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J. H. Shi, S. M. Huang,
J. B. Chu,
H. B. Zhu,
Z. A. Wang,
X. D. Li,
D. W. Zhang,
Z. Sun,
W. J. Cheng,
F. Q. Huang,
X. J. Yin
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ABSTRACT: Aluminum-doped ZnO (AZO) transparent conducting films were deposited on glass substrates with and without intrinsic ZnO (i-ZnO)
buffer layers by a home made and low cost radio-frequency (RF) magnetron sputtering system at room temperature in pure argon
ambient and under a low vacuum level. The films were examined and characterized for electrical, optical, and structural properties
for the application of CIGS solar cells. The influence of sputter power, deposition pressure, film thickness and residual
pressure on electrical and optical properties of layered films of AZO, i-ZnO and AZO/i-ZnO was investigated. The optimization
of coating process parameters (RF power, sputtering pressure, thickness) was carried out. The effects of i-ZnO buffer layer
on AZO films were investigated. By inserting thin i-ZnO layers with a thickness not greater than 125nm under the AZO layers,
both the carrier concentration and Hall mobility were increased. The resistivity of these layered films was lower than that
of single layered AZO films. The related mechanisms and plasma physics were discussed. Copper indium gallium selenide (CIGS)
thin film solar cells were fabricated by incorporating bi-layer ZnO films on CdS/CIGS/Mo/glass substrates. Efficiencies of
the order of 7–8% were achieved for the manufactured CIGS solar cells (4–5cm2 in size) without antireflective films. The results demonstrated that RF sputtered layered AZO/i-ZnO films are suitable for
application in low cost CIGS solar cells as transparent conductive electrodes.
Journal of Materials Science Materials in Electronics 05/2012; 21(10):1005-1013. · 1.08 Impact Factor
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ABSTRACT: Double-walled carbon nanotubes (DWCNTs) have been studied for counter-electrode application in dye-sensitized solar cells
(DSCs). Mesoporous TiO2 films are prepared from the commercial TiO2 nanopowders by screen-printing technique on optically
transparent-conducting glasses. A metal-free organic dye (indoline dye D102) is used as a sensitizer. DWCNTs are applied to
substitute for platinum as counter-electrode materials. Morphological and electrochemical properties of the formed counter
electrodes are investigated by scanning electronic microscopy and electrochemical impedance spectroscopy, respectively. The
electronic and ionic processes in platinum and DWCNT-based DSCs are analyzed and discussed. The catalytic activity and DSC
performance of DWCNTs and Pt are compared. A conversion efficiency of 6.07% has been obtained for DWCNT counter-electrode
DSCs. This efficiency is comparable to that of platinum counter-electrode-based devices.
KeywordsDye-sensitized solar cell-Nanocrystallined TiO2-Metal-free organic dye-Counter electrode-Double-walled carbon nanotube (DWCNT)
Journal of Solid State Electrochemistry 04/2012; 14(9):1541-1546. · 2.13 Impact Factor
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ABSTRACT: This paper presents further insights and observations of the chemical bath deposition (CBD) of ZnS thin films using an aqueous
medium involving Zn-salt, ammonium sulfate, aqueous ammonia, and thioure. Results on physical and chemical properties of the
grown layers as a function of ammonia concentration are reported. Physical and chemical properties were analyzed using scanning
electron microscopy (SEM), X-ray energy dispersive (EDX), and X-ray diffraction (XRD). Rapid growth of nanostructured ZnO
films on fluorine-doped SnO2 (FTO) glass substrates was developed. ZnO films crystallized in a wurtzite hexagonal structure and with a very small quantity
of Zn(OH)2 and ZnS phases were obtained for the ammonia concentration ranging from 0.75 to 2.0M. Flower-like and columnar nanostrucured
ZnO films were deposited in two ammonia concentration ranges, respectively: one between 0.75 and 1.0M and the other between
1.4 and 2.0M. ZnS films were formed with a high ammonia concentration of 3.0M. The formation mechanisms of ZnO, Zn(OH)2, and ZnS phases were discussed in the CBD process. The developed technique can be used to directly and rapidly grow nanostructured
ZnO film photoanodes. Annealed ZnO nanoflower and columnar nanoparticle films on FTO substrates were used as electrodes to
fabricate the dye sensitized solar cells (DSSCs). The DSSC based on ZnO-nanoflower film showed an energy conversion efficiency
of 0.84%, which is higher compared to that (0.45%) of the cell being constructed using a photoanode of columnar nanoparticle
ZnO film. The results have demonstrated the potential applications of CBD nanostructured ZnO films for photovoltaic cells.
