Continuous production of photovoltaic silicon ribbons by the new pendant drop growth (PDG) method

Directorate-General For Research And Innovation

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Energy research
Renewable sources of energy

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• Sciences et techniques

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• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION
• Nombre de lectures: 13
• Langue: English
• Poids de l'ouvrage: 4 Mo

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Commission of the European Communities
energy
CONTINUOUS PRODUCTION OF
PHOTOVOLTAIC SILICON RIBBONS BY
THE NEW PENDANT DROP GROWTH
(PDG) METHOD
Report
EUR 9864 EN
(ilow up flOIII 11.11 »I till III' ¡il It |H 1.H Commission of the European Communities
energy
CONTINUOUS PRODUCTION OF
PHOTOVOLTAIC SILICON RIBBONS BY
THE NEW PENDANT DROP GROWTH
(PDG) METHOD
PCUK
Produite chimiques Ugine Kuhlmann
Centre de recherches de Grenoble
F-38560 Jarrie
SUMMARY REPORT: J. Ricard
FINAL REPORT: J. Ricard and TH. Duffar
Contract No. ESC-R-072-F (SS)
Directorate-General Science, Research and Development
1985 EUR 9864 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of then is responsible for the use which might be made of the following
information
© ECSC—EEG— EAEC Brussels - Luxembourg, 1985 - III -
REPORT SUMMARY 1. Objectives of the research
In manufacturing silicon cells for photovoltaic panels it is advantageous
to have a method for producing the silicon in strips about 0.5 to 1mm thick,
Square or rectangular cells can be cut from a strip cheaply and with
hardly any loss of material, and they cover the panel surface better than
round cells cut from a cylinder. When round cells are replaced with square
there is a 27.3 % gain in surface coverage. There are thus three initial
advantages for this type of production :
- far less loss of material during manufacture;
- the square or rectangular shape of the cells obtained;
- the possibility of production by a continuous process.
Producing silicon ribbon by the PDG process
2.1 - PPG process principle -
In order to produce crystals with particular geometrical shapes
differing from the cylinders conventionally manufactured through
Czochralsky, Verneuil or zone melting techniques, PUK has developed
a so-called PDG (Pendant Drop Growth) patented process wherein
crystals are shaped by a die.
The process principle is simple : the powdered crystallizing product
is dropped in a high frequency heated crucible, melts in it and flow
into a capillary duct. Crystallization takes place at the outlet of
that duct whose configuration induces the crystal shape. As a principle,
any shape can be imparted to the crystal : strip, sheet, wire,
cylinder, tube, etc.
(0
(1) powder supply
(2) crucible
(3) liquid
'f.) c ry s t a 1
Γ>) -
PLAQUE
SILICIUM
Side view 2.
2.2 ­ Features observed or confirmed during the contract ­
2.21 ­ Recap of other crystals studied
The PDG pre­shaped crystallization method has multiple applications.
It has already been successfully used for :
­ NaCjl (melting point 800°C) : strips and small cylinders;
­ AlgOg.«. sapphire (melting point 2050°C) : strips 27 χ 200
χ 0.8 mm ; 6mm­diameter cylinders;
­ r.uJ»«Lefi of A^O . 9C doped with Cr**+ : 6mm­diameter cylinders;
­ lanthanum aluminate doped with Nd : r .
2.22 ­ Theses by J. PUFFAR
¡ιΓ.ιι"υιΤ~ιι> Οιιιι» fin -Jini »J."i
After the term of the contract (February 1982) the research was
continued until November 1982, when T. Duffar presented his thesis
at Grenoble, "Crystallization of silicon ribbons by the pendant drop
method, for use in solar cells".
This thesis increased our experience and developed our theoretical
models.
2.23 ­ Proven advantages of the PPG method for silicon
2.231 ­ The crystallization process
. Continuous production· Two manufeeturers, CAMBRIDE INSTRUMENTS (GB)
and LPA, have SMjppJ­ied estimates for building PDG apparatus based on
our prototypes. Since we operate with a chamber pressure slightly
above atmospheric, a pressure lock is specified at the strip outlet
so that the strip can be extracted continuously, with intermittent
cutting.
. Automatic control. The crystallization operations were carried out
with :
­ Adjustment of ".r.e induction heating source power, controlled by
a pyrcme*;*:­­ ti'.áí lontiruously measured crucible lip temperature
■ with set po­nt. ; 3.
- Continuous weighing of the silicon supplied from a vibrating bowl
programmed by a CRG system.
Self-stabilizing characteristic. Once the liquid meniscus has formed
above the strip during crystal growth, and provided the lip tempera­
tures remain stable, the slight instantaneous variations in the
silicon supply or in the drawing rate are compensated by variations
in the meniscus volume, which continuously returns to an equilibrium
situation. This phenomenon is due to the surface tension of the
liquid meniscus.
This characteristic of the PDG method is confirmed by T. DUFFAR's
calculations.
This characteristic facilitates; automatic control.
Purification. Two purification processes were observed :
- oxygen is removed, no doubt because of CO and CO combinations
due to the graphite crucible;
- some impurities (Na, Al) migrate to the surfaces of the strip.
Dimensional capabilities.
. Strip width. The range 25 - 100 mm can be covered merely by
changing the crucible and the induction coil.
. Length. The length is limited by the length of our crystallization
chamber.
. Thickness. Thicknesses of 0.9mm have been obtained in some tests
over 1 to 2 cm. we established at the end of 1982 the theoretical
and practical requirements for achieving 0.6mm. We have found a
manufacturer who is able to produce the thin-lipped crucibles.
Structural capabilities. Columnar structure is achieved consistently
with the correct seed. In these conditions the joints are mostly
twinning joints perpendicular to the surface of the strip. 4.
2.232 - Apparatus
. Our prototype apparatus has worked with no failure. Two manufac­
turers are prepared to supply series production (cf. §2.231).
. Crucibles. Our tests have proved that graphite lined with SiC is
the best material. These crucibles are inexpensive (less than FF3000)
and their service life is hoped to be about 200 hours. Crucible replace­
ment time is about 3 hours before drawing can be resumed.
The amount of silicon residing in the crucible is less than 0.5cu.cm
for a strip 27mm wide. The residence time is 4 to 6 minutes, which
minimizes the reaction Si + C.
Crucible size remains small : 50mm diameter and 50mm depth for strip
widths up to 45mm.
. Maintenance· Maintenance is simple : cleaning the crystallization
chamber and ancillary equipment. Crucible replacement is easily per­
formed .
2.233 - Economic aspects
The cost priée simulation programme based on various parameters
(drawing speed, crucible life, strip width and thickness) indicates
that there are several possibilities for manufacturing the ribbon
industrially for less than FF500 per sq.m where the cost of silicon
is FF70 per kilo.
The cost of equipment is estimated to be 1 + 0.2 million French francs
where there is a single drawing apparatus and a two-die crucible.