Juras Ulbikas - Academia.edu (original) (raw)

Papers by Juras Ulbikas

Reinventing EU energy system on a low carbon model through utilization of RES is one of the criti... more Reinventing EU energy system on a low carbon model through utilization of RES is one of the critical challenges of the 21st Century for EU economy. In recent years PV technology was the leading renewable energy technology in terms of capacity growth in Europe. Over the last 20 years, PV has already shown impressive price reductions, but without radically new technological solutions previously demonstrated linear learning rate is be hardly being achieved. Concentrated PV systems are demonstrating possibilities for significant price reduction in terms of used material cost, but are not able to defeat flat panel PV because of the need for costly tracking systems. Therefore eliminating the need of tracking by utilizing novel nanocomposite material solutions for optical elements in CPV system can be way forward overcoming CPV shortcomings proposing an effective solution for stationery CPV design.

Epitaxial silicon foils (<50 um) lifted-off using the porous silicon-based layer transfer proc... more Epitaxial silicon foils (<50 um) lifted-off using the porous silicon-based layer transfer process are used to fabricate heterojunction (HJ) solar cells. Mini-modules with efficiencies above 15% have been fabricated using standard lamination and encapsulation techniques, which have been applied to freestanding epi-Si based HJ solar cells. Analysis of this module highlights the need for bonding these cells onto supporting substrates before module fabrication. We suggest using very low-cost conductive Si carriers as the supporting substrates. Sintering of low-cost Si powder-based ingots, assisted by in-situ doping, has been done by hot pressing or casting of ingots using different types of Si powders and was followed by multi-wire sawing to fabricate thin (~170 μm) supporting highly conductive substrates. The Si material used for these substrates can, in principle, be obtained from Si waste streams, e.g. broken wafers or end-of-line cells in production lines, Si kerf or end-of-life PV modules, making this even more attractive proposition. One important aspect is the development of conductive bonding of epitaxial foils onto low-cost sintered silicon substrates.We evaluated different types of conductive bonding agents. Good mechanical stability was achieved for the bonding processes. These efforts represent the first step towards the wafer-equivalent approach of high efficiency solar cells on thin Si (<50 μm) conductively bonded to low-cost Si substrates. This approach is considered as a promising route for the low-cost Si based PV and a solution module integration of thin Si. This work is done in framework of H2020 EU project CABRISS.

Conditions for the effective phosphorus diffusion through the spun-on sol-gel layers were investi... more Conditions for the effective phosphorus diffusion through the spun-on sol-gel layers were investigated and the results are presented in this work. The n+ areas were doped to obtain sheet resistance as low as 10-20Ω/sq, and surface resistance of n area which was created underneath the barrier layer was in the interval 100-3000Ω/sq with respect to diffusion temperature, barrier material and thickness.

Journal of Sol-Gel Science and Technology, 2014

This work focuses on the dependence preparation conditions-structure-physical properties of hydro... more This work focuses on the dependence preparation conditions-structure-physical properties of hydrophobic silica aerogels, all of them prepared under subcritical drying conditions (70°C and 0.4 atm.), thus aiming at potential application as case insulation filling in heat pumps. The so prepared, millimeter scaled nanoporous hydrophobic silica aerogel granules were analyzed with standard electron microscope and atomic force microscopy, IR spectroscopy, UV/Vis spectroscopy, differential scanning calorimetry and thermal conductivity measurements. The physical properties of the aerogels were compared with commercial aerogel granules. A method for contact angle measurement of micro-droplets situated on the silica granules was proposed to quantify the level of their hydrophobicity.

Paper is devoted to the sol-gel containing dopands preparation technology. Sol-gel doping can be ... more Paper is devoted to the sol-gel containing dopands preparation technology. Sol-gel doping can be promising alternative to gas doping source for Si wafer based solar cells p-n junction formation. Sol–gel process is also an attractive alternative to other methods for synthesis of thin films for silicon solar cells because of low temperature synthesis, simple equipment to be used, thin film formability and so on. In this study sol-gel silica was synthesized using tetraethoxysilane (TEOS) as a precursor and phosphoric acid as a source of phosphate ions. Thin layer of this material is spread by spin-coating process on a surface of silicon wafer and dried to form the phosphosilicate glass (SiO2 : (P2O5)n. Coated wafer is placed into diffusion furnace and held at high temperature under nitrogen ambient for p-n junction formation. Obtained sol-gel composition were analysed by FTIR to estimate dopant concentrations. Further p-n junctions from various sol-gel were produced, sheet resistance Rs and phosporous concentrations profiles were measured for comparative analysis.

