Seung Wook Shin

Korea Basic Science Institute KBSI, Sŏul, Seoul, South Korea

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Publications (36)54.03 Total impact

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    ABSTRACT: Quaternary kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) have been synthesized using a simple, size and shape tunable, and low-cost hydrothermal technique without using toxic chemicals. The size and shape of the kesterite CZTS NCs could be controlled by using different complexing agents including non-complexing agent, hydrazine hydrate, tri-sodium citrate (Na3-citrate), and tetra-acetate disodium salt (Na2EDTA). The hydrothermally synthesized CZTS nanocrystals showed a kesterite structure, high optical absorption, and suitable band gap energy characteristics, indicating potential for application to thin film solar cells.
    RSC Advances 07/2014; 4(61). · 3.71 Impact Factor
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    ABSTRACT: With the earth's abundance of kesterite, recent progress in chalcogenide based Cu2ZnSn(Sx,Se1-x)4 (CZTSSe) thin films has drawn prime attention in thin film solar cells (TFSCs) research and development. This review is focused on the current developments in the synthesis of CZTS nanocrystals (NCs) using a hot injection (HI) technique and provides comprehensive discussions on the current status of CZTSSe TFSCs. This article begins with a description of the advantages of nanoparticulate based thin films, and then introduces the basics of this technique and the corresponding growth mechanism is also discussed. A brief overview further addresses a series of investigations on the developments in the HI based CZTSSe NCs using different solvents in terms of their high toxicity to environmentally benign materials. A variety of recipes and techniques for the NCs ink formulation and thereby the preparation of absorber layers using NC inks are outlined, respectively. The deposition of precursor thin films, post-deposition processes such as sulfurization or selenization treatments and the fabrication of CZTSSe NCs based solar cells and their performances are discussed. Finally, we discussed concluding remarks and the perspectives for further developments in the existing research on CZTSSe based nanoparticulate (NP) TFSCs towards future green technology.
    Chemical Communications 06/2014; · 6.38 Impact Factor
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    ABSTRACT: The kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) were successfully synthesized using a relatively simple and one-step hydrothermal route. The structural, compositional, and optical properties of the kesterite CZTS NCs have been studied in detail. The pH-dependent CZTS phase formation has been elucidated for the first time. The X-ray diffraction and Raman spectroscopy confirmed the formation of a main phase kesterite CZTS structure only at pH 7. However, for pH values (4.3, 5, and 9), the formation of CZTS alongwith few secondary phases like Cu2SnS3 (CTS), Cu2−xS, and SnS2/Sn2S3 have been detected. CZTS NCs of size 10–100 nm were obtained at 200 °C and pH 7. The synthesized NCs showed a pH-dependent variation in optical band gap values from 1.15 to 1.44 eV, which is near optimum value for low cost thin film solar cells.
    Physica Status Solidi (A) Applications and Materials 03/2014; · 1.46 Impact Factor
  • Materials Research Bulletin. 01/2014; 55:106–113.
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    ABSTRACT: CuInS2 (CIS) thin films were prepared by sulfurization of In/Cu stacked precursor films. Prior to sulfurization the stacked metallic precursors were subjected to the soft annealing in Ar atmosphere at different time (10, 30, and 60 min) and temperature (100 °C and 300 °C). The effect of soft annealing condition on the structural, morphological and optical properties of CIS films was investigated. X-ray diffraction, Raman, and X-ray photoelectron spectroscopy studies showed that the sulfurized thin films exhibited a CIS tetragonal structure with minor secondary phases such as Cu2−xS and CuIn5S8. The secondary phases were minimized by introducing soft annealed process in the CIS thin films. Void free CIS microstructures have been observed for soft annealed CIS films. The band gap energy of CIS films were increased from 1.37 to 1.5 eV depending on the soft annealing conditions.
