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- 저자 : Chalapathy, R.B.V. (검색결과 34 건)
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Chalapathy, R.B.V.,Jung, Gwang Sun,Ko, Young Min,Ahn, Byung Tae,Kwon, HyukSang Korea Photovoltaic Society 2013 Current Photovoltaic Research Vol.1 No.2
$Cu_2ZnSnS_4$ thin film have been fabricated by rapid thermal annealing of dc-sputtered metal precursor with Cu/ZnSn/Cu stack in sulfur ambient. A CZTS film with a good uniformity was formed at $560^{\circ}C$ in 6 min. $Cu_2SnS_3$ and $Cu_3SnS_4$ secondary phases were present at $540^{\circ}C$ and a trace amount of $Cu_2SnS_3$ secondary phase was present at $560^{\circ}C$. Single-phase large-grained CZTS film with rough surface was formed at $560^{\circ}C$. Solar cell with best efficiency of 4.7% ($V_{oc}=632mV$, $j_{sc}=15.8mA/cm^2$, FF = 47.13%) for an area of $0.44cm^2$ was obtained for the CZTS absorber grown at $560^{\circ}C$ for 6 min. The existence of second phase at lower-temperature annealing and rough surface at higher-temperature annealing caused the degradation of cell performance. Also poor back contact by void formation deteriorated cell performance. The fill factor was below 0.5; it should be increased by minimizing voids at the CZTS/Mo interface. Our results suggest that CZTS absorbers can be grown by rapid thermal annealing of metallic precursors in sulfur ambient for short process times ranging in minutes.
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Chalapathy, R.B.V.,Gang, Myeng Gil,Hong, Chang Woo,Kim, Ji Hun,Jang, Jun Sun,Yun, Jae Ho,Kim, Jin Hyeok Elsevier 2018 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.159 No.-
<P><B>Abstract</B></P> <P>In this work, earth-abundant CZTSSe thin film solar cells were fabricated by sulfo-selenization of the Mo/Zn/Cu/Sn/Cu metallic precursors. The influences of morphological and compositional properties of the absorbers on performance of solar cells were investigated by tuning Cu content in the films. The Raman analysis showed that absorbers consist of a kesterite CZTSSe phase with ZnSe as a minor secondary phase. X-ray photoelectron spectroscopy (XPS) analyses revealed that the surfaces are Cu depleted and Zn enriched compared with the bulk composition of the absorbers. The results indicate that during sulfo-selenization the Cu diffused into the film and the Zn towards the film surface. The performance of the solar cells initially improved with the increasing of the Cu content and then decreased. By tuning the Cu content in the absorbers, the minority-carrier life time improved from 0.8 to 1.6 ns. The power conversion efficiency increased from 5.1 to 8.03% with fine controlling of Cu composition of the CZTSSe absorbers. The diode-ideality factors are higher than 2, suggesting an increased interfacial recombination in the devices. The high ideality-factors A and low minority carrier life times may originate from surface and bulk related defects, which in turn limits the V<SUB>oc</SUB> and the achievable high conversion efficiency for the CZTSSe thin film solar cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CZTSSe thin film solar cells were fabricated by sulfo-selenization of sputtered metallic Mo/Zn/Cu/Sn/Cu precursors. </LI> <LI> The surface composition of the absorbers was Cu depleted and Zn rich compared to the bulk of the absorbers. </LI> <LI> The ideality factors ‘A’ over 2 suggest that increased interface recombination in the devices which reduced the open circuit voltage of the devices. </LI> <LI> By tuning the Cu content in the absorbers solar cells with conversion efficiency about 8.03% was obtained. And the best efficiency of 8.17% was achieved without an antireflection coating. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Chalapathy, R.B.V.,Jung, Gwang Sun,Ko, Young Min,Ahn, Byung Tae,Kown, HyukSang Korea Photovoltaic Society 2013 Current Photovoltaic Research Vol.1 No.2
$Cu_2ZnSnS_4$ (CZTS) nanoparticles were synthesized by a solvothermal method using copper (II) acetate, zinc acetate, tin chloride, and sulfur in diethylenetriamine solvent. Binary sulfide particles such as CuS, ZnS, SnS, and $SnS_2$ were obtained at $180^{\circ}C$; single-phase CZTS nanoparticles were obtained at $280^{\circ}C$. CZTS nanoparticles with spherical shape and grain size of 40 to 60 nm were obtained at $280^{\circ}C$. In the middle of 180 and $280^{\circ}C$, CZTS and ZnS phases were found. The time variation of reaction at $280^{\circ}C$ revealed that an amorphous state formed first instead of binary phases and then the amorphous phase was converted to crystalline CZTS state; it is different reaction path way from conventional solid-state reaction path of which binary phases react to form CZTS. CZTS films deposited and annealed from single-phase nanoparticles showed porous microstructure and poor adhesion. This indicates that a combination of CZTS and other flux phase is necessary to have a dense film for device fabrication.
