Solar Cells and Modules on Flexible Substrates
High-Efficiency Thin Film Solar Cells and Modules Based on Complex Quaternary Chalcopyrite Materials on Flexible Dielectric and Metal Substrates
Tech Area / Field
- NNE-SOL/Solar Energy/Non-Nuclear Energy
- INF-ELE/Microelectronics and Optoelectronics/Information and Communications
- NNE-BCM/Batteries and Components/Non-Nuclear Energy
- NNE-EPP/Electric Power Production/Non-Nuclear Energy
8 Project completed
Senior Project Manager
Ryzhova T B
B.I. Stepanov Institute of Physics, Belarus, Minsk
- Scientific-Practical Materials Research Centre NAS of Belarus, Belarus, Minsk
- University of Strathclyde, UK, Glasgow\nSolarion GmbH, Germany, Leipzig\nUniversity of Toronto, Canada, ON, Toronto\nUniversitat Leipzig / Institut fuer Mineralogie, Kristallographie und Materialwissenschaft, Germany, Leipzig\nTechnical University, Germany, Freiberg
Project summaryThe main objectives of the Project are to develop the design and manufacturing technology of high efficiency solar cells and solar modules on the basis of chalcopyrite Cu(InGa)Se2 and Cu(InZn)Se2 compounds on flexible metal and anodized metal substrates by utilization of standard industrial equipment.
Present status of the field. The project relates to development of non-nuclear ecologically clean renewable energy sources based on utilization of solar radiation energy. Solar radiation is most common, cheap, ecologically clean, and renewable energy source. There are many national and international state and private companies attributing attention to development of solar radiation direct conversion photovoltaic devices and station. The final goal of it is to replace non-renewable natural resources (oil, gas, coal, etc.) by just “endless” widespread energy source to every country.
The tendency of the recent decade has been connected with development of cheaper technologies of SC formation based on thin films of semiconductor materials. Recent research results have shown that the quaternary chalcopyrite semiconductors Cu(In,Ga)Se2 (CIGS), Cu(In,Zn)Se2 (CIZS) are among the most promising materials for application as light absorbing layers in thin-film SCs. Compared with other materials, these compounds possess very large values of the light absorption coefficient in the visible and near-infrared range allowing the production of high-efficiency and lightweight solar cells (an efficiency of more than 18% has been achieved). At present, high-temperature polished glass is mainly used as support substrate for thin-film SCs. However, such glasses are rather expensive. The SCs, based on them, have large weight, low reliability under wind stresses and mechanical impacts. Flexible metal substrates present an alternative fabrication route. The latter are advantageous owing to reduced mass parameters, higher durability and effective heat sink, which re-enforce their undoubted prospects for self-contained and space energy source applications.
However, the development of solar cells and solar modules based on thin-film semiconductor quaternary compounds and flexible substrates has not yet moved beyond the laboratory investigations bounds. So far there has been no well-reproducible and inexpensive process for fabrication of such solar cells suitable for commercial production of high-efficiency large-area devices. Nor there has been a technology developed to form SC modules on such substrates. Advancement in the field of photovoltaic energy sources resulting in about two-fold reduction of SC and SM cost as compared to the present level will create conditions for a wide use of SCs in industry and will considerably lower the dependence of consumers on non-renewable resources (oil, gas and coal).
Influence of the project on progress in the field. In principle, the novelty of the Project consists in using an original approach to solutions of a number of problems which, as a whole, are directed at increasing the efficiency of thin-film SCs on flexible substrates. Thus, a simple and inexpensive technology will be developed for anodizing and modification of metal foils (in particular, of Al), which will ensure good dielectric properties of coatings required for SM formation on a common substrate and will be determined by the possibility of realizing controlled orientation and growth of quaternary compound crystals and the controllable contents of sodium introduction ways. Absolutely new in the field will be the use of a Cu(In,Zn)Se2 compound, proposed by the authors, which is simpler synthesized and offers high efficiency. Works will be performed to find materials for buffer layers alternative to CdS and develop methods of deposition more suitable for commercial applications as compared with CBD, will be investigated the influence of luminescent additives to a buffer layer. Based on mathematical modelling and experimental results will be determined the perspective ways of SC efficiency increase, will be evaluated the influence of some new technical decisions on improvement of SC photo-electric characteristics, and will be worked out simple SC and SM fabrication technology. This technology could be used to fabricate high-efficiency solar cells and may be successfully extended to manufacture large-area photovoltaic modules on flexible substrates.