Hot Carriers in Semiconductors, 1988

ABSTRACT

Solid State Phenomena, 2004

Self-formation as a concept for irreversible evolution of the artificial object with complexity i... more Self-formation as a concept for irreversible evolution of the artificial object with complexity increase was introduced for understanding of the processes existing in microelectronics technology [1]. The concept of self-formation by itself was to some extend influenced by principles existing in biological world therefore from the very beginning there was an open question about limits of self-formation application: are we limited to the understanding of some technological processes or we can think about predicting new technological applications by applying selfformation concept. Recently developed tools for simulation of technological processes for Solar Cells manufacturing [2] clearly indicates that self-formation is becoming interesting tool for technologists trying to create and optimize microelectronic devices. The next step exploring selfformation application boundaries can be analysis of possibilities of the self-formation to demonstrate usual in biological life development and...

Journal of Solid State Electrochemistry, 2011

Gold-capped silicon nanocolumns regularly distributed over silicon substrate were obtained. The c... more Gold-capped silicon nanocolumns regularly distributed over silicon substrate were obtained. The columns length was roughly 100 nm; their deviation from perpendicular axis was less than 2°. The diameter of the columns was of the order of 10 nm or below of that. The proposed procedure of nanostructuring included the following main steps: deposition of aluminum thin layer (100–500 nm) by magnetron sputtering on (100) oriented Si wafers; formation of porous self-ordered alumina structures by electrochemical anodizing of the Al film in oxalic acid; electroless inversion of Au in alumina pores; and reactive ion etching. The obtained Si–Au structures are of importance as the platforms for biosensing applications, while the gold-free structures are of interest in photovoltaics.

Applied Physics A Solids and Surfaces, 1989

A method for quantitative characterization of chaotic dynamical systems is discussed. An electron... more A method for quantitative characterization of chaotic dynamical systems is discussed. An electronic instrument for determining the number of independent variablesk*, involved in the motion, is described. It allows one to obtain these in real time from a single observable. The suggested technique has been applied to quantification of strange attractors underlying chaotic instabilities in semi-insulating GaAs:Cr, and n-Ge, irradiated

Gels

A cost-effective solution for the synthesis of high-porosity TiO2 aerogels, which can be used as ... more A cost-effective solution for the synthesis of high-porosity TiO2 aerogels, which can be used as a mesoporous perovskite network charge-carrier material during the manufacture of solar cells, is described. The effects of the synthesis parameters (precursor (titanium (IV) isopropoxide (TIP) and tetrabutyl orthotitanate (TBOT)), additional solvent exchange (n-hexane (nH), cyclohexane (CH), and diethyl ether (DE)), subcritical drying (800 mbar vacuum, 70 °C, 8 h), aging, and calcination on the aerogel’s structure have been investigated. Methods of XRD, FT-IR, BET, Raman, STA, SEM, UV–vis, and thermal conductivity measurements were applied to find out the relation between the synthesis conditions and the properties of the synthesized aerogels. Amorphous aerogels are polydispersed systems with the highest probability of pore diameter from 0.5 to 15 nm. An nH-exchanged, aged aerogel synthesized from the precursor TIP shows the highest diameter of pores. After calcination, the aerogels ten...

