Technical Program

AM2: Advanced Solar Cell Characterization including PL/EL/thermography

Instructors: Dr. Martin Schubert, Fraunhofer Institute for Solar Energy Systems, Freiburg, Germany
Prof. Thorsten Trupke, UNSW and BT Imaging, Australia

In part I of this tutorial we will show that photoluminescence data can be used to measure implied IV curves on passivated wafers in a contactless fashion and without the need for a pn-junction. In this context, it will be argued that the exponential relationship between current and voltage in any solar cell is determined by the total recombination rate throughout the device volume as a function of the separation of the quasi-Fermi energies. The relationship between the luminescence intensity emitted by a silicon wafer or solar cell and the quasi Fermi energies, which is known as the generalised Planck equation and which provides the basis for analysing luminescence data in terms of a device voltage will be introduced. Experimental data will be presented for implied IV curves measured on passivated, non-diffused wafers, which prove the origin of the exponential IV characteristics to be unrelated to the presence of a pn junction or in fact of any specific device structure.

Part II of the tutorial will introduce the concepts of photoluminescence imaging, electroluminescence imaging and lock-in thermography, which are commonly used today in R&D and in high volume manufacturing for the characterisation of PV devices. A broad overview of applications will be provided and the pros and cons of each technique discussed. One specific application for each technique will then be presented in more detail. For PL imaging we will review the quantitative analysis of bulk lifetime on non-passivated bricks and ingots. EL imaging is primarily used for quality control on fully assembled PV modules, some examples for that application will be presented. Lock-in thermography is a valuable technique for shunt analysis on cells. Series resistance imaging will be used as an example of the benefits arising from combining data from two or all of the above imaging techniques. As final step it is shown how these inputs together with related techniques such as LBIC can be used for a detailed solar cell efficiency loss analysis.

Martin Schubert studied physics in Freiburg, Germany, and Montpellier, France. He is group leader at Fraunhofer ISE, Germany, and active in silicon material and solar cell characterization. He is concentrating on identifying and quantifying performance limitations on both, silicon materials and solar cells by combining established methods, developing novel analysis methods and by modelling approaches. He is particularly focussing on the role of impurities and their impact on cell performance as well as on specific loss mechanisms in solar cells. For his work, Dr Schubert was awarded the Ulrich Gösele Young Scientist Award in Fukuoka, Japan in 2013.

Thorsten Trupke is a semiconductor scientist with expertise in photovoltaic (PV) devices and the theory of solar energy conversion. The focus of his scientific work is on silicon solar cells, with emphasis on the development and application of novel characterisation methods for silicon bricks, wafers, solar cells and modules. He co-invented a range of novel characterisation methods, including various luminescence imaging based methods, which are now used for routine inspection in laboratories and in high volume manufacturing. Thorsten is a Professor at the School for Photovoltaic Renewable Energy Engineering, where he leads a research team of two postdocs and five PhD students, currently in a part time role. He is also co-founder and CTO of BT Imaging Pty Ltd, a UNSW start-up company commercializing the PL imaging technology.

AM3: Simulating Optical Losses in Solar Cells and Modules

Instructor: Dr Keith McIntosh, PV Lighthouse, Australia

Optical simulation is key to effective PV research. By combining simulation with experimentation, a researcher can rapidly (i) quantify losses in cells and modules; (ii) select the optimal module materials for a particular cell design; (iii) assess the benefit of new technologies, like textured ribbons, black silicon and bifacial modules; (iv) set control limits on fabrication steps like texturing, ARC deposition, and metallisation; (v) calculate cell-to-module (CTM) losses; and (vi) predict module behaviour in the field, accounting for incident angle, region-dependent spectra, and bifacial illumination.

This tutorial will provide a demonstration of how to determine the optical losses in a silicon solar cell and module. It will include tips on ray tracing, spectrophotometry, ellipsometry and quantum-efficiency measurements. It will also mention recent advances in the accurate modelling of textured surfaces, including random pyramids, isotexture and black silicon. The seminar will conclude by describing how to maximise the absorption of sunlight in a solar cell and module.

