20130328 Robert Opila - Role of Surfaces and Their Analysis in Photovoltaics
28 March 2013
Role of Surfaces and Their Analysis in Photovoltaics
Professor Robert Opila
University of Delaware
Surface chemistry is intrinsically related to the performance of solar cells. In solar cells the generation and collection of charge carriers determines their efficiency. Effective transport of charge carriers across interfaces and minimization of their recombination at surfaces and interfaces is of utmost importance. Thus, the chemistry at the surfaces and interfaces of these devices must be determined, and related to their performance. In this talk we will discuss the role of two important interfaces. First, the role of surface passivation is very important in limiting the rate of carrier recombination. We have been studying organic passivants on H-terminated Si surfaces, and establishing extremely low surface recombination rates. Here we are combining spectroscopic measurements of the surface of a-Si device with electrical measurements to ascertain what factors determine the quality of a solar cell passivation. In addition, the quality of the heterojunction interface in a ZnSe/CdTe solar cell affects the output voltage of this device. X-ray photoelectron spectroscopy gives some insight into the composition of the interface, while ultraviolet photoemission yields the relative energy of the two materials’ valence bands at the junction, which controls the open circuit voltage of the solar cell. The relative energies of ZnSe and CdTe at the interface are directly affected by the material quality of the interface through processing.
Robert Opila graduated from the University of Chicago with a PhD in Chemistry in 1982 and immediately began work at Bell Laboratories. While there, he studied the role of surfaces and interfaces in electronic materials and devices. He was named a Distinguished Member of Technical Staff and promoted to technical supervisor. In 2002 Opila joined the Department of Materials Science and Engineering at the University of Delaware, where his interest in the surfaces and interfaces of electronic materials has grown to include photovoltaics and thermoelectrics. Opila has been a member of the AVS since 1980 and has served as chair of the Applied Surface Science Division and the Electronic Materials and Processing Division. He is a fellow of the AVS and is currently an editor of Applied Surface Science. Last semester, Opila was a recipient of a Fulbright Fellowship, and lectured and studied at Bilkent University in Ankara, Turkey. He is a visiting professorial fellow at UNSW for this semester.