Applied Physics A 04/2012; 95(3):849-855. · 1.63 Impact Factor
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ABSTRACT: Investigation on the optical resonance and near field effects of a 2D periodic dielectric spheres on metallic surfaces by
combining theoretical calculations with experimental studies were carried out. The light scattering and coupling was numerically
studied. Nanostructures were fabricated on the metallic surfaces using these arrays of micro- and nano-spheres with a single
laser pulse (KrF, λ=248nm). The occurrence of such nanostructures is well explained by the theoretical calculations. The results can be useful
in investigation and development of spheres-assisted nano-patterning.
Applied Physics A 04/2012; 96(2):459-466. · 1.63 Impact Factor
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ABSTRACT: Graphene nanosheets (GNs) have been investigated as a counter electrode for dye-sensitized solar cells (DSCs). Mesoporous TiO<sub>2</sub> films are prepared from the commercial TiO<sub>2</sub> nano-powders by screen-printing technique on fluorine-doped tin oxide (FTO) slides. GNs are applied to substitute for platinum as counter-electrode materials. GN films are screen printed on FTO glass using a paste based on GNs dispersed in a mixture of terpineol and ethylcellulose. GN counter-electrodes were prepared by annealing the GN films at different temperatures. A metal-free organic dye (indoline dye D102) is used as a sensitizer. Morphological and electrochemical properties of the formed counter-electrodes are investigated by scanning electronic microscopy and electrochemical impedance spectroscopy (EIS), respectively. The electronic and ionic processes in platinum and GNs based DSCs are analysized and discussed. A conversion efficiency of 2.94 % has been obtained for GNs based DSCs. It is found that the quality of the GN counter-electrode and the photovoltaic performance are strongly affected by the annealing temperature of GN materials.
Nanoelectronics Conference (INEC), 2010 3rd International; 02/2010
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ABSTRACT: The stability of transparent conducting oxide (TCO) films with bi-layered structures has been tested in air at temperatures up to 550°C. Aluminum-doped ZnO and Sn-doped In<sub>2</sub>O<sub>3</sub> (AZO/ITO) transparent conducting oxide (TCO) films were deposited on glass substrates by a home made radio-frequency (RF) magnetron sputtering system at room temperature in pure argon ambient. A typical commercial ITO and AZO films by mid-frequency (MF) magnetron sputtering at a substrate temperature of 350°C were also investigated for comparison. A strong decrease of electrical conductivity was observed after testing at temperature above 350°C for RF deposited bi-layered TCO as well as for the commercial ITO, while the AZO films deposited by MF magnetron sputtering showed a quite stable electrical property at temperature not greater than 500°C. The optical absorption edge was found to shift to the longer wavelength with an increase in testing temperature for all the TCO. MF sputtered AZO films were used as transparent front contacts for the fabrication of copper indium gallium selenide (CIGS) superstrate thin film solar cells.
Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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ABSTRACT: Structured ZnO films have been fabricated on soda-lime glass slides at a low temperature (80–85 °C) by a chemical bath deposition method in one step without seed layers. Mixed aqueous solutions of zinc sulfate, ammonia and thiourea were used at alkaline conditions. The influence of the ammonia concentration in the initial solution on the property of the deposited film was investigated systematically. The morphology, structural and optical properties of the deposited films were examined and characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy x-ray diffraction (EDX), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectroscopy. Structural analyses with XRD, EDX and SEM revealed that the formed films exhibit a wurtzite hexagonal phase. The deposited film was more preferentially oriented in the (0 0 2) direction with an increase in the ammonia concentration from 0.75 to 2 mol l−1. The optical-phonon E2 mode at 437 cm−1 in the Raman spectrum, together with the XRD and EDX analyses, showed that flower-like and columnar crystalline ZnO films were formed in two ammonia concentration ranges, 0.75–1.4 mol l−1 and 1.6–2.0 mol l−1, respectively. Furthermore, PL spectra showed strong and high intensity peaks of UV emission with suppressed green emission for these deposited ZnO films. ZnS films were formed with a high ammonia concentration of 3.0 M. The formation mechanisms of ZnO, Zn(OH)2 and ZnS phases were discussed.