Keith McIntosh is a leading expert in the characterisation, simulation and design of silicon solar cells and modules. He completed his PhD at the University of New South Wales in 2001 before working at SunPower Corporation for four years, where he was a core member of the team that developed SunPower’s rear-contact solar cell, and at the Australian National University for six years, where he led a research group that focused on the optics and recombination of silicon solar cells. Keith is now CEO of PV Lighthouse, which creates research software for PV scientists and engineer. He has co-written over 150 scientific articles on silicon solar cells.

AM4: Utility-Scale PV Systems: Design Constraints, Considerations and Performance Modeling

Instructors: Erika Brosz, Recurrent Energy, USA
Dr. Clifford Hansen, Sandia National Laboratories, USA

Beyond PV technology, a plethora of external factors influence viability of utility scale PV systems. Project development, design, financing and construction each present obstacles which must be overcome in order to successfully achieve commercial operation.

A comprehensive system design is required to deliver a fully permitted and compliant system. The design encompasses aspects beyond selection of modules and inverters, such as: a substation and transmission connection to achieve grid interconnection; balance of plant equipment specifications throughout the PV array; and managing regulatory and contractual requirements. PV system financial viability depends to a large extent on projections of future revenue from energy production. Models are used to estimate future production using historical data.

The first half of this tutorial provides a high-level view of system design constraints, both technical and contractual in nature, influencing equipment specifications and well as a discussion of potential fatal flaws which must be avoided through the project development and implementation processes. The second half of the tutorial outlines the process for modeling large-scale PV systems, describing available models and data, and providing insight into practices which promote confidence in model results.

Erika Brosz is a Senior Engineer with expertise in the design and implementation of utility-scale PV systems, currently at Recurrent Energy Inc. Her recent projects include designs for 350 MWp under construction in Texas and a 20 MWp system currently operating in Nevada. Erika has spent the entirety of her career in system-level engineering of commercial and utility-scale renewable energy generating facilities validating design criteria, equipment specifications, workmanship, etc.

Clifford Hansen is a Distinguished Member of the Technical Staff at Sandia National Laboratories, currently in the Photovoltaics and Distributed Systems department. He leads research and engineering efforts to improve modeling for energy systems and to innovate methods for operating electrical grids with many distributed energy resources. Recent projects include development of the open-source PV modeling library PVLib (Matlab and python), developing performance models for bifacial PV systems, and characterizing uncertainty in PV production models.

AM5: Reliability of Photovoltaic Modules and the Impact on Life Cycle Cost

Instructors: Dr. Sarah Kurtz, National Renewable Energy Laboratory, USA
Dr. John Wohlgemuth, PowerMark Corporation, USA

As PV has grown into a large worldwide business, reliability of the modules and systems has become extremely important. This combined with pressure to reduce costs means that ensuring PV component reliability is critical. This tutorial will cover:

• Introduction to PV Modules, the purpose of module packaging.
• History of field failures and how accelerated stress tests for PV modules were developed.
• What are Qualification Tests, how effective have they been and what are their limitations?
• Some measurement tools for failure analysis of PV modules.
• How does the reliability of PV modules and their degradation rate effect lifecycle costs?
• How has the PV industry been ensuring the quality and reliability of deployed modules?
• Why that system is no longer good enough.
• Creation of PVQAT to develop an improved system.
• What do investors look for?
• Quality control: An inspector camped out in the factory or IEC 62941?
• Accelerated testing: Random sampling of modules subjected to extended testing
• Track record of field performance
• When is quantitative accelerated testing important? What must we do to make a prediction better than 25 years plus or minus 25 years?

John Wohlgemuth is the Executive Director of PowerMark Corporation and the Technical Advisor to the US TAG for IEC TC82, the PV Technical Committee of IEC. Dr. Wohlgemuth retired from NREL in 2017 after 6 years of work on PV reliability and standards. Before that he spent 34 years in the PV industry at Solarex and BP Solar. Dr. Wohlgemuth has been an active member of working group 2 (WG2), the module working group within TC-82, the IEC Technical Committee on PV since 1986 and was the convenor of the group for more than 15 years.

Sarah Kurtz is Research Fellow at the National Renewable Energy Laboratory (Golden, CO) where she works with a team to study PV reliability ranging from modules to systems. She is active with the standards organizations IEC and IECRE and is one of the leaders of the International PV Quality Assurance Task Force (PVQAT). These organizations work together in a coordinated way to better understand the various ways that PV modules can fail or degrade and to create standard methods for trying to avoid these problems.