    Journal of Crystal Growth 01/2014; 394:49–54. · 1.55 Impact Factor
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    ABSTRACT: In the present work, CZTS thin films have been prepared by sulfurization of electrodeposited Cu-Zn-Sn (CZT) precursor. Prior to sulfurization, as-deposited CZT precursors have been soft annealed in Ar atmosphere at different temperatures (250-350 °C). The structural, morphological, compositional and optical properties of the films have been investigated in detail. It is found that, soft annealing temperature has a significant impact on the properties of CZTS thin films. The systematic study on the improvement in the properties of CZTS films using soft annealing route has been studied and discussed.
    Applied Surface Science 10/2013; · 2.54 Impact Factor
  • Current Applied Physics 10/2013; 13(8):1837-1843. · 2.03 Impact Factor
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    ABSTRACT: CuInS2 (CIS) absorber thin films were prepared by sulfurization of In/Cu metallic stacked precursor. The precursor thin films were sulfurized using a commercial furnace system in the S2 (s) + Ar atmosphere at 425 °C for 1 h. Effects of different S vapor temperature from 150 to 400 °C on the structural, morphological, compositional and optical properties of CIS thin films were investigated. X-ray diffraction and Raman studies showed that the sulfurized thin films with S vaporization temperature below 300 °C exhibited CIS tetragonal structure with secondary phases such as CuxSy, CuIn5S8, and InxSy. The sulfurized thin films with S vaporization temperature over 350 °C showed a single CIS tetragonal structure. Compositional ratio of CIS thin films showed that Cu/In and S/(Cu + In) ratio in the CIS thin films with S vaporization temperature over 350 °C were 1.0–1.2 and 0.9–1.1, respectively, while compositional ratio deviated from stoichiometry when the sulfurized thin films below S vaporization temperature of 350 °C. Optical study showed that the band gap energy and the absorption coefficient of CIS thin films were estimated from 1.18 eV to 1.5 eV and over 104 cm−1, respectively.
    Applied Surface Science 04/2013; 270:572–577. · 2.54 Impact Factor
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    ABSTRACT: Cu(2)ZnSnS(4) (CZTS) thin films were prepared by the sequential sulfurization of a co-sputtered precursor with a multitarget (Cu, ZnS, and SnS(2)) sputtering system. In order to investigate the crystallization behaviour of the thin films, the precursors were sulfurized in a tube furnace at different temperatures for different time durations. The Raman spectra of the sulfurized thin films showed that their crystallinity gradually improved with an increase in the sulfurization temperature and duration. However, transmission electron microscopy revealed an unexpected result-the precursor thin films were not completely transformed to the CZTS phase and showed the presence of uncrystallized material when sulfurized at 250-400 °C for 60 min and at 500 °C for 30 min. Thus, the crystallization of the co-sputtered precursor thin films showed a strong dependence on the sulfurization temperature and duration. The crystallization mechanism of the precursor thin films was understood on the basis of these results and has been described in this paper. The understanding of this mechanism may improve the standard preparation method for high-quality CZTS absorber layers.
    Nanotechnology 02/2013; 24(9):095706. · 3.84 Impact Factor
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    ABSTRACT: a b s t r a c t Zinc sulphide (ZnS) thin films are deposited using chemical bath deposition method on the glass sub-strates 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 dif-fraction 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 photo-electron spectroscopy reveals that the ZneS bonding energy is at 1022.5 and 162.1 eV for Zn 2p 3/2 and S 2p 1/2 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 spec-troscopy shows that the ZnS thin films are relatively stoichiometric having Zn:S atomic ratio of 55:45. It is shown by ultravioletevisible spectroscopy that w90% transmittance and w10% 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.
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    ABSTRACT: (CZTSSe) thin films were prepared by sulfurization of evaporated precursor thin films. Precursor was prepared using evaporation method at room temperature. The sulfurization was carried out in a graphite box with S powder at different temperatures. The temperatures were varied in a four step process from to . The effects of the sulfurization temperature on the micro-structural, morphological, and compositional properties of the CZTSSe thin films were investigated using X-ray diffraction (XRD), Raman spectra, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The XRD and Raman results showed that the sulfurized thin films had a single kesterite crystal CZTSSe. From the FE-SEM and TEM results, the (MoSSe) interfacial layers of the sulfurized CZTS thin films were observed and their thickness was seen to increase with increasing sulfurization temperature. The microstructures of the CZTSSe thin films were strongly related to the sulfurization temperatures. The voids in the CZTSSe thin films increased with the increasing sulfurization temperature.
