M I D E M 2 0 0 9 - International Conference on
Microelectronics, Devices and Materials
and the Workshop on Advanced Photovoltaic Devices and Technologies
INVITED SPEAKERS
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Dr. Andreas Bett, Institut fuer Solarenergietechnik, Freiburg, Germany
III-V Multi-junction Solar Cells - Simulation and Experimental Realisation
Monolithically stacked multi-junction solar cells based on III–V semiconductor materials, such as the GaInP/GaInAs/Ge triple-junction solar cell, are the state-of-the-art approach for high-efficiency photovoltaic energy conversion. Consisting of stacked p-n junctions with different bandgap energies, these devices can exploit the solar spectrum very profitably. Just recently an efficiency of 41.1 % was achieved for a metamorphic GaInP/GaInAs/Ge triple-junction solar cell under the standard AM1.5d spectrum and a concentration of 454 suns. A multi-junction solar cell structure typically consists of more than 20 layers of different III-V compound semiconductor materials. Due to the complex electrical and optical interactions between the different layers, a pure experimental optimization of these sophisticated structures would be very expensive and protracted. An accurate and reliable modeling is desirable in order to accelerate the optimization procedure considerably.
In this talk the current status of III-V multi-junction solar cells will be presented. In particular, a focus is set on different techniques of numerical modeling and simulation, which have found increasing attention in recent years. In addition, a short overview will be given about the application of III-V multi-junction solar cells in PV concentrator systems.
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Prof. Dr. Andrzej Dziedzic, Wroclaw University of Technology, Poland
Modern thick-film and LTCC passives and passive integrated components
The dimensions of modern passives and passive integrated components should be reduced significantly in the nearest future. The aim of this paper is to present current situation in the area of discrete, integrated and integral passives made using thick-film or Low Temperature Co-Fired Ceramic (LTCC) technologies. The role of these components in modern electronic circuits is discussed too. The concept of such passives is very simple and they are very cheap in mass production. But from materials science point of view they are complicated, non-equilibrium systems with physical and electrical properties dependent on microstructure, which is determined in turn by proper arrangement of raw materials properties and conditions of fabrication process.
The material, technological and constructional solutions and their relation with electrical and stability properties are analyzed in details in this paper for thick-film and LTCC micropassives – microresistors (linear and nonlinear), microcapacitors and microinductors – both described in the literature as well as made and characterized at the Faculty of Microsystem Electronics and Photonics, Wroc³aw University of Technology. Moreover the relations between minimal geometrical dimensions, technological accuracy and limitations and electrical properties are presented and discussed.
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Dr. Hubert Fechner, University of Applied Sciences Technikum Wien, Austria
High Penetration of Photovoltaic Systems in Electricity Networks
While the global Photovoltaic market is extremely growing and this technology is more and more seen as important future energy supply which will significantly contribute to the electricity generation, current electricity grids are not yet designed to integrate a steadily increasing penetration of photovoltaic electricity. This talk discusses the main technical challenges as well as the currently onging international activities in order to make the electricity grids smarter with a focus on inverter technology as key element in this process.
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Dr. Andrea Feltrin, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Technology of thin film silicon photovoltaics
In this presentation an introduction to several aspects of the science and technology of thin film silicon for photovoltaic applications will be given. The potential advantages of this approach which has recently been gaining market share from the well established crystalline wafer technology will be discussed. At an introductory level, a basic understanding of the material properties of thin film silicon layers allows to quickly assess their potential and limitations when used in photovoltaic devices. For instance, it explains why light trapping and optically transparent electrical contacts play such an important role in this technology.
The ease with wich different phases of silicon and silicon compounds can be prepared and scaled up to large surfaces certainly count among the advantages of thin film silicon photovoltaics. A brief review of the production technology for thin film silicon based materials by plasma glow discharges will be given with particular focus on the synthesis of amorphous and microcrystalline silicon.
Like for other photovoltaic technologies, the push for higher efficiency of thin film silicon devices is strong. An appealing feature of these materials is that they can be easily integrated in multi-junction tandem devices. For instance, stacking amorphous and microcrystalline silicon thin films in one tandem cell, the micromorph cell, allows to increase the efficiency well above the characteristic values of single junction devices.
The Institute of Microengineering has been a pioneer in the research and development of thin film silicon photovoltaics over the last 30 years. Several latest developments on micromorph tandem cells are reviewed in this presentation. In particular, by optimizing light trapping a 13.3% initial efficiency micromorph tandem cell has been obtained. The development of an intermediate reflector layer between single cells was essential in order to achieve such high efficiencies.
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Prof. Dr. Jerzy Krupka, Institute of Microelectronics and Optoelectronics, Warsaw University of Technology, Poland
Measurements of materials at microwave frequencies
Recent advances in measurements of various electronic materials at microwave frequencies are presented. Special attention is devoted to resonance techniques that are more sensitive and accurate than the transmission-reflection methods. Measurement techniques of the complex permittivity and in some cases the complex permeability are described for the following four groups of materials.
- Bulk low loss dielectric materials including ceramics and uniaxially anisotropic single-crystals.
- Laminar type dielectric materials such as LTCC ceramics, PWB substrates and thin ferroelectric films.
- Semiconductors and conductors (bulk materials wafers and thin films).
- Metamaterials
Several specific measurement methods are described. Simultaneous use of whispering gallery and quasi TE modes allows for multi-frequency measurements of low loss materials. Modification of the split post dielectric resonator technique can be used for measurements of both permittivity and permeability of laminar low and medium loss metamaterial. Resistivity of conductive materials such as semiconductors metals and polymers can be measured in the range of several decades employing single post dielectric resonator technique.
