Photoconverters with hetero-interface structure for powerful electrical systems
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| Дата: | 1999 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Назва видання: | Вопросы атомной науки и техники |
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| Цитувати: | Photoconverters with hetero-interface structure for powerful electrical systems / A.N. Dovbnya, V.P. Yefimov, S.V. Yefimov, A.N. Sleptsov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 113-114. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-813592015-05-15T03:02:41Z Photoconverters with hetero-interface structure for powerful electrical systems Dovbnya, A.N. Yefimov, V.P. Yefimov, S.V. Sleptsov, A.N. 1999 Article Photoconverters with hetero-interface structure for powerful electrical systems / A.N. Dovbnya, V.P. Yefimov, S.V. Yefimov, A.N. Sleptsov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 113-114. — Бібліогр.: 5 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81359 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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English |
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Article |
| author |
Dovbnya, A.N. Yefimov, V.P. Yefimov, S.V. Sleptsov, A.N. |
| spellingShingle |
Dovbnya, A.N. Yefimov, V.P. Yefimov, S.V. Sleptsov, A.N. Photoconverters with hetero-interface structure for powerful electrical systems Вопросы атомной науки и техники |
| author_facet |
Dovbnya, A.N. Yefimov, V.P. Yefimov, S.V. Sleptsov, A.N. |
| author_sort |
Dovbnya, A.N. |
| title |
Photoconverters with hetero-interface structure for powerful electrical systems |
| title_short |
Photoconverters with hetero-interface structure for powerful electrical systems |
| title_full |
Photoconverters with hetero-interface structure for powerful electrical systems |
| title_fullStr |
Photoconverters with hetero-interface structure for powerful electrical systems |
| title_full_unstemmed |
Photoconverters with hetero-interface structure for powerful electrical systems |
| title_sort |
photoconverters with hetero-interface structure for powerful electrical systems |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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1999 |
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http://dspace.nbuv.gov.ua/handle/123456789/81359 |
| citation_txt |
Photoconverters with hetero-interface structure for powerful electrical systems / A.N. Dovbnya, V.P. Yefimov, S.V. Yefimov, A.N. Sleptsov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 113-114. — Бібліогр.: 5 назв. — англ. |
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Вопросы атомной науки и техники |
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2025-07-06T06:05:26Z |
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| fulltext |
PHOTOCONVERTERS WITH HETERO-INTERFACE STRUCTURE FOR
POWERFUL ELECTRICAL SYSTEMS
A. N. Dovbnya, V. P. Yefimov, S. V. Yefimov, A. N. Sleptsov
NSC KIPT, Kharkov, Ukraine
INTRODUCTION
At present single crystalline silicon (ñ-Si)
photocells (PC) with protective quartz (SiО2) coatings
are widely applied to energy provision of autonomous
and mobile objects during long-time operation in rigid
conditions of the Earth and outer space. However, their
use has been revealed by a number of serious lacks.
They are (1) low conversion efficiency of PC (12-17
%); (2) shallow n-p-junction in c-Si-photocells, which
collapses while being in service in extreme conditions
of thermo-cycling, erosive influence on the PC surface
of chemically active atoms and molecules, meteorite
streams, charged electrization, rigid UV and irradiation;
(3) optical properties of SiO2 protective coating are not
optimum and moreover become worsened under the
influence of rigid UV [1].
The application of cascade system from photo-
voltaic materials with the different optical performances
is considered as the most perspective technology of
PC`s efficiency raising. The maximal efficiency can be
reached in silicon hetero-photocells with multiinterface
structure, providing the creation of cascade distribution
of band-gap (Eg) in the semiconductor material. The
frontal surface in such heterosystem should have the
width band-gap structure (Eg ~ 4 eV), while for other
structures the quantity Eg must consecutively decrease.
For exception of losses of low-energy quantums, the
least value of Eg must be small. For PC silicon the least
Eg is determined by c-Si(Al)-structure (Eg ~ 0,8 eV).
The sharp hetero-junctions in material bulk are realized
only under the condition of changing crystalline
structure on width of ~ 20 angstrom. The creation of
such crystalline interface structures with sharp (δ)
transition layers by traditional chemical and diffusion
methods is not possible. Using radiation methods of
crystalline structure disordering of hydrogenated c-Si-
photocell can be solve this problem. In such disordered
structures it is possible to achieve the electrostatic fields
E > 104 V/cm. The formation of amorphous-crystalline
interface structures with gradient distribution in
semiconductor bulk provides the creation of strong
pulling electrostatic (δ-BSF)∇Еg fields
Е= (-∇Еg)./q, (1)
where q-is an electron charge. The width of photo-
convertors 0,5-1 mm is necessary for the full absorption
of solar radiation in monocrystal silicon. It allows to
execute (с-Si)-photocells with deep p-n-junction and to
protect it from destroying influence of electrization in
outer space conditions. Besides, such hetero-system
from amorphouse-crystalline structures allows to use
the broad range of solar spectrum (UV, visible light,
short-range IR-radiation) with high intensity of
quantum fluxes. These electrostatic fields will create
the directional motion of minority charge carriers in c-
Si heterostructure with deep p-n-junction (see Fig. 1).