    Korean Journal of Materials Research 01/2013; 23(11).
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    ABSTRACT: ZnO thin films co-doped with Mg and Ga (MxGyZzO, x + y + z = 1, x = 0.05, y = 0.02 and z = 0.93) were prepared on glass substrates by RF magnetron sputtering with different sputtering powers ranging from 100W to 200W at a substrate temperature of . The effects of the sputtering power on the structural, morphological, electrical, and optical properties of MGZO thin films were investigated. The X-ray diffraction patterns showed that all the MGZO thin films were grown as a hexagonal wurtzite phase with the preferred orientation on the c-axis without secondary phases such as MgO, , or . The intensity of the diffraction peak from the (0002) plane of the MGZO thin films was enhanced as the sputtering power increased. The (0002) peak positions of the MGZO thin films was shifted toward, a high diffraction angle as the sputtering power increased. Cross-sectional field emission scanning electron microscopy images of the MGZO thin films showed that all of these films had a columnar structure and their thickness increased with an increase in the sputtering power. MGZO thin film deposited at the sputtering power of 200W showed the best electrical characteristics in terms of the carrier concentration (), charge carrier mobility () and a minimum resistivity (). A UV-visible spectroscopy assessment showed that the MGZO thin films had high transmittance of more than 80 % in the visible region and that the absorption edges of MGZO thin films were very sharp and shifted toward the higher wavelength side, from 270 nm to 340 nm, with an increase in the sputtering power. The band-gap energy of MGZO thin films was widened from 3.74 eV to 3.92 eV with the change in the sputtering power.
    Korean Journal of Materials Research 01/2013; 23(3).
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    ABSTRACT: Transparent conductive and flexible Mg and Ga co-doped ZnO (MGZO) thin films were prepared on poly-ethylene terephthalate (PET) by RF magnetron sputtering technique at room temperature. The effects of different working pressures on the structural, chemical, morphological, optical and electrical properties of MGZO thin films were investigated. X-ray diffraction results indicate that all the MGZO thin films were grown as polycrystalline wurtzite structures without secondary phases such as MgO, Ga2O3, MgGa2O4, or ZnGa2O4. The MGZO thin film prepared at 6 mTorr has the lowest value of full width at half maximum. A typical survey spectrum of all the MGZO thin films confirmed the presence of Mg, Ga, Zn and O. The MGZO thin film prepared at 6 mTorr showed the widest optical band gap energy of 3.91 eV and lowest electrical resistivity of 5.3 × 10−3 Ω cm.
    Journal of Asian Ceramic Societies. 01/2013; 1(3):262–266.
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    ABSTRACT: In this paper, we report a facile, low cost synthesis and characterization of kesterite Cu2ZnSn(Sx,Se1−x)4 (CZTSSe) nanocrystals (NCs) by a two-step process involving a solution-based precursor and a post-annealing route. The effects of different Se vaporization temperatures, ranging from 350 °C to 550 °C, on the structural, chemical, compositional, and optical properties of CZTSSe NCs were investigated. X-ray diffraction patterns, Raman spectroscopy, and transmission electron microscopy results indicated that the precursor powder showed several broad peaks that could not be assigned to Cu2ZnSnS4 (CZTS), ZnS, Cu2−xS, Sn2S3 and Cu2SnS3. However, the post-annealed NCs with and without Se vaporization were a single kesterite CZTS phase without a secondary phase. UV-vis spectroscopy results showed that the absorption coefficients of all the post-annealed NCs were over 104 cm−1 in the visible region, and the optical band gap energy decreased systematically from 1.46 eV to 1.14 eV with increasing Se vaporization temperatures.
