Effect of twin growth on unidirectional solidification control of multicrystal silicon for solar cells

Hirofumi Miyahara, Seiko Nara, Masayuki Okugawa, Keisaku Ogi

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

The solidification microstructure and crystal orientation have been investigated for solar cell grade high purity multicrystal silicon through a unidirectional solidification technique. The mechanism of the twin growth on a reentrant corner has been also discussed. A columnar structure is observed at solidification velocities of 1.25-30μm/s and positive temperature gradient of 20K/cm in the rod-like silicon specimens in an electric resistance furnace. In the solidification velocity range of 1.25-2.5 μm/s, the grain size enlarges as solidification progresses. Furthermore, large columnar grains contain many twin boundaries. However, the average grain size decreases as the solidification velocity increases and above the critical velocity around 40 μm/s, equiaxed structure appears at the central part of specimens. Therefore, molten silicon must be solidified at the velocity below 2.5 μm/s where twins are always introduced into grains to obtain large columnar crystal grains. The undercooling for directional growth is less than 4 K in the solidification velocity range of 1.25-30 μm/s. A model of two-dimensional nucleation on the reentrant corner was established, and the critical nucleus could be estimated to be 70 to 80% of the radius of the general two-dimensional nucleus. The nucleation undercooling on the surface containing twins also decreased to 70% of the general undercooling. The reduction of the critical radius and undercooling on the reentrant corner could eventually influence on the priority growth direction and the enlargement of the grain size.

Original languageEnglish
Pages (from-to)935-943
Number of pages9
JournalMaterials Transactions
Volume46
Issue number5
DOIs
Publication statusPublished - May 1 2005

Fingerprint

Silicon
solidification
Solidification
Solar cells
solar cells
Undercooling
supercooling
silicon
grain size
Nucleation
nucleation
nuclei
radii
critical velocity
Crystal orientation
Thermal gradients
crystals
furnaces
Molten materials
grade

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

Effect of twin growth on unidirectional solidification control of multicrystal silicon for solar cells. / Miyahara, Hirofumi; Nara, Seiko; Okugawa, Masayuki; Ogi, Keisaku.

In: Materials Transactions, Vol. 46, No. 5, 01.05.2005, p. 935-943.

Research output: Contribution to journalArticle

Miyahara, Hirofumi ; Nara, Seiko ; Okugawa, Masayuki ; Ogi, Keisaku. / Effect of twin growth on unidirectional solidification control of multicrystal silicon for solar cells. In: Materials Transactions. 2005 ; Vol. 46, No. 5. pp. 935-943.
@article{c6692f7f4cd9458a9e2112df25025817,
title = "Effect of twin growth on unidirectional solidification control of multicrystal silicon for solar cells",
abstract = "The solidification microstructure and crystal orientation have been investigated for solar cell grade high purity multicrystal silicon through a unidirectional solidification technique. The mechanism of the twin growth on a reentrant corner has been also discussed. A columnar structure is observed at solidification velocities of 1.25-30μm/s and positive temperature gradient of 20K/cm in the rod-like silicon specimens in an electric resistance furnace. In the solidification velocity range of 1.25-2.5 μm/s, the grain size enlarges as solidification progresses. Furthermore, large columnar grains contain many twin boundaries. However, the average grain size decreases as the solidification velocity increases and above the critical velocity around 40 μm/s, equiaxed structure appears at the central part of specimens. Therefore, molten silicon must be solidified at the velocity below 2.5 μm/s where twins are always introduced into grains to obtain large columnar crystal grains. The undercooling for directional growth is less than 4 K in the solidification velocity range of 1.25-30 μm/s. A model of two-dimensional nucleation on the reentrant corner was established, and the critical nucleus could be estimated to be 70 to 80{\%} of the radius of the general two-dimensional nucleus. The nucleation undercooling on the surface containing twins also decreased to 70{\%} of the general undercooling. The reduction of the critical radius and undercooling on the reentrant corner could eventually influence on the priority growth direction and the enlargement of the grain size.",
author = "Hirofumi Miyahara and Seiko Nara and Masayuki Okugawa and Keisaku Ogi",
year = "2005",
month = "5",
day = "1",
doi = "10.2320/matertrans.46.935",
language = "English",
volume = "46",
pages = "935--943",
journal = "Materials Transactions",
issn = "0916-1821",
publisher = "The Japan Institute of Metals and Materials",
number = "5",

}

TY - JOUR

T1 - Effect of twin growth on unidirectional solidification control of multicrystal silicon for solar cells

AU - Miyahara, Hirofumi

AU - Nara, Seiko

AU - Okugawa, Masayuki

AU - Ogi, Keisaku

PY - 2005/5/1

Y1 - 2005/5/1

N2 - The solidification microstructure and crystal orientation have been investigated for solar cell grade high purity multicrystal silicon through a unidirectional solidification technique. The mechanism of the twin growth on a reentrant corner has been also discussed. A columnar structure is observed at solidification velocities of 1.25-30μm/s and positive temperature gradient of 20K/cm in the rod-like silicon specimens in an electric resistance furnace. In the solidification velocity range of 1.25-2.5 μm/s, the grain size enlarges as solidification progresses. Furthermore, large columnar grains contain many twin boundaries. However, the average grain size decreases as the solidification velocity increases and above the critical velocity around 40 μm/s, equiaxed structure appears at the central part of specimens. Therefore, molten silicon must be solidified at the velocity below 2.5 μm/s where twins are always introduced into grains to obtain large columnar crystal grains. The undercooling for directional growth is less than 4 K in the solidification velocity range of 1.25-30 μm/s. A model of two-dimensional nucleation on the reentrant corner was established, and the critical nucleus could be estimated to be 70 to 80% of the radius of the general two-dimensional nucleus. The nucleation undercooling on the surface containing twins also decreased to 70% of the general undercooling. The reduction of the critical radius and undercooling on the reentrant corner could eventually influence on the priority growth direction and the enlargement of the grain size.

AB - The solidification microstructure and crystal orientation have been investigated for solar cell grade high purity multicrystal silicon through a unidirectional solidification technique. The mechanism of the twin growth on a reentrant corner has been also discussed. A columnar structure is observed at solidification velocities of 1.25-30μm/s and positive temperature gradient of 20K/cm in the rod-like silicon specimens in an electric resistance furnace. In the solidification velocity range of 1.25-2.5 μm/s, the grain size enlarges as solidification progresses. Furthermore, large columnar grains contain many twin boundaries. However, the average grain size decreases as the solidification velocity increases and above the critical velocity around 40 μm/s, equiaxed structure appears at the central part of specimens. Therefore, molten silicon must be solidified at the velocity below 2.5 μm/s where twins are always introduced into grains to obtain large columnar crystal grains. The undercooling for directional growth is less than 4 K in the solidification velocity range of 1.25-30 μm/s. A model of two-dimensional nucleation on the reentrant corner was established, and the critical nucleus could be estimated to be 70 to 80% of the radius of the general two-dimensional nucleus. The nucleation undercooling on the surface containing twins also decreased to 70% of the general undercooling. The reduction of the critical radius and undercooling on the reentrant corner could eventually influence on the priority growth direction and the enlargement of the grain size.

UR - http://www.scopus.com/inward/record.url?scp=22444450096&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=22444450096&partnerID=8YFLogxK

U2 - 10.2320/matertrans.46.935

DO - 10.2320/matertrans.46.935

M3 - Article

AN - SCOPUS:22444450096

VL - 46

SP - 935

EP - 943

JO - Materials Transactions

JF - Materials Transactions

SN - 0916-1821

IS - 5

ER -