Seminars Archive

The applied science of photovoltaics: characterization of Cu(In1-xGax)Se2

Abstract
The ternary A^IB^IIIX2^VI chalcopyrite semiconductor, Cu(In1-xGax)Se2 (Eg = 1.0 - 1.5 eV, x dependent), has proved to be a superior absorber for heterojunction photovoltaic device applications. Cu(In1-xGax)Se2 is amphoteric, thus enabling intrinsic, compositional control of its conductivity, as well as its electronic structure. Historically, CdS/Cu(In,Ga)Se2 photovoltaic devices were believed to operate as heterojunction devices with a 0.08 eV conduction band offset to explain the heterojunction`s performance as a minority carrier device. Direct experimental measurements showed that this model was not valid and further examination of the surface electronic properties was required. X-ray photoemission spectroscopy, positron annihilation spectroscopy, and Raman spectroscopy have been applied to the comprehensive analysis of this material system in an effort to understand surface versus bulk composition and electronic structure, and their effect on photovoltaic device performance. Efforts to chemically modify the surface composition and electronic structure are also being studied to eliminate the need for the toxic CdS window layer.