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R.B.V. Chalapathy,Gwang Sun Jung,Young Min Ko,Byung Tae Ahn,HyukSang Kown 한국태양광발전학회 2013 Current Photovoltaic Research Vol.1 No.2
Cu2ZnSnS4 (CZTS) nanoparticles were synthesized by a solvothermal method using copper (II) acetate, zinc acetate, tin chloride, and sulfur in diethylenetriamine solvent. Binary sulfide particles such as CuS, ZnS, SnS, and SnS2 were obtained at 180°C; single-phase CZTS nanoparticles were obtained at 280°C. CZTS nanoparticles with spherical shape and grain size of 40 to 60 nm were obtained at 280°C. In the middle of 180 and 280℃, CZTS and ZnS phases were found. The time variation of reaction at 280°C revealed that an amorphous state formed first instead of binary phases and then the amorphous phase was converted to crystalline CZTS state; it is different reaction path way from conventional solid-state reaction path of which binary phases react to form CZTS. CZTS films deposited and annealed from single-phase nanoparticles showed porous microstructure and poor adhesion. This indicates that a combination of CZTS and other flux phase is necessary to have a dense film for device fabrication.
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R.B.V. Chalapathy,Gwang Sun Jung,Young Min Ko,Byung Tae Ahn,HyukSang Kwon 한국태양광발전학회 2013 Current Photovoltaic Research Vol.1 No.2
Cu2ZnSnS4 thin film have been fabricated by rapid thermal annealing of dc-sputtered metal precursor with Cu/ZnSn/Cu stack in sulfur ambient. A CZTS film with a good uniformity was formed at 560℃ in 6 min. Cu2SnS3 and Cu3SnS4 secondary phases were present at 540°C and a trace amount of Cu2SnS3 secondary phase was present at 560℃. Single-phase large-grained CZTS film with rough surface was formed at 560ºC. Solar cell with best efficiency of 4.7% (Voc = 632 mV, jsc = 15.8 mA/cm<SUP>2</SUP>, FF = 47.13%) for an area of 0.44cm<SUP>2</SUP> was obtained for the CZTS absorber grown at 560℃ for 6 min. The existence of second phase at lower-temperature annealing and rough surface at higher-temperature annealing caused the degradation of cell performance. Also poor back contact by void formation deteriorated cell performance. The fill factor was below 0.5; it should be increased by minimizing voids at the CZTS/Mo interface. Our results suggest that CZTS absorbers can be grown by rapid thermal annealing of metallic precursors in sulfur ambient for short process times ranging in minutes.
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문선홍,장유성,Chalapathy R.B.V.,안병태,안진형,박정우,김기환,윤재호 한국물리학회 2021 Current Applied Physics Vol.21 No.-
An appropriate Ga slope is required in Cu(In,Ga)Se2 (CIGS) film to enhance the cell performance of CIGS thinfilm solar cells. In the conventional three-stage-co-evaporation process, the Ga slope was obtained by controlling Ga/In flux during deposition process. However, in two-step process, where a precursor was deposited first and then annealed in a Se environment for mass production, the desirable Ga slope was not achievable with the Ga/In flux control. We observed that the Ga/(Ga + In) ratio was nearly flat in CIGS film for Se-rich precursor and the ratio was nearly zero at surface and very high on bottom side of CISG film for Se-deficient precursor. We were able to generate a CIGS film with a Ga non-zero Ga surface and desired slope in the bulk by devising a precursor with Se-rich layer on top and Se-deficient layer on bottom, resulting in the enhancement of Cell performance.
