Thin film solar cells of CdS/Sb2S3/C-Ag are developed on glass substrates coated with SnO2:F (FTO) by thermal evaporation of Sb2S3 powder. At a thickness of 110nm, Sb2S3 thin film which is heated at ...300°C has an optical band gap Eg of 1.75eV; optical absorption coefficient in the visible region of >105cm−1; and photoconductivity (n-type) of 1.5×10−6Ω−1cm−1. The film with 450nm in thickness is of Eg 1.5eV. A solar cell, FTO/CdS/Sb2S3 (450nm)/C-Ag, prepared with this film has an open circuit voltage, Voc, of 600mV, short circuit current density, Jsc, of 6.1mA/cm2, and a solar energy conversion efficiency of 1.27%.
•Antimony sulfide thin films are prepared by thermal evaporation.•Structural, optical and electrical properties of the films are presented.•CdS/Sb2S3 solar cell has a Voc at 600mV and conversion efficiency at 1.27%.
The tin sulfide solar cell has acquired prominence in recent years. We present the characteristics of two polymorphs of SnS and their perspectives in thin‐film solar cells. Thin‐film SnS with cubic ...crystalline structure (SnS‐CUB) was obtained via two chemical routes. This semiconductor is distinct from the more common SnS thin films of orthorhombic crystalline structure (SnS‐ORT), also obtained by chemical routes. The SnS‐CUB reported here with a lattice constant a of 11.587 Å replaces the zinc blende structure previously reported for this material with a of 5.783 Å. Thin films of SnS‐CUB have an optical bandgap (Eg) of 1.66–1.72 eV and electrical conductivity (σ) of 10−6 Ω−1 cm−1. These characteristics distinguish them from SnS‐ORT presented here with an Eg of 1.1 eV and σ typically higher by two orders of magnitude. We discuss the uncertainties that have prevailed in the assignment of crystalline structure for SnS‐CUB and SnS‐ORT. The optical and electrical properties of these two polymorphs of SnS are contrasted in the context of light‐generated current density in solar cells. We conclude that the two SnS polymorphs when considered together as optical absorbers offer wider prospects for tin sulfide thin‐film solar cells.
Solar cells with a short-circuit current density (J sc ) of 6mA/cm2, an open circuit voltage (V oc ) of 280mV and a conversion efficiency of 0.5% under a 1000W/m2 solar radiation were prepared by ...sequential chemical deposition of Bi2S2 (160nm) and PbS (400nm) thin films. The optical band gap (E g ) of Bi2S3 (160nm) decreased from 1.67 to 1.61eV upon heating the as-deposited film at 250A degree C in air for 15min to make it crystalline, but also reduced its thickness to 100nm. Photoconductivity of this film is 0.003 (a"brvbarcm)a degree 1. The E g of PbS film (200nm) deposited at 25A degree C (24h) is 0.57eV, and is 0.49eV for the film deposited at 40A degree C. The electrical conductivity of the latter is 0.48 (a"brvbarcm)a degree 1. The photo-generated current density for a Bi2S3(100nm)/PbS(300nm) absorber stack is above 40mA/cm2 under AM 1.5G (1000W/m2) solar radiation. However, the optical losses in the cell structure reduces the J sc . Spectral sensitivity of the external quantum efficiency of the cell establishes the contribution of Bi2S3 and PbS to J sc . The energy level diagram of the cell structure suggests a built-in potential of 470mV for the present case. Six series-connected cells gave the V oc of 1.4V and J sc of 5mA/cm2.
Antimony sulfide thin films of thickness ≈
500 nm have been deposited on glass slides from chemical baths constituted with SbCl
3 and sodium thiosulfate. Smooth specularly reflective thin films are ...obtained at deposition temperatures from −
3 to 10 °C. The differences in the film thickness and improvement in the crystallinity and photoconductivity upon annealing the film in nitrogen are presented. These films can be partially converted into a solid solution of the type Sb
2S
x
Se
3
−
x
, detected in X-ray diffraction, through heating them in contact with a chemically deposited selenium thin film. This would decrease the optical band gap of the film from ≈
1.7 eV (Sb
2S
3) to ≈
1.3 eV for the films heated at 300 °C. Similarly, heating at 300 °C of sequentially deposited thin film layers of Sb
2S
3–Ag
2Se, the latter also from a chemical bath at 10 °C results in the formation of AgSb(S/Se)
2 with an optical gap of ≈
1.2 eV. All these thin films have been integrated into photovoltaic structures using a CdS window layer deposited on 3 mm glass sheets with a SnO
2:F coating (TEC-15, Pilkington). Characteristics obtained in these cells under an illumination of 850 W/m
2 (tungsten halogen) are as follows: SnO
2:F–CdS–Sb
2S
3–Ag(paint) with open circuit voltage (
V
oc) 470 mV and short circuit current density (
J
sc) 0.02 mA/cm
2; SnO
2:F–CdS–Sb
2S
3–CuS–Ag(paint),
V
oc
≈
460 mV and
J
sc
≈
0.4 mA/cm
2; SnO
2:F–CdS–Sb
2S
x
Se
3
−
x
–Ag(paint),
V
oc
≈
670 mV and
J
sc
≈
0.05 mA/cm
2; SnO
2:F–CdS–Sb
2S
3–AgSb(S/Se)
2–Ag(paint),
V
oc
≈
450 mV and
J
sc
≈
1.4 mA/cm
2. We consider that the materials and the deposition techniques reported here are promising toward developing ‘all-chemically deposited solar cell technologies.’