    Journal of Materials Chemistry 09/2012; 22(40):21727-21732. · 5.97 Impact Factor
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    ABSTRACT: This article reports the epitaxial growth and characterization of 1 wt% Ga-doped ZnO (GZO) thin films prepared without buffer layer and with three different buffer layers of ZnO, GaN and MgO on Al2O3 (0 0 0 1) substrates by RF magnetron sputtering at a growth temperature of 250 °C. X-ray diffraction and transmission electron microscopy studies showed that the GZO thin films deposited on the GaN- and ZnO-buffered substrates were grown epitaxially. However, the GZO thin films deposited on the non- and MgO-buffered substrates had a polycrystalline hexagonal wurtzite phase with a highly c-axis preferred out-of-plane and a random in-plane orientation. Electrical studies of the GZO thin film deposited on the non-buffered substrate showed the lowest resistivity of 6.8 × 10−3 Ω cm as compared to these deposited on three buffered substrates. The crystallinity, microstructure, morphological, optical and electrical properties of the GZO thin films were influenced by the nature of the three investigated buffered layers.
    Applied Surface Science 04/2012; 258(12):5073–5079. · 2.54 Impact Factor
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    ABSTRACT: This study reports the design growth and characterization of quaternary Mg and Ga codoped ZnO (MGZO) thin films with transparent conductive characteristics deposited on glass substrates by RF magnetron sputtering. The effects of the Ga concentration (from 0 to 2 at %) on the structural, chemical, morphological, optical, and electrical properties of MGZO thin films were investigated. X-ray diffraction study showed that all the MGZO thin films were grown as a polycrystalline hexagonal wurtzite phase with a c-axis preferred orientation and random in-plane orientation. The 2θ value of the (0002) peak of MGZO thin films decreased with increasing Ga concentration. X-ray photoelectron spectroscopy confirmed the Mg and Ga binding energy peaks from the MGZO thin films. The MGZO thin films had a smoother surface morphology. The optical study showed that the band gap energy of MGZO thin films systematically increased from 3.25 to 3.75 eV with increase Ga concentration. The electrical resistivity of the MGZO thin films was improved from 9.5 × 10–2 to 6.89 × 10–4 Ω cm with increasing Ga concentration.
    Crystal Growth & Design. 09/2011; 11(11).
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    ABSTRACT: 3 wt% Ga-doped ZnO (GZO) thin films were deposited on Al2O3 (0 0 0 1) substrates by RF magnetron sputtering at different growth temperatures ranging from 350 to 750 °C. The crystallinity, microstructure, epitaxial nature, and optical and electrical properties of the GZO thin films were examined by X-ray diffraction (XRD), transmission-electron microscopy (TEM), UV–visible spectroscopy and Hall measurements. XRD and TEM showed that the GZO thin films deposited below a growth temperature of 450 °C grew epitaxially with an orientation relationship of . However, the GZO thin films deposited above 550 °C were in polycrystalline hexagonal wurtzite phase with c-axis preferred. The crystallinity of the GZO thin films deteriorated with increasing growth temperature. The GZO thin film deposited at 350 °C showed the lowest electrical resistivity of 1.13×10−4 Ω cm. The electrical properties of the GZO thin films also deteriorated with increasing growth temperature. UV–visible spectroscopy showed that the GZO thin films are highly transparent (from 75% to 90%) in the visible region. In addition, the band gap of the deposited thin films decreased from 3.5 to 3.2 eV with increasing growth temperature.
