structural, morphological and optoelectronic properties of
TRANSCRIPT
Structural, Morphological and Optoelectronic Properties of Screen-Printed Film Deposited using Sb2Se3 Nanowires
Sushil Kumar1, a), Parly2, Riya2, M. P. Saravanan1, Uday Deshpande1, R.Venkatesh1
1UGC-DAE-Consortium for Scientific Research, University campus, Khandwa road, Indore 452001, M.P, India. 2School of Physics, DAVV,Takshashila campus, Indore 452001, M.P. India.
a) Corresponding author:[email protected]
Abstract. Structural, morphological and Optoelectronic properties of Sb2Se3 film prepared by optimized screen-printing method is investigated and presented in this work. Sb2Se3 nanowires synthesized by microwave assisted solvothermal method along with ethylene glycol is used as the ink for the preparation of Sb2Se3screen printed film. Structural analysis confirms the orthorhombic phase while the energy dispersive spectroscopy confirms the formation of Sb2Se3 composition. Crystallite size of the nanocrystalline powder (film) is found to be 60nm (104nm). The surface morphological properties as investigated from field emission scanning electron microscope (FESEM) show that the film is covered with nanowires of length 1-3μm and diameter 100-200nm uniformly distributed over the substrate but agglomerated uniformly as a spherical particle with diameter of ~0.8μm.Interestingly, optoelectronic properties of the film and nanocrystalline powder show a band gap value of 1.19eV and 1.22eV respectively with an infinitesimal change in the band gap of the order of 0.03eV which is in correspondence with the morphological properties.Sb2Se3 being a potential material for solar cells, photodetectors and thermoelectric applications, this combination of fast and facile solvent-mediated microwave synthesis and screen-printing approach exhibits importance towards the wearable technology application for harvesting alternate electrical energy.
INTRODUCTION
V-VI group binary compounds are typical narrow band semiconductors and their nanostructures are of prime interest because of their dimensional-dependent properties [1]. Among these materials, antimony selenide (Sb2Se3) has gained great attention because of its potential technical applications in many areas including photoelectric, photoluminescence, thermoelectric and photon conducting devices. [1] Research on nanotechnology concerns the fabrication of nanomaterials and their applications in a variety of areas. From last few decades it has emerged as a fast-growing field as the properties of nanomaterials are quite different than to those of bulk materials. In particular, one dimensional nanostructure such as nanowires, nanorods and nanotubes have attracted considerable attention due to their potential use in optical, electronic, magnetic and mechanical devices [2]. Among these compounds, the direct band-gap semiconductor Sb2Se3 (Eg ≈ 1.11 to 1.8 eV), with an orthorhombic crystal structure and Pbnm space group, has been extensively studied as an important thermoelectric material and photoconductive semiconductor and because of its high thermoelectric power (~1800μV/K) and unique solar characteristics [3.] It can be used in thermoelectric applications, as absorber in solar cells memory switching devices, [4,5]. In the past decade, various chemical methods have been developed for the synthesis of Sb2Se3 and other chalcogenide nanomaterials, such as vapor-phase processing, the template-directed method, the solgel route, the microwave-assisted chemical bath method, and hydrothermal/solvothermal synthesis. All of these methods have advantages and disadvantage [3.] Therefore, developing a rapid, green, high-yield synthesis of uniform Sb2Se3nanowires is still highly desired. Here we successfully synthesized Sb2Se3 nanostructures via a reliable and facile method. However, as far as we know, most of previous studies involve high-toxic reducing agent, time- consuming protocol and exhibit low yield feature. Further, Sb2Se3 thin film can be deposited by different of deposition techniques, such as chemical bath deposition (CBD), vapor transport deposition (VTD), co-evaporation and so on. All these techniques are high cost and involves
a lengthy procedure for the preparation of the film, so a low cost and less time-consuming technique is desirable. Screen printing is as such a low cost and fast results giving techniques [6]. Wet deposition of nanocrystalline -based colloidal inks using screen printing, inkjet printing, direct writing, or other layer-by-layer methods hold many advantages due to the ability to directly convert nanocrystalline inks into micro/macroscale functional materials and devices with great scalability, flexibility, and cost effectiveness Now a days, screen printing has also been explored as a more efficient way to fabricate thermoelectric devices [7]. We have prepared the film in air atmosphere by screen printing method and investigated its optoelectronic and structural properties. Surface morphology of the nanocrystalline powder Sb2Se3 and screen printed Sb2Se3film has also been investigated and reported in this work.
EXPERIMENTAL DETAILS
Sb2Se3 nanostructures has been synthesized via fast and facile microwave assisted solvothermal process. Sb2Se3 has been synthesized in the nanocrystalline powder form as follows. We have taken SbCl (80mg) and added SeO2(60mg) to it followed by addition of (12ml) oleyl amine in a conical flask and kept on magnetic stirring for 5hours.Then, the solution was microwave heated in “CEM” made “Discover” research-based microwave for 10 minutes. The colour of the solution changed to black. After heating, the solution was cooled down and cleaned with water and ethanol several times. Finally, Sb2Se3 precipitate has been collected in the dry powder form.
Preparation of the ink: The nanocrystalline powder solution of Sb2Se3 was mixed with SbCl3, which act as binding agent along with ethylene glycol (solvent) for the preparation of slurry.
Screen printing process: Homemade screen-printing setup was used for the deposition of film as shown in Fig1. Glass is used as the substrate for the preparation of the film.
After the preparation of the film, it isannealed for 4 hours at 1250C at atmospheric pressure and then left the film to cool down and dry so that it sticks to the glass substrate properly. After drying of the film, further measurement has been performed.
