Photovoltaic Research Group

Yuseong Gu, South Korea

Photovoltaic Research Group

Yuseong Gu, South Korea
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Agawane G.L.,Chonnam National University | Shin S.W.,Korea Basic Science Institute | Shin S.W.,KAIST | Kim M.S.,Chonnam National University | And 10 more authors.
Current Applied Physics | Year: 2013

Zinc sulphide (ZnS) thin films are deposited using chemical bath deposition method on the glass substrates in an aqueous alkaline reaction bath of zinc acetate and thiourea along with non-toxic complexing agent tri-sodium citrate at 95 °C. The results show noteworthy improvement in the growth rate of the deposited ZnS thin films and thickness of the film increases with the deposition time. From X-ray diffraction patterns, it is found that the ZnS thin films exhibit hexagonal polycrystalline phase reflecting from (101) and (0016) planes. The high resolution transmission electron microscopy studies confirmed the formation of hexagonal phase from the d-value calculation which was 0.3108 nm. X-ray photoelectron spectroscopy reveals that the Zn-S bonding energy is at 1022.5 and 162.1 eV for Zn 2p3/2 and S 2p1/2 states, respectively. Field emission scanning electron microscopy study shows that deposited thin films are highly uniform, with thin thickness and completely free from large ZnS clusters which usually form in aqueous solutions. Atomic force microscopy investigates that root mean square values of the ZnS thin films are from 3 to 4.5 nm and all the films are morphologically smooth. Energy dispersive spectroscopy shows that the ZnS thin films are relatively stoichiometric having Zn:S atomic ratio of 55:45. It is shown by ultraviolet-visible spectroscopy that ∼90% transmittance and ∼10% absorbance for the ZnS films in the visible region, which is significantly higher than that reported elsewhere and the band gap energy of the ZnS films is found to be 3.76, 3.74, and 3.71 eV, respectively. © 2013 Elsevier B.V. All rights reserved.


Hong C.W.,Chonnam National University | Shin S.W.,KAIST | Gurav K.V.,Chonnam National University | Vanalakar S.A.,Chonnam National University | And 4 more authors.
Applied Surface Science | Year: 2015

Comparative studies on the properties of Cu2ZnSnS4 (CZTS) thin films and performance of CZTS thin film solar cells (TFSCs) prepared by different sulfurization types such as commerical furnace (CF) and rapid thermal annealing (RTA) systems have been investigated. The CZTS thin film prepared using CF showed the dense microstructure with many voids and secondary phases, while that prepared using RTA showed the dense microstructure without void and with some secondary phases. The RTA annealed CZTS TFSC have shown better performance than that prepared using CF. The best performance of CZTS TFSC using RTA was 1.9% efficiency (Voc: 505 mV, Jsc: 7.5 mA/cm2 and FF: 50.2%). © 2014 Elsevier B.V. All rights reserved.


Agawane G.L.,Chonnam National University | Shin S.W.,KAIST | Vanalakar S.A.,Chonnam National University | Moholkar A.V.,Shivaji University | And 5 more authors.
Materials Research Bulletin | Year: 2014

An environmentally benign chemical bath deposition (CBD) route was employed to deposit zinc sulfide (ZnS) thin films. The CBD-ZnS thin films were further selenized in a furnace at various temperatures viz. 200, 300, 400, and 500 °C and the S/(S + Se) ratio was found to be dependent on the annealing temperature. The effects of S/(S + Se) ratio on the structural, compositional and optical properties of the ZnSxSe1-x (ZnSSe) thin films were investigated. EDS analysis showed that the S/(S + Se) ratio decreased from 0.8 to 0.6 when the film annealing temperature increased from 200 to 500 °C. The field emission scanning electron microscopy and atomic force microscopy studies showed that all the films were uniform, pin hole free, smooth, and adhered well to the glass substrate. The X-ray diffraction study on the ZnSSe thin films showed the formation of the cubic phase, except for the unannealed ZnSSe thin film, which showed an amorphous phase. The X-ray photoelectron spectroscopy revealed ZnS, ZnSe, and insignificant ZnOH bonds formation from the Zn 2p3/2, S 2p, Se 3d5/2, and O 1s atomic states, respectively. The ultraviolet-visible spectroscopy study showed ∼80% transmittance in the visible region for all the ZnSSe thin films having various absorption edges. The tuning of the band gap energy of the ZnSSe thin films was carried out by selenizing CBD-ZnS thin films, and as the S/(S + Se) ratio decreased from 0.8 to 0.6, the band gap energy decreased from 3.20 to 3.12 eV. © 2014 Elsevier Ltd.


