Detailed information on energy research

Projektinfo 10/2013

Development of high-efficiency solar cells and modules Optimised production processes and more durable modules can reduce the costs for producing solar power by a third

Research institutes, photovoltaic producers, system manu-facturers and solar industry suppliers are working together to produce more powerful and durable modules in a more efficient manner. In the SONNE project, companies and researchers are optimising the output and production of modules made of crystalline silicon cells, whereby they are covering the entire production chain and are making the new developments ready for production in a short time. With their developments they want to reduce the costs of solar power by a third.

In the “SONNE” project, researchers and developers from ten companies and four research institutes are working to increase the efficiency of models made of crys-talline silicon cells in comparison with previous standard modules. At the same time they also want to improve the service life of the modules. Their production shall be further automated at an industrial scale and thus made cheaper. The technology developer Solarworld Innovations is coordinating this research con-sortium and the German government is funding the cooperation as part of the “Photovoltaics Innovation Alliance”. “We have quite a lot in store. We intend to increase the module output from today’s 240 to 250 watts to considerably more than 300 watts. By achieving longer module service lives and optimised production processes, we intend to reduce the cost of solar power by around a third,” explains Dr Karl-Heinz Stegemann, coordinator of the research project and section head at Solarworld Innovations. The aim is to achieve module efficiencies of at least 20 % for monocrystalline silicon and 17.8 % for multicrystalline silicon. This will make it necessary to optimise all parameters along the process chain: the researchers and developers are improving the process flows as well as the cell and module design, and are selecting optimum

This research project is funded by the

Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)

materials as well as process stages and technologies. Prototypes are being used to verify their ability to be transferred into practice. The initial results of the research project, which is divided into four sub-projects (Fig. 1), are already available. Better efficiency through narrower contactsOne way to improve the efficiency of solar cells is to print thinner contact lines on the cells. This increases the active cell surface area and reduces the shading. A demonstration system has been developed and begun operation at the specialist mechanical engineering com-pany, Jonas & Redmann. It applies the silver paste for contacting as part of a non-contact, fine line print process. The first pilot production was conducted at the end of 2012 with a 40-µm finger width and 80 fingers. An increase in efficiency of 0.2 % was verified on mcSi and cSi high-efficiency cells. For a 30-µm finger width and 96 fingers, an increase in efficiency of 0.35 % was achieved at the laboratory scale. This was based on a new paste gen-eration that was developed as part of the project. It is planned to implement this on a mass production scale by the end of 2013. With high-efficiency cells with new rear side passivation and fine line printing with a 40-µm line width (Fig. 2), an increase in efficiency of 0.35 % with a cell efficiency of around 20 % was achieved on monocrystalline p-type Cz silicon.

Half-cell modules increase the outputThe project partners are investigating various possibilities for increasing the module output. In one of the sub-projects they are dividing high-performance solar cells before connecting them together to form a module. The results of an expenditure-benefit analysis have led them to use half-cells (78 x 156 mm), whereby the cells are halved during a newly developed laser-based separation pro-cess. For this purpose the solar cells are positioned and aligned on a conveyor belt and a laser cuts a groove (Fig 3) on the rear side of the cells. The cells are divided at this rupture point. The connection concept developed for this cell size can be implemented with both standard connection technology and a wire electrode. The new connection concept enables the output of modules to be increased by 6 Wp (relative to 245 Wp) (Fig. 4).

Reducing optical lossesResearchers at the Institute for Solar Energy Research Hameln (ISFH) are increasing the module efficiency by reducing the optical losses caused, for example, by refrac-tion and reflection. They have carried out initial simula-tions based on theoretical investigations to reduce the optical losses. In order to reduce the light reflection and increase the energy yield, particularly in poor light con-ditions, they are developing improved antireflective coatings that provide broadband antireflection proper-ties. By reducing the amount of backscattered light, they have been able to achieve an increase of 5 Wp in the initial tests relative to 245 Wp. Developers from Solarworld Innovations are measuring the light capturing effects caused by diffusely scattering rear side films in the cell cavities. The white surfaces between the cell matrix and the frame help to increase the output. In terms of the module output, no negative interactions were verified between the light capturing and antire-

flective coatings. Experiments have also confirmed that both effects largely behave additively. The ISFH is planning to carry out refined simulation cal-culations.

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Fig. 1 Science and industry are developing improved technology building blocks at all manufacturing stages for producing high-efficiency Si-cells and modules. Source: Solarworld Innovations

Fig. 2 Electron microscope image of a 40-µm-wide contact finger on monocrystalline silicon. Source: Solarworld Innovations

Fig. 3 Pilot plant for dividing solar cells: Mechanical cell divider after laser-scribing the rear side. Up to 3,600 cells can be divided per hour.Source: Solarworld Innovations

“Silicon High-efficiency Cells and Modules” Project

Sub-project 1 Sub-project 2 Sub-project 3 Sub-project 4 Development of Resistance losses & Module optics & Demonstration on high-efficiency cells cell contacting embedding pilot line

Further development of solar cells and PV modules based on the current standard technology

Development of modular technology building blocks:

n-type Si | New embedding materials | Light capturing | New electrodes | Selective emitters Laser-assisted processes | New metallisation concepts | Surface passivation

Cell efficiency Reduction of optic and ohmic losses; Verification of 2 % absolute increase in the module service life production-readiness

3.5 % absolute increase in module efficiency 5-year increase in the module service life

33 % reduction in cost of PV electricity

The antireflective coating still needs to be improved in terms of homogeneity, adaptation to the solar cell colours, ageing resistance and cleaning behav-iour. Comparing different processes and coatings has shown that cheaply

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The photovoltaic industry of the future