Chemically deposited SnS thin films possess p-type electrical conductivity. We report a photovoltaic structure: SnO
2:F–CdS–SnS–(CuS)–silver print, with
V
oc
>
300 mV and
J
sc up to 5 mA/cm
2 under ...850 W/m
2 tungsten halogen illumination. Here, SnO
2:F is a commercial spray-CVD (Pilkington TEC-8) coating, and the rest deposited from different chemical baths: CdS (80 nm) at 333 K, SnS (450 nm) and CuS (80 nm) at 293–303 K. The structure may be heated in nitrogen at 573 K, before applying the silver print. The photovoltaic behavior of the structure varies with heating:
V
oc ≈ 400 mV and
J
sc
<
1 mA/cm
2, when heated at 423 K in air, but
V
oc decreases and
J
sc increases when heated at higher temperatures. These photovoltaic structures have been found to be stable over a period extending over one year by now. The overall cost of materials, simplicity of the deposition process, and possibility of easily varying the parameters to improve the cell characteristics inspire further work. Here we report two different baths for the deposition of SnS thin films of about 500 nm by chemical deposition. There is a considerable difference in the nature of growth, crystalline structure and chemical stability of these films under air-heating at 623–823 K or while heating SnS–CuS layers, evidenced in XRF and grazing incidence angle XRD studies. Heating of SnS–CuS films results in the formation of SnS–Cu
x
SnS
y
. ‘All-chemically deposited photovoltaic structures’ involving these materials are presented.
Tin selenide thin film with a simple cubic crystalline structure (SnSe‐CUB) of unit cell dimension a = 11.9632 Å is obtained via chemical deposition on a tin sulfide (SnS‐CUB) thin film base layer of ...simple cubic structure of a = 11.5873 Å. The SnSe‐CUB films obtained this way are thermally stable while heating to 300 °C. Its optical band gap is 1.4 eV. A thin film of 200 nm in thickness of this material in a solar cell may lead to a light generated current density of 23 mA cm−2 and a maximum of 29 mA cm−2. Thin film of SnSe‐CUB possesses p‐type electrical conductivity of 5 × 10−5 Ω−1 cm−1, which is three orders of magnitude lower than that of SnSe films of orthorhombic crystalline structure. Overall, these characteristics make SnSe‐CUB thin film a novel solar cell absorber material.
Chemical bath deposition yields SnS thin films of cubic, SnS-CUB, or of orthorhombic, SnS-ORT, crystal structures. They have optical bandgaps (Eg) of 1.7 eV and 1.1 eV, respectively. We present solar ...cells produced by depositing these SnS thin films on glass substrates coated with F-doped SnO2 (SnO2:F) as transparent conducting oxide (TCO) and CdS film of Eg, 2.6 eV as window layers. Chemical bath for depositing SnS-CUB thin films contained thioacetamide, while that for SnS-ORT contained thiosulfate as the source of sulfide. With SnS-CUB, TCO/CdS(80 nm)/SnS-CUB(400 nm)/C-Ag solar cells showed open circuit voltage (Voc) of 0.368 V, short circuit current density (Jsc) of 2.7 mA/cm2, fill factor (FF) of 33% and conversion efficiency (η) of 0.33%. Solar cells with CdS (120 nm) SnS-ORT (1200 nm) thin films showed Voc, 0.336 V; Jsc, 13 mA/cm2; FF, 25% and η, 0.96%. For a solar cell with both SnS-CUB and SnS-ORT absorber films: TCO/CdS(80 nm)/SnS-CUB(200 nm)/SnS-ORT(300 nm)/C-Ag, Voc was 0.488 V; Jsc, 6.96 mA/cm2, FF, 41% and η, 1.38%.
•All-chemically deposited solar cells of SnS absorber layers•Composite absorber of orthorhombic SnS (SnS-ORT) on cubic SnS (SnS-CUB)•TCO/CdS/SnS-CUB (1.7 eV)/SnS-ORT (1.3 eV)/C solar cell•Open circuit voltage of 0.488 V with conversion efficiency of 1.38%•Cubic-SnS/Orthorombic-SnS solar cell holds prospects for future work.
PbSe thin films were prepared by chemical deposition using dimethylselenourea as a source of selenide ions. Depending on the duration (30
min to 4
h) and temperature (30–60
°C) of the deposition, and ...the substrate, the films show a high degree of preferred orientation for the (111) planes. The texture coefficients could be up to 5 for these planes. The crystallite diameters are in the 30–35
nm range, and optical bad gap, 0.4–0.7
eV. The electrical conductivity is p-type, 0.01–10 (Ω
cm)
−
1
. These films were deposited over CdS/Sb
2S
3 or CdS/Sb
2Se
3 solar cell structures as an additional absorber. In a CdS/Sb
2Se
3/PbSe cell, this addition increases the short circuit current density (
J
sc
) from 0.2
mA/cm
2 to 8.9
mA/cm
2 and conversion efficiency (
η) from 0.04% to 0.99%. In a CdS/Sb
2S
3/PbSe cell,
J
sc
is 5.91
mA/cm
2;
η, 0.98%; and open circuit voltage, 560
mV.
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