LEAD SULPHIDE (PBS) NANOSTRUCTURED THIN FILMS
AND PbS NANOPARTICLES FOR PHOTOVOLTAIC APPLICATION
Jayesh D. Patel1,2, Frej Mighri1,2, and Abdellah Ajji1,3
1
2
3
Center for Applied Research on Polymers and Composites, CREPEC
Chemical Engineering Department, Laval University, Quebec, QC, G1K 7P4 Canada
Chemical Engineering Department, Ecole Polytechnique, C.P. 6079, Succ. Centre- Ville
Montreal, QC, H3C 3A7 Canada
Lead sulphide (PbS) nanoparticles and
Pbs-based nanostructured thin films have
remarkable physical properties leading to
interesting applications in photovoltaics [1].
Pbs has a large excitonic Bohr radius of
around 18 nm and hence the band gap of
PbS particles can be easily tuned to
anywhere between 0.41 to 3.5 eV covering
the entire visible spectrum [2]. Recent
discovery of multiple exciton generation in
PbS nanoparticles [3] has opened up the
possibility of developing low-cost highefficiency solar cell materials. However, the
use of PbS in these materials requires
adequate control to stabilize Pbs particle
size.
reflections from (111), (200), (220), (311),
(222), (400), (331), (420), (422) and (511)
planes. No other phases were detected,
which confirms that pure PbS film were
obtained by CBD. The broadening of XRD
lines indicates that particles size in PbS film
is small. The average grain size estimated by
the following equation ‘Scherrer equation’
from line (111), (200) and (220) is around
10 nm (Figure 1 (b)).
D = k  / B Cos
(Scherrer equation)
Where, D
k
λ
B
is the particle size.
is the shape factor taken as 0.9.
is the wavelength of X-ray used.
is the broadening of line at half
intensity.
θ is the diffraction angle of line
under consideration.
In this work, PbS nanostructured films
were developed by chemical bath deposition
(CBD) technique at room temperature using
a trietanolamine complex of lead ions,
ammonia and thiourea solutions. For PbS
nanoparticles, lead-thiourea complex, oleic
acid and hexane were used for low
temperature synthesis (100°C). Thickness
and
surface
parameters
of
PbS
nanostructured films were examined by
Atomic Force Microscopy (AFM) (Figure
1(a)). It was found that these films were
highly uniform (with 1mm in thickness,
measured from AFM three dimensions
image) and show a porous network of PbS
nanoparticles. Film composition was
characterized by X-ray diffraction (XRD).
The lines were identified to be those of
cubic PbS (JCPDS File No. 05-592) with
The influence of oxygen and other
species on chemical content and structure
conformation were studied by EnergyDispersive X-ray analyses (EDAX).
Corresponding results are shown in figure 2
(a). Peaks in the EDAX from C, SI, Na, Cl
and Ca are due to glass used for the film
deposition. Figure 2(b) shows the optical
absorption spectra of a PbS nanostructured
film. It indicates that the film strongly
absorbs light in visible region with a suitable
band gap for photovoltaic application (~
1.75 eV).
The transmission electron microscope
(TEM) image (Figure 3(a)) indicates that
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PbS nanoparticles are monodisperse and the
average size of particles is around 10nm
with cubic/spherical shape.
interaction between nanoparticle surface and
surfactant (oleic acid) was confirmed by
Fourier Transform Infrared Spectroscopy
(FTIR) and oleic acid hydrocarbon chain is
strongly bound with particle surface (Figure
5 (b)).
As confirmed by selected area electron
diffraction (SAED), PbS nanoparticles are
crystalline with a rock salt structure. The
SAED
rings
obtained
from
PbS
nanoparticles matched well with the PbS
rock salt structure (JCPDS File No. 05-592)
(Figure 3(a)). Figure 3 (b) shows that PbS
nanoparticles absorb strongly in visible
region with band gap of 1.7 eV. X-ray
photoelectron spectroscopy (XPS) was
carried out in order to study nanoparticle
surface stability. It was observed that the
surface of PbS nanoparticles are highly
stable in air due to capping of oleic acid and
there is no evidence of PbO phase
(Figure 4).
From Thermogravimetric Analysis (TGA)
characterisation curve, it was found that 90
to 95% of surfactant was absorbed on
particle surface (Figure 5 (a)). The
References
1. Watt AAR, Blake D, Warner JH,
Thomsen EA. Tavenner EL, RubinszteinDunlop H, Meredith P. J. Phys. D: Appl.
Phys.(2005); 38:2006.
2. Wang Y, Suna A, Mahler W, Kasowski
R. J. Chem. Phys (1987); 87:7315-7322.
3. Ellingson RJ, Beard MC, Johnson JC, Yu
P, Micic OI, Nozik AJ, Shabaev A,. Efros
AL. Nano Lett (2005); 5; 865-871.
Figure1. (a) AFM image and (b) X-ray diffractograph of a PbS nanostructured film.
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Figure2. (a) EDAX and (b) absorption spectrum with inset band gap determination plot of a PbS
nanostructured film.
Figure3. (a) TEM micrograph with inset SAED image and (b) absorption spectrum with inset
band gap determination plot of oleic acid capped PbS nanoparticles.
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Figure4. XPS spectra of oleic acid capped PbS nanoparticles.
Figure5. (a) TGA of oleic acid capped nanoparticles and (b) FTIR spectra of (a) oleic acid, (b)
oleic acid capped PbS nanoparticles and (c) non capped PbS nanoparticles.
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