Solid State Phenomena, 2004

Considering optimization of the technology and production of Solar Cells an overall goal is to lo... more Considering optimization of the technology and production of Solar Cells an overall goal is to lower the production costs per Watt through optimization of the parameters of Solar Cell. The dominant material up to now for the majority of commercially produced solar cells is crystalline silicon (c-Si). A lot of efforts has been undertaken to increase the electrical efficiency of Si based solar cells above 20% [3-5]. Unfortunately, efficiency improvements are often reached only with the help of costly process steps and as result without possibility to use such improvements in industrial products. One of the trends in achieving higher efficiency in monocristalline Si based Solar Cells is introduction of complicated spatial structure on absorbing surface of SC. Reports indicates expectations of efficiencies as high as 24% in laboratory samples but with significant raise in costs for Spatial SC production (Fig. 1). It is clear that optimization of technological steps and parameters must b...

The poster presents PV module innovations introducing and combining five PV module innovations ap... more The poster presents PV module innovations introducing and combining five PV module innovations applied to c-Si based bifacial modules and CIGS modules.

PV deployment growth is an unmatched success story in the energy sector over recent years. Howeve... more PV deployment growth is an unmatched success story in the energy sector over recent years. However, European PV manufacturers are facing a decline in production due to competition from third countries. The fragmentation of the value chain is believed to be one of the major factors for this decrease in the competitiveness. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. It pursues a significant LCOE reduction for innovative PV systems based on a hybrid combination of technological innovations and data management solutions along the PV value chain. Responding to the need of evaluating proposed innovations in terms of economic feasibility and market trends, a dedicated task force, an Exploitation Team, was introduced at the beginning of the project as a main instrument for overseeing achievement of KPI's and beyond, in the ever-changing landscape of the PV sector.

Microscopy and Microanalysis, 2018

Numerous studies in the literature report on titanium dioxide nanoparticles as a harmless, cheap,... more Numerous studies in the literature report on titanium dioxide nanoparticles as a harmless, cheap, facile, bio-compatible, chemically and mechanically stable and highly efficient photo-catalyst which can be exploited in many large-scale applications. One of the most promising techniques for the synthesis of titania nanoparticles in liquids or in polymeric matrices is pulsed laser ablation in liquids (PLAL), e.g. [1,2]. Thereby only a titanium plate and a 'green' solvent are the necessary materials.

Lithuanian Journal of Physics

ABSTRACT

Physica Status Solidi (a), 1988

ABSTRACT

Today photovoltaics (PV) has become one of the most cost-effective forms of electricity productio... more Today photovoltaics (PV) has become one of the most cost-effective forms of electricity production globally and in some regions is already the most competitive unsubsidised form of electricity. Despite positive cost and growing developments, European PV manufacturers are facing a decline in production due to competition from third countries. This decrease in the competitiveness of European PV actors is due to several factors, including a greater fragmentation of the value chain compared to competing actors. Chinese manufacturers have in particular been able to achieve synergies, economies of scale and information sharing throughout the value chain. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. Together, they target a significant LCOE reduction (26%-37%) for European-made PV by adopting a hybrid approach combining technological innovations and data management methods.

The aim of this investigation was to synthesize high porosity TiO2 aerogel by applying sol-gel an... more The aim of this investigation was to synthesize high porosity TiO2 aerogel by applying sol-gel and subcritical drying methods and to identify the influence of reagent’s nature and synthesis conditions on their structural and optical properties. Methods of XRD, FT-IR, BET, STA, SEM, and UV-vis were applied to investigate and compare the properties of synthesized TiO2 aerogels and to determine the most effective synthesis route. The structural parameters of the synthesized materials can be varied by changing the precursor type (titanium (IV), isopropoxide (TIP), or tetrabutylorthotitanate (TBOT)) and the nature of the solvent used for additional exchange (n-hexane (nH), cyclohexane (CH), or diethyl ether (DE)). All of the subcritical dried samples show the amorphous structure, which tends to crystallize into the anatase phase after calcination. The number of micro and mesopores and the specific surface area depends on the synthesis conditions. The pores with the highest diameter have ...

PV deployment growth is an unmatched success story in the energy sector over recent years. Howeve... more PV deployment growth is an unmatched success story in the energy sector over recent years. However, European PV manufacturers are facing a decline in production due to competition from third countries. The fragmentation of the value chain is believed to be one of the major factor for this decrease in the competitiveness. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. It pursues a significant LCOE reduction for innovative PV systems based on a hybrid combination of technological innovations and Data management solutions along the PV value chain.