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Prof. Dr. Antonio Luque, Universidad Politécnica de Madrid, Spain
Progress in understanding the Intermediate band solar cell
The intermediate band (IB) solar cells has been proposed to increase the current of a solar cell by electron-hole pair generation by successive absorption of two sub-bandgap photon by means of a band located within the bandgap of a semiconductor. To keep the voltage the Fermi level in operation has to split into three quasi Fermi levels (QFLs). Cell have been manufactured using the confined levels of InAs quantum dots (QD) in GaAs as IB. This structure has not the optimal bandgaps but it has permitted to prove the two photon absorption mechanism and also the three QFL splitting. The topic has attracted many researchers and progress will be presented.
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Prof. Dr. Michael A. Morris, University College Cork, Ireland
Scaling Beyond Lithographic Limits – Polymer Self-Assembly Mediated Sub-20 nm FET devices
The relentless miniaturisation of electronic circuitry has spawned the ICT revolution that has impacted every aspect of modern life. However, this trend in scaling is facing a number of significant challenges if the progress defined in International Roadmaps is to be delivered. As well as facing barriers associated with fundamental physical limits such as interconnect related delay times and power issues there is the cost of improving light sources for photolithography and implementing new mask/resist technologies. This paper presents some very recent work on how self-organisation of block copolymers may be used to generate very small device structures whilst allowing integration into current fabrication technologies for industrial manufacture.
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Prof. Dr. Jože Rakovec, Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
Exploiting Solar Energy with Photovoltaics
Energy balance of a solar panel is considered in relation to its efficiency. The monthly, seasonal and yearly means of solar radiance exposures are presented in a form of geo-referenced maps for whole Slovenia with a spatial resolution 100 m x 100 m, as well as the diagrams of the optimal tilts and orientation of solar collectors for selected places in Slovenia. In rough relief not only the whole landscape is divided into more or less sunny parts, but also different sky-view factors influence strongly the diffuse part of radiance exposure. The trend of increasing global solar radiance exposure during the last few decades can partly be explained with the trend of the reduced fog occurrence over Slovenia.
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Prof. Dr. Wim Sinke, Energy Research Center of the Nethelands
Trends in Wafer-Based Silicon Photovoltaic Cell and Module Technology
Wafer-based crystalline silicon photovoltaic technology has been commercially available for more half a century and has been able to build a good track record in terms of lifetime and reliability. Its current share in the global photovoltaic market is around 85%. The technology can be roughly characterised by a relatively high performance, but also by a challenging cost structure. Research and development efforts worldwide are therefore aimed at reducing costs, while maintaining or even increasing performance and lifetime. The European Integrated Project CrystalClear was the biggest publicly co-funded project in this field worldwide and aimed at bringing down module manufacturing costs by 50% to 1 Euro per watt-peak or less, while further increasing the efficiency and improving the environmental profile. Witin this project several distinctly different cell and module design and manufacturing approaches have been investigated and demonstrated on a pilot level. This presentation will provide an overview of the project results in the context of global wafer-based crystalline silicon and thin-film developments. Special attention will be given to the technology that has yielded a world record module efficiency for multicrystallline silicon.
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Prof. Dr. James R. Sites, Colorado State University, United States of America
Impact of grain boundaries on thin-film PV performance
Grain-boundary recombination is a potential source of major performance loss for polycrystalline thin-film solar cells, because the forward diode current can be significantly enhanced and thus limit the cell's voltage. High-efficiency CIGS cells are an exception and can achieve voltages comparable to crystalline silicon cells. The voltage of CdTe cells, however, is much more limited at present by the grain boundaries. The talk will present an explanation of why CIGS is fortuitously anomalous and it will give an alternative approach that may lead to higher voltages and efficiencies with CdTe cells.
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Prof. Dr. Miro Zeman, Delft University of Technology, Netherlands
Advanced thin-film silicon solar cells: metastability and light-trapping
Thin-film silicon solar cell technology is one of the promising photovoltaic technologies for delivering low-cost solar electricity. In 2008, according to Photon International, thin-film silicon modules of 402 MW peak power were produced. Based on the companies’ announcements the production capacity of thin-film silicon modules is expected to grow to almost 8 GW in the year 2010. Today the thin-film silicon PV market is dominated by amorphous silicon based modules; however it is expected that the tandem amorphous/microcrystalline silicon modules will take over in near future. Two manufacturing methods for thin film silicon solar cells can be distinguished; the silicon-on-glass approach and the roll-to-roll approach, in which solar cells are deposited on flexible substrates.
A drawback of the amorphous silicon solar cell technology is a relatively low stabilized efficiency of modules that varies between 5 to 8%. A challenge of this technology is to suppress the light-induced degradation of amorphous silicon solar cells. A widely used method for obtaining more stable amorphous silicon material is based on applying hydrogen dilution of silane during its growth. The properties of silicon films grown from the mixture of hydrogen and silane will be discussed and the solar cell behavior will be presented.
An efficient utilization of the sun spectrum is a key issue in the field of thin-film silicon solar cell technology. The tandem approach employing the combination of amorphous silicon and microcrystalline silicon absorber layers offers an improved performance of the modules reaching efficiencies above 10%. The tandem approach allows using thinner absorber layers in the component cells that contributes to a suppression of light induced degradation of amorphous silicon component cell. When applying thinner absorber layers photon management plays an important role in increasing the absorption in the absorber layers resulting in a higher stabilized efficiency. The novel approaches for photon management such as i) optimal surface texture of the electrodes for introducing efficient light scattering and ii) development and implementation of optically-active layers for enhanced reflection at the back contact will be discussed.
MIDEM Conference 2009 homepage is edited by the
Laboratory of Photovoltaics and Optoelectronics,
Faculty of Electrical Engineering,
University of Ljubljana