Technical Program

AM2: Introduction to Device and Module Characterization

Instructor: Ronald A. Sinton , Sinton Instrument, Boulder CO USA

This tutorial will discuss cell and module testing. A particular emphasis will be placed on best practice for testing Silicon devices under industrial conditions, at calibration laboratories, and in R&D. Strategies for minimizing uncertainties will be presented, based on the fundamentals of the equipment and also the device physics behind concepts such as the effects of cell capacitance, illumination non-uniformity, cell mismatch, and the module circuits including bypass diodes. Approaches to data-based assessment of measurement uncertainties will be described. The ambiguities in measuring the “efficiency” of cells with vanishingly little Ag in the busbars is an especially-challenging reality. The use of production IV testing to implement cell-by-cell advanced diagnostics and process control will be described.

Ron Sinton did his PhD work at Stanford University developing 28%-efficient silicon concentrator cells and 23% efficient backside-contact one-sun cells. He then continued this work by adapting the fabrication processes to be more industrial as a founding member of SunPower Corporation. After founding Sinton Instruments in 1992, he focused the company on bringing the systematic device physics approach that was used to develop very high-efficiency silicon solar cells to the design of test and measurement instruments for the broader Silicon field. He was involved in the development of many techniques that are commonly used today, such as the Suns-Voc technique and the methodology for extracting and reporting implied voltage from lifetime data. Sinton Instruments provides metrology for nearly all of the research labs and production facilities working in silicon PV technology. Ron enjoys blurring the boundaries between metrology and device physics in order to report parameters that are key inputs to physical models. He participates in conference program organization, especially the IEEE PVSC (1987-2008) and the annual NREL Silicon Workshop (1994-present). Ron received the Cherry Award at the 2014 IEEE PVSC.

AM3: Status and Issues in Si PV

Instructor: Silvana Ayala Pelaez, National Renewable Energy Laboratory, Golden CO, USA

Silicon PV is the prevalent photovoltaic technology, and it is also an area that continues to provide surprising results even with the impressive work done through the years. In this tutorial, we will begin by setting a framework to understand Si PV devices. Several silicon solar cell technologies will be surveyed (including amorphous, crystalline silicon, and bifacial), considering both their present laboratory status and manufacturing processes. We will survey simulation and experimentation to predict silicon module behavior in the field.

In particular, the tutorial will give a detailed overview covering, but not limited to, the performance and cost development of bifacial technology, half-cut cells, and other new silicon technologies, and analyze their market potential. The tutorial will conclude with a brief perspective on possible future scenarios for technological evolution and solving current challenges.

Silvana Ayala Pelaez is a Post-doc at the National Renewable Energy Laboratory, working with the Performance & Reliability group on bifacial silicon technology. She has a PhD in Electrical and Computer Engineering from the University of Arizona. She also has a M.S. in Optical Sciences at the same University. She received a B.S. in Mechatronics Engineering from Monterrey Tec (ITESM 2007). Current projects are focused on bifacial photovoltaic performance and modeling. Her research includes characterization and energy simulation for bifacial and bifacial/holographic system energy productions. She edited and published the book “Solar Outreach Handbook” in 2018.

AM4: Hybrid Perovskite PV

Instructor: Dr. Joseph Berry, National Renewable Energy Laboratory, Golden CO, USA

Halide perovskites are poised to become a transformational photovoltaic technology with demonstrations of power conversion efficiency in excess 23% for single junctions and rapidly approaching 30% for multijunction devices in which they are incorporated. The basic physical properties that enable these amazing advances in efficiency present key scientific challenges in understanding in order to fully exploit the promise of halide perovskite-based absorber materials.

This tutorial will provide an overview of these material systems and their application to solar including recent advances in single junction and tandem/multijunction configurations. Basic physical properties such as defect tolerance, their link to processing as well as their implications on performance, as defined by efficiency, scalability and stability will be discussed. Advances in device architectures, ink formulation or processing approach, as well as strain and compositional engineering that are critical to advancing the technology will also be addressed.

Joe Berry is the team lead for the National Center for Photovoltaics' Hybrid-perovskite solar cell program. He is a graduate of the Penn State Department of Physics, receiving his PhD for work on spin physics of magnetic II-VI, III-V and hybrid metallic/semiconductor systems. After his PhD work he was awarded a National Research Council Fellowship at the National Institute of Standards and Technology (NIST/JILA), where he worked on the development and application of high-resolution spectroscopic techniques to solid-state electro-optical systems, including self-assembled quantum dots and related nanostructures. Since joining NREL he has worked on a range of next generation photovoltaic materials and devices with an emphasis on relating basic interfacial properties to device level performance. He has worked on these issues in several Energy Frontier Research Centers (EFRCs) to connect basic science developments to technological applications and is currently a PI in the CHOISE EFRC. His work at NREL continues to focus on addressing semiconductor heterostructure systems, but has moved beyond traditional compound semiconductor systems to include oxide, organic and other hybrid semiconducting materials of technological relevance.

