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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.
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.
Singh, Manjeet,Rana, Tanka R.,Kim, SeongYeon,Kim, Kihwan,Yun, Jae Ho,Kim, JunHo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.20
<P>Silver nanowire (AgNW) film has been demonstrated as excellent and low cost transparent electrode in organic solar cells as an alternative to replace scarce and expensive indium tin oxide (ITO). However, the low contact area and weak adhesion with low-lying surface as well as junction resistance between nanowires have limited the applications of AgNW film to thin film solar cells. To resolve this problem, we fabricated AgNW film as transparent conductive electrode (TCE) by binding with a thin layer of sputtered ZnO (40 nm) which not only increased contact area with low-lying surface in thin film solar cell but also improved conductivity by connecting AgNWs at the junction. The TCE thus fabricated exhibited transparency and sheet resistance of 92% and 20 Omega/boxed dot], respectively. Conductive atomic force microscopy (C-AFM) study revealed the enhancement of current collection vertically and laterally through AgNWs after coating with ZnO thin film. The CuInGaSe2 solar cell with TCE of our AgNW(ZnO) demonstrated the maximum power conversion efficiency of 13.5% with improved parameters in comparison to solar cell fabricated with conventional ITO as TCE.</P>
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.