automatic loading and sorting.

Keywords: Modules, Encapsulation, Sealing quality

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2008 - Doping - Beneficial Effects of Dopant Compensation on Carrier Lifetime in Upgraded Metallurgical Silicon
Poster Presentation at the 23rd PVSEC, September 2008, Valencia, Spain

This study is devoted to the variations of the carrier lifetime and minority carrier diffusion length with the compensation level in solar-grade crystalline silicon. Especially we show, by using the Shockley-Read-Hall statistics, that an increase in the compensation level reduces the recombination strength of doping species and of some metal impurities.

These theoretical results are confirmed by the chemical and electrical characterizations of strongly compensated multicrystalline silicon wafers and solar cells, from silicon purified by the metallurgical route.

These results are of paramount importance since an accurate control of the compensation level can lead to strong improvements in silicon solar cells efficiencies. Nevertheless, possible limits of too high compensation levels are also evoked.

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2008 - Crystallisation - Innovative Crystallisation of Multi-Crystalline Silicon Ingots from different types of Silicon Feedstock
Oral Presentation at the 23rd PVSEC, September 2008, Valencia, Spain

Solar Grade Silicon obtained by purification of metallurgical grade Silicon becomes an important source of Silicon feedstock for the crystalline Silicon based PV industry. This paper presents a new process and furnace for the crystallization of multi-crystalline Silicon ingot, using purified metallurgical grade Silicon as feedstock. In particular, the influence of the remaining dopant concentrations, such as Boron and Phosphorus, in purified metallurgical Silicon on the electrical characteristics of the obtained ingots, wafers and solar cells are discussed.

Indications have been found that compensation of n-type and p-type dopants can lead to an improved minority carrier diffusion length, improving the overall efficiencies of solar cells: Efficiencies of 14 % have been obtained on ingots that were grown from feedstock with relatively high concentrations of Boron (2.5x1017 cm-3) and Phosphorus (3.5x1017 cm-3) respectively. Although the feedstock is n-type due to the higher concentration of Phosphorus, the ingot showed a p-type polarity with a resistivity of 0.5 Ohm-cm over 75% of its height starting from the bottom, which is due to a more effective segregation of Phosphorus.

This also leads to an accumulation of Phosphorus atoms in the top region of the ingot, which turns n-type again and a transition region of high compensation.

Keywords: Multi-Crystalline, Compensation, Solar grade Silicon

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2008 - Crystallisation - Crystallisation of Purified Metallurgical Silicon
Presentation at the 33rd IEEE Photovoltaic Specialists Conference,  en May 2008 à San Diego, USA

The crystallization of purified metallurgical Silicon often leads to multi crystalline ingots which present regions of strong compensation and an inversion of the polarity type. These effects result from the presence of different dopant atoms, donors and acceptors, in this type of Silicon and their different segregation behavior during the crystallization process.

The most commonly found dopant atoms in Silicon, Boron and Phosphorous, have relatively high segregation coefficients with an important difference in their absolute value. As a result, suitable resistivities in the 0.5 to 1.0 Ωcm range are obtained in an important part of the ingot, but at a relatively high compensation ratio.

This paper discusses these compensation effects, as observed on upgraded metallurgical Silicon from the PHOTOSIL project and using a new crystallization process and furnace developed by CYBERSTAR and APOLLONSOLAR.

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2007 - Crystallisation - Innovative Crystallisation of Multi-Crystalline Silicon
Presentation at the 17th PVSEC, Japan, 2007

A new, innovative crystallisation process and furnace for the growth of multi-crystalline Silicon ingots is presented. Important key features of the furnace and process include a newly designed, thermally anisotropic quartz crucible and a very uniform inductive heating and cooling system. This thermal configuration allows for a perfect lateral and vertical temperature control during crystallisation so that high temperature gradients can be obtained, which are especially beneficial for the segregation of remaining impurities in lower quality silicon.

Solar cells have been processed on wafers from multi-crystalline Silicon ingots that were  crystallized with this new process and furnace, using doped electronic grade silicon and purified metallurgical silicon.

The resulting efficiencies were 14.3% in case of the purified metallurgical Silicon and 15.0% in case of the doped electronic grade Silicon.

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2006 - Photosil - Simplified Production of Solar Silicon from Metallurgical Silicon
21st PVSEC, Dresden, 2006

This article presents the status the PHOTOSIL project, which includes partners from industry, R&D institutes and equipment manufacturers. The objectives of this project are the production of solar grade (SoG) silicon at costs <15€/kg and of multi-crystalline ingots at costs <35€/kg, starting with metallurgical silicon and using a combination of innovative up-grading and purification techniques. On the basis of encouraging results on laboratory level, the PHOTOSIL consortium has obtained the funding for the construction of an industrial scale pilot line. This line will become fully operational in October 2006 and it will serve to demonstrate the industrial viability of the PHOTOSIL technology by up scaling the different laboratory scale processes to an industrial level. In a first stage, the pilot line operates with batch sizes of 60kg which will be doubled to 120 kg in a second stage, arriving at a nominal capacity of 200 tons per year.