AM5: High Efficiency III-V PV

Instructor: Richard R. King, Arizona State University, Tempe AZ, USA

III-V photovoltaics has often been the testing ground for pushing the limits of what is possible in light-to-electricity conversion efficiency. The ability to grow low-defect III-V semiconductor material, highly effective interface passivation, and wide bandgap tunability have enabled the development of highly efficient multijunction cell technology in the III-V material system. III-V multijunction solar cells have historically been the highest efficiency PV technology since the early 1990s, with efficiencies now up to 46%. III-V multijunction cells represent the only 3rd generation solar cell technology so far to exceed the efficiency of widely deployed 1st and 2nd generation photovoltaics.

With increasing interest in low-cost, flat-plate tandem (2-junction) or multijunction (2 or more junction) solar cells as a way to break through the efficiency ceiling of widely deployed single-junction PV, there is much to be learned from III-V multijunction technology. Analogs to the structures in demonstrated III-V multijunction cells may be found in new low-cost materials, and the III-V materials themselves may be deposited much more cheaply with new growth methods. Interestingly, III-V multijunction PV has often included group-IV cells in the multijunction stack, as in lattice-matched and metamorphic GaInP/GaInAs/Ge 3-junction cells, and GaPAs/Si tandem cells. In single-junction photovoltaics, photon recycling enhancement in direct bandgap III-V solar cells has pushed their efficiency closer to the detailed balance limit than in any other material system, increasing our understanding of the fundamental physics of energy conversion.

This tutorial is an introduction to the basic semiconductor physics of III-V solar cells, III-V materials growth, processing and characterization, multijunction (MJ) solar cell structure, measurement and applications, and new concepts in III-V cells, III-V/Si, and other types of multijunction cells. We start with a comparison of detailed balance thermodynamic efficiency limits with semi-empirical efficiency models, and examine PV passivation, device structure and growth considerations to minimize the difference between theory and practice. We look at the main III-V growth methods as well as new higher-throughput deposition methods, and at key characterization methods for crystal structure, doping, and recombination rate measurement. The structures of important families of III-V multijunction cells are reviewed, such as lattice-matched, metamorphic, inverted metamorphic, wafer bonded, and III-V on silicon cells. Low-cost, flat-plate multijunction cells in other materials systems such as II-VI/Si and perovskite/Si tandem cells are also studied for comparison. The past, present, and future of III-V photovoltaic cell applications are reviewed. Finally, the physics of photon recycling and luminescent coupling in single and multijunction cells, nanostructured PV, and other advanced concepts in III-V solar cells are studied.

Richard King has worked in high-efficiency photovoltaics for over 30 years. He is currently Professor in the School of Electrical, Computer and Energy Engineering at Arizona State University, and received his Ph.D. and M.S. in electrical engineering from Stanford University, and his B.S. degree in physics, also from Stanford. His research has explored defects and recombination in compound semiconductors, silicon and compound semiconductor interface passivation, interdigitated back-contact silicon solar cells, metamorphic III-V materials, dilute nitride GaInNAs, sublattice ordering, high-transparency tunnel junctions, and high-efficiency multijunction solar cells with 3 to 6 junctions. In 2006, this work led to the first solar cell of any type to reach over 40% efficiency. Dr. King is recipient of the 2010 William R. Cherry Award given by the IEEE for "outstanding contributions to photovoltaic science and technology," an IEEE Fellow, a co-founding editor of the IEEE Journal of Photovoltaics, and was general chair of the 40th IEEE Photovoltaic Specialists Conference (PVSC) in Denver, CO in 2014. He teaches courses in solar cells, advanced photovoltaics, as well as general courses in semiconductor electronic properties.

PM1: Introduction to Photovoltaic Device Modeling

Instructors: Dr. Jeff Bailey, MiaSolé Hi-Tech Corp., Santa Clara, CA USA

Modeling of photovoltaic devices is an increasingly necessary tool for understanding and improving the performance of PV cells and modules. In this tutorial we will review capabilities of several simulation tools that are available for the engineer and scientist—tools that vary in complexity and scope of the underlying physics, dimensionality, applicability to complex geometrical structures, and cost. We will review some methods and measurements for generation of device modeling input data beyond simple I-V characterization: materials- and device-level electrical characterization, optical data, and physical/compositional data. And we will spend a large fraction of our time in a hands-on demonstration of the utility of a very useful simulation package for thin-film solar cells: SCAPS. We will examine several prototype device models and demonstrate model definition from scratch, predict the changes in device responses (e.g. QE, admittance spectroscopy) as a function of fundamental defect parameters, derive material characteristics and properties through automated fitting to experimental data, explore scripts to modify the operation of SCAPS, and examine a particular class of metastable defects and their interaction with device operational states. Attendees are encouraged to bring laptops and will be given instructions for pre-installing SCAPS in advance of the session.

