Figure 1: Scheme of the "roof tile" interconnection of solar cell stripes to strings of defined voltage and the interconnection of the strings in parallel by using bus bars for definition of output power.
This research project is supported by the European Commission under the Fifth Framework Programme and contributing to the implementation of the Key Action 6 "Economic and efficient energy for a competitive Europe" within the Energy, Environment and Sustainable Development.
| Title | Improved CISCuT Solar Cells, Manufactured Roll-to-Roll in a Base Line |
|---|---|
| Acronym | CISLINE |
| Proposal No. | NNE5-2001-00069 (CISLINE) |
| Contract No. | ENK6-CT-2001-00519 |
| Type of Project | RS |
| Thematic Priority | 6.5.2 |
| Project Start | January 2002 |
| Project Duration | 36 Months |
| Contact | Dr. Michael Winkler IST - Institut für Solartechnologien gGmbH Im Technologiepark 7 D-15236 Frankfurt (Oder) Telephone (+49 335) 5 63 32 09 Facsimile (+49 335) 5 63 31 50 E-Mail cisline@ist-ffo.de |
A new approach has been introduced for a thin film technology, in which Cu/In/S based solar cells are continuously fabricated on a Cu-tape (CISCuT). Flexible modules encapsulated into polymer foils are assembled by roof tile interconnecting of stripes of this cell tape (figure 1). This technology is suitable for mass production of low cost photovoltaic systems. In middle to long terms production costs will be reached that are below 0,5 Euro/Wp for solar cells and in the range of about 1 Euro/Wp for complete modules. It can help to reach the target defined in the EU-white paper to install a photovoltaic capacity of up to 3 GWp by 2010.
Figure 1: Scheme of the "roof tile" interconnection of
solar cell stripes to strings of defined voltage and the
interconnection of the strings in parallel by using bus
bars for definition of output power.
The basis of this project is a base line, which can fabricate solar cells in five consecutive roll-to-roll processes and modules in an automated assembly line. Assuming a module efficiency of 5 %, a throughput of 1,8 m2/h, an availability of 85 % and a yield of also 85 %, a theoretical production output of 100 kWp/year has been estimated for the base-line.
The main argument to work on CISCuT based cells and modules is to arrive at low cost solar devices suitable for fabrication with regard to market and manufacturing prospects. Therefore the basis of the technology - the quasi endless solar cell tape - must have a reproducible high performance and stability. This is why the project is mainly focused on research of the absorber and the cell.
Individual solar cells that have been prepared with this technique at project start show best efficiencies up to 7 %. Recombination processes and shunting problems are the main reasons for the efficiency losses. One of the main challenges of this project is to detect the efficiency losses in detail, in order to improve the cell performance. The achievement of a cell efficiency of 7 % on large areas, produced completely roll to roll in the base line, (proved at standard test structures with grid and an area of 4 cm2) and a best efficiency of 9 % will be the most important outputs of the project.
The stability of the cells will be another essential criterion for the implementation of this thin film technology. First stability tests of the above mentioned devices under one sun illumination at MPP have generally shown a decrease of the shunt resistance. The research during the project should finally improve the cell stability to a level that is suitable for pilot production planning.
The maximum cell efficiency as well as modifications in the base-line concept will give a more realistic basis for the estimation of the investment and running costs in a future pilot and series production line.
Solar modules, fabricated by this new approach are adaptable in output voltage, current and power as well as in shape and size. Thus, the modules can easily be manufactured for different applications.
A road map will be exploited to describe the further investigation and development of the CISCuT technology in middle and long terms with respect to the results of the research and development tasks. The objectives of the project will help to transform the laboratory achievements of the potential low-cost CISCuT technique into affordable and durable photovoltaic modules.
Summarised the aims of CISLINE are
to improve the efficiency and the stability of solar cell tapes, which are fabricated by the CISCuT technology in the base line, to a level, suitable for fabrication with regard to market and manufacturing prospects;
to estimate the production costs of the solar cells corresponding to the maximum of cell efficiency as well as to modifications in the base-line concept;
to exploit a road map describing the further investigation and development of the CISCuT technology in middle and long terms.
The project work is divided in five work packages (WPs):
The target of WP 1 is a better fundamental understanding of the phase formation as well as the improvement of the electronic properties of the absorber layers in order to meet the solar-device requirements. The preparation and analysis of the absorber layer samples will be focused on: Phase composition, layer thickness as well as microscopic and macroscopic morphology (optical microscopy, XRD, RAMAN, TEM, REM, AFM), defect physics (PL), diffusion length of the minorities (DSR, EBIC), and charge carrier concentration (hall effect, conductivity). The work will be divided into four tasks in order to improve the absorber quality in a step-by-step manner.
The target of WP 2 is to arrive at consistent models of the internal electronic behaviour of the cells, which are compatible with all results of electrical and non-electrical measurements of cells based on CISCuT absorber layers. The device and separately several possible buffer layers and the window layer will be investigated. The principle limitations of CISCuT based device structures will determined and an outlook will be given about the maximum value of the performance which can be expected. The results will directly be used for the experimental work for the optimisation of the cell performance.
In WP 3 the shunt behaviour of CISCuT solar cells will be studied with the main emphasis put on local defects and impurities as well as on the Cu migration inside the absorber. Local defects are investigated to analyse critical shunts with regard to the long term stability of the devices. As local shunts (hot spots) cannot be excluded during absorber preparation, a procedure for shunt passivation by electrochemical treatment will be developed. The possibility of stability limitations in CISCuT devices because of the infinite Cu source which is currently used will be investigated. Finally, it will be demonstrated that devices show a stable performance, suitable for implementation aspects.
In WP 4 the focus will be onto the technological process as a whole, fabricating devices completely. The results of the previous work packages to increase the cell performance and the stability will be transferred into the device fabrication process. Photovoltaic devices with improved properties will be fabricated by completion of the absorber in batch processes as well as by roll-to-roll processes. Devices for efficiency measurements will be prepared in standard sizes of 5 mm2, 10 mm2 and 400 mm2. The complete roll-to-roll technology for solar cell fabrication will be developed into a stable manufacturing process. For the efficiency goals the homogeneity of the layer deposition will be investigated.
The main objective of WP 5 is to ensure efficient management of the project with respect to time table, work packages, milestones, resources and partners. The second goal is the development of a detailed exploitation plan.
The project work has been started successfully. The first year of project work was characterised by an intensive sample transfer between the partners and working visits of different partners (RUG, PGE, INM) at IST. The WWW-based communication inside the project has been proven as a guarantee of effective information flow. The first half year meeting took place at ECN in Petten (NL), the second meeting was held at the new partner INM in Saarbrücken (DE). Results of successful work that has been done as planned in all five work packages have been presented.
A consortium agreement has been signed and a contract amendment for the introduction of the new partner INM has been finished.
The author of this WWW page is the IST - Institut für Solartechnologien gGmbH, which is solely responsible for the content. The WWW page does not represent the opinion of the Community, and the Community is not responsible for any use that might be made of the data appearing herein.
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