The projects in the Photovoltaic Innovation Alliance are carrying out research on future production and on increasing competitiveness. In the CIGSfab project, the MANZ plant engineering company and the Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW) Baden-Württemberg are optimising the production of thin-film modules on a factory scale. In September 2012, they achieved a world record module efficiency of 14.6 % under production conditions. This corresponds to the efficiency of multi crystalline silicon. The developers believe that the efficient production technology deployed by CIGS-fab will therefore lower the production costs of solar power to a price level of around 8 euro-cents/kWh in Germany and to around 4 euro-cents/kWh in southern Europe.The aim of “FutureFab” is to achieve the next genera-tion of solar factory: cell and module manufacturers are also working together with photovoltaic suppliers to drive forward innovations in cell and module con-struction. The intention is to combine newly developed cell and module concepts with photovoltaic system components to form optimised process chains.This close cooperation accelerates the learning cycles and thus the development and implementation of in-novations. New solar cell technologies such as laser doping can be immediately tested in demonstration plants at cell and module manufacturers. Based on cell efficiencies above 20 % for crystalline silicon solar cells, the intention is to show that it is possible to lower the manufacturing costs per watt-peak by 30 %.The manufacture of conventional silicon modules will become cheaper if expensive materials can be replaced. This will be even better if the cell efficiency can be increased at the same time. For this purpose, re-searchers in the “LasVeGas” project are developing a new kind of coating technology for the metallisation of the cell surface. The coordinator, Dr Holger Kühnlein from Rena GmbH, explains: “The material costs can be drastically reduced by using copper instead of silver. With optimised process and operational steps, we also want to further improve the capacity of conven-tional silicon modules – while saving up to 10 % of the total production costs.” The results shall be transferred to industry-compatible plant technology and implemen-ted in production.

producible sol-gel coatings do not bond well enough. Expensively annealed vacuum coatings, on the other hand, are durable and homogenous. Data from the test field belonging to the INTERPANE project partner confirm that AR coatings increase the yield by approximately 4 % (Fig. 5).

New glass-glass module The newly developed glass-glass module is more durable (lasts 30 years), the degradation with 0.35 % p. a. is lower and the yield is therefore 20 % higher. The use of two 2-mm-thick panes makes it lighter than a comparable glass-film module. It is already scheduled to enter the market this year.

Fig. 5 The broadband antireflection caused by the applied antireflective coating improves the light absorption and the behaviour in oblique light. Source: Solarworld Innovations

Fig. 4 The halved cells are connected together according to an optimised concept. The resulting modules are considerably more powerful than comparable modules with entire cells. The expected power increment of approximately 6 Wp has been confirmed in experiments. Source: Solarworld Innovations

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BINE-Projektinfo 10/2013

Photovoltaic Innovation Alliance With the support of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety and the German Federal Ministry of Education and Research, more than 120 research institutes and solar companies from all production levels joined the Photovoltaic Innovation Alliance in 2010 with the aim of further developing PV technology in Germany to ensure its international competitiveness. The German government is contributing more than 100 million euros to the projects in the Innovation Alliance, which runs from 2011 to 2015. As part of a further funding announcement, 50 million euros can now be applied for as part of further research projects.At the presentation of the initial interim results for the ongoing projects, the Director General of the German Solar Industry Association (BSW), Carsten Körnig, said: “Hardly any other industry has been able to show similar cost reduction curves in such a short space of time. The prices for solar power systems have more than halved in the last three years alone.” The research initiative is funding 28 industry-led joint projects, and industry and research institutes are working closely together in all projects to ensure that companies can implement the new developments as quickly as possible. The experts are investigating the entire process chain to find ways to improve it. Whereas the researchers in one sub-project are endeavouring to reduce the material costs for solar power systems, others are working to increase the efficiency and durability of the solar modules or to improve the manufacturing processes in technical and economic terms. All are united by the goal of making the jump from the laboratory to practice as quickly as possible. Thanks to the close integration of research, development and industry in the respective projects, new ideas can be directly tested under realistic production conditions and innovations can be quickly implemented in practice.With this joint initiative for quality and efficiency, the German researchers and manufacturers can stabilise their high technical quality in photovoltaics.

Project participants >> Project coordination: Solarworld Innovations GmbH, Freiberg, Germany, Dr Karl-Heinz Stegemann,

Karl-Heinz.Stegemann@sw-innovations.de>> Project partners:

Solar Factory GmbH, Freiberg, Germany University of Applied Sciences Mittweida, Germany Technische Universität Chemnitz, Germany Momentive Performance Materials GmbH, Leverkusen, Germany Fraunhofer Institute for Solar Energy Systems (ISE), Freiburg im Breisgau, Germany Institute for Solar Energy Research Hameln (ISFH), Germany Heraeus Materials Technology GmbH & Co, Hanau, Germany SITEC Solar GmbH, Neuruppin, Germany Berkenhoff GmbH – BEDRA intelligent wires, Heuchelheim, Germany RENA GmbH, Gütenbach, Germany JRT Photovoltaics GmbH & Co. KG, Malterdingen, Germany USK Karl Utz Sondermaschinen GmbH, Limbach-Oberfrohna, Germany Jonas & Redmann – The Automation Company, Berlin, Germany

Links and literature (in German) >> www.innovationsallianz-photovoltaik.de | www.photonikforschung.de

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Project organisationFederal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)11055 Berlin Germany

Project Management Organisation Jülich Research Centre Jülich Dr. Sven Macko 52425 Jülich Germany

Project number 0325277A-K

ImprintISSN0937 - 8367

Publisher FIZ Karlsruhe · Leibniz Institute for Information InfrastructureHermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen Germany

AuthorGerhard Hirn

Cover imageSolarworld Freiberg

CopyrightText and illustrations from this publication can only be used if permission has been granted by the BINE editorial team. We would be delighted to hear from you.

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