“Achieving a Solar Cell of Greater than 50 Percent: Physics, Technology, Implementation and Milestones”
Dr. Allen Barnett and Dr. Christiana Honsberg
Room HEC 101
September 19, 2007
10:45 AM to 12:15 PM
ABSTRACT
The theoretical limit of solar energy conversion is over 85%, yet the maximum efficiency of any solar cell in the laboratory is less than half this value, and commercial solar cells are only one fifth. For solar cells to meet world’s future energy demands, the challenge is to develop solar cells that achieve efficiencies that approach the thermodynamic limit.
The $53 million DARPA funded program on Very High Efficiency Solar Cell is led by Drs. Christiana Honsberg and Allen Barnett of the University of Delaware. The program’s goal is to develop solar cell modules, photovoltaic (PV) modules, for portable applications that can operate at greater than 50 percent efficiency. The approach uses proven quantitative models for the solar cell design coupled with high optical efficiency and system integration. The resulting optical/solar cell allows efficiency improvements while retaining low costs, and expanding photovoltaic applications. The new cell design utilizes multiple junctions for the high and low energy photons, a new silicon cell for the mid-energy photons and novel cell architectures and optical elements. The DARPA team has produced multiple junction solar cells with a record-efficiency of 42.9%.
Multiple junction solar cells, called tandems cells, theoretically allow the approaching of the thermodynamic limit with an “infinite” stack of homojunctions. However, material-related issues have limited these devices to three-junction design. Recently, new physical mechanisms have been proposed which allow higher efficiency for a given number of materials and also offer other advantages such as reduced sensitivity to temperature or use of low-cost nano-materials.
These talks will present our approaches to producing ultra-high efficiency solar cells and discuss the experimental and theoretical challenges in making these cells. These routes include multi junction solar cells consisting of integrated pn junctions, multiple transition cells (quantum well or intermediate band quantum dot cells) and multiple exciton generation. In addition, physical insights into operation and design rules for advanced concept cells will be presented.
BIOS OF PRESENTERS
Dr. Allen Barnett is Executive Director of the Solar Power Program, a Research Professor of the Department of Electrical and Computer Engineering and Senior Policy Fellow at the University of Delaware. He was Program Manager for the $53 million Very High Efficiency Solar Cell, VHESC, project for developing a 50% efficient solar cell and he and Dr. Honsberg are the PIs on a new DuPont-University of Delaware consortium funded by DARPA, industry and others to commercialize the VHESC products with total funding over three years of more than $100 million. He serves on the Steering Committee and Head of Research Committee of NSF-IGERT for Sustainable Energy from Solar Hydrogen. His engineering research is focused on developing very high performance, next generation photovoltaic solar cells and on the interdisciplinary basic research needs to further advance solar power. Dr. Barnett’s policy work is focused on further developing the value propositions for the solar electric power industry and includes providing the leadership for the U. S. Department of Energy’s Solar Power Industry Roadmap, a national, domestic solar power plan.
Dr. Christiana Honsberg is Director, High Performance Solar Power Program at the University of Delaware and is PI with Dr. Barnett on the multi-million DARPA sponsored DuPont-University of Delaware consortium VHESC program. There are 16 participating organizations. Her research is focused on ultra-high efficiency solar cells. Dr. Honsberg’s research includes the development of three-level systems, which allow a range on new semiconductor devices including new approaches to LEDs and photodetectors. Her interest in fundamental advances and theory, coupled with attention to detail in the analysis of devices, led to her early involvement in advanced concept solar cells. She has provided several significant research contributions to the solar field. In addition, her interest in new device theory and materials has produced the InGaN material system, a promising new material in which her research group has demonstrated the first InGaN solar cell. Dr. Honsberg provides effective and motivational classroom lectures, leads the development of new courses, contributes to design of new engineering curricula, and advances the practice of teaching by adapting new tools or pedagogical approaches to engineering.
