• Solar Energy
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• v.20 no.2
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• pp.43-54
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• 2000

We prepared and characterized $Cu(In_{1-x}Ga_x)Se_2$(CIGS) films using a elemental co-evaporation method for absorbing layer of high efficiency thin film solar cells. The CIGS films deposited on a soda-lime glass exhibited low resistivity because of higher carrier concentration. Na was accumulated at the CIGS surface and the 0 and Se were also accumulated at the surface, suggesting that oxidation is a driving force of Na accumulation. The structure of CIGS film was modified or a secondary phase was formed in the Cu-poor CIGS bulk films probably due to the incorporation of Na into Cu vacancy sites. As the Ga/(In+Ga) ratio increased, the diffraction peaks of $Cu(In_{1-x}Ga_x)Se_2$ films were shifted to larger angle and splitted, and the grain size of $Cu_{0.91}(In_{1-x}Ga_x)Se_2$ films became smaller. All $Cu_{0.91}(In_{1-x}Ga_x)Se_2$ films showed the p-type conductivity regardless of the Ga/(In+Ga) ratio. Ag/n-ZnO/i-ZnO/CdS/$Cu_{0.91}(In_{0.7}Ga_{0.3})Se_2$/Mo solar cells were fabricated. The currently best efficiency in this study was 14.48% for $0.18cm^2$ area ($V_{oc}=581.5mV,\;J_{sc}=34.88mA$, F.F=0.714).

• Journal of Biomedical Engineering Research
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• v.28 no.2
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• pp.306-309
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• 2007

PXLM(Phosphor based x-ray light modulator) has a combined structure by phosphor, photoconductor, and liquid crystal and it can realize x-ray image of high resolution in clinical diagnosis area. In this study, we fabricated a photoconductor and investigated electrical and optical properties to confirm application possibility of radiator detector of PXLM structure. As photoconductor, amorphous selenium(a-Se), which is used most in DR(Digital radiography) of direct conversion method, was used and for formation of thin film, it was formed as $20{\mu}m-thick$ by using thermal vacuum evaporation system. For a produced a-Se film, through XRD(X-ray diffraction) and SEM(Scanning electron microscope), we investigated that amorphous structure was uniformly established and through optical measurement, for visible light of 40 $0\sim630nm$, it had absorption efficiency of 95 % and more. After fabricated a-Se film on the top of ITP substrate, hybrid structure was manufactured through forming $Gd_2O_3:Eu$ phosphor of $270{\mu}m-thick$ on the bottom of the substrate. As the result to confirm electrical property of the manufactured hybrid structure, in the case of appling $10V/{\mu}m$, leakage current of $2.5nA/cm^2$ and x-ray sensitivity of $7.31nC/cm^2/mR$ were investigated. Finally, we manufactured PXLM structure combined with hybrid structure and liquid crystal cell of TN(Twisted nematic) mode and then, investigated T-V(Transmission vs. voltage) curve of external light source for induced x-ray energy. PXLM structure showed a similar optical response with T-V curve that common TN mode liquid crystal cell showed according to electric field increase and in appling $50\sim100V$, it showed linear transmission efficiency of $12\sim18%$. This result suggested an application possibility of PXLM structure as radiation detector.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.1
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• pp.37-43
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• 1998

Batch experiments were conducted to study the dissolution behavior of gasoline components. First, the dissolution kinetics of gasoline components and the applicability of Raoult's law in predicting their solubilities were investigated. In addition, the effects of compositional change of gasoline due to evaporization on the solubilities of individual components and TPH were determined. The kinetics of gasoline-water man transfer was found to be very similar for most components except for MTBE, which is a major additive for commercial gasoline. At equilibrium, the gasoline-water partitioning coefficients of individual components showed a log-linear relationship with their pure solubilities, though the slope was a little less than that predicted by Raoult's law. The concentrations of the individual components in the gasolines concentrated by volatilization could be characterized by the initial increase followed by substantial decrease. Almost the same behavior was observed for their solubilities. The total solubility (TPH) of gasoline decreased rapidly with the initial volume reduction and gradually decreased afterwards. The solubilities of BTEX, the major regulatory compounds, decreased even faster than the TPH solubilities. It was concluded that the compositional change of gasoline by volatilization may greatly affect their leaching potential and the toxicity of the contacting groundwater. The toxicity reduction efficiency by evaporating gasoline could be much more than the mass removal efficiency.

