ANM
2010
3rd
International Conference on Advanced Nano Materials
12-15 September 2010 - Agadir, Morocco
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Abstract
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ANMM300 |
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POLYMORPHOUS SILICON SOLAR CELLS WITH INCUBATION FREE
LAYER NANOCRYSTALLINE SILICON CARBIDE P-TYPE DEPOSITED WITH
TRIMETHYLBORON (TMB) |
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H. Águas, S.A. Filonovich,
A. Araujo, A. Vicente, S. Ram, E. Fortunato, R. Martins |
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CENIMAT/I3N, Departamento de Ciência dos
Materiais, FCT-UNL, 2829-516 Caparica, Portugal
Departamento de Conservação e Restauro, FCT-UNL, 2829-516
Caparica, Portugal |
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P-type
hydrogenated nanocrystalline silicon films with carbon incorporation
(nc-Si:C:H) films are attractive for use in amorphous and
nanocrystalline silicon solar cell (SCs) application as a window layer.
Those films have high electrical conductivity and transparency, being
more stable under illumination (decreased degradation) then its
amorphous counterpart.
Trimethylboron (TMB) has been receiving attention as a better
alternative to diborane and methane mixtures for the deposition of
p-type silicon films for application in solar cells. TMB is
particularly well suited for the solar cell deposition process; since
it has a superior thermal stability relative to the more conventional
boron sources such as diborane. Moreover, the fact the TMB has already
carbon in its composition, makes unnecessary the addition of CH4 to the
mixture to increase the optical gap and reduce optical absorption.
In spite of these advantages, p-type nc-Si:C:H films are difficult to
obtain using TMB. It has been shown that under the same deposition
conditions, TMB reduces crystalline fraction from 87% to 53% as
compared to diborane, which results that very thin p-type nc-Si:C:H
films (~ 20 nm) necessary for solar cells are difficult to obtain using
standard deposition conditions. To overcome this difficulty, we used
novel deposition conditions that featured relatively high gas pressure
(3 Torr), high hydrogen dilution (98%) and low deposition temperature
(150ºC). Leading us to achieve dark conductivity, σd, values
of 1 S/cm for 20 nm films, without incubation layer confirmed by
Spectroscopic Ellipsometry analysis of the films.
These p-type nc-Si:H layers were used as a window layers in
polymorphous silicon SCs, and preliminary results of non-optimized SCs
exhibit low series resistance and efficiency about 6%. A study in
underway to further improve the SCs efficiency to 8 to 9 % by inclusion
of a buffer layer between the P and I layers, to match the band gaps of
these two layers, which results in an increase of the SCs open circuit
voltage, from 0.7 to 1.0 V. |
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