Reinventing EU energy system on a low carbon model through utilization of RES is one of the criti... more Reinventing EU energy system on a low carbon model through utilization of RES is one of the critical challenges of the 21st Century for EU economy. In recent years PV technology was the leading renewable energy technology in terms of capacity growth in Europe. Over the last 20 years, PV has already shown impressive price reductions, but without radically new technological solutions previously demonstrated linear learning rate is be hardly being achieved. Concentrated PV systems are demonstrating possibilities for significant price reduction in terms of used material cost, but are not able to defeat flat panel PV because of the need for costly tracking systems. Therefore eliminating the need of tracking by utilizing novel nanocomposite material solutions for optical elements in CPV system can be way forward overcoming CPV shortcomings proposing an effective solution for stationery CPV design.

Epitaxial silicon foils (<50 um) lifted-off using the porous silicon-based layer transfer proc... more Epitaxial silicon foils (<50 um) lifted-off using the porous silicon-based layer transfer process are used to fabricate heterojunction (HJ) solar cells. Mini-modules with efficiencies above 15% have been fabricated using standard lamination and encapsulation techniques, which have been applied to freestanding epi-Si based HJ solar cells. Analysis of this module highlights the need for bonding these cells onto supporting substrates before module fabrication. We suggest using very low-cost conductive Si carriers as the supporting substrates. Sintering of low-cost Si powder-based ingots, assisted by in-situ doping, has been done by hot pressing or casting of ingots using different types of Si powders and was followed by multi-wire sawing to fabricate thin (~170 μm) supporting highly conductive substrates. The Si material used for these substrates can, in principle, be obtained from Si waste streams, e.g. broken wafers or end-of-line cells in production lines, Si kerf or end-of-life PV modules, making this even more attractive proposition. One important aspect is the development of conductive bonding of epitaxial foils onto low-cost sintered silicon substrates.We evaluated different types of conductive bonding agents. Good mechanical stability was achieved for the bonding processes. These efforts represent the first step towards the wafer-equivalent approach of high efficiency solar cells on thin Si (<50 μm) conductively bonded to low-cost Si substrates. This approach is considered as a promising route for the low-cost Si based PV and a solution module integration of thin Si. This work is done in framework of H2020 EU project CABRISS.

Conditions for the effective phosphorus diffusion through the spun-on sol-gel layers were investi... more Conditions for the effective phosphorus diffusion through the spun-on sol-gel layers were investigated and the results are presented in this work. The n+ areas were doped to obtain sheet resistance as low as 10-20Ω/sq, and surface resistance of n area which was created underneath the barrier layer was in the interval 100-3000Ω/sq with respect to diffusion temperature, barrier material and thickness.

Journal of Sol-Gel Science and Technology, 2014

This work focuses on the dependence preparation conditions-structure-physical properties of hydro... more This work focuses on the dependence preparation conditions-structure-physical properties of hydrophobic silica aerogels, all of them prepared under subcritical drying conditions (70°C and 0.4 atm.), thus aiming at potential application as case insulation filling in heat pumps. The so prepared, millimeter scaled nanoporous hydrophobic silica aerogel granules were analyzed with standard electron microscope and atomic force microscopy, IR spectroscopy, UV/Vis spectroscopy, differential scanning calorimetry and thermal conductivity measurements. The physical properties of the aerogels were compared with commercial aerogel granules. A method for contact angle measurement of micro-droplets situated on the silica granules was proposed to quantify the level of their hydrophobicity.

Paper is devoted to the sol-gel containing dopands preparation technology. Sol-gel doping can be ... more Paper is devoted to the sol-gel containing dopands preparation technology. Sol-gel doping can be promising alternative to gas doping source for Si wafer based solar cells p-n junction formation. Sol–gel process is also an attractive alternative to other methods for synthesis of thin films for silicon solar cells because of low temperature synthesis, simple equipment to be used, thin film formability and so on. In this study sol-gel silica was synthesized using tetraethoxysilane (TEOS) as a precursor and phosphoric acid as a source of phosphate ions. Thin layer of this material is spread by spin-coating process on a surface of silicon wafer and dried to form the phosphosilicate glass (SiO2 : (P2O5)n. Coated wafer is placed into diffusion furnace and held at high temperature under nitrogen ambient for p-n junction formation. Obtained sol-gel composition were analysed by FTIR to estimate dopant concentrations. Further p-n junctions from various sol-gel were produced, sheet resistance Rs and phosporous concentrations profiles were measured for comparative analysis.

