On the Stability of Operation of Antimony Sulfide
Selenide Thin Film Solar Cells Under Solar Radiation
Bernardino Ríos-Ramirez and P. K. Nair*
Operational stability of FTO/CdS/Sb
2
S
1.08
Se
1.92
/C-Ag thin film solar cells
under solar radiation is presented. These solar cells are produced on fluorine-
doped SnO
2
(FTO) by thermal evaporation of Sb
2
S
3
and Sb
2
Se
3
powders.
Thin film of Sb
2
S
1.08
Se
1.92
(300 nm) shows a bandgap of 1.45 eV. Its electrical
conductivity is 10
7
Ω
1
cm
1
(dark) and 10
5
Ω
1
cm
1
under illumination.
Thin film of CdS (120 nm) for the solar cell is obtained on FTO by chemical
deposition. Antimony chalcogenide film is deposited on FTO/CdS substrates
maintained at 425
C via thermal evaporation from a mixture of Sb
2
S
3
and
Sb
2
Se
3
powders. Subsequently, graphite paint and silver paint electrodes of
area 0.49–0.64 cm
2
are applied on it. Efficiency of conversion (η) is 5.9 % for
the best solar cell and 5.6% on an average for eight cells. Open circuit
voltage (V
oc
) of the cell is 0.453 V; short circuit current density ( J
sc
),
24.7 mA cm
2
; and fill factor, 0.53. For solar cells placed under the sun over
5 days in the exterior with exposure of 24 kWh m
2
, η dropped to 5%. Under
30 suns, V
oc
of 0.54 V and J
sc
of 130 mA cm
2
are recorded. The cells
remained functional.
1. Introduction
Antimony sulfide (Sb
2
S
3
) as well as antimony selenide (Sb
2
Se
3
)
condense into orthorhombic crystal system and hence they can
form solid solutions of Sb
2
S
x
Se
3-x
.
[1]
The optical bandgap (E
g
) of
such materials may be continuously varied between 1.1 eV
(Sb
2
Se
3
) and 1.88 eV (Sb
2
S
3
),
[2]
thereby offering in them E
g
of
1.3–1.6 eV recommended for successful solar cells.
[3]
Solar cells
have been prepared by thermal evaporation of powder samples
of precipitates and/or commercial Sb
2
S
3
powder with solar-to-
electric energy conversion efficiency (η) of up to 4.27%.
[4,5]
Progress made in thin film solar cells of Sb
2
S
x
Se
3-x
produced by
various modifications of thermal evaporation and/or post-
deposition processing of the cell structures with η close to 7%
has been reviewed in 2016–2017.
[6,7]
Stability of these solar cells
during long term storage has been found exceptionally good.
[7]
Widespread availablity of antimony would support large-scale
module production in case η of these solar cells surpasses 20%.
More than 60 minerals have antimony content of 40–100%.
Native antimony (100%), valentinite (Sb
2
O
3
, Sb – 83%),
stibnite, and metastibnite (Sb
2
S
3
, Sb –
71.7%) are among them.
[8]
With seem-
ingly attractive cost, availability and low
toxicity of antimony for solar cell develop-
ment,
[4–7]
an assurance on the stability of
operation of Sb
2
S
x
Se
3-x
solar cells under
solar radiation is relevant prior to dedicat-
ing further research on it. We report a
study made on solar cells of η,5–6%
produced by thermal evaporation of
chemical precipitates prepared in our
laboratory: Sb
2
S
3
from a solution of
antimony trichloride and thiousulfate
[9]
and Sb
2
Se
3
, from a solution of potassium
antimony tartrate and selenosulfate.
[4,5]
Solar cell parameters were tracked as a
function of exposure under solar radiation
for up to 24 kWh m
2
during 5 days and
under concentrated sunlight of up to 30
suns at mid-day. We report good stability
for these solar cells.
2. Experimental Section
2.1. Chemical Reactions
Reagents used for the preparation of the solution for the
precipitates of Sb
2
S
3
[9]
and Sb
2
Se
3
[4,5]
were from Sigma–Aldrich
and “Baker Analyzed” of laboratory reagent grade (98–99%
assay). Chemical reactions leading to the formation of
precipitates are found in
[10]
:
2Sb
3þ
þ 3S
2
! Sb
2
S
3
; and 2Sb
3þ
þ 3Se
2
! Sb
2
Se
3
:
2.2. Sb
2
S
3
Precipitate
Solution contained antimony trichloride dissolved in acetone and
thiosulfate in deionized water. For the reaction to generate the
precipitate, it was maintained at 60
C for 4–5 h. It was
subsequently cooled down to room temperature during overnight;
filtered, rinsed, dried, and stored. Energy dispersive x-ray emission
spectra (EDS) of this precipitate gave Sb:S proportion of 40:60.
2.3. Sb
2
Se
3
Precipitate
Solution contained potassium antimony tartrate, triethanol-
amine, ammonia (aq.), silicotungstic acid, selenosulfate
B. Ríos-Ramirez, Prof. P. K. Nair
Instituto de Energía Renovables
Universidad Nacional Aut onoma de M exico Temixco
Morelos 62580, M exico
E-mail: pkn@ier.unam.mx
DOI: 10.1002/pssa.201800479
status
solidi
physica
a
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ORIGINAL PAPER
Phys. Status Solidi A 2018, 1800479 © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1800479 (1 of 8)