Defense of the dissertation for the degree of Doctor of Philosophy (PhD) by Kalygulov Dastan in the specialty «6D072300 – Technical Physics»

L.N. Gumilyov Eurasian National University, a dissertation defense for the degree of Doctor of Philosophy (PhD) by Kalygulov Dastan on the topic «Purification of Kazakhstan metallurgical silicon to «solar» quality for use in the production of photovoltaic elements» in the field of «6D072300 - Technical Physics».

 

The dissertation was completed at the Physics Center of the International School of Engineering of the East Kazakhstan Technical University named after D. Serikbaev and the ECM GreenTech laboratories in the city of Ust-Kamenogorsk (Kazakhstan Solar Silicon LLP plant).

 

The language of defense is russian

Official reviewers:

Shunkeyev Kuanyshbek Shunkeevich - Doctor of Physical and Mathematical Sciences, Professor, Director of the Research Center «Radiation Physics of Materials» of Aktobe Regional University named after. K. Zhubanova (Aktobe, Republic of Kazakhstan);

Dina Igorevna Bakranova - Doctor of Philosophy (PhD), Associate Professor of the General Education Faculty (Physics Faculty), Kazakh-British Technical University (Almaty, Republic of Kazakhstan).

 

Temporary members of the Dissertation Committee:

Tnyshtykbaev Kurbangali Bainazarovich - Doctor of Physical and Mathematical Sciences, State Scientific Research Laboratory of Functional Materials and Electronic Engineering, Institute of Physics and Technology (Astana, Republic of Kazakhstan);

Serikov Timur Maratovich - Doctor of Philosophy (PhD), Associate Professor of the Department of Physics and Nanotechnology at Karaganda University named after E.A. Buketova (Karaganda, Republic of Kazakhstan);

Baimukhanov Zein Kairbekovich - Doctor of Philosophy (PhD), Associate Professor of the Department of Technical Physics, ENU named after. L.N.Gumilyov (Astana, Republic of Kazakhstan);

Daurenbekov Dulat Khayretenovich - Doctor of Philosophy (PhD), Associate Professor of the Department of Technical Physics, ENU named after. L.N. Gumilev (Astana, Republic of Kazakhstan).

 

Academic Advisors:

Plotnikov Sergey Viktorovich - Doctor of Physical and Mathematical Sciences, Professor of the Center for Physics of the International School of Engineering, East Kazakhstan Technical University named after D. Serikbaev (Ust-Kamenogorsk, Republic of Kazakhstan);

Philippe Lay - Doctor of Philosophy (PhD), General Director of ECM Greentech (Grenoble, France).

 

The defense will take place on March 06, 2024, at 02:00 PM at the Dissertation Council in the field of training «8D053 - Physical and Chemical Sciences» («6D072300 - Technical Physics», «8D05323 - Technical Physics») of the L.N. Gumilyov Eurasian National University. The defense meeting is planned to be held online.

Link: https://clck.ru/38Hng4  

Address: Astana, K.Munaitpasov str. 13, № 3 academic building of  L.N. Gumilyov Eurasian National University.