• Korean Journal of Soil Science and Fertilizer
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• v.23 no.2
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• pp.94-99
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• 1990

A field experiment was conducted to study seasonal evapotranspiration above soybean canopy and its relationship with dry matter production by the Bowen ratio-energy balance method. The soybean "Paldalkong" was sown with the space of $47{\times}10cm$ at Suwon on May 27, 1988. The daily net radiation ranged from 59 to 76 percents of the total shortwave radiation under cloudless conditions, which was lower than cloud overcast condition with recorded 63 to 83 percents. The latent heat flux under overcast condition was sometimes larger than the sum of net radiation, implying transportation of energy by advection of ambient air. The linear relationship was obtained between daily or daytime net radiation and evapotranspiration. The evapotranspiration calculated by Bowen ratio-energy balance method was about 150 percent of class A pan evaporation during the growing season. The total solar radiation from June 20 to August 27 was $1043MJm^{-2}$. The 85 percent of the total shortwave radiation was used for evaporative heat. The dry matter production within the period was $836gm^{-2}$ and the water use efficiency was $2.31gDM\;kg^{-1}\;H_2O$.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.1 s.38
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• pp.51-55
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• 2006

The green emitting high performance OLEDs using the $Alq_3$-C545T fluorescent system have been fabricated and characterized. In the device fabrication, 2-TNATA [4,4',4'-tris(2-naphthylphenyl-phenylamino)-triphenylamine] as a hole injection material and NPB [N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine] as a hole transport material were deposited on the ITO(indium thin oxide)/glass substrate by vacuum evaporation. And then, green color emission layer was deposited using $Alq_3$ as a host material and C-545T[10-(2-benzothiazolyl)-1,1,7,7- tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]/benzopyrano[6,7,8-ij]-quinolizin-11-one] as a dopant. Finally, small molecule OLEDs with structure of ITO/2-TNATA/NPB/$Alq_3$:C545T/$Alq_3$/LiF/Al were obtained by in-situ deposition of $Alq_3$, LiF and Al as the electron transport material, electron injection material and cathode, respectively. Green OLEDs fabricated in our experiments showed the color coordinate of CIE(0.29, 0.65) and the maximum power efficiency of 7.3 lm/W at 12 V with the peak emission wavelength of 521 nm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.2037-2042
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• 2013

A TCO-less palladium (Pd) catalytic layer on the glass substrate was assessed as the counter electrode (CE) in a dye sensitized solar cell (DSSC) to confirm the stability of Pd with the $I^-/I_3{^-}$electrolyte on the DSSC performance. A 90nm-thick Pd film was deposited by a thermal evaporator. Finally, DSSC devices of $0.45cm^2$ with glass/FTO/blocking layer/$TiO_2$/dye/electrolyte(10 mM LiI + 1 mM $I_2$ + 0.1 M $LiClO_4$ in acetonitrile solution)/Pd/glass structure was prepared. We investigated the microstructure and photovoltaic property at 1 and 12 hours after the sample preparation. The optical microscopy, field emission scanning electron microscopy (FESEM), cyclic voltammetry measurement (C-V), and current voltage (I-V) were employed to measure the microstructure and photovoltaic property evolution. Microstructure analysis showed that the corrosion by reaction between the Pd layer and the electrolyte occurred as time went by, which led the decrease of the catalytic activity and the efficiency. I-V result revealed that the energy conversion efficiency after 1 and 12 hours was 0.34% and 0.15%, respectively. Our results implied that we might employ the other non-$I^-/I_3{^-}$electrolyte or the other catalytic metal layers to guarantee the long term stability of the DSSC devices.