Journal of Physics D Applied Physics 02/2009; 42(5):055412. · 2.54 Impact Factor
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Microelectronics Journal. 01/2009; 40:108-114.
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ABSTRACT: The effect of annealing temperature on the magnetic and giant magnetostriction (GMS) of [Fe/Tb/Fe/Dy]n multilayer films were investigated. X-ray diffraction showed that the multilayer films' microstructures were still in amorphous at annealing temperature 300°C. The multilayer films began to crystalline at annealing temperature 400°C. The saturation magnetization of multilayer films increased by the increasing annealed temperature. The coercivity first decreased at annealing temperature 300°C and then increased when the annealing temperature was higher than 400°C. The multilayer films had good low-field GMS, and the magnetostriction of the multilayer films increased by the increasing annealing temperature.
Surface Review and Letters (SRL). 01/2009; 16(01):123-126.
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ABSTRACT: Single-phase CuInSe2 films were grown by high vapor selenization of CuIn alloy precursors within a partially closed graphite box. The CuIn precursors were prepared using CuxIny alloy targets with different composition rates under low vacuum level by a homemade sputtering system. The Cu and In composition rates of the used targets are 11:9, 10:10, and 9:11, respectively. The metallic precursor films were selenized using a two-step temperature profile, i.e. at 250°C and 400–500°C, respectively. The influence of the temperature at the second selenization step on the quality of the CIS absorbing layers was investigated. The CIS films were characterized by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy. The deposited CIS absorbers selenized at a high temperature of 500°C for 30 min exhibited a single-phase chalcopyrite structure with a preferential orientation in the (112) direction. These layers display uniform, large, and densely packed crystals with a grain size of about 3–5 μm. Cadmium sulfide buffer layer was manufactured by chemical bath deposition method. Bilayers ZnO/ZnO:Al were prepared by RF magnetron sputtering deposition. CIS solar cells with an efficiency of about 6.5% were produced without antireflective films. The method to fabricate CIS solar cells by a combination of the low vacuum sputtering deposition and the graphite box selenization process has provided a simple control process and shown a promising potential for developing high efficient and low-cost CuInSe2 solar cells.
Surface Review and Letters (SRL). 01/2009; 16(03):381-386.
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ABSTRACT: The titanium dioxide nanotubes (TiNTs) were directly fabricated from commercial P25 TiO<sub>2</sub> via alkali hydrothermal transformation. The optimized synthesis, thermal and hydrothermal stability, and consequent optical properties of the titanate nanotubes were systematically studied. The TiO<sub>2</sub> nanotubes were characterized by transmission electron microscopy. Dye-sensitized solar cells (DSSCs) were constructed with films made of grown TiO<sub>2</sub> nanotubes as working electrodes. The nanocrystalline TiO<sub>2</sub> pastes were prepared with PEG (Mw 20000) and as made TiO<sub>2</sub> nanotubes. The titania thin films were grown by screen printing method in order to efficiently control the DSSC fabrication process. The microstructures of nanoporous films in solar cells were characterized by scanning electron microscope (SEM) and Brunauer Emmett Teller (BET) analysis. A metal-free organic dye (referred to as D102 dye) was used as a sensitizer. A high conversion efficiency of light-to-electricity of around 6% under illumination of simulated AM1.5 sunlight (65mW/cm<sup>2</sup>) was achieved with the TiO<sub>2</sub> nanotube cell. Compared with the case of DSSCs with TiO<sub>2</sub> nanoparticles, the open-circuit voltage and fill factor of DSSCs with TiO<sub>2</sub> nanotubes increased significantly. The related mechanisms are discussed.
Nanoelectronics Conference, 2008. INEC 2008. 2nd IEEE International; 04/2008
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ABSTRACT: Indium tin oxide (ITO) films were deposited at room temperature with no oxygen flow on glass substrates by RF magnetron sputtering. The effects of sputtering power and argon ambient pressure were investigated. The morphology, structural and optical properties of ITO films were examined and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and UV-VIS transmission spectroscopy. The deposited ITO films with 300 nm thickness show a high transparency between 80 and 90% in the visible spectrum and 15Omega/square sheet resistance. The ITO films are suitable for application in CuInSe<sub>2</sub> thin film solar cell as transparent conductive electrode layers.