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Park, Ju Young,Chalapathy, R.B.V.,Lokhande, A.C.,Hong, Chang Woo,Kim, Jin Hyeok ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.695 No.-
<P><B>Abstract</B></P> <P>Cadmium free ZnS buffer layers were deposited on Cu<SUB>2</SUB>ZnSn(SSe)<SUB>4</SUB> (CZTSSe) absorber layer by chemical bath deposition method. The thickness of ZnS buffer layers was tuned by varying deposition time and its effect on CZTSSe thin film solar cells were investigated. The thickness of the buffer layers increased linearly with the deposition time. The films showed lower optical transmittance with increasing ZnS buffer layer thickness. The optical band gaps of the films were found to be in the range from 3.52 to 3.68 eV. The best solar cell with conversion efficiency of 3.8% was obtained with ZnS buffer layer deposited with 56 nm thickness obtained at 40 min. External quantum efficiency (EQE) of the CZTSSe solar cell showed higher transmittance in the short wavelength region indicating less absorption. The performance of the solar cells increased with increasing deposition time initially and then decreased for a long deposition times. The variation in short circuit current density of the solar cells was attributed to increase in transmittance of the ZnS buffer layers. However, the cell exhibited poor collection efficiency at mid and long wavelengths suggesting defects at the interface and in the bulk of the CZTSSe absorber. Further, fine tuning the buffer layer and controlling the defects at the interface between ZnS and CZTSSe absorbers may lead to improved conversion efficiencies.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cadmium free buffer ZnS layers were successfully deposited onto CZTSSe absorbers by chemical bath deposition. </LI> <LI> CZTSSe solar cell with photo conversion efficiency η = 3.8% was achieved with Se rich absorber. </LI> <LI> Increasing ZnS buffer layer thickness the solar cells showed poor performances. </LI> <LI> Optimum thickness of buffer layer is found to be 56 nm to obtain better photo conversion efficiencies. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Lokhande, A.C.,Chalapathy, R.B.V.,Jang, J.S.,Babar, P.T.,Gang, M.G.,Lokhande, C.D.,Kim, Jin Hyeok North-Holland 2017 Solar Energy Materials and Solar Cells Vol. No.
<P><B>Abstract</B></P> <P>In the present work, Ge doped CZTGeS thin films are pulsed laser deposited followed by annealing treatment in selenium environment. The influence of selenization condition on the structural, morphological, optical and electrical properties of the absorber thin films are investigated. The thin films characterized using X-ray diffraction (XRD) and Raman spectroscopy techniques confirm the formation of Kesterite CZTGeSSe thin film compound with dominant A1 mode vibration. The morphological and optical studies of the thin films reveal the formation of compact and void free microstructure with optimal band gap in the range of 1–1.2eV. The impact of selenization temperature on the quality of thin films has been studied and thin film solar cells are fabricated with CZTGeSSe absorbers grown at various annealing temperatures from 525 to 575℃ to evaluate the performance of devices as a function of an annealing temperature. The elemental Ge and Sn losses from the absorber compound confirmed from X-ray fluorescence spectroscopy (XRF) depended on the annealing temperature and linearly increased with increasing temperature affecting the optical, compositional and microstructural properties of the thin films. Compositional non uniformity is one of the factors that limit the performance of solar cell device. PLD technique due to its advantage of achieving precise stoichiometry control combined with optimized selenization conditions can potentially address the issue. Compared to solar cell fabricated from absorber compound annealed at 525 and 575℃, the solar cell fabricated from the absorber annealed at 550℃ exhibited the best conversion efficiency of 3.82% with V<SUB>oc</SUB> 434mV, J<SUB>sc</SUB> 18.33mA/cm<SUP>2</SUP>, FF 47.0% and retained nearly 90% power conversion efficiency (PCE) stability after time period of 60 days.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pulsed laser deposition of Ge doped CZTS thin films. </LI> <LI> Band gap tuning of CZTGeS thin films with selenization treatment. </LI> <LI> Effect of annealing conditions on structural, optical and morphological properties of CZTGeSSe thin films. </LI> <LI> Fabrication of CZTGeSSe thin film solar cells with efficiency over 3.82%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Cho, Yang Hwi,Chalapathy, R. B. V.,Park, Do Hyung,Ahn, Byung Tae The Electrochemical Society 2010 Journal of the Electrochemical Society Vol.157 No.3
<P>A [Formula] or [Formula] flux was added to a mixture of BaS, EuS, Al, and S to synthesize a Eu-doped cubic [Formula] phosphor. The formation temperature of the cubic [Formula] phase was lowered to [Formula], which was [Formula] below the temperature of a case without a flux. To improve the crystallinity and color purity, a two-step annealing process that involved low temperature annealing ([Formula] for [Formula] and [Formula] for [Formula]) was proposed for a uniform immersion of a flux into a starting mixture and a high temperature annealing [Formula] for the formation of [Formula]. The phosphor synthesized by the two-step process with a 2 wt % [Formula] flux showed a distinct cubic [Formula] phase and a strong photoluminescence (PL) intensity at 475 nm. The PL intensity was 6.6 times stronger than that of the phosphor without a flux. The phosphor synthesized with a [Formula] flux showed only an orthorhombic phase, while direct annealing at 600° with the flux showed a mixture of cubic and orthorhombic phases. The role of the fluxes in the formation mechanism of the cubic and orthorhombic [Formula] phases was described.</P>
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