New Junction Capacitance Methods for the Study of Defect Distributions and Carrier Properties in the Copper Indium Disel
- PDF / 314,741 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 158 Views
B9.1.1
New Junction Capacitance Methods for the Study of Defect Distributions and Carrier Properties in the Copper Indium Diselenide Alloys J. David Cohen, Jennifer T. Heath∗, and William N. Shafarman1 Department of Physics, University of Oregon, Eugene, OR 97403, U.S.A. 1 Institute for Energy Conversion, University of Delaware, Newark, DE 19716, U.S.A. ABSTRACT We have recently been successful utilizing two methods which are new to the study of CIGS thin film samples: drive-level capacitance profiling, and transient photocapacitance spectroscopy. In this paper we review several of the key results that we have obtained by applying these methods to the study of the CIGS alloys over the past 2 years. This has resulted not only in new information concerning the deep defects and their spatial distributions in these materials, but also to more accurate determinations of free carrier densities, and of minority carrier trapping dynamics within the junction region. Light-induced metastable changes in the deep defect properties of these alloys are also documented through the use of these techniques. INTRODUCTION The chalcopyrite CuIn1-xGaxSe2 (CIGS) materials have been actively studied over the past decade because of their successful application to thin film solar cell technology. In the course of such research it has also become increasingly clear that they have quite complex electronic properties. However, the detailed relationship between these electronic properties and the photovoltaic device performance has yet to be established. This is an extremely important issue since, although quite high efficiencies for such devices have been achieved in the laboratory [1], much lower efficiencies are generally realized using fabrication methods that are more suitable for large scale manufacturing. The reasons for this difference are not well understood. Moreover, an understanding of the connection between the basic electronic properties of the CIGS alloys and device performance is definitely needed to aid in the development of the higher bandgap alloys since these have consistently performed much below theoretical expectations. To begin to understand such issues it seems crucial to determine, at the very least, such basic properties as the net free carrier densities in these films, the density of defect states within the bandgap, as well as the spatial variation of those electronic properties across the film within the photovoltaic device. It has long been recognized that measurements of junction capacitance can yield valuable insight into the density of defect states in the bandgap of semiconductor materials, as well as many of their other electronic properties. Techniques based on junction capacitance have the advantage that they investigate the semiconductor in its working device environment. This is particularly important in the study of materials, such as polycrystalline CIGS, whose electronic properties actually appear to be altered the environment within the device. That is, the behavior of bare thin films may differ sign
Data Loading...
