메뉴 건너뛰기




Volumn 120, Issue 18, 2016, Pages 9619-9627

Well-Organized Mesoporous TiO2 Photoanode by Using Amphiphilic Graft Copolymer for Efficient Perovskite Solar Cells

Author keywords

[No Author keywords available]

Indexed keywords

FILM THICKNESS; GRAFT COPOLYMERS; GRAFTING (CHEMICAL); MESOPOROUS MATERIALS; ORGANIC SOLVENTS; PEROVSKITE; POLYVINYL CHLORIDES; PORE SIZE; SOLAR CELLS; SOLAR POWER GENERATION; TITANIUM DIOXIDE;

EID: 84971287266     PISSN: 19327447     EISSN: 19327455     Source Type: Journal    
DOI: 10.1021/acs.jpcc.6b01980     Document Type: Article
Times cited : (44)

References (57)
  • 1
    • 84931272007 scopus 로고    scopus 로고
    • High-Performance Photovoltaic Perovskite Layers Fabricated Through Intramolecular Exchange
    • Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. High-Performance Photovoltaic Perovskite Layers Fabricated Through Intramolecular Exchange Science 2015, 348, 1234-1237 10.1126/science.aaa9272
    • (2015) Science , vol.348 , pp. 1234-1237
    • Yang, W.S.1    Noh, J.H.2    Jeon, N.J.3    Kim, Y.C.4    Ryu, S.5    Seo, J.6    Seok, S.I.7
  • 2
    • 84937122763 scopus 로고    scopus 로고
    • Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead (II) Iodide
    • Ahn, N.; Son, D. Y.; Jang, I. H.; Kang, S. M.; Choi, M.; Park, N. G. Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead (II) Iodide J. Am. Chem. Soc. 2015, 137, 8696-8699 10.1021/jacs.5b04930
    • (2015) J. Am. Chem. Soc. , vol.137 , pp. 8696-8699
    • Ahn, N.1    Son, D.Y.2    Jang, I.H.3    Kang, S.M.4    Choi, M.5    Park, N.G.6
  • 3
    • 84904403218 scopus 로고    scopus 로고
    • A Hole-Conductor-Free, Fully Printable Mesoscopic Perovskite Solar Cell with High Stability
    • Mei, A.; Li, X.; Liu, L.; Ku, Z.; Liu, T.; Rong, Y.; Xu, M.; Hu, M.; Chen, J.; Yang, Y.; Grätzel, M.; Han, H. A Hole-Conductor-Free, Fully Printable Mesoscopic Perovskite Solar Cell with High Stability Science 2014, 345, 295-298 10.1126/science.1254763
    • (2014) Science , vol.345 , pp. 295-298
    • Mei, A.1    Li, X.2    Liu, L.3