Hot Carriers in Semiconductors, 1988

ABSTRACT

Solid State Phenomena, 2004

Self-formation as a concept for irreversible evolution of the artificial object with complexity i... more Self-formation as a concept for irreversible evolution of the artificial object with complexity increase was introduced for understanding of the processes existing in microelectronics technology [1]. The concept of self-formation by itself was to some extend influenced by principles existing in biological world therefore from the very beginning there was an open question about limits of self-formation application: are we limited to the understanding of some technological processes or we can think about predicting new technological applications by applying selfformation concept. Recently developed tools for simulation of technological processes for Solar Cells manufacturing [2] clearly indicates that self-formation is becoming interesting tool for technologists trying to create and optimize microelectronic devices. The next step exploring selfformation application boundaries can be analysis of possibilities of the self-formation to demonstrate usual in biological life development and...

Journal of Solid State Electrochemistry, 2011

Gold-capped silicon nanocolumns regularly distributed over silicon substrate were obtained. The c... more Gold-capped silicon nanocolumns regularly distributed over silicon substrate were obtained. The columns length was roughly 100 nm; their deviation from perpendicular axis was less than 2°. The diameter of the columns was of the order of 10 nm or below of that. The proposed procedure of nanostructuring included the following main steps: deposition of aluminum thin layer (100–500 nm) by magnetron sputtering on (100) oriented Si wafers; formation of porous self-ordered alumina structures by electrochemical anodizing of the Al film in oxalic acid; electroless inversion of Au in alumina pores; and reactive ion etching. The obtained Si–Au structures are of importance as the platforms for biosensing applications, while the gold-free structures are of interest in photovoltaics.

Applied Physics A Solids and Surfaces, 1989

A method for quantitative characterization of chaotic dynamical systems is discussed. An electron... more A method for quantitative characterization of chaotic dynamical systems is discussed. An electronic instrument for determining the number of independent variablesk*, involved in the motion, is described. It allows one to obtain these in real time from a single observable. The suggested technique has been applied to quantification of strange attractors underlying chaotic instabilities in semi-insulating GaAs:Cr, and n-Ge, irradiated

Gels

A cost-effective solution for the synthesis of high-porosity TiO2 aerogels, which can be used as ... more A cost-effective solution for the synthesis of high-porosity TiO2 aerogels, which can be used as a mesoporous perovskite network charge-carrier material during the manufacture of solar cells, is described. The effects of the synthesis parameters (precursor (titanium (IV) isopropoxide (TIP) and tetrabutyl orthotitanate (TBOT)), additional solvent exchange (n-hexane (nH), cyclohexane (CH), and diethyl ether (DE)), subcritical drying (800 mbar vacuum, 70 °C, 8 h), aging, and calcination on the aerogel’s structure have been investigated. Methods of XRD, FT-IR, BET, Raman, STA, SEM, UV–vis, and thermal conductivity measurements were applied to find out the relation between the synthesis conditions and the properties of the synthesized aerogels. Amorphous aerogels are polydispersed systems with the highest probability of pore diameter from 0.5 to 15 nm. An nH-exchanged, aged aerogel synthesized from the precursor TIP shows the highest diameter of pores. After calcination, the aerogels ten...

Solid State Phenomena, 2004

Considering optimization of the technology and production of Solar Cells an overall goal is to lo... more Considering optimization of the technology and production of Solar Cells an overall goal is to lower the production costs per Watt through optimization of the parameters of Solar Cell. The dominant material up to now for the majority of commercially produced solar cells is crystalline silicon (c-Si). A lot of efforts has been undertaken to increase the electrical efficiency of Si based solar cells above 20% [3-5]. Unfortunately, efficiency improvements are often reached only with the help of costly process steps and as result without possibility to use such improvements in industrial products. One of the trends in achieving higher efficiency in monocristalline Si based Solar Cells is introduction of complicated spatial structure on absorbing surface of SC. Reports indicates expectations of efficiencies as high as 24% in laboratory samples but with significant raise in costs for Spatial SC production (Fig. 1). It is clear that optimization of technological steps and parameters must b...

