Solar Cells Based on Tin Sulfide Compounds
Thin Film Solar Cells Based on SnSx and Cu2SnZnS4 Semiconductor Compounds on Flexible, Nanostructured Metal Substrates and Superstrates
Tech Area / Field
- NNE-SOL/Solar Energy/Non-Nuclear Energy
- INF-ELE/Microelectronics and Optoelectronics/Information and Communications
- MAT-SYN/Materials Synthesis and Processing/Materials
- NNE-EPP/Electric Power Production/Non-Nuclear Energy
3 Approved without Funding
B.I. Stepanov Institute of Physics, Belarus, Minsk
- Scientific-Practical Materials Research Centre NAS of Belarus, Belarus, Minsk
- Hoseo University, Korea, Asan\nKorea Polytechnic University, Korea, Kyonggi-do\nUniversitat Leipzig / Institut fuer Mineralogie, Kristallographie und Materialwissenschaft, Germany, Leipzig\nUniversity of Strathclyde, UK, Glasgow\nGumi Electronics and Information Research Institute, Korea, Gumi\nIlie Murgulescu Institute of Physical Chemistry, Romania, Bucharest\nINFOVION Inc., Korea, Seoul
Project summaryThe Project aim. is to demonstrate new concept and enhanced performance of SnSx and Cu2SnZnS4 – based thin film solar cells (TFSC) on flexible, nanostructured metal substrates and superstrates to provide the basis for further efficiency improvements in solar module production and to develop new device concepts enabling cost reduction on the long term using relatively abundant materials, as well as environment and human health friendly design and fabrication technologies.
Current status. One of the major hurdles for photovoltaics to become more popular is that the price of electricity (cost per watt) produced by solar modules is not yet, in the most cases, competitive with that produced by conventional methods. The cost can be reduced by either improving the efficiency or reducing the production cost of photovoltaic modules. However, the roadblock to substantial cost reduction of silicon solar cells has prompted the research workers to take up the two major challenges: (i) to develop new photovoltaic materials which are also cheap, nontoxic and easy to manufacture; (ii) to fabricate low-cost high-performance solar cells for commercial mass production. Recent interest in thin film photovoltaics is primarily due to improvements in conversion efficiency of the cells and effective lowering of manufacturing cost compared to expensive crystalline and polycrystalline silicon technology. Thin film solar cells based on CuIn(Ga)Se2 and CdTe absorber materials have been produced with efficiencies of 20% and 16.5%, respectively. These results clearly indicate that high efficiency solar cells could be produced using polycrystalline materials. Problems, however, remain with these technologies. It is generally perceived that the lack of abundance of In and Ga may limit the large scale use of chalcopyrite-based technology. There are also concerns with respect to the toxicity of cadmium leading to problems with the CdTe modules disposal after use. It is possible that other materials could be used to produce thin film cells without these problems. Such candidates are SnSx and Cu2SnZnS4. These semiconductor materials have direct optical energy band gap of 1.2 – 1.7 eV, close to the optimum value required for efficient light absorption and exhibit p-type electrical conductivity with absorption coefficient as high as 104 cm-1. Furthermore, the constituent elements of these compounds are non-toxic and abundant in nature. The main argument to serve as a prerequisite to establish this work was large-scale industrial production of constituent materials (elements), their large stocks in nature and, correspondingly, low cost.. Theoretical studies indicate that solar conversion efficiencies 25% could be achieved using these semiconductor materials.
The project’ influence on progress in this area. The Project contributes in development and application of renewable ecologically clean energy sources. Research and development of solar cells composed of abundant materials without using any rare metals are extremely important in Belarus as a country of insufficient natural resources from the viewpoint of energy consumption. It also promotes long term investigations by involving Republic of Korea and EU human potential and keeping the involved Project participants’ research potential in the field of solar energy.
The participants’ expertise. The scientists taking part in the Project have considerable experience in photovoltaics proved by their publications, participation in international conferences and successful performance of two ISTC projects (ISTC – B 542 and ISTC – B 1029). This information is available on the Internet web-sites http://www.physics.by/ and http://www.istc.ru/.
Expected results and their application.
The Project category is applied research and technology demonstration.
The Project goals are to develop fabrication processes of SnSx and Cu2SnZnS4 thin films synthesis and to investigate their viability for low-cost solar cells production using standard industrial equipment and processing steps. It is expected that SnSx and Cu2SnZnS4-based solar cells will have considerable advantages compared to all known thin-film solar cells. By present, a limited amount of publications are devoted to various techniques for SnSx and Cu2SnZnS4 absorber layers synthesis and its characteristics investigation. However, significant discrepancies are observed under measuring physical characteristics depending on synthesis techniques.
