Polycrystalline silicon

HAL Id: jpa-00245568

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Submitted on 1 Jan 1987

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Polycrystalline silicon

Bernard Equer, Pierre Pinard, André Rocher, Michel Rodot

To cite this version:

Bernard Equer, Pierre Pinard, André Rocher, Michel Rodot. Polycrystalline silicon. Re- vue de Physique Appliquée, Société française de physique / EDP, 1987, 22 (7), pp.513-513.

�10.1051/rphysap:01987002207051300�. �jpa-00245568�

Polycrystalline ^silicon

Foreword

This

special

issue of the Revue de

Physique Appliquée

^{forms a}

report

^on five years of research aided and’

coordinated

by

^the

photovoltaic

programme of the CNRS and AFME on the

general

^{theme of}

grain

boundaries in silicon. It contains about

twenty

contributions from

public

and industrial research laboratories which are involved

together

^on

polycrystalline

^silicon solar cells

projects.

^It

presents

^{also some results on the :}

same field from other groups.

The main

objective

^{of this}

activity

^{was to} understand how the

crystallographic

^{structure and the}

chemical

impurities governed

^the

photoelectric properties

^of

grain

boundaries. The materials studied included different

types

^of

polycrystals

^{and a} number of artificial

bicrystals ; they

have been submitted to various thermal treatments. The structure of the

grain

boundaries and the interfacial defects were studied

by TEM

^and

X-ray topography.

Electrical

properties

^were determined

by DLTS, conductance,

^{SEM/EBIC and}

LBIC measurements. The chemical

analysis

^{has been}

performed by SIMS,

^neutron

activation,

^electron and infrared

spectroscopies. Finally

^some theoretical work was devoted to energy levels

brought

^about

by interfacial

defects and to the 3-d

modelling

^of

polysilicon

solar cells.

From the results

presented

^{in this}

special issue,

^some conclusions of this collective work can be

quoted.

Large bicrystalline ingots

^{have been obtained}

by

^the Czochralski

pulling

process without

intragrain

dislocations.

They

contain well defined

grain

boundaries which

permit

^{us to} obtain correlations between a

large

number of studies. It has been shown that the

dangling

^{bond is not the main}

agent

^{of the electrical}

activity

^{of the}

grain boundary.

^This

activity,

^often

drastically

^modified

by

thermal treatments, ^is

mainly

related to

impurity

^effects

(diffusion

^or

segregation). Oxygen

^{is one of the}

impurities

^{involved. The}

complete

thermal

history

^{of the}

samples

^is

important

^to understand the electrical

activity

^{of a defect.}

The removal of surface

impurities by gettering

^{has been}

studied,

^{as well as} the role of

deliberatly

introduced

impurities.

Several of the

phenomena

^{observed were ascribed to} interactions between

impurities (e.g.

^{H and}

acceptors,

^{Al and}

oxygen).

^The introduction of

hydrogen

^causes

multiple

^{effects : it increases}

particulary

^the

photoelectrical properties by passivation

of defects.

The studies

bearing

^on industrial

crystals,

in which various

types

^of

grain

boundaries are

present,

allowed the effect of

grain

^{size on cell}

efficiency

^{to be} characterized :

they

^showed that the effects of

intragrain

defects and

impurities

^{such as C or 0 are often dominant}

compared

^{to those of}

grain

boundaries.

Finally,

it appears that the

efficiency

^{of a}

photovoltaic panel using polycrystalline

square cells is ^now

equivalent

^to that obtained with

monocrystalline

^circular

cells,

^the

efficiency

^{loss of}

polysilicon being compensated by

the fact that the surface cover is 25 %

higher

than that of an as grown

monocrystal.

Bernard

Equer,

^Pierre

Pinard,

André Rocher and Michel

Rodot,

^{March 1987}

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01987002207051300