The PHOTOSIL process includes metallurgical and plasma purification techniques, giving rise to a complete vertical integration from the metallurgical Silicon production to the fabrication of exploitable multi-crystalline Silicon ingots for the PV industry, of either p- or n-tpye. At present, a resistivity level of 0.3 – 0.5 Wcm has been reached after the combined metallurgical and plasma purification. Metal impurity concentrations have been reduced to 20 ppm for Fe, 15 ppm for Al and <2 ppm for Ti after the metallurgical purification by segregation.

Keywords: Silicon, Metallurgical Grade, Multicrystalline

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2005 - Photosil - Photovoltaic Grade Silicon, Vers la révolution des panneaux solaires (FR)
Article in SCIENCE & VIE, September 2005

Fabriquer un silicium précisément adapté aux capteurs photovoltaïques : tel est l’exploit d’un procédé qui promet de réduire leur prix… d’un tiers. De quoi relancer la filière !

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2005 - NICE - Recent Progress with Apollon Solar's NICE Module Technology
20th PVSEC, Barcelona, 2005

ABSTRACT: APOLLON SOLAR’s NICE (New Industrial Solar Cell Encapsulation) technology aims at drastically reducing the manufacturing costs of PV modules, while at the same time increasing the total module lifetime. It makes use of a sealing technology which is well established in the insulating glass industry to replace the state-of-the-art lamination technology for PV modules.

An additional feature is the soldering free electrical series connection of the solar cell busbars with the metal interconnectors, thanks to an under-pressure inside the module. Thanks to these features, the NICE process is completely inline and easy to automate.

Modules with 36 silicon solar cells have been produced with the NICE technology and evaluated, including by tests according to the IEC 61215 standard. Although the power degradation of the tested modules remained largely in the acceptable range, the evaluation revealed two areas onto which additional work was necessary to increase the overall performance and reliability of the NICE modules: (i) mechanical aspects concerning the stability of cells and migration of cells and interconnectors during thermo-cycling tests, (ii) performance losses due to a lack of optical continuity between front glass and solar cell. This work reports on solutions to overcome both performance limiting factors.

Keywords: Module Manufacturing, Cost Reduction, Encapsulation

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2004 - Photosil - Refining of metallurgical silicon for crystalline solar cells
19th PVSEC, Paris, 2004

A plasma-refining technique is applied to upgraded metallurgical grade silicon (UMG) to produce solar grade silicon for multi-c silicon ingots at direct costs lower than 15€/kg. Using oxygen and hydrogen as reactive gases injected in the plasma, boron is removed from the material mainly in form of BOH and BO. The boron volatilization time has been reduced to 50 min compared to previous processes, by increasing the temperature of the silicon bath. At the same time, the Al, Ca, C, O concentrations are strongly reduced. From a first batch of purified UMG Silicon, mutli-crystalline ingots (12 kg), wafers (125x125 mm²) and solar cells have been produced for an evaluation of this intermediate material. The obtained solar cells gave efficiencies of up to 11.7 %. Process development towards an up-scaled pilot equipment is on the way to further increase the purification efficiency.

Keywords: Silicon, Metallurgical-Grade, PV Materials

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2004 - NICE - New Industrial solar Cell Encapsulation (NICE) technology for PV module fabrication at drastically reduced costs
19th PVSEC, Paris, 2004

The direct production costs of state-of-the-art PV modules, produced with solar cells fabricated on wafers, represent between 30% and 40% of the total costs per Watt peak of the entire PV production chain, including ingot production, wafer cutting, cell production and module assembly. The NICE technology aims at reducing these costs by more than 50%.

It combine an air- and humidity tight sealing technique, which is already known and proven from the insulating glass industry, with a solar cell interconnection that makes use of an underpressure between the front and back sheet which delimitate the module. The underpressure inside the module assures low resistivity contacts between cells and metal interconnectors. The entire NICE process takes place at room temperature avoiding all heat related risks of cell degradation. Compared to the state-of-the-art technology the solder connection between the cells and metal connectors is completely avoided, as well as the batch type lamination process, largely facilitating the automation of the NICE module fabrication process.

A number of test modules with 36, 16 and 6 125x125 mm² silicon solar cells have been produced with the NICE technology and tested according to the IEC 61215 standard, resulting in no degradation of the module power.

Keywords: Module Manufacturing, Cost Reduction, Encapsulation

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