    Journal of Crystal Growth 01/2011; 322(1):51-56. · 1.55 Impact Factor
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    ABSTRACT: Cu2ZnSnS4 (CZTS) thin films were deposited by sputtering on glass substrates using stacked precursors. The stacked precursor thin films were prepared from Cu, SnS2 and ZnS targets at room temperature with different stacking orders of Cu/SnS2/ZnS/glass (A), ZnS/Cu/SnS2/glass (B) and SnS2/ZnS/Cu/glass (C). The stacked precursor thin films were sulfurized using a tubular rapid thermal annealing system in a mixed N2 (95%)+H2S (5%) atmosphere at 550°C for 10min. The effects of the stacking order in the precursor thin films on the structural, morphological, chemical, electrical and optical properties of the CZTS thin films were investigated. X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy studies showed that the annealed CZTS thin film using a stacking order A had a single kesterite crystal structure without secondary phases, whereas stacking orders B and C have a kesterite phase with secondary phases, such as Cu2−xS, SnS2 and SnS. The annealed CZTS thin film using stacking order A showed a very dense morphology without voids. On the other hand, the annealed CZTS thin films using stacking orders B and C contained the volcano shape voids (B) and Sn-based secondary phases (C) on the surface of the annealed thin films. The direct band gap energies of the CZTS thin films were approximately 1.45eV (A), 1.35eV (B) and 1.1eV (C).
    Solar Energy Materials and Solar Cells - SOLAR ENERG MATER SOLAR CELLS. 01/2011; 95(12):3202-3206.
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    ABSTRACT: Epitaxial ZnO/Mg0.1Zn0.9O (MZO) nano-scale multilayer thin films were prepared on Al2O3 (0001) substrates by pulsed laser deposition. The ZnO/MZO multilayer thin films were grown by stacking alternate layers of ZnO and Mg0.1Zn0.9O with a laser fluence, repetition rate, substrate temperature and oxygen partial pressure of 3J/cm2, 5Hz, 600°C and 3.8×10−7Pa, respectively. The thickness of an individual ZnO layer was maintained at 3nm, whereas that of the MZO layers was varied from 3nm to 15nm. Cross-sectional transmission electron microscopy revealed alternating layers of bright and dark contrast, indicating the formation of a ZnO/MZO multilayer. X-ray diffraction results showed that multilayer thin films were epitaxially grown as a hexagonal wurzite phase with orientation relationship of (0001)[101¯1]multilayer||(0001)[101¯1]substrate. The 2θ value of the (0002) peak of the ZnO/MZO multilayer thin films increased from 34.30° to 34.71°, indicating that Mg is replaced with Zn in the hexagonal lattice in the MZO of ZnO/MZO multilayer. UV–visible spectroscopy showed a systematic increase in the band gap of the ZnO/MZO multilayer thin films from 3.34eV to 3.70eV with increasing MZO layer thickness, which suggests that the band gap energy of a ZnO/MZO multilayer thin film can be controlled by varying the thickness of each constituent layer.
    Thin Solid Films 01/2011; 519(13):4282-4285. · 1.87 Impact Factor
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    ABSTRACT: Zinc sulfide (ZnS) thin films have been prepared by chemical bath deposition method with improving growth rate and morphology using the mixed complexing agents of ethylenediamine tetra-acetate disodium salt (Na2EDTA) and hexamethylenetetramine (HMTA). The effects of HMTA quantity on the morphological, compositional, optical, structural and electrical properties of ZnS thin films with fixed Na2EDTA concentration have been investigated. ZnS thin films were deposited on glass substrates using aqueous solutions containing zinc acetate dehydrate and thioacetamide in acidic medium (pH 4). Field emission scanning electron microscopy results show that the morphology of a deposited ZnS thin film using HMTA as a complexing agent is rough. However, very uniform and smooth ZnS thin films are obtained using mixed complexing agents of Na2EDTA and HMTA. The growth rate and root mean square of ZnS thin films are improved with increasing HMTA quantities. X-ray diffraction patterns show that all the ZnS thin films are grown as a hexagonal structure without secondary phase (ZnO) regardless of HMTA quantity. Optical band gap energy of ZnS thin films deposited using mixed complexing agents increase from 3.75 to 3.87eV with increasing quantity of HMTA.
    Solar Energy - SOLAR ENERG. 01/2011; 85(11):2903-2911.