Nanoelectronics Conference, 2008. INEC 2008. 2nd IEEE International; 04/2008
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ABSTRACT: The simultaneous electrodeposition of the Cu-In-Se system was investigated. The study was carried out at pH 1.8 using sodium citrate as complexing agent for the Cu<sup>2+</sup> ion. The synthesis of CuInSe<sub>2</sub> semiconductor thin film was carried out by electrodeposition on indium-tin oxide (ITO) /soda-lime glass. The simultaneous composition of the Cu, In, and Se was achieved by constant potential electrolysis technique in aqueous solutions containing CuCl<sub>2</sub>, InCl<sub>3</sub>, and H<sub>2</sub>SeO<sub>3</sub>. The as-deposited and annealed films were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy. Homogeneous films were deposited with a well-defined composition and chalcopyrite structure. The crystallinity of the films was improved by annealing. The deposited stoichiometric CuInSe<sub>2</sub> layers were about 2 mum in thickness. The annealed film is with a perfect crystallized and single chalcopyrite structure. It is suitable for photovoltaic applications.
Nanoelectronics Conference, 2008. INEC 2008. 2nd IEEE International; 04/2008
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ABSTRACT: A simply modified bath deposition technique has been successfully used to deposit uniform CdS thin films using cadmium chloride or cadmium acetate as the cadmium ion source, and thiourea as the sulfur source on glass substrates. Both the traditional magnetic agitation and the frequent substrate vibration by hand were done simultaneously during the deposition. Various properties of the deposited films such as surface morphology, crystallinity, and optical properties were investigated. The CdS films deposited from cadmium acetate show a good crystallinity and exhibit a preferential orientation along the hexagonal (002) direction. Their surface morphologies are more homogeneous with smaller grains than those from cadmium chloride. The CdS films prepared from both cadmium ion sources present a high optical transmission (more than 80%) in the visible range with the band gap value of about 2.4 eV. The substrate vibration reduces the formation and residence of gas bubbles on the glass substrate during growth and resulted in deposition of CdS thin films with high quality. XRD, SEM, and UV–Vis measurements have provided the supported data. The fundamental CBD growth mechanisms involving different cadmium salts are discussed.
Surface Review and Letters (SRL). 01/2008; 15(03):265-270.
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ABSTRACT: Copper indium diselenide (CuInSe2) thin films were grown on indium–tin oxide (ITO)/soda-lime glass using a one-step cathodic electrodeposition process at potentials lower than -0.6 V vs SCE, and in the presence of a large excess of In3+. The source solution contained CuCl2, InCl3, and H2SeO3 complexed by citric acid. The concentration of InCl3 in the electrochemical bath affected the structure, composition, stoichiometric ratio, and morphological properties of electrodeposited films. CuInSe2 films with a chalcopyrite structure and quite good stoichiometry were directly electrodeposited from a solution of 20 mM InCl3, 5 mM CuCl2, and 8 mM H2SeO3. Annealing of these CuInSe2 films in the temperature range from 300°C to 500°C improves their crystallinity and increases their grain size. Good chalcopyrite CuInSe2 films with a (112) preferential orientation suitable for the production of efficient solar cells are obtained after annealing at 500°C. The formation mechanism of the ternary CuInSe2 compound during the electrodeposition process was discussed.
Surface Review and Letters (SRL). 01/2008; 15(04):419-426.
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ABSTRACT: An improved chemical bath deposition (CBD) technique has been provided to prepare zinc sulfide (ZnS) thin films on glass substrates deposited at 80–82°C using a mixed aqueous solution of zinc sulfate, ammonium sulfate, thiourea, hydrazine hydrate, and ammonia at the alkaline conditions. Both the traditional magnetic agitation and the substrates vibration by hand frequently were done simultaneously during the deposition. The substrates vibration reduced the formation and residence of gas bubbles on the glass substrates during growth and resulted in growth of clean ZnS thin films with high quality. Ammonia and hydrazine hydrate were used as complexing agents. It is found that hydrazine hydrate played an important role in growth of ZnS films. The structure and microstructure of ZnS films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis spectroscopic methods. The XRD showed a hexagonal structure. The formed ZnS films exhibited good optical properties with high transmittance in the visible region and the band gap value was estimated to be 3.5–3.70 eV.