AM6: Physics and Technology of Silicon Solar Cells

Instructors: Prof. Andres Cuevas, Australian National University, Australia
Dr. Ronald A. Sinton, Sinton Instruments, Boulder, CO USA

Crystalline silicon is the prevalent photovoltaic technology. It keeps getting cheaper and, surprisingly after so many years, better. Can we make it even better? In this tutorial we will start with a silicon wafer and discuss how to convert it into an efficient solar cell, taking good care of the optics, so that it absorbs as many photons as possible, and the electronics, to extend the life expectancy of electrons and holes. A revision of the physics of solar cell operation will tell us that we need to form two distinct regions or layers that separately transport either electrons or holes with a high degree of selectivity. We will discuss different approaches to make such selective transport regions, from the traditional to the latest ideas, including: a) the introduction of dopants by thermal diffusion, b) the geometrical restriction of doped regions, c) the deposition of "passivating contacts" such as those based on polycrystalline and amorphous silicon. We will “go to the lab” and learn how to measure the main electronic properties that characterise the absorber and contact regions of the solar cell: carrier lifetime, surface recombination parameters and contact resistivity. Special attention will be given to test and measurement techniques for process control during cell and module fabrication, to ensure high quality products. Special topics in solar cell and module measurement techniques will also be touched upon, including outdoor characterization.

Andres Cuevas is a Professor at the Research School of Engineering of The Australian National University. He has contributed to the scientific and technological development of silicon solar cells since 1976, and in 2015 he was awarded the Becquerel Prize for outstanding merits in Photovoltaics. His current research interests include the development of advanced interfaces and materials for a new generation of silicon solar cells.

Ron Sinton received his Ph.D. from Stanford University in 1987 for work on high-efficiency (28%) silicon concentrator solar cells. Following graduation, he was a founding member of SunPower as manager of R&D. In 1992, he founded Sinton Consulting, later Sinton Instruments, which has focused on developing many novel test and measurement instruments that have become central to both R&D and process control during the enormous expansion of the silicon solar cell industry. In particular, Sinton Instruments has been at the forefront in developing instruments for characterizing carrier recombination lifetime at each stage in the process from as-crystallized brick or ingot material through wafers through the entire fabrication process, and then in finished devices. Cell and module characterization is another specialty. In 2014, Ron received the Cherry Award at the IEEE PVSC.

PM1: Building Integrated PV

Instructors: Dr. Tilmann E. Kuhn, Fraunhofer ISE, Germany
Christof Erban, SUNOVATION, Netherlands

Building integrated PV (BIPV) deals with the integration of PV functionality in building components for roofs and facades. The tutorial consists of

• an overview of the design parameters for BIPV on cell-, module-, building- and district-level.
• a review of evaluation criteria for BIPV systems.
• a summary of legal requirements for BIPV components and systems in the US, EU and Asia.
• a detailed analysis of examples of BIPV roof installations.
• a detailed analysis of examples of BIPV facade installations.

The tutorial will start with a collection of questions and desired focus topics from the audience. We will try to answer these questions within the presentations and the discussions. Questions that not covered will be answered bilateral. Additional spontaneous questions are welcome during the presentations.

Dr. Tilmann E. Kuhn studied physics at the University in Heidelberg, Germany. Since 1999 he is working for Fraunhofer ISE. He is the head of the group for Solar Facades since 2004. The group is dealing with all aspects of the interaction of solar radiation with the building skin. The activities of the group range from visual comfort and daylighting to the integration of PV and solar thermal collectors. He co-ordinated several national and international research projects and he is a member of several national and international standardization committees. For a list of publications see http://publica.fraunhofer.de/jsp/StarXmlQuery?style=ise.xsl&query=author=kuhn,+t* or https://www.researchgate.net/profile/Tilmann_Kuhn

Dipl Ing. Christof Erban studied energy- and thermal engineering at the RWTH University in Aachen, Germany. Since 1993 he has been working in the field of BIPV for Pilkington, Saint-Gobain, Schüco, Fraunhofer ISE and Meyer Burger. Currently he is the head of research and development at Sunovation Produktion GmbH. Christof Erban holds several patents on photovoltaic panels and is chair of the German and European standardization working group for building integrated photovoltaics. Speeches on BIPV were held e.g. at the European Solar Conferences in Glasgow, 2000, Munich, 2001, Dresden, 2006, Hamburg, 2011, at the German Solar Conferences in Staffelstein in 2001, 2008, 2009, 2011, 2012 and 2015, and at the TUV Module workshop in 2006, 2009, 2011, 2013, 2015.