In this case the dimensional distribution of charge
carriers (CC) will not depend on their diffusion length.
The coefficient of CC assembly and internal quantum
yield of photoionization determine spectral
characteristic of photoconverters. The throughput
capacity of frontal PC plane in the short-wave range of
solar spectrum increases at formation of both width
band-gap а-SiС:H structures and polycrystalline
diamond coatings (poly-DC). The CC photogeneration
in long-wave range of solar spectrum increases by
multiple luminous flux passage in semiconductor bulk.
This process is provided by texturization of frontal c-Si
matrix surface and creation of reflecting back contact
plane. The conversion efficiency of c-Si-hetero-
photocell at execution of these technological features
can be increased up to 40%. Such photoconverter with
deep p-n-junction and diamond coatings will be
protected from destroying influence of environmental
activity.
window UV (δ -BSF)∇ Eg interface
a-Si:H( D) /c- Si:H( D)
Si<Al>
(BSF) L-H interface
n+ +
p-n
junction
B-basa
E-emitter
e hν
IR radiation reflector
DC film
(p)
grid contact
(Al)
(δ -BSF)∇ Eg layers interface
rear sheet contact (Ag)
Fig.1. с-Si-heterophotocells with transformed
structure.
Eg
0 10 20 30 40
1.5
1.6
1.7
1.8
1.9
2.0
1
2
Hydrogen content, at. %
Fig.2 Dependences of width optical gap Еg on
hydrogen concentrations in а-Si film:
1- deposited film, 2 - annealed film [3].
FORMATION OF AMORPHOUS CLUSTERS IN
с-Si SEMICONDUCTOR BULK
The presence of localized states continuum is the
main particularity of amorphous semiconductors. The
long-range order in a-Si materials is absent, but the
short-range order is maintained by presence of the
chemical bond. The a-Si structure is characterized by
randomly lattice with a covalent binding of atoms. The
absence of the long-range order causes both the
diffusion of fundamental absorption edge and
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 113-114.
113
appearance of tails of both valence zone and conduction
band. It is note, the state of amorphous clusters in
crystal lattice is metastable. For their stabilization in
order to conservations of the dimensional disordering in
crystalline matrix is used hydrogenation method. The
concentration of chemically connected hydrogen atom
influences a degree of a disordering structure, that it
determines the energy magnitude of optical gap, Eg.
The dependence Еg on concentration of hydrogen atoms
in a-Si materials is shown in fig. 2. As following from
presented data, the Еg value is increased up to ~ 1,8 eV
in a-Si structure while the growth of hydrogen
concentration is reached value up to 20 at.%. The
photons absorption coefficient for a-Si structure under
condition of direct quantum transition is:
α(λ) = В2 (hν - Еg)2/hν, (2)
where B = 700 eV-1/2 cm-1/2. . The α value for UV is ∼106
cm-1 that is on the order more than in c-Si structure.
Doping the a-Si:H materials by boron (В) does not
cause the degeneration processes, as it has a place in c-
Si matrix, but creates a new structure defects which are
to be eliminated.The formation of disodering clusters in
silicon is observed under irradiation by high-energy
particles when a primary knocked out atom get the
energy Е0 ≥ 5 keV. In the case of electron irradiation
the primary energy of particles should be as Ее ≥ 10
MeV. The disordered ranges represent local defect
clusters with the size 100-1000 angstrom. These
clusters are surrounded by a layer of space charge and
are blocked by fluxes of charge carriers. The point
defects are being created only in the case when a recoil
energy of atom is below 5 keV (threshold energy of
disordered structures creation). The irradiation of
silicon crystals is being carried out by intensive electron
beams with energy Ее ≥ 20 MeV up to doses 10-3
displacement per atom (dpa) at temperature 450 K. The
formation of ñ-Si(Al) structures is being created by the
method of nuclear microdoping using the
bremsstrahlung gamma-quantums with energy E > 25
МeV and irradiation dose up to 10-5 dpa [2]. The p-type
of electrical conductivity of c-Si(B) semiconductor is
being saved during gamma-irradiation. As the
irradiation dose increasing, the number of nonradiating
recombination centres in the semiconductor increases
and the CC concentration and their mobility is being
decreased. Hydrogenation of c-Si matrix, which is
necessary for both stabilization of amorphous clusters
and neutralization of recombination centres, is carried
out by two methods - (i) isostatic pressing treatment of
the semiconductor in the temperature range 300-800 K
and pressure up to 100 MPa; (ii) irradiation by
hydrogen-helium plasma up to dose 1.1017 cm-2. In such
hydrogenated material the time (t) of radiation defects
neutralization and formation of (a-Si:H)-structures in
dependence on the annealing temperature Т(K) is being
described by equation [4]:
t = t0 exp (1,6 10-19 εа /kT), (3)
where εа - activation energy (1,18 eV); t0 = 10-11 s for
(Si:H)-compound. The hydrogen distribution and their
concentration in volume of such material determines the
distribution profile of а-Si/с-Si interface structures in a
matrix and the intensity of pulling electric (δ-ВSF)∇Еg
fields, respectively.