Project participants. The State Scientific Institution 'Institute of Electronics’ of the Belarus National Academy of Sciences and the State Scientific Institution 'Institute of Solid State Physics' of the Belarus National Academy of Sciences have been engaged for several decades in research and development for military applications. Specialists of these institutions have accumulated a solid experience in the fabrication and characterization of optoelectronic detectors based on semiconductor structures, optoelectronic components for optical guiding of seen and near IR ranges of a spectrum. High qualifications and experience of the staff are demonstrated by a successful implementation of the previous research and development projects aimed at creation of optoelectronic devices, solar cells, and micromechanical devices based on anodizing aluminium. The project is based on the results of detailed research conducted by the Project participants, in particular, within the ISTC B542 project. Thin film samples have been studied in the Leipzig University and demonstrated high structural, physical and photoelectric properties and reproducible composition. [E.P. Zaretskaya, V.F. Gremenok, V.B. Zalesski et.al. Properties of CuInSe2 Polycrystalline Thin Films Prepared by Selenization of Co-Sputtered Cu-In Alloys // Solid State Phenomena, 2001. Vols.80-81. P. 287-292] [Efremov G.I., Mukhurov N.I. Anodic alumina as a basis for various purposes microelectromechanical devices // SPEI,P, 2001. Vol.4557. P.467-470].
Expected results. Project category – applied research and demonstration of technology. The following scientific results will be obtained: materials will be chosen and method will be found for processing of metal foils, including anodizing and modification of surface, which will improve the characteristics of absorbing CIGS and CIZS layers; methods will be developed for formation of Cd-free buffer layers which will be suitable for large-scale production; the materials, layout and technology of formation of contacts will ensure low electric resistance and low surface recombination rate on contacts to the buffer and absorbing layers; a technology will be worked out for fabrication of SCs and SMs on flexible substrates. It will be possible to use the technology for making highly efficient SCs and production of large-area solar modules.
Commercial importance of the Project is based on the fact that thin-film SCs and SMs on flexible metallic substrates are cheaper and have essential advantages in various applications as compared with monocrystalline and thin-film SCs based on glass substrates. The devices will find a wide area of applications as reliable self-contained sources of electricity supply. Implementation of the Project based on standard process equipment available at microelectronic production facilities will make it possible to ensure fast manufacturing application of Project results.
Project results application domains. Grid-connected residential photovoltaic (PV) systems, communication, consumer products, off-grid rural PV systems (developing countries), PV-diesel hybrids, off-grid residential and commercial PV systems, on-grid central power PV systems, space equipment.
Meeting ISTC goals and objectives.
- Providing weapons scientists and engineers of the Institute of Solid State and Semiconductor Physics, and Institute of Electronics, Minsk, Republic of Belarus (there quota of participation in the project is more than 67%) opportunities to redirect their talents to peaceful activities.
- Promoting integration of scientists involved in the Project into the international scientific community.
- Supporting basic and applied research and developing technologies for peaceful purposes, notably in fields of environmental protection and energy production. The scientific objective will be the preparation and modification of thin film solar cells and modules on flexible substrates containing non-toxic compounds by means of using cheap techniques.
- Contributing to the solution of national and international technical problems (other than those mentioned above). An important objective of this joint project is scientific exchange between different participants. Therefore a part of requested financial support is related to maintenance grants for researches coming from CIS states.
