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Materials Science at Oregon State University

Surface Science and Growth of Cu(In,Ga)Se2 for Solar Cell Applications - PLEASE NOTE: Seminar in Weniger 305 at 3:30 pm

Date: Monday, Feb 16th
Presenter: Dr. Angus Rockett, Materials Science and Engineering, University of Illinois at Urbana-Champaign

Abstract


Production of thin film solar cells is growing at over 40% per year. However, advances are limited by a lack of fundamental understanding of the materials. This talk reviews our studies of the growth mechanisms, optoelectronic properties and surface science of one class of materials applied to these cells: Cu(In,Ga)Se2. The work focuses on epitaxial single crystals grown with a variety of orientations to provide controlled surfaces for study. Scanning probe measurements show how surface morphology, atomic dynamics, and surface energy are connected. Surprisingly, the lowest energy surface is the polar close packed plane. Non polar {110} type Cu(In,Ga)Se2 surfaces, favored in semiconductors such as GaAs, decompose into highly faceted polar planes. Grain boundaries also favor these planes and show evidence of grooving. Certain dislocation cores decompose into internal nanovoids, which were analyzed to confirm relative surface energies by Wulff construction. The surfaces show Fermi energy pinning by ultraviolet photoelectron spectroscopy but the pinning can be relieved by formation of the heterojunction used in solar cells. Reduction in surface energies of the close packed polar planes must include a surface reconstruction. Preliminary evidence has been obtained that supports one of the proposed reconstructions by scanning tunneling microscopy. Cathodoluminescence shows the connection of radiant recombination to the microstructure and defects in the material. Cu(In,Ga)Se2 is found to be a remarkable semiconductor with unique and fascinating properties that contribute significantly to its success in solar cell applications.