Interactions Of Structural Defects With Metallic Impurities In Multicrystalline Silicon

Abstract

Portions ABSTRACTInteractions between structural defects and metallic impurities were studied in multicrystalline silicon for solar cell applications. The objective was to gain insight into the relationship between solar cell processing, metallic impurity behavior and the resultant effect on materiddevice performance. With an intense synchrotron x-ray source, high sensitivity x-ray fluorescence measurements were utilized to determine impurity distributions with a spatial resolution of = 1jm. Diffusion length mapping and final solar cell characteristics gauged materiddevice performance. The materials were tested in both the as-grown state and after full solar cell processing. Iron and nickel metal impurities were located at structural defects in asgrown material, while after solar cell processing, both impurities were still observed in low performance regions. These results indicate that multicrystalline silicon solar cell performance is directly related to metal impurities which are not completely removed during typical processing treatments. A discussion of possible mechanisms for this incomplete removal is presented.

A Phase Diagram of Low Temperature Epitaxial Silicon Grown by Hot-wire Chemical Vapor Deposition for Photovoltaic Devices

“…This suggests that HWCVD at low temperatures allows hydrogen to effectively passivate the grain boundaries in these films. Although nickel is known to degrade minority carrier lifetimes, even in small concentrations [5], the lifetimes of films on SNSPE large-grained templates are comparable to the lifetimes of films on Si(lOO). Under low light injection (LLI) conditions, the minority carrier lifetimes for films on Si(lOO) range from 5.7 to 7.5 ps, and the minority carrier lifetimes for films on SNSPE templates range from 5.9 to 19.3 ps as measured by resonantly coupled photo-conductive decay (RCPCD) [6].…”