Under the Project we expect to obtain the following results:
- On the base of theoretical investigations, including computer modeling of both physical processes of solar energy conversion in thin film solar cells based on SnSx and Cu2SnZnS4 and their physical parameters optimization, defining the concept for creating new designs of SnSx and Cu2SnZnS4 thin film solar cells (TFSC) on different kinds of flexible substrates and superstrates;
- carrying out experimental investigations including development of new methods and technologies to fabricate SnSx and Cu2SnZnS4 thin films;
- improving front and back contacts in view of long-term stability, conductivity, transparency (TCO),
- developing the interface engineering techniques to increase device performance and stability, as well as to reduce SnSx and Cu2SnZnS4 - type devices cost;
- providing wide range of optical, electrical and structural analysis techniques to characterize and improve the cells,
- fabricating the high performance SnSx and Cu2SnZnS4 - type solar cells up to 5 × 5 cm² device area,
Research and development of solar cells composed of abundant materials are extremely important for all countries with insufficient natural resources. Implementation of this Project will lead to techniques to be used to allow industrial production of high-efficiently thin film solar cells in Belarus. The TFSC will find applications especially at locations where no connection to the electrical power grid exists. For example, cooling of covered trucks can be performed by refrigerators powered by light-weight flexible solar cells. Another possible application is flexible solar cells on the awnings which produce electric energy under high level of solar irradiation and could be rolled for protection under bad weather conditions. High-technology applications like space technique would also profit from light-weight flexible TFSC. Besides these technical applications, combining of experimental and theoretical work will lead to new knowledge about thin films. The database and 2D simulation software will be useful for other researches working with thin films and solar cells.
Meeting the ISTC goals and objectives. Since former “weapons” scientists take part in this Project implementation and because it is exceptionally peaceful, the Project meets the ISTC goals. Adherence to these objectives can be attained by planned wide involvement of scientists and participating institutions into international scientific community through providing information on the Project during international conferences and workshops.
Scope of activities. Project duration is 30 months. Total amount of Person*days is 9140, including 5500 for weapon scientists and engineers. The Project will be performed by two institutions, namely Institute of Physics of NASB (IP NASB), and Scientific and Practical Materials Research Center of NASB (SPMRC NASB). The Institute of Physics will perform preparation of SnSx and Cu2SnZnS4 films by different techniques, fabrication of thin-film solar cells, theoretical modeling of such cells, and measure photoelectrical characteristics of heterojunctions and solar cells. The Scientific-Practical Materials Research Centre will investigate the structure properties, the surface topology and morphology, phase and chemical composition, electrical and optical (transmission, absorption and photoluminescence spectra) characteristics of the films depending on the deposition technique and conditions. Analysis of the obtained results and further investigations planning will be performed jointly.
The Project includes 5 interconnected tasks directed to solution of the final goal – fabrication of thin-film solar cells based on SnSx and Cu2SnZnS4 films. All the tasks are closely interrelated and overlap with each other. The amounts of Person*days for the tasks are: Task 1 – 600, Task 2 – 1400, Task 3 – 1300, Task 4 – 2710, Task 5 – 3130. They are:
- Task 1. Development of preparation methods for formation of SnSx thin films and nanostructured metal substrates
- Task 2. Development of deposition methods for synthesis of Cu2ZnSnS4 thin layers and investigation of their physical characteristics
- Task 3. Preparation of front and back contacts in view of long-term stability, conductivity, transparency (TCO)
- Task 4. Choice of material and technique to form buffer layer providing fabrication of high-quality p-n junction
- Task 5. Design development and fabrication of solar cells prototypes on different substrates
Role of Foreign Collaborators/Partners.
Participation of Collaborators will include joined consultations and discussions of plans and results of the Project, preparation of joined publications, comparing of results of the Project with those obtained abroad, as well as commenting on accounts (quarterly, yearly, and final). Collaborators are supposed to take part in mutual testing of the Project results, visiting laboratories, and in joint seminars.
Technical approach and methodology. The main innovation of the Project work is use of SnSx and Cu2SnZnS4 as alternative absorber materials for thin film solar cells. The constituent elements and the compounds themselves are safe for both environment and human health and abundant in nature. Defining the concept to create new designs of thin film solar cells and carrying out experimental investigations including development of new methods and technologies, using coevaporation, sulfurization, CVD and electrochemical methods, to fabricate laboratory types of SnSx and Cu2SnZnS4 solar cells on flexible, nanostructured metal substrates and superstrates. The final goal is to define the technique and, correspondingly, the processing conditions to produce high-performance solar cells, under the criteria of band-gap optimization, surface planarization, composition and physical characteristics of the films. Carry out theoretical investigations including computer modeling of both physical processes of solar energy conversion and thermal-physical processes in multilayer thin film solar cells based on SnSx and Cu2SnZnS4 as well as optimization of their physical parameters including characteristics of inpidual constituent components of solar cells. The modeling will be performed using AMPS-1D and SCAPS software to determine the optimum design components of solar cells – layers thicknesses, criteria to choose buffer layer and transparent conductive oxide, etc.. The optimized design of SnSx and Cu2SnZnS4 cells will be proposed. The choice of materials and synthesis technology for n-type buffer layer, investigation of its physical characteristics is the most complicated task. Therefore, it is planned to be guided by modeling results and experiments to choose the wide band-gap semiconductor materials having crystal lattice parameters close to SnSx and Cu2SnZnS4. As a transparent conductive layer material, it is planned to investigate ZnO:Al, ITO, TiO2, SnO2, etc. Fabrication of SnSx and Cu2SnZnS4 single solar cells and modules (up to 5 x 5 cm2 device area) and their testing to identify the critical processing conditions which could lead to optical and electrical losses affecting the performance or stability. The first solar cells will be prepared on glass substrates, then, the solar cells on flexible, nanostructured metal substrates and superstrates will be fabricated and investigated. The results of investigations will be confirmed on the Collaborators' equipment.