Jeff Bailey joined MiaSole in May 2014 as Senior Member of the Technical Staff in the Advanced Films Development group. His work focuses on advanced device characterization techniques to understand defect and impurity properties in CIGS solar cells. In previous roles Jeff was Senior Development Engineer at two solar startups (SoloPower and NanoGram), both CIGS- and silicon-based, where he developed processes and hardware for innovative front-end manufacturing. Jeff also managed an advanced technology group at Aviza Technology where he established the use of computational fluid dynamics (CFD) and simulations as the foundation of new product and sustaining engineering efforts. His work in PV extends for more than 20 years from his groundbreaking work as a graduate student in defect-impurity interactions in multicrystalline silicon solar cell material at the University of California, Berkeley, in the Department of Materials Science and Engineering.

PM2: Introduction to Photovoltaic Materials Characterization

Instructor: Dr. Harvey Guthrey and Dr. John Moseley, National Renewable Energy Laboratory, Golden CO, USA

The performance of photovoltaic devices is governed by the structural and chemical properties of the materials used as well as the interactions between the different materials that make up the devices. Understanding these properties requires the use of a variety of characterization techniques based on different probing methods designed to expose specific material properties. This tutorial will survey the characterization techniques used to study materials used in photovoltaic devices from routine analyses through cutting edge methods. The discussion of each technique will focus on what information can be attained (as well as what cannot) and how that information can be related to photovoltaic parameters. Following the technique introductions, there will be a survey of current material problems related to different photovoltaic materials (CdTe, CIGS, silicon, hybrid-perovskites). It is often the case that multiple characterization techniques must be combined to study a particular problem in the most effective manner. Thus, a discussion of necessary considerations and effective approaches to experimental design will also be included.

Dr. Harvey Guthrey is currently a research scientist in the Microscopy and Imaging Group at the National Renewable Energy Laboratory in Golden, Colorado. He received his Bachelor of Science in Physics from the University of North Texas and his PhD in Materials Science from the Colorado School of Mines in 2013. His research is primarily focused on the application of electron microscopy based characterization techniques to photovoltaic materials. However, he has also worked on thin-film materials processing and device fabrication during a one year GA-SERI research exchange program at the Advanced Institute for Industrial Science and Technology in Tsukuba, Japan. The overarching theme of his research is to gain better understanding of how the structural and chemical properties of photovoltaic materials can be altered to achieve higher efficiency devices.

John Moseley is presently a researcher in the Analytical Microscopy group at NREL with 8 years’ experience in solar cell Materials Characterization. John earned a Ph.D. in Materials Science from the Colorado School of Mines in 2016, advised by Dr. Richard Ahrenkiel. John began working at NREL in 2012 as an intern (Science Undergraduate Laboratory Internship (SULI)) working with the Reliability Group. He then completed graduate research and a postdoctoral appointment as part of the Analytical Microscopy group, collaborating extensively with industry (First Solar). His current research is focused on quantifying thin-film solar cell device parameters using SEM-based techniques, cathodoluminescence (CL) and electron-beam-induced current (EBIC), and numerical modeling

PM3: Module Stability and Reliability

Instructor: John Wohlgemuth, PowerMark Corporation, Union Hall, VA, USA

This tutorial will describe field experiences with early PV modules and how identification of failure modes led to the development of accelerated stress tests that were used to develop more reliable and durable products. Proper application of these stress tests through qualification testing along with implementation of quality management systems in module manufacturing led to rapid improvements in module lifetimes and extensions of the product warranties. The tutorial will also review recent research being done to improve reliability and durability with an ultimate goal of developing a method for assessing module lifetimes.

Dr. John Wohlgemuth recently became the Executive Director of PowerMark Corporation where he is serving as the Technical Advisor to IEC Technical Committee 82 on Photovoltaics. He retired from the National Renewable Energy Laboratory where he served as a Principle Scientist in PV Reliability from 2010 until 2017. While at NREL he was responsible for establishing and conducting research programs to improve the reliability and safety of PV modules. Before joining NREL Dr. Wohlgemuth worked at Solarex/BP Solar for more than 30 years. His PV experience includes cell processing and modeling, Si casting, module materials and reliability, and PV performance and standards. 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 convenor of the group for more than 15 years. Dr. Wohlgemuth was a member of the Steering Committee for the PV Module QA Task Force (PVQAT) and is a member of the STP for UL 1703. Dr. John Wohlgemuth earned a Ph.D. in Solid State Physics from Rensselaer Polytechnic Institute.

