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Phase engineering of CBD grown tin sulfide films by post-sulfurization and solar cell application
Tanka Raj Rana,JunHo Kim 한국물리학회 2016 Current Applied Physics Vol.16 No.12
We report on post-annealing effects on structures, compositions and surface morphology of chemical bath deposition (CBD) grown tin sulfide thin films. For post-annealing of as-grown tin sulfide films, we carried out three types of sulfurization at different temperatures. As grown tin sulfide films followed by sulfurization at different conditions showed modified surface morphologies and crystalline phases; SnS, Sn2S3 and SnS2 according to the sulfurization conditions. Experimental results showed that these earthabundant thin films could be engineered to have different structural, electrical and optical properties by simple post-sulfurization process, possessing significant potentials for wide fields of applications. Moreover, we made solar cell using SnS as photo absorber, which showed ~0.1% power conversion efficiency.
Fabrication and device characterization of potassium fluoride solution treated CZTSSe solar cell
Tanka Raj Rana,김준호,심준형,양기정,김대환,강진규 한국물리학회 2017 Current Applied Physics Vol.17 No.10
ost deposition treatment (PDT) for Cu2ZnSn(S,Se)4 (CZTSSe) was carried out by simply dipping the absorber into the KF solution at 80 C. The dipping time of absorber in KF solution was found to be crucial to device parameters of CZTSSe solar cell. The K-doping improved the solar cell efficiency from 4.4% to 7.6% by 1 min dipping whereas the longer than 5 min dipping solar cells showed distorted kink J-V curves. The activation energy of CZTSSe solar cell was increased upto 1 min KF treatment from 0.83 eV to 0.92 eV which indicates interface recombination is reduced significantly. However, the activation energies of 5 min and 10 min dipping solar cells were found to be 0.81 eV and 0.63 eV where dominant recombination was interface recombination. Furthermore, trap energies of 49 meV and 298 meV of pristine CZTSSe solar cell were modified to 33 meV and 117 meV for 1 min treated CZTSSe solar cell. Trap energies of 5 min were calculated to be 112 meV and 147 meV. The proper KF doping passivated the shallow as well as deep defects of CZTSSe solar cell which is reflected in photovoltaic performances directly.
Tanka Raj Rana,김성연,김준호 한국물리학회 2018 Current Applied Physics Vol.18 No.6
Tin sulfide (SnS) film is grown by sputtering process with subsequent post-sulfurization. As-deposited SnS consists of orthorhombic and cubic structure SnS whereas post-sulfurized films showed pure orthorhombic crystal structure. This structural transformation was confirmed by X-ray diffraction (XRD), Raman spectroscopy and UV–Vis spectroscopy. We used post-annealed SnS film as an absorber layer of solar cell. The fabricated SnS solar cell was composed of SLG/Mo/SnS/CdS/i-ZnO/ITO. We measured current density-voltage (J-V) and external quantum efficiency (EQE) curves for the completed devices. The best efficiency of SnS solar cell was ∼0.5%. The EQE curve showed existence of multiple phases of SnS, even though XRD and Raman spectroscopy showed pure SnS phase. The multiple phases were observed again by photoluminescence (PL). PL also revealed deep defect states of SnS absorber. Thus, the inhomogeneous SnS absorber is one of the main bottlenecks for high efficiency SnS solar cell.
Mukhiya, Tanka,Dahal, Bipeen,Ojha, Gunendra Prasad,Kang, Dawon,Kim, Taewoo,Chae, Su-Hyeong,Muthurasu, Alagan,Kim, Hak Yong Elsevier 2019 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.361 No.-
<P><B>Abstract</B></P> <P>Engineering nanostructures in the desired design and suitable size is one of the key issues for persuading high-performance supercapacitors (SCs). In this work, we report a successful synthesis of a new type of nanohaired three-dimensional cobalt hydroxide wheels/carbon nanofibers (3D Co(OH)<SUB>2</SUB>/CNFs) composite by a cost-effective electrospinning cum hydrothermal method. The 3D Co(OH)<SUB>2</SUB> wheels are composed of many partially-fused, nanohaired and serrated sheet-like nanoleaflets furnishing abundant active sites. This novel architecture is quite significant for the stability of the composite since the wheels encircle one or more conductive CNFs firmly rather than the simple attachment on the surface of substrate. The growth process of 3D Co(OH)<SUB>2</SUB> wheels on CNFs has been studied by synthesizing other two novel Co(OH)<SUB>2</SUB>/CNFs composites. The as-prepared material exhibits a specific capacitance of 1186 F g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP> with excellent cyclic stability which is the highest reported value for Co(OH)<SUB>2</SUB>/CNFs composites. The asymmetric supercapacitor (ASC) device assembled using 3D Co(OH)<SUB>2</SUB>/CNFs as a positive electrode and nitrogen doped graphene hydrogel (NGH) as a negative electrode exhibits a high energy density of 60.31 W h kg<SUP>−1</SUP> at power density of 740.8 W kg<SUP>−1</SUP> which still remains 37 W h kg<SUP>−1</SUP> even at a higher power density of 7500 W kg<SUP>−1</SUP> with remarkable cycle life. Therefore, the composite stands as a promising candidate for SCs electrode material. This unique nanoengineering gives an insight into the synthesis of other stable nanocomposites for diverse applications like sensors, catalysis, etc.