- Reinforcing the transition to market-based economies responsive to civil needs.
Scope of activities. Project duration is estimated to be 30 months. Total Person-Days of Project Effort is 12799 man*days, including 8749 man*days for weapon scientists and engineers. The proposed Project will focus on the following five tasks which will be solved in succession: 1) investigation of processes of formation of insulating layers on the surface of foils of valve metals to be used as substrates of thin-film solar cells and modules, 2) development of methods to improve structural and electrophysical characteristics of CIGS and CIZS films on metal and dielectric substrates, 3) development of methods for formation of Cd-free buffer layer suitable for use in commercial production, 4) development of a technology for making low-resistance contacts, 5) development of fabrication technology for high-efficiency SCs and SMs on flexible substrates. For resolving this tasks will be (it is) carried out: preparation and modification of valve metals foils surfaces, dielectric layer formation on their surface by dint of anodizing and deposition methods, deposition of Cu, In, Ga, Zn precursors by vacuum deposition methods, and compound synthesis in metal selenium vapours. CdS, ZnO, Zn(O,S)OH buffer layers will be deposited by CBD, spray, pyrolysis, and modified ILGAR methods, Mo, and ZnO films will be deposited by magnetron sputtering method. The methods for measuring electrical and physical parameters, optical characteristics of films, methods of X-ray and structural analysis, IR spectroscopy, transmission and scanning electron microscopy, Auger spectroscopy, STM, AFM, computer modelling of solar cells, and measurements of SC photoelectrical parameters will be used for investigations. Some part of studies will be performed jointly by using collaborators' equipment.
Role of foreign collaborators. It is planned to conduct information exchange and joint research at all stages of the Project implementation. Discussions will be arranged of scientific and practical issues as well as testing of SC samples fabricated within the Project. Joint recommendations will be worked out on how to improve SC and SM parameters. The results of the Project will be demonstrated by means of the joint publications and participation in international conferences and seminars.
Technical approach and methodology. It is anticipated to form dielectric coatings by using both deposition techniques and anodizing technology well developed and established by the Project participants. It is planned to select a number of valve metals meeting the above requirements, work out anodizing regimes and study their electrophysical and mechanical properties. It is planned to use methods of controlled sodium incorporation in the process of synthesis of CIGS and CIZS compounds. In particular, the possibility will be studied of formation of nanoporous structure in the process of foil anodizing and introduction of controlled amount of sodium therein. The effect of sodium concentration, the size of nanopores and method of porosity generation on the growth and size of crystals of chalcopyrite compounds will be investigated with the view to optimize modes of formation of CIGS and CIZS films on metallic and modified substrates. Studied will be conducted which will enable selection of technology and materials for making Cd-free buffer layers based on methods more acceptable for commercial production (Spray pyrolysis, modified ILGAR method) of SCs and SMs on flexible metallic substrates. To evaluate the amount of these effects, mathematical model will be developed of a CIGS solar cell with due account of surface recombination losses on the contacts. Based on this model requirements for contact metallization will be defined. Experimental works will be carried out to optimize material and contacts to absorbing and buffer layers. Materials will be selected and technology developed for formation of luminescent layer, which will improve conversion efficiency in the short-wave radiation region. These works will be done by using methods available for measurement of electric parameters of contact pairs, SEM, mathematical modelling and photoluminescence. Based on the obtained results, SC samples will be produced with various compositions, buffer layer and contact materials to achieve maximum conversion efficiency in terrestrial environment (AM 1.5). Their output photoelectric characteristics will be examined and SC design/fabrication technology selected which will ensure the best possible characteristics. Based on obtained results will be proposed SMs formation technology on flexible substrates with SC interconnections made by integrated technology. It is supposed that this task will be completed in close co-operation with the collaborators.
The rights for intellectual property created in the course of the Project implementation will be protected in accordance with the legislation of the Republic of Belarus and the procedures established by the ISTC.