FIGURE 1. Schematic illustration of overall fabrication process of screen-printing film.
RESULTS and DISCUSSION
XRD measurement has been performed for confirming the crystal structure of the synthesized sample using Bruker D8 Advance X-ray diffractometer The XRD spectra of nanocrystalline powder and film of Sb2Se3 has been taken and analyzed as shown in Fig1. Nanocrystalline powder XRD spectrum is matching with the JCPDS file00-015-0861. From the spectra we observed that the crystal structure of Sb2Se3is orthorhombic with Pbnm Space group and the lattice parameter of the Sb2Se3 was found to be a =11.780Å b =11.633 Å c =3.985 Å.
FIGURE 2. showing the Sb2Se3 XRD spectra of the (a) nanocrystalline line powder and (b) screen printed film. Crystal size of the Sb2Se3 nanocrystalline powder is calculated by using the Debye Scherrer formula: -
퐷 = (1)
Where, k is a dimensionless shape factor, with a value close to unity. The shape factor has a typical value of
about 0.9, but varies with the actual shape of the crystallite, 휆 is the X-Ray wavelength.β is the line broadening at half the maximum intensity (FWHM) and θ is the Bragg’s angle. The crystallite size of the nanocrystalline powder and film is found to be 60nm and 104nm respectively.
For confirming the surface morphology of the synthesized Sb2Se3nanocrystalline powder and film field emission scanning electron microscopy (FESEM) measurement has been performed by using FEI made “Nova Nano SEM 450”. Figure 3a shows that Sb2Se3 nanowire has been formed with length of 1 to 3um and diameter of 100-200 nm as calculated through the image-J software. Morphology of Sb2Se3 film shows that the nanowires are agglomerated and uniformly distributed over the substrate as shown in Fig 3b.
FIGURE3. Surface morphology of Sb2Se3(a) nanocrystalline powder(b)screen-printed film having agglomeration of the nanowires in the form of a sphere of diameter ~ 0.8μm.
For studying the optical properties of the synthesized nanocrystalline powder and film Sb2Se3 diffuse reflectance
spectroscopy measurement has been performed by Parkinson made UV-visible spectrophotometer. Absorbance (α)
10 20 30 40 50 60 70 80 902q (Degree)
Powder
(130
)(2
30)
(211
)(2
21)
(301
)(3
11)
(240
)(3
21)
(141
)(2
50)
(501
)(0
02)
(531
)
(242
)(7
20)
(020
) (061
)
Inte
nsity
(a.u
.)(a)
10 20 30 40 50 60 70 80 90
(130
)
(301
)(221
)(2
11)
(020
)
Inte
nsity
(a.u
.)
2q(Degree)
Film
(311
)(2
40)
(141
) (250
)(0
02)
(061
)
(b)
has been calculated from the reflectance by Kubelka-Munk equation α=(1-R)2/2R where α is the absorbance and R is the reflectance. Using Tauc equation optical band gap has been calculated given by [8].
퐴(퐸 − ℎ휈) = (훼ℎ휈) (2)
Where Egis the band gap, ν is the frequency of the radiation, h is the Planck’s constant, n is an integer, A is
constant. For the direct band gap semiconductor n=2 and for Indirect band gap semiconductor n=1/2. Interestingly, the Tauc plot indicate that the nanocrystalline powder and film have a direct band gap value of the order of the 1.22eV and 1.19eV respectively as shown in Fig 4. Inset of Fig 4 shows the sharp transition of nanocrystalline powder (inset of Fig 4a) when compared to smeared transition in screen printed films (inset of Fig 4b) in absorbance spectra of investigated samples. A similar infinitesimal decrease in band gap termed as redshift has been reported due to heat treatment [9]and also in annealed screen-printed films [10] when compared to as prepared nanoparticles. In our case the screen-printed films were heated to 1250C for 4 hours on hotplate for evaporation of binder which has resulted in agglomeration of nanowires in the form of spherical particles of ~0.8μm as inferred from morphological studies. This is in correspondence with the increase in crystallite size as observed from the structural analysis.
FIGURE 4. shows the Tauc plot of Sb2Se3(a) nanocrystalline powder (b) film. Inset figure shows the respective absorbance spectra.
Conclusion
Sb2Se3 nanowires has been successfully synthesized using the novel microwave-assisted solvothermal method in the presence of oleyl amine. Its morphology shows the presence of nanowires with a high aspect ratio. Screen printed film has been successfully prepared using the Sb2Se3 nanocrystalline powder at atmospheric pressure. Optical Band gap of the nanocrystalline powder and film is found to be 1.22eV and 1.19eV respectively. Change in band gap of nanocrystalline powder when compared to screen printed film is attributed to the agglomeration of nanostructures during heat treatment of the screen-printed films. This combination of microwave synthesis and Screen-printed film has potential applications in wearable technology for harvesting the electrical energy from the waste heat and light sources.
ACKNOWLEDGMENTS
I would like to thank director and center director of UGC-DAE-CSR, Indore family. Er. LaynthBehra is thanked for XRD measurements. Dr. Dileep Kumar is thanked for his support.
0.6 0.8 1.0 1.2
0
1
2
3
4
5
1000 1250 1500 1750 2000
0.0
0.4
0.8
1.2
1.6
(ahn
)2 (eV
cm-1
)2
Energy(eV)
Powder
(a)
a(c
m)-1
l (nm)
Absorbance
0.8 0.9 1.0 1.1 1.20.0
0.2
0.4
0.6
0.8
1000 1100 1200 1300
0.24
0.32
0.40
0.48
(ahn
)2 (eV
cm-1
)2
Film
Energy(eV)
(b)Absorbance
a(c
m)-1
l(nm)
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