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel nanohaired 3D cobalt hydroxide wheels have been uniformly inserted in CNFs. </LI> <LI> Growth process of 3D cobalt hydroxide wheels in CNFs has been proposed. </LI> <LI> 3D Co(OH)<SUB>2</SUB>/CNFs//NGH ASC exhibits high energy density with remarkable cycle life. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Cu(In,Ga)Se2 Solar Cells with In2S3 Buffer Layer Deposited by Thermal Evaporation
김성연,Tanka R Rana,김준호,윤재호 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.12
We report on physical vapor deposition of indium sulfide (In2S3) buffer layers and its application to Cu(In,Ga)Se2 (CIGSe) thin film solar cell. The Indium sulfide buffer layers were evaporated onto CIGSe at various substrate temperatures from room temperature (RT) to 350 C. The effect of deposition temperature of buffer layers on the solar cell device performance were investigated by analyzing temperature dependent current-voltage (J-V -T), external quantum efficiency (EQE) and Raman spectroscopy. The fabricated device showed the highest power conversion efficiency of 6.56% at substrate temperature of 250 C, which is due to the decreased interface recombination. However, the roll-over in J-V curves was observed for solar cell device having buffer deposited at substrate temperature larger than 250 C. From the measurement results, the interface defect and roll-over related degradation were found to have limitation on the performance of solar cell device.
Design of the Integrated Monitoring System to Improve the Safeness of Underground Space
Jeongeun Lee,Tanka Nath Sharma,Hyunsuk Hwang,Kiuk Kim,Sungje Kim,Kyooseok Park,Kyubark Shim,Changsoo Kim 한국멀티미디어학회 2008 한국멀티미디어학회 국제학술대회 Vol.2008 No.-
Even though the use of the underground space increases, the reaction for the safety is a shortage of something. Particularly, the minimum supplement of safety facilities and the unprepared method for checking threaten the occurrence of disasters. In this paper, we design an integrated monitoring system using new IT technology to cope rapidly with disasters. Our system collects basic data for recognizing the disasters using sensor networks, detect the escape path using 3D GIS for rapidly escaping from the disaster area, and include the facility management system for recognizing the operation status. Also, the effectiveness of the proposed system is assured by presenting the reaction process based on the monitoring system with a disaster scenario.
Characterization of CBO and defect states of CZTSe solar cells prepared by using two-step process
김성연,김준호,Tanka R Rana,김강우,권명회 한국물리학회 2018 Current Applied Physics Vol.18 No.2
We fabricated kesterite Cu2ZnSnSe4 (CZTSe) solar cells and studied device characteristics, where CZTSe absorbers were made by using two-step process. First, we deposited precursor CZTSe films with spincoating or sputtering, and performed sulfurization and subsequent selenization. To complete the device, we applied In2S3 as a buffer layer. We obtained power conversion efficiency (PCE) of 4.18% with spin-coated CZTSe absorber and 5.60% with sputtered CZTSe absorber. Both devices showed deep defects in the bulk and strong interface recombinations near the pn junction. In addition, we observed red-kinks in the current density-voltage (J-V) curves for both devices under the filtered light illumination (>660 nm), which is attributed to large conduction band offset (CBO) between the CZTSe absorber and the buffer layer and defect states in the buffer/CZTSe absorber or in the buffer. The red-kink was also observed in CZTSe (PCE of 7.76%) solar cell with CdS buffer. Hence, to enhance the PCE with CZTSe absorber, along with suppression of deep defects which act as recombination center, optimization of CBO between absorber and buffer is also required.
A System Framework for Managing and Analyzing Disaster History Information
Hyunsuk Hwang,Tanka Nath Sharma,Changsoo Kim 한국멀티미디어학회 2009 한국멀티미디어학회 국제학술대회 Vol.2009 No.-
Hazard maps have recently been constructed to protect people's lives and estates from the damage caused by natural disasters such as flooding, wave-storms, landslides, and windstorms. The hazard maps need previous disaster records and related information such as weather, rainfall sensors, and CCTV information. This paper focuses on the development of a framework to manage and analyze disaster history data. The framework consists of the layers of raw data collection, data management, analysis models, integrated systems, and required services. This paper will introduce the components and implement the procedures needed in constructing a digital hazard map system.