PM4: Utility Scale System Issues

Instructors: Dr. Mahesh Morjaria, First Solar, USA

Several key factors have enabled utility-scale solar generation to be both cost-effective and commercially viable. Apart from a dramatic improvement in PV module cost, these factors include plant system design, BOS component selection as well as grid interconnection capability required to deliver a fully permitted and compliant solar system. The system design, including selection of optimal DC/AC ratio, row spacing, tracking or fixed tilt mounting is focused on reducing LCOE (Levelized Cost of Energy) that maximizes the project revenue and makes it financeable.

Meeting regulatory and contractual requirements also plays a critical role in the viability of utility-scale plants. The capability of utility-scale PV plants to address grid reliability and stability concerns is critical to integrate large amounts of PV generation into the electric power grid. PV plants with “grid-friendly” features such as voltage regulation, active power controls, and ramp rate controls have successfully alleviated these reliability concerns. More recently, the ability of PV plants to provide essential grid reliability services was demonstrated. It has been shown that PV Plants even out-perform conventional generation in providing services such as frequency regulation. As solar penetration increases further, grid operators face new challenges in managing the variable nature of solar electricity and maintaining grid balance between supply and demand. During low load periods in spring and fall, there is often more midday solar electricity produced than can be incorporated into the grid. In the evening when the sun sets and solar production decreases, other generation needs to rapidly ramp up to meet the increasing demand. Recent advances have shown that solar can provide cost-effective flexible capability that enables operators to more effectively manage resources to maintain grid balance during daytime and early evening transitions. With the addition of storage, solar can even provide firm capacity that can be dispatched as needed – just like a conventional generation plant.

This tutorial provides a high-level view of utility-scale PV system design, equipment selection, as well as a discussion of various plant optimization approaches that makes the plant viable. It also includes a discussion of several factors that have made significant PV growth possible. Next insights into practices that are necessary to meet current and future grid integration challenges will be discussed. Finally, the tutorial provides guidance on factors that make the combination of solar and storage more effective in addressing challenges arising from increased solar penetration.

Mahesh Morjaria, Ph.D. VP, PV Systems, First Solar. Dr. Mahesh Morjaria is the VP for PV Systems Development at First Solar. He leads the R&D effort in PV systems technologies for utility-scale solar plants. Over the past eight years, he has established himself as a leading expert in the area of solar generation and in addressing key challenges associated with integrating utility-scale solar plants into the power grid. Dr. Morjaria previously worked at GE for over twenty years where he held various leadership positions including a significant role in expanding the wind energy business. He brings more than 35 years of advanced technology, and product development experience. He is the author of numerous industry leading papers and patents in the area of solar, wind generation & grid integration. His academic credits include B.Tech from IIT Bombay and M.S. & Ph.D. from Cornell University.

PM5: Thin Film PV: Overview of CdTe, Cu(InGa)Se2, Cu2ZnSn(S,Se), and Related Material and Device Technologies

Instructor: Mike Scarpulla, University of Utah, Salt Lake City, UT, USA

The promise of thin film photovoltaic technologies has always been to reduce material and production costs while maintaining high conversion efficiency to achieve competitive cost per Watt. CdTe and Cu(In,Ga)Se2 (CIGSe) (and of course, thin film perovskites) have in the past decade demonstrated conversion efficiencies in the same >20% range as multicrystalline Si. The fact that these technologies can achieve such high performance is truly remarkable because they consist of heterogeneous stacks of polycrystalline material layers with grain boundaries and interfaces spaced only microns from each other. So how do these remarkable materials do it? What special attributes allow such high performance from such defective devices? This tutorial will introduce participants to the leading thin film technologies ranging from the commercially successful to those in the research phase. We will examine the materials, fabrication methods, device structures, and how these come together. The outstanding challenges will be examined for each technology and materials and device concepts on the horizon will be introduced.

Mike Scarpulla has worked in thin film photovoltaics for over a decade and in compound semiconductors for 18 years. He holds a joint appointment as an Associate Professor in the departments of Materials Science and Engineering and Electrical and Computer Engineering at the University of Utah. He has served in organizing the PVSC in various roles including chairing Area 2 multiple times. His current photovoltaic research is in group-V doping and the Cl activation process in CdTe as well as electrical defect spectroscopies. He enjoys the nexus of defect physics, materials, crystal growth, processing, device physics, materials and device characterization, and product engineering offered by thin film photovoltaics. His specialties are crystal growth and processing, point defects, and structural and electrical characterization. He is an author on more than 95 peer-reviewed publications and many conference proceedings. Mike earned his Sc.B. from Brown University in 2000 and PhD from UC Berkeley in 2006, both in Materials Science and Engineering. He was a postdoctoral scholar at UC Santa Barbara from 2006-2008 when he joined the University of Utah. In his spare time he enjoys family, friends and colleagues, hiking, climbing, biking, and skiing.

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.