PM2: Market- and TechnologyDevelopment of Stationary Storage Systems

Instructor: Kai-Philipp Kairies (M. Sc.), RWTH Aachen University, Germany

Electricity storage systems can help to level the dynamic variations between generation and load in power grids with increasing shares of fluctuating renewable energies. In addition to growing markets in residential- and off-grid applications, storage systems will also become a major supplier of system services, such as frequency control. Increasing amounts of electric cars will be able to offer short-term storage capacities at extremely low opportunity costs in the mid-term and open up new opportunities for energy suppliers and system operators.

The tutorial will give a detailed overview about the performance and cost development of today’s most important electricity storage technologies and analyze their market potentials in a variety of applications, including utility-scale storage, behind-the-meter applications and off-grid electrification. For each application, estimations regarding the current and future market size and potential revenue streams are presented. The tutorial will conclude with an overview about a range of international real-life storage projects.

Kai-Philipp Kairies studied electrical engineering in Aachen and Singapore. Since 2017 he heads the research section “Grid Integration and Storage Systems Analysis” at RWTH Aachen University. Mr. Kairies’ work focuses on the grid integration of decentralized storage systems, efficient charging strategies for electric cars, market potentials of utility-scale storage systems and future developments in rural electrification. Additionally, he works as a consultant to several governmental and intergovernmental organizations.

PM3: Solar Cell and Module Characterization

Instructors: Dr. Gerald Siefer, Fraunhofer ISE, Germany
Dr. Yoshihiro Hishikawa, AIST, Japan

The conversion efficiency is one of the most prominent parameters characterizing the quality of a solar cell or photovoltaic module. However it is often forgotten that determining this number with low uncertainty is still challenging and involves significant measurement effort.

The tutorial will give an overview about state of the art calibration procedures covering, but not limited to:

• Reference cells/detectors and their traceability to the World Radiometric Reference / SI units
• Standard Testing Conditions – reference spectra
• Adjustment of solar simulator irradiance – a major source of PV measurement uncertainty
• Area determination – still a challenge especially for tiny cells
• Spectral response / EQE – differential measurement method, non linearity, multi-junction devices
• Spectral correction procedures for single junction (mismatch factor) and multi-junction cells
• Current voltage curve measurement principles, sun simulator types, transient measurement effects – including special features of novel PV devices, such as slow response and hysteresis of high efficiency crystalline silicon and various thin film devices
• Cell contacting - fill factor underestimation and boosting
• Outdoor measurements
• CPV cell/module characterization

The tutorial will be held by Dr. Yoshihiro Hishikawa from AIST in Japan and Dr. Gerald Siefer from Fraunhofer ISE in Germany. Both researchers are involved in the calibration of PV devices since decades and have measured many of the PV cells which are included in the efficiency tables of e.g. Progress in Photovoltaics.

Dr. Yoshihiro Hishikawa is a team leader of Calibration, Standards, and Measurement Team at Research Center for Photovoltaics (RCPV) of National Institute of Advanced Industrial Science and Technology (AIST), Japan. He has focused on the R&D of precise performance characterization for various PV cells and modules since he joined AIST in 2003. He participates in IEC and JIS committees for standardizing performance measurements of PV devices. He entered Sanyo Electric. Co., Ltd. in 1982, and was engaged in development and characterization of amorphous silicon solar cells. He received his Ph.D. from Kyoto University in 1988.

Dr. Gerald Siefer has joined the Fraunhofer Institute for Solar Energy Systems in Freiburg Germany as assistant student in 1997. Since then his work at the calibration laboratory at Fraunhofer ISE is focused on the characterization and calibration of photovoltaic devices. He finished his PhD on the topic of “Analysis of the performance of multi-junction cells under realistic operating conditions” in 2008. Since 2009 he is leading the team “III-V cell and module characterization” at Fraunhofer ISE. He is also active member of the IEC working group 7 working on the development of international standards related to CPV.