Surface Review and Letters (SRL). 01/2008; 15(06):821-827.
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ABSTRACT: The magnetic properties and giant magnetostriction effect (GMS) of the amorphous alternant [Tb/Fe/Dy]n (named S1) and [Fe/Tb/Fe/Dy]m (named S2) nano-multilayer films have been studied. The magnetic hysteresis loops show that easy magnetic direction changes from perpendicular to the film plane (S1) to parallel to the film plane (S2). S2 has better soft magnetic properties and low-field giant magnetostriction effect than that of S1, due to the exchanging interaction between the hard GMS layer and the soft layer Fe. The different magnetic behavior is explained by considering the nature of the magnetization process, i.e. domain-wall motion and spin rotation.
Surface Review and Letters (SRL). 01/2008; 15(05):619-623.
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ABSTRACT: The dynamics and the conditions of amorphous transitions induced in a Ge1Sb2Te4 system upon a single femtosecond (fs) pulse melting were studied by real-time reflectivity measurements. The system has a multilayer structure of 100 nm ZnS–SiO2/(15–100 nm) Ge1Sb2Te4/120 nm ZnS–SiO2/0.6 mm polycarbonate substrate. It is shown that under optimum conditions amorphization is completed within 900 ps. The thickness of the phase change layer plays an important role in controlling the heat flow conditions in the system upon a fs pulse irradiation. The use of the fs laser pulse leads to a situation in which the pulse energy is deposited within a very short time in a thin surface layer, leading to heating or melting. The so-generated steep temperature gradient is subsequently smoothed by heat diffusion toward the substrate. The relative thermal process and effects are estimated. The calculated results are consisted with those from real-time reflectivity measurements. The mechanism of crystalline to amorphous transition triggered by single fs laser pulses is discussed.
Surface Review and Letters (SRL). 01/2007; 14(02):261-267.
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ABSTRACT: Intrinsic zinc oxide (i-ZnO) film was prepared for CuInSe2 (CIS) solar cell application [L. Stolt and J. Hedstrom, Appl. Phys. Lett. 62 (1993) 8; D. Rudmann, Ph.D. Thesis, University of Basel, Basel, (2004)] on glass substrate by inductively coupled plasma (ICP)-assisted DC magnetron sputtering and under a quite low temperature of 50°C. The sputtering was done in an Ar and O2 gas mixture and a ceramic ZnO target was used. The microstructures of the film were investigated by X-ray diffractometer and scanning electron microscope. It was shown that all of the films had a c-axis preferred orientation perpendicular to the substrate. In our work, film with resistivity of 7 × 108Ω·cm and transmittance of about 80% in the visible range was prepared under the conditions of 4 mTorr working pressure and 50°C temperature.
Surface Review and Letters (SRL). 01/2007; 14(06):1083-1087.
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ABSTRACT: Indium tin oxide (ITO) thin films were prepared by radio frequency (RF) magnetron sputtering and under a quite low vacuum level of 2.3 × 10-3 Pa. The sputtering was done in an Ar and O2 gas mixture at a temperature of 200°C. A ceramic In2O3:SnO2 target (10 wt% SnO2) was used. The microstructures of the films were investigated by a field emission scanning electron microscope (FESEM) and an X-ray diffractometer (XRD). X-ray photoelectron spectroscopy (XPS) was performed to characterize the composition of the films. ITO films with a high transparency in the visible wavelength range (80–95%) were obtained. The dependency of the electrical, optical and structural properties of ITO films on both the O2 flow ratio (O2/(O2 + Ar)) and the working pressure was investigated. In the case of low working pressure (1 Pa), the more highly transparent and conducting films were produced at the lower O2 flow ratio. High working pressure (2 Pa) gave rise to low quality, low transparency and amorphous films. Under RF sputtering at low vacuum level, the main contribution to the chamber atmosphere is due to water vapor. Oxygen originating from water vapor dissociation induced by plasma plays the same role as an oxygen or water vapor flux usually intentionally introduced in the system in order to have good quality films.
Surface Review and Letters (SRL). 01/2006; 13(06):833-840.