Agawane G.L.,Chonnam National University | Wook Shin S.,KAIST | Suryawanshi M.P.,Chonnam National University | Suryawanshi M.P.,Shivaji University | And 7 more authors.
Materials Letters | Year: 2013

In this paper, a comparative study reported on the characteristics of Zinc Selenide (ZnSe) thin films prepared by a chemical bath deposition method using the non-toxic tri-sodium citrate (Na3-citrate) and toxic hydrazine hydrate (HH) as complexing agents. Morphological, structural, chemical, and optical properties were investigated using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy. FE-SEM and AFM studies revealed that the ZnSe thin film prepared using Na3-citrate was highly uniform with very low surface roughness (3 nm) compared to those prepared using HH. XRD and XPS studies revealed formation of a cubic ZnSe phase and exhibited insignificant ZnOH formation along with ZnSe binding energies for both the films. UV-vis study showed that the band gap energies of ZnSe thin films prepared using HH and Na3-citrate were 3.1 eV and 2.9 eV, respectively. These investigations show that ZnSe thin films could be grown with good optical, structural, chemical, and compositional characteristics without using a toxic HH complexing agent. © 2013 Elsevier B.V.


Agawane G.L.,Chonnam National University | Shin S.W.,KAIST | Shin S.W.,Korea Basic Science Institute | Suryawanshi M.P.,Chonnam National University | And 7 more authors.
Ceramics International | Year: 2014

The synthesis of chemical bath deposited zinc selenide (ZnSe) thin films using a mixture of non-toxic complexing agent tri-sodium citrate (Na 3-citrate) and hydrazine hydrate (HH) and their physico-chemical properties are reported. Various amounts of complexing agent Na 3-citrate and HH solutions were prepared and used, listed as A, B, C, D, E and F. The effects of Na3-citrate and HH concentration on the morphological, structural, compositional, chemical and optical properties of ZnSe thin films were investigated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Energy dispersive X-ray spectroscopy (EDS) and ultraviolet-visible spectroscopy, respectively. FE-SEM and AFM studies revealed that the uniformity of the ZnSe thin films decreased whilst RMS values increased for the films deposited from solutions A to F. XRD studies showed that the ZnSe thin films had no well resolved peaks showing an amorphous nature while peaks from (111), (220) and (311) planes corresponding to the ZnSe cubic phase were observed for the film deposited with solution A. EDS analysis revealed that the presence of Zn atom in the ZnSe thin films increased for the films deposited from solutions A to F. UV-visible study showed that the band gap energy increased from 2.65 to 3.55 eV for the ZnSe thin films deposited from solutions A to F. © 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Agawane G.L.,Chonnam National University | Shin S.W.,KAIST | Moholkar A.V.,Shivaji University | Gurav K.V.,Chonnam National University | And 3 more authors.
Journal of Alloys and Compounds | Year: 2012

This study demonstrates the growth and characterizations of chemical bath deposited zinc sulfide (ZnS) thin films prepared at pH 10. Aqueous zinc acetate and thiourea were used as precursors along with the non-toxic complexing agent, Na 3-citrate. The effects of different concentrations of Na 3-citrate from 0 to 0.2 M on the structural, morphological, compositional, chemical, and optical properties of ZnS thin films were studied. It was revealed through field emission scanning electron microscopy studies that an increase in the concentration of Na 3-citrate leads to an improvement of the uniformity of the ZnS thin films and decrease in the grain size. Atomic force microscopy showed that the RMS value decreases with an increase in Na 3-citrate concentration. X-ray diffraction study revealed that crystallinity of ZnS thin films improves upon increasing concentration of Na 3-citrate and that the films exhibit a hexagonal polycrystalline ZnS phase while deposited with 0.2 and 0.1 M Na 3-citrate. X-ray photoelectron spectroscopy revealed that the signal intensity decreases for Zn 2p 3/2 and S 2p 1/2 as the concentration of Na 3-citrate decreases from 0.2 to 0 M. It was shown by ultraviolet-visible spectroscopy that approximately 80% transmission in the visible region and absorption edge shifts towards blue when the concentration of Na 3-citrate increases from 0 to 0.2 M. The band gap energy of the ZnS film deposited without Na 3-citrate was found to be 3.53 eV, while it increases from 3.73 to 3.80 eV with a decrease in Na 3-citrate concentration from 0.2 to 0.025 M. The growth mechanism of CBD-ZnS thin film was found to be dependent on Na 3-citrate concentration. © 2012 Elsevier B.V. All rights reserved.

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