PM4: Multijunction Solar Cells: III-V and III-V/Si Tandems

Instructors: Dr. Myles Steiner, NREL, USA
Dr. Tyler Grassman, Ohio State University, USA

III-V multijunction solar cells have recently demonstrated power conversion efficiencies >46% under concentrated light, the highest of any photovoltaic technology. Silicon cells, on the other hand, dominate the terrestrial market, and combining III-Vs with Si into a tandem offers the possibility of high efficiency at a competitive cost.

This tutorial will give a general introduction to the field of multijunction solar cells for the use in terrestrial and space systems. It will start from basic theoretical considerations and explain the benefits of using several pn-junctions to convert the broad solar spectrum into electricity. We will review the III-V alloy system and the various techniques that are available for growing these highly crystalline semiconductors. We will consider different multijunction architectures including designs based on upright and inverted growths, and both lattice-matched and metamorphic growth. Some of the specific requirements for the use of multijunctions in different environments will be introduced, such as high current capacity and energy yield for concentrators, radiation hardness for space applications, and low cost for one-sun applications.

New and on-going efforts toward III-V/Si tandems will then be covered in detail. Si-based multijunction devices offer the promise of similarly high conversion efficiencies as traditional III-Vs, but at a fraction of the cost. However, this integrated materials system also comes with a set of further, unique issues that arise due to the various dissimilarities between III-V alloys and Si, including chemistry mismatch (i.e. polar vs. non-polar bonding) and thermal expansion mismatch, in addition to lattice mismatch. To this end, we will discuss the sources and impact of these issues as they relate to III-Vs grown on Si substrates, and methods to avoid and/or mitigate the related problems, including nucleation and metamorphic grading strategies for epitaxial approaches, as well as wafer/epilayer bonding. We will finish with a discussion of recent successful developments and demonstrations within this burgeoning area.

Myles Steiner is a senior scientist in the High Efficiency Crystalline Photovoltaics group at the National Renewable Energy Laboratory, in Golden, Colorado, where he works on III-V multijunction solar cells. His recent projects include developing 5- and 6-junction solar cells for high concentration operation; dual junction solar cells for operation at 400°C and high concentration in conjunction with solar thermal applications; and IMM solar cells for hydrogen production through water splitting.

Tyler Grassman is an assistant professor at The Ohio State University (Columbus, OH) in the Materials Science and Engineering and Electrical and Computer Engineering departments. His areas of interest and current research topics include III-V/Si tandem cell development, large-gap metamorphic materials and cells for space application, electron microscopy/spectroscopy-based semiconductor materials characterization and methods development, and investigations of nanostructured semiconductor photocatalyst materials.

PM5: Thin Film Photovoltaics: CdTe, Cu(In_xGa_1-x)Se₂ and a-Si/nc-Si

Instructor: Dr. Steven Hegedus, University of Delaware, USA
Dr. Sylvain Marsillac, Old Dominion University, USA

Thin film semiconductors have been investigated as absorber layers for large scale photovoltaic since the 1960’s based on the promise of low manufacturing cost for large-area high-throughput PV modules. Three thin film absorber materials emerged in the 1980’s as being technically and commercially viable for solar cells: CdTe, CuInSe₂-based, and Si-based. The first two are polycrystalline while the Si films are either amorphous or nanocrystalline. Each is configured as a multilayer heterojunction device fabricated on glass, foil, or plastic substrates. Sustained worldwide research and development have significantly increased our understanding of the materials chemistry and physics leading to advanced device structures and high-throughput processing. In this tutorial, we will provide an overview of the basic processing sequence, device structures, manufacturing options, and key challenges for CdTe, Cu(In_xGa_1-x)Se₂s, and a-Si/nc-Si materials, cells, and modules. We will describe the evolution of each thin film technology into today’s commercial success and identify critical issues limiting wider commercialization. The course is intended for researchers and technologists interested in an overview of the technologies as well has understanding the fundamental materials chemistry, device operation and characterization and process engineering.

Dr. Steven Hegedus has been involved in solar cell research for over 30 years. He is a Senior Scientist at the Institute of Energy Conversion (IEC) at the University of Delaware (UD), the world's oldest photovoltaic research laboratory. He also has an appointment as an Associate Professor in Electrical and Computer Engineering. He received Masters Degree from Cornell and a Ph.D. in Electrical Engineering from UD.