Abstract (English): Relevance of the work. In recent years, there has been an upward trend in energy consumption throughout the world, driven by the rapid pace of global economic development, population growth, and the depletion of available fossil fuel reserves. In this regard, the use of renewable energy sources is gaining popularity in many countries around the world. Among renewable energy sources in most countries of the world, solar energy is of paramount importance since it has no equal in terms of environmental friendliness and accessible resource base. As evidenced by global experience in energy development, the future belongs to solar energy based on the latest technologies. The main and most promising form of using solar energy is photovoltaic semiconductor systems for directly converting solar radiation into electrical energy. The advantages of such semiconductor converters of solar energy into electrical energy are efficiency, noiselessness, environmental friendliness, and the ability to work in diffuse light, cloudy conditions, and even rain. Despite numerous studies and new materials used to create solar cells, silicon remains the most popular raw material in solar energy. Currently, the share of solar cells created based on crystalline silicon is about 95% versus 5% created based on thin-film technologies. The cost of a solar cell directly depends on the price of silicon, since 70-75% of the cost of a solar cell is determined by the cost of silicon. Therefore, for the further development of the photovoltaic industry Improvements in lower-cost technologies for producing crystalline silicon are needed. In Kazakhstan, according to expert estimates the potential of solar energy is very significant. In this regard, at present, alternative energy in the Republic of Kazakhstan is positioned as one of the vectors for the development of the energy complex, as evidenced by the work carried out at the State level to form a regulatory framework and support measures in this area. Purpose and objectives of the research. The purpose of this work is to study the mechanisms of generation and propagation of characteristic defects present in quasi-monocrystalline silicon and their effect on the electrical properties of the material. Optimization of directional crystallization processes to reduce impurities that reduce the efficiency of photovoltaic elements. To achieve the goal, experiments and studies were carried out, including the following tasks: 1. Production of semi-industrial-scale silicon ingots for modeling production process parameters and studying the mechanism of formation of background dislocations during crystal growth; 2. Study of the influence of impurities on the properties of silicon, by annealing and four-point bending tests at high temperatures to obtain information on the kinetics of defect formation; 3. Determination of mechanisms for reducing the nucleation and propagation of defects in silicon crystals; 4. Study of the recombination activity of crystal defects. The object of study. Quasi-monocrystalline silicon ingots grown using the “monolike” technology, and a study of the formation of dislocation structures during the growth of ingots, silicon blocks of various sizes (156mm x 156mm x 240mm, 75mm x 15mm x 3mm), and wafers (156mm x 156mm x 200 µm) from the obtained ingots. The choice of this type of silicon and growth method is due to its practical significance and prospects for use in the photovoltaic industry. Research methods. To grow silicon crystals and obtain more detailed data, four different directional crystallization furnaces of different sizes and growth modes were used. A four-point hot bend test was performed on silicon samples using alumina wafers and rods. Two methods were used to study crystallographic defects: classical X-ray topography and rocking curve imaging (RCI). Wafers produced from ingots have been used to obtain characterizations such as resistivity, minority carrier lifetime, photoluminescence and Fourier transform infrared spectroscopy (FTIR). Main provisions submitted for defense: 1. Systematic etching of the damaged layer on the surface of the seed and adaptation of the atmosphere above the melt of the growing silicon crystal minimize the concentration of background dislocations when growing quasi-monocrystalline silicon ingots. 2. Doping with germanium slows down the propagation of dislocations in the direction of the volume of crystalline silicon up to complete suppression in single crystals. The germanium impurity interacts with point defects and causes deformations of the silicon lattice, slowing down the movement of dislocations. The presence of grain boundaries in quasi-monocrystalline silicon partially absorbs excess radial stress, so that Ge doping potentially reduces the dislocation density in grains where local shear stress does not exceed ~1 MPa. 3. The formation of subgrain boundaries from seed compounds can be avoided by adjusting the relative disorientation between the seeds. When a crystal grows with an <100> orientation, instead of subgrains, defect-free grain boundaries are formed with a disorientation of no higher than ~ 6°. 4. Silicon ingots grown using monolike technology are less expensive and can be used to produce wafers of silicon to create solar elements. Scientific novelty. During the work, the following results were obtained for the first time: 1. Data on the mechanisms of formation of background dislocations during the growth of quasi-monocrystalline silicon ingots of various sizes in different furnaces are analyzed. 2. The positive effect of germanium impurity on slowing down the propagation of dislocations in the bulk of crystalline silicon has been established. 3. Based on theoretical research and experimental work, optimal conditions for growing quasi-monocrystalline silicon ingots have been developed. 4. Experimental studies were carried out on the defects present in quasi-monocrystalline silicon and their effect on the electrical properties of the material, which showed the possibility of using the resulting silicon to produce photovoltaic elements. Practical significance of the work. Practical results have been obtained in the study of the structure and dynamics of the formation of background dislocations in a quasi-monocrystalline silicon ingot with the influence of Ge doping on the formation of these structures (analysis of dislocations in silicon, deformation, and the influence of impurities on the quality of blocks and wafers). The introduction of an experimental method of growing silicon crystals using the “monolike” technology has prospects for reducing energy costs for the production and purification of silicon to produce solar elements, using raw materials from Kazakhstan. By using the “monolike” technology, it is possible to reduce the consumption of expensive resources to produce solar cells with an efficiency value no lower than analogs made from monocrystalline silicon on an industrial scale. It is possible to modernize the existing line at the Ust-Kamenogorsk plant in the form of the production of silicon wafers and photovoltaic cells. Connection