Current status of photovoltaic technology and application of spectroscopic ellipsometry in photovoltaic research

Sukgeun Choi

National Renewable Energy Laboratory, Golden, Colorado

Society has a strong demand for environmentally friendly energy resources at stable prices.  Because of pollution and their finite nature, fossil fuels are increasingly failing to meet these demands, thus creating a drive towards alternative and renewable energy technologies.  Among a number of options for our low-carbon future, solar energy is frequently cited as a promising candidate. 

In this talk, I first introduce various solar cell technologies including III-V multi-junctions and polycrystalline thin-films.  Current issues associated with each technique and their future direction are discussed. The primary function of a solar cell is to convert incoming sunlight to electrical power.  Thus, knowledge of the optical properties of constituent materials in the device stack is of great importance to enhance device performance.  I present applications of a nondestructive optical method, spectroscopic ellipsometry, in the studies of emerging solar cell materials, including several examples.  The fundamental optical function data determined by ellipsometry are used to (1) optically model the performance of solar cells and (2) better understand the material’s electronic structure by comparing the data with theoretical predictions. 

Dr. Sukgeun Choi is a senior scientist at the National Renewable Energy Laboratory (NREL), where he characterizes the optical properties of a wide variety of photovoltaic materials.  Dr. Choi received his B.S. and M.S. degrees in Physics from Kyung Hee University (Seoul, Korea), and Ph.D. degree in Materials Science and Engineering from the University of Minnesota (Minneapolis, MN).  His Ph.D. thesis work was on the eptaixial growth and characterization of narrow-gap III-V semiconductors and related semimetals under the supervision of Dr. Chris Palmstrøm.  Before joining NREL in early 2008, Dr. Choi worked at the Center for Integrated Nanotechnologies (CINT) of Los Alamos National Laboratory as a postdoctoral research associate, where he conducted growth studies of SiGe alloy nanowires in a cold-wall chemical vapor deposition system with Dr. S. Tom Picraux.  He has more than 15 years of hands-on experience with vacuum deposition systems and is also specialized in spectroscopic studies of solid-state materials primarily using spectroscopic ellipsometry.  Dr. Choi has authored and co-authored 50 peer-reviewed journal articles and about 80 technical presentations.