At IEC, he has worked on all of the commercially active solar cell technologies – a-Si, CdTe, Cu(InGa)Se2, organic, and c-Si. Areas of active research over 3 decades have included optical enhancement, a-Si alloys, textured TCOs, thin film device analysis and characterization, a-Si/c-Si heterojunctions, CdTe device processing and stability of various thin film solar cell technologies under accelerated degradation conditions. With funding from the Dept of Energy, he leads a team to fabricate interdigitated back contact heterojunction solar cells (IBC-HJ). Dr. Hegedus has been an author of over 100 papers in the field of solar cell device analysis, processing, reliability and measurements. He has consulted for several companies in the PV supply chain. He co-edited the 1st and 2nd editions of the "Handbook of Photovoltaic Science and Engineering" (Wiley 2003, 2011). Prof. Hegedus has taught a graduate class at UD in “Solar Electric Technology and Applications” for over 10 years and has advised over ten graduate students.

Sylvain Marsillac is a Professor of Electrical Engineering at Old Dominion University, Norfolk, VA. He received his Ph.D. in Materials Science and Engineering (1996) from the University of Nantes (France). After receiving his Ph.D., he worked for the University of Delaware (IEC), the University of Hawaii, and the University of Toledo, where he was the co-director of the Wright Center for Photvoltaic Innovation and Commercialization. In 2011, he joined Old Dominion University where he is now leading the effort on Photovoltaic Science and Engineering as the Director of the Virginia Institute of Photovoltaics. His current research interests include high efficiency solar cells, low cost manufacturing and solar energy integration to the grids. He has published over 160 papers in peer reviewed journals and conference proceedings and has supervised over 25 Ph.D. and Masters students. In the last 5 years, Dr. Marsillac has developed a strong portfolio of research spanning work in the field of PV from the nano-scale to the giga-scale, funded by federal, state and private resources. He is also the lead of a new pedagogic effort at ODU to develop an undergraduate and graduate program for Photovoltaic engineering education.

PM6: Perovskite and Dye Sensitized Solar Cells - The Vesatility of Mesoscopic Solar Cells

Instructor: Prof. Anders Hagfeldt, École Polytechnique Fédérale de Lausanne, Switzerland

Hot Research Topic in PV!

Systems for solar energy conversion based on mesoscopic materials are intensively studied today. They show efficient electricity as well as fuel production and hold promise for large volume production at low cost. Dye-sensitied (DSSC) and perovskite solar cells (PSC) are two examples of photovoltaic technologies, which will be described in details in this tutorial.

Photoelectrochemistry is a useful platform to these solar cell and fuel devices and the tutorial introduces fundamental and applied aspects of photoelectrochemical systems with a particular focus on nanostructured materials and devices. We will go through the formation of the semiconductor/electrolyte junction and explain the origin of electricity and fuel production in traditional compact/bulk photoelectrodes and in mesoscopic electrodes. The concept of dye-sensitization leads us to DSSCs and the tutorial will present basic operational principles, materials science development, industrial status and the latest research findings of these systems.

Photoelectrochemical systems for water splitting will be overviewed starting with the original Fujishima-Honda cell to the latest development of efficient oxide semiconductors such as Cu2O and hematite, as well as molecular systems utilizing the material platform of DSSC.

Perovskite solar cells have shown an unprecedented development of efficiencies with at present a world record of 22.1%. PSCs have their roots in DSSC and the tutorial will present the fundamental properties of this hybrid organic-inorganic semiconductor, preparation methods, materials and device development and the directions for further improvement in efficiencies. A big question mark for PSCs has been their long-term durability. Recently, breakthroughs in demonstrating very promising stability data have been obtained in our laboratories at EPFL as well as in others. The materials development for these developments will be presented during the tutorial.

Anders Hagfeldt is Professor in Physical Chemistry at EPFL, Switzerland. He obtained his Ph.D. at Uppsala University in 1993 and was a post-doc with Prof. Michael Grätzel (1993-1994) at EPFL, Switzerland. His research focuses on the fields of dye-sensitized solar cells, perovskite solar cells and solar fuels. From web of science January 2017, he has published more than 400 scientific papers that have received over 37,000 citations (with an h-index of 98). He was ranked number 46 on a list of the top 100 material scientists of the past decade by Times Higher Education. In 2014-2016 he was on the list of Thomson Reuter’s Highly Cited Researchers. He is a visiting professor at Uppsala University, Sweden and Nanyang Technological University, Singapore.