of work with research projects. This study was conducted at KazPV production sites at factories of the Republic of Kazakhstan in the cities of Ushtobe (Silicon plant) and Ust-Kamenogorsk (Assembly of photovoltaic elements) with the participation of the French industrial company ECM Greentech (France). Approbation of work. The results of the dissertation work were presented and discussed at 5 international and republican conferences: III international scientific and practical conference. Innovations in science and practice (Prague, Czech Republic, 2017); XXXII International Scientific Conference. Current scientific research in the modern world (Pereyaslav-Khmelnitsky, Ukraine, 2017); 13 Russian conference. Physic-chemical problems of renewable energy (St. Petersburg, Russia, 2017); International scientific and technical conference dedicated to the 60th anniversary of the formation of EKSTU named after. D. Serikbaev. The role of universities in creating an innovative economy. (Ust-Kamenogorsk, Kazakhstan, 2018); Second International Scientific Conference "AESMT'19" ALTERNATIVE ENERGY SOURCES, MATERIALS AND TECHNOLOGIES (Sofia, Bulgaria, 2019). Publications. The main results of the research were published in 6 articles, of which 1 article in a highly rated scientific publication indexed in the Web of Science Core Collection and Scopus database, 5 articles in a publication recommended by the Committee for Quality Assurance in Science and Higher Education of the Ministry of Science and Higher Education of the Republic of Kazakhstan, 5 abstracts of reports in collections of republican and international conferences. of Science Core Collection and Scopus databases indicating their scient metric indicators: 1. D. Kalygulov, Plotnikov, S., Lay, P. Characteristics of photovoltaic cells using monolike technology with technical and economical efficacy, and comparison with the traditional preparation method //Eastern-European Journal of Enterprise Technologies - 2022, Vol. 5 No. 5 (119), pp. 6-15. (IF= 1.074, Q3, CiteScore =2.1, 45% percentile). Articles recommended by the Committee for Quality Assurance in the Field of Science and Higher Education of the Ministry of Science and Higher Education of the Republic of Kazakhstan: 1. I.A. Klinovitskaya S.V. Plotnikov, D. Kalygulov, Research into the production technology of photoelectric converters. Bulletin of EKSTU named after. D.Serikbaeva. - 2017. - No. 4(78). - P.67-73. ISSN 1561-4212. 2. Klinovitskaya I.A. Betekbaev A.A., Plotnikov S.V., D. Kalygulov, Prospects for the development of production of photoelectric converters in the Republic of Kazakhstan. Bulletin of the Eurasian National University. L.N. Gumileva. - Ust-Kamenogorsk. 2017. - No. 4 (119). - P.103-111. ISSN 2616-6836. 3. D. Kalygulov, I. Klinovitskaya, T. Turmagambetov, A. Pavlov, S. Plotnikov, B. Mukashev, A. Serikkanov, Zh. Agabekov, D. Kantarbaeva. High-tech production of photo-energy in Kazakhstan based on the Sarykol quartz deposit. "Izvestia of the National Academy of Sciences of the Republic of Kazakhstan. Physics and mathematics series", Volume 3, Number 325 (2019), 120 - 129 p. ISSN 2518-1726 (Online), ISSN 1991-346X (Print). 4. Klinovitskaya, S. Plotnikov, D. Kalygulov, P. Lay. The investigation of the properties of solar cells based on Kazakhstan silicon. Bulletin of the Karaganda State University, “Physics series” - English. 2019. - No3(95)/2 - С.34-4 ISSN 2518-7198. 5. Klinovitskaya, S. Plotnikov, D. Kalygulov, P. Lay. Increasing the efficiency of photovoltaic cells based on Kazakhstan silicon. Bulgarian chemical communications - Bulgaria.2019.-V51, Special Issue F. - 41-48p. ISSN: 0324-1130. Personal contribution of the author: A preliminary literature analysis of the study, conduct of the experiment, and data processing were performed. The evaluation of the experiment results and the main conclusions were carried out under the guidance of the domestic scientific consultant S.V. Plotnikov, as well as the foreign scientific consultant Phillip Lay. Structure and scope of work. The dissertation consists of 98 typewritten pages of text, including 50 figures, as well as 117 literary sources reflecting the use of literary and experimental data obtained during the study. The dissertation includes an Introduction, four main chapters, a Conclusion, and a List of References. Each chapter of the dissertation ends with brief conclusions, and the Conclusion presents the main results and conclusions of the experimental work carried out. The Introduction provides brief information about the relevance of this research, the reasons for choosing crystalline silicon as objects of research, formulate the purpose and objectives of the research, reflect the main provisions submitted for defense, and describes the scientific and practical significance of the dissertation. Chapter 1 summarizes the current state of the art in the study area. Various methods for growing silicon crystals are described, with an emphasis on quasi-monocrystalline processes. This chapter also includes a review of the effects of impurities on silicon dislocations, strain, and crystalline material quality. In addition, it describes the presence of intrinsic impurities in silicon and two-dimensional extended defects. The electrical properties of silicon are also described. Chapter 2 describes the experimental methods used for the crystal growth process, four-point bending tests, and advanced characterization using a synchrotron X-ray source. Other structural, chemical, and electrical properties are also described, including methods for determining the rate of charge carrier recombination induced by defects. Chapter 3 is devoted to the analysis of the structure and dynamics of the formation of a background network of dislocations in quasi-monocrystalline ingots. The corresponding deformation of the crystal lattice is expressed quantitatively. The effects of stress, stress time, and impurity doping on the formation of such structures are studied through silicon wafer annealing experiments and four-point bending tests at elevated temperatures. The development of two-dimensional extended defects, i.e. subgrains and grain boundaries, in quasi-monocrystals, is also studied, with particular attention to the influence of misorientation between grains and the use of defective grains for defect propagation. Part 3 of the chapter relates the structure and level of contamination of defects by impurities with their recombination activity. Chapter 4 discusses B, P, and Ge doping during the growth of quasi-monocrystalline ingots. The main attention is paid to the isolation of an element associated with the specific conditions of the growth process of a quasi-monocrystalline grain, and the associated crystalline defects caused by increased local stress. The Conclusion presents the results obtained and formulates the main conclusions of the experiments. General conclusions summarize the information obtained about the mechanisms of defect formation and the practical conclusions made regarding this process. In addition, further directions of research in this direction are proposed.

Dissertation