The poster presents PV module innovations introducing and combining five PV module innovations ap... more The poster presents PV module innovations introducing and combining five PV module innovations applied to c-Si based bifacial modules and CIGS modules.

PV deployment growth is an unmatched success story in the energy sector over recent years. Howeve... more PV deployment growth is an unmatched success story in the energy sector over recent years. However, European PV manufacturers are facing a decline in production due to competition from third countries. The fragmentation of the value chain is believed to be one of the major factors for this decrease in the competitiveness. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. It pursues a significant LCOE reduction for innovative PV systems based on a hybrid combination of technological innovations and data management solutions along the PV value chain. Responding to the need of evaluating proposed innovations in terms of economic feasibility and market trends, a dedicated task force, an Exploitation Team, was introduced at the beginning of the project as a main instrument for overseeing achievement of KPI's and beyond, in the ever-changing landscape of the PV sector.

Microscopy and Microanalysis, 2018

Numerous studies in the literature report on titanium dioxide nanoparticles as a harmless, cheap,... more Numerous studies in the literature report on titanium dioxide nanoparticles as a harmless, cheap, facile, bio-compatible, chemically and mechanically stable and highly efficient photo-catalyst which can be exploited in many large-scale applications. One of the most promising techniques for the synthesis of titania nanoparticles in liquids or in polymeric matrices is pulsed laser ablation in liquids (PLAL), e.g. [1,2]. Thereby only a titanium plate and a 'green' solvent are the necessary materials.

Lithuanian Journal of Physics

ABSTRACT

Physica Status Solidi (a), 1988

ABSTRACT

Today photovoltaics (PV) has become one of the most cost-effective forms of electricity productio... more Today photovoltaics (PV) has become one of the most cost-effective forms of electricity production globally and in some regions is already the most competitive unsubsidised form of electricity. Despite positive cost and growing developments, European PV manufacturers are facing a decline in production due to competition from third countries. This decrease in the competitiveness of European PV actors is due to several factors, including a greater fragmentation of the value chain compared to competing actors. Chinese manufacturers have in particular been able to achieve synergies, economies of scale and information sharing throughout the value chain. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. Together, they target a significant LCOE reduction (26%-37%) for European-made PV by adopting a hybrid approach combining technological innovations and data management methods.

The aim of this investigation was to synthesize high porosity TiO2 aerogel by applying sol-gel an... more The aim of this investigation was to synthesize high porosity TiO2 aerogel by applying sol-gel and subcritical drying methods and to identify the influence of reagent’s nature and synthesis conditions on their structural and optical properties. Methods of XRD, FT-IR, BET, STA, SEM, and UV-vis were applied to investigate and compare the properties of synthesized TiO2 aerogels and to determine the most effective synthesis route. The structural parameters of the synthesized materials can be varied by changing the precursor type (titanium (IV), isopropoxide (TIP), or tetrabutylorthotitanate (TBOT)) and the nature of the solvent used for additional exchange (n-hexane (nH), cyclohexane (CH), or diethyl ether (DE)). All of the subcritical dried samples show the amorphous structure, which tends to crystallize into the anatase phase after calcination. The number of micro and mesopores and the specific surface area depends on the synthesis conditions. The pores with the highest diameter have ...

PV deployment growth is an unmatched success story in the energy sector over recent years. Howeve... more PV deployment growth is an unmatched success story in the energy sector over recent years. However, European PV manufacturers are facing a decline in production due to competition from third countries. The fragmentation of the value chain is believed to be one of the major factor for this decrease in the competitiveness. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. It pursues a significant LCOE reduction for innovative PV systems based on a hybrid combination of technological innovations and Data management solutions along the PV value chain.