FORMATION OF OPTICAL WINDOW ON THE
FRONTAL PHOTOCELL PLANE
The heterosystem consists from band-gap poly-
DC (Eg = 5,5 eV) and a-SiC:H (Eg = 3,5 eV) structures
is formed on the photovoltaic material surface in order
to increase the throughput capacity of the frontal photo-
converters plane in the short-wave range of solar
spectrum. The formation of poly-DC-structures with
properties like natural diamond is realized by CVD
method in dense hydrogenous plasma of UHF-resonator
with E011- wave mode. Specifity of texturization,
creations of a-Si and diamond coatings on the frontal
photocells plane does not allow the polutions of their
surface. At the working gas 99% H2+ 0,7% CH4+ 0,3%
O2 the synthesis temperature of fine-grained poly-DC
can be decreased up to 725-925 K by sensibilization
oxygen of reaction [5].
The texture formation on c-Si-matrix surface is
realized by a laser irradiation in intensive fluxes of
UHF hydrogenous plasma. The 30 МW power of laser
irradiation with a pulse length in 15 ns is required for
melting of silicon shallow layer by thickness of 0,2
microns. The detraping hydrogen during a solidification
of hydrogenated shallow layer deforms it and creates
blisters with sizes which are close to a wave length of
visible spectrum and IR-radiation. These blisters are
scattering the incident photons and increasing a passage
trajectory of light and its general absorption. The
continuous back contact of photocell intensifies the
radiation reflection and by that increases its full internal
absorption in the photocell emitter. The texturization of
the frontal surface causes a short-circuit current
increasing. The interferograms of a laser radiation are
used for measurements of film thickness and blisters
sizes during the texturization.
The pulling electrostatic fields for majority
charge carriers (BSF)L-H in plane base of n-c-Si(P)-
photocell are being created in structure of n-n+-type.
The methods combination of radiation-induced
disordering structures, CVD and laser irradiation allows
to advance a new technologies for creation of silicon
photo-converters with high conversion efficiency in a
broad range of waves lengths of solar radiation. The
protected silicon photocells from irradiation, charged
electrization, temperature and mechanical influences
will allow considerably increase their operation
resource in conditions of high-intensive fluxes of solar
radiation.
REFERENCES
1. S. Bailey, H. Curtis, K. Long, Proc. of 2-nd World Conference and
Exhibition on Photovoltaic Solar Energy Conversion, Vienna,
Austria, 6-10 July, 1998 (in press).
2. A. N. Dovbnya, V. P. Yefimov, S. V. Yefimov Using beams
technologies in development of photocells for solar batteries
spacecrafts. Problem At. Sci. Technol. 1(28) (1997) p. 58. (in
Russian)
3. А. Madan, M. P.Shaw. The Physics and Application of Amorphous
Semiconductors. M.: Mir, 1991, 670p.
4 A. N. Dovbnya, V. P. Yefimov, S. V. Yefimov, Radiation
transformation of photovoltaic materials structure, Problem At.
Sci. Technol. 1(73), 2(74) (1999) p. 143.
5. A. N. Dovbnya, V. P. Yefimov, S. V. Yefimov, Formation of width
band gup a-SiC:H(D)/ с-Si(B):H(D) interface structure and
diamond coatings in (с-Si)-photocells, 14th Int. Conf. on Ion
114
-Surface Interactions (ISI-99), Zvenigorod (Moscow), Russia, 30
Aug.-3 Set. 1999, (in press).
114
INTRODUCTION
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