• Journal of Sensor Science and Technology
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• v.7 no.1
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• pp.67-72
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• 1998

The crystallized CuPc and PbTe films are formed by thermal evaporation and pulsed ArF excimer laser ablation. Structural and electrical properties of thin film is observed by XRD and current-voltage(I-V) curves. From XRD analysis, both PbTe and CuPc thin films show a-axis oriented structure. For the measurement of photovoltaic effect, the transverse current-voltage curve of CuPc/Si, PbTe/Si and PbTe/CuPc/Si junctions have been analyzed in the dark and under illumination. The PbTe/CuPc/Si junction exthibits a strong photovoltaic characteristics with short circuit current($J_{sc}$) of $25.46\;mA/cm^{2}$ and open-circuit voltage($V_{oc}$) of 170 mV. Quantum efficiency and power conversion efficiency are calculated to be 15.4% and $3.46{\times}10^{-2}$, respectively. Based on the results of QE and ${\eta}$, the photocurrent process of PbTe/CuPc/Si junction can be explained as following three effective steps; photocarrier generation in the CuPc layer, carrier separation at PbTe/CuPc interface, and finally a transportation of electrons through the PbTe layer.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.65-65
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• 2012

Copper zinc tin sulfide ($Cu_2ZnSnS_4$, CZTS) is a very promising material as a low cost absorber alternative to other chalcopyrite-type semiconductors based on Ga or In because of the abundant and economical elements. In addition, CZTS has a band-gap energy of 1.4~1.5eV and large absorption coefficient over ${\sim}10^4cm^{-1}$, which is similar to those of $Cu(In,Ga)Se_2$(CIGS) regarded as one of the most successful absorber materials for high efficient solar cell. Most previous works on the fabrication of CZTS thin films were based on the vacuum deposition such as thermal evaporation and RF magnetron sputtering. Although the vacuum deposition has been widely adopted, it is quite expensive and complicated. In this regard, the solution processes such as sol-gel method, nanocrystal dispersion and hybrid slurry method have been developed for easy and cost-effective fabrication of CZTS film. Among these methods, the hybrid slurry method is favorable to make high crystalline and dense absorber layer. However, this method has the demerit using the toxic and explosive hydrazine solvent, which has severe limitation for common use. With these considerations, it is highly desirable to develop a robust, easily scalable and relatively safe solution-based process for the fabrication of a high quality CZTS absorber layer. Here, we demonstrate the fabrication of a high quality CZTS absorber layer with a thickness of 1.5~2.0 ${\mu}m$ and micrometer-scaled grains using two different non-vacuum approaches. The first solution-processing approach includes air-stable non-toxic solvent-based inks in which the commercially available precursor nanoparticles are dispersed in ethanol. Our readily achievable air-stable precursor ink, without the involvement of complex particle synthesis, high toxic solvents, or organic additives, facilitates a convenient method to fabricate a high quality CZTS absorber layer with uniform surface composition and across the film depth when annealed at $530^{\circ}C$. The conversion efficiency and fill factor for the non-toxic ink based solar cells are 5.14% and 52.8%, respectively. The other method is based on the nanocrystal dispersions that are a key ingredient in the deposition of thermally annealed absorber layers. We report a facile synthetic method to produce phase-pure CZTS nanocrystals capped with less toxic and more easily removable ligands. The resulting CZTS nanoparticle dispersion enables us to fabricate uniform, crack-free absorber layer onto Mo-coated soda-lime glass at $500^{\circ}C$, which exhibits a robust and reproducible photovoltaic response. Our simple and less-toxic approach for the fabrication of CZTS layer, reported here, will be the first step in realizing the low-cost solution-processed CZTS solar cell with high efficiency.

• Current Photovoltaic Research
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• v.1 no.1
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• pp.38-43
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• 2013

$Cu(In,Ga)_3Se_5$ is a candidate material for the top cell of $Cu(In,Ga)Se_2$ tandem cells. This phase is often found at the surface of the $Cu(In,Ga)Se_2$ film during $Cu(In,Ga)Se_2$ cell fabrication, and plays a positive role in $Cu(In,Ga)Se_2$ cell performance. However, the exact properties of the $Cu(In,Ga)_3Se_5$ film have not been extensively studied yet. In this work, $Cu(In,Ga)_3Se_5$ films were fabricated on Mo-coated soda-lime glass substrates by a three-stage co-evaporation process. The Cu content in the film was controlled by varying the deposition time of each stage. X-ray diffraction and Raman spectroscopy analyses showed that, even though the stoichiometric Cu/(In+Ga) ratio is 0.25, $Cu(In,Ga)_3Se_5$ is easily formed in a wide range of Cu content as long as the Cu/(In+Ga) ratio is held below 0.5. The optical band gap of $Cu_{0.3}(In_{0.65}Ga_{0.35})_3Se_5$ composition was found to be 1.35eV. As the Cu/(In+Ga) ratio was decreased further below 0.5, the grain size became smaller and the band gap increased. Unlike the $Cu(In,Ga)Se_2$ solar cell, an external supply of Na with $Na_2S$ deposition further increased the cell efficiency of the $Cu(In,Ga)_3Se_5$ solar cell, indicating that more Na is necessary, in addition to the Na supply from the soda lime glass, to suppress deep level defects in the $Cu(In,Ga)_3Se_5$ film. The cell efficiency of $CdS/Cu(In,Ga)_3Se_5$ was improved from 8.8 to 11.2% by incorporating Na with $Na_2S$ deposition on the CIGS film. The fill factor was significantly improved by the Na incorporation, due to a decrease of deep-level defects.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.285-295
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• 1999

Electroluminescent(EL) devices based on organic materials have been of great interest due to their possible applications for large-area flat-panel displays. They are attractive because of their capability of multi-color emission, and low operation voltage. An approach to realize such device characteristics is to use active layers of lanthanide complexes with their inherent extremely sharp emission bands in stead of commonly known organic dyes. In general, organic molecular compounds show emission due to their $\pi$-$\pi*$ transitions resulting in luminescence bandwidths of about 80 to 100nm. Spin statistic estimations lead to an internal quantum efficiency of dye-based EL devices limited to 25%. On the contrary, the fluorescence of lanthanide complexes is based on an intramolecular energy transfer from the triplet of the organic ligand to the 4f energy states of the ion. Therefore, theoretical internal quantum efficiency is principally not limited. In this study, Powders of TPD, $Eu(TTA)_3(phen) and AlQ_3$ in a boat were subsequently heated to their sublimation temperatures to obtain the growth rates of 0.2~0.3nm/s. Organic electrolumnescent devices(OELD) with a structure of $glass substrate/ITO/Eu(TTA)_3(phen)/AI, glass substrate/ITO/TPD/Eu(TTA)_3(phen)/AI and glass substrate/ITO/TPD/Eu(TTA)_3(phen)/AIQ_3AI$ structures were fabricated by vacuum evaporation method, where aromatic diamine(TPD) was used as a hole transporting material, $Eu(TTA)_3(phen)$ as an emitting material, and Tris(8-hydroxyquinoline)Aluminum$(AlQ_3)$ as an electron transporting layer. Electroluminescent(EL) and current density-voltage(J-V) characteristics of these OELDs with various thickness of $Eu(TTA)_3(phen)$ layer were investigated. The triple-layer structure devices show the red EL spectrum at the wavelength of 613nm, which is almost the same as the photoluminescent(PL) spectrum of $Eu(TTA)_3(phen)$.It was found from the J-V characteristics of these devices that the current density is not dependent on the applied field, but on the electric field.