%0 Journal Article
%T Detection and Localization of Defects in Monocrystalline Silicon Solar Cell
%A P. Tom¨¢nek
%A P. £¿karvada
%A R. Mack£¿
%A L. Grmela
%J Advances in Optical Technologies
%D 2010
%I Hindawi Publishing Corporation
%R 10.1155/2010/805325
%X Near-surface defects in solar cell wafer have undesirable influence upon device properties, as its efficiency and lifetime. When reverse-bias voltage is applied to the wafer, a magnitude of electric signals from defects can be measured electronically, but the localization of defects is difficult using classical optical far-field methods. Therefore, the paper introduces a novel combination of electric and optical methods showing promise of being useful in detection and localization of defects with resolution of 250£¿nm using near-field nondestructive characterization techniques. The results of mapped topography, local surface reflection, and local light to electric energy conversion measurement in areas with small defects strongly support the development and further evaluation of the technique. 1. Introduction Although the concept of photovoltaic (PV) devices descends from the mid-19th century, its modern age began after 1950 [1]. Solar cells fulfill two principal functions: photo-generation of charge carriers¡ªelectrons and holes¡ªin a light-absorbing material, and separation of the charge carriers to a conductive contact that transmits the electric current [2]. Their efficiency is limited by a number of factors, which include fundamental power losses (incomplete absorption of light or dissipation of a part of the photon energy as heat); losses caused by the reflection of light from the cell surface; and finally, a recombination of the electron-hole pairs in the substrate. The basic methods for the characterization of silicon solar cells are generally electrical measurements [3¨C5]. Electrical methods represent an integral measurement on the whole cell. Unfortunately, they do not enable to localize defects occurring in the structure. Local defects in the p-n junction may be associated with structural imperfections (such as grain boundaries, dislocations, and scratches), impurities, higher concentrations of donors and acceptors, or both [6]. Therefore, it is important not only to find most harmful defects, but also to understand their nature and identify the factors which affect adversely their formation and recombination properties. The used PV analytical tools are generally divided into two groups. (i)Mapping techniques which allow the access to the areas of interest (usually the areas with high probability of defects). For materials analysis, lifetime-mapping tools such as surface photo voltage (SPV) [7], microwave photo conductance decay (MW PCD) [8] are frequently applied. Other methods map spatial distribution of photocurrent induced by laser beam
%U http://www.hindawi.com/journals/aot/2010/805325/