Hydrogenation of Si from SiN(x):H Films: How Much Hydrogen Is Really in the Si?

Presented at the 3rd World Conference on Photovoltaic Energy Conversion; Osaka, Japan; May 11-18, 2003.A promising method to introduce H into Si solar cells in order to passivate bulk defects is by the post-deposition annealing of an H-rich, SiN(x) surface layer. It previously has been difficult to characterize the small concentration of H that is introduced by this method. IR spectroscopy has been used together with marker impurities in the Si to determine the concentration and depth of H introduced into Si from an annealed SiN(x) film

Investigation of Spatially Non-Uniform Defect Passivation in EFG Si by Scanning Photoluminescence Technique

Presented at the 31st IEEE Photovoltaic Specialists Conference, Orlando, Florida; January 3-7, 2005. ©2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.This paper shows that both hydrogenation of defects from SiN(x) coating and thermally-induced dehydrogenation of defects are rapid and occur simultaneously in EFG Si during cell processing. Room-temperature scanning photoluminescence mappings, before and after the SiN(x) induced hydrogenation, revealed that hydrogenation of defective regions is effective and pronounced, with more than an order of magnitude increase in lifetime, compared to the rest of the bulk. In addition, FTIR measurements showed the concentration of bonded hydrogen in the SiN(x) film decreases with the increase in annealing temperature and time. However, the rate of release of hydrogen from the SiN(x) film decreases sharply after the first few seconds. Based on this understanding, a process was developed for a co-firing of SiN(x) film and screen-printed Al and Ag in RTP unit, which produced 4 cm(2) EFG Si cell with highest efficiency of 16.1%

A Comprehensive Study of the Performance of Silicon Screen-Printed Solar Cells Fabricated with Belt Furnace Emitters

Presented at the 20th European Photovoltaic Solar Energy Conference and Exhibition, Barcelona, Spain; June 6-10, 2005.ABSTRACT: In this paper we report on the screen-printed solar cells fabricated on three types of silicon materials; float zone (FZ), HEM multicrystalline and EFG ribbon with POCl3 and belt furnace diffused emitters. The belt furnace diffused emitters involved one- and two-side phosphorus spin-on to assess the contaminating effect of the IR belt. The solar cells with POCl3 emitters and co-firing of screen-printed contacts produced efficiencies of 17.3% on FZ, 16.4% on HEM and 15.5% on EFG ribbon silicon. Solar cells with two-side phosphorus emitters diffused on the belt furnace, produced efficiencies of 17.2%, 16.0%, and 15.1%, respectively, on FZ, HEM and EFG ribbon silicon. However, appreciably lower efficiencies of 15.5%, 15.5%, and 14.1% were obtained, respectively, on FZ, HEM and EFG ribbon silicon for belt-diffused emitters with only one-side phosphorus spin-on with the other side on the belt. This difference in efficiency is reflected in Voc loss for the belt-diffused emitters compared to the POCl(3) emitter cells. The IQE measurements supported that solar cells with belt-diffused emitter with two-side phosphorus spin-on and POCl(3) emitter cells had comparable Jsc. However, the cell with phosphorus spin-on on one-side gave much lower IQE because of poor bulk lifetime or the contamination due to direct contact with the belt. These results indicate that the belt emitters can account for appreciable loss in the performance of the many current commercial cells; however, this loss can be regained by applying phosphorus dopant to both side of the wafer

Chemical natures and distributions of metal impurities in multicrystalline silicon materials

We present a comprehensive summary of our observations of metal‐rich particles in multicrystalline silicon (mc‐Si) solar cell materials from multiple vendors, including directionally‐solidified ingot‐grown, sheet, and ribbon, as well as multicrystalline float zone materials contaminated during growth. In each material, the elemental nature, chemical states, and distributions of metal‐rich particles are assessed by synchrotron‐based analytical x‐ray microprobe techniques. Certain universal physical principles appear to govern the behavior of metals in nearly all materials: (a) Two types of metal‐rich particles can be observed (metal silicide nanoprecipitates and metal‐rich inclusions up to tens of microns in size, frequently oxidized), (b) spatial distributions of individual elements strongly depend on their solubility and diffusivity, and (c) strong interactions exist between metals and certain types of structural defects. Differences in the distribution and elemental nature of metal contamination between different mc‐Si materials can largely be explained by variations in crystal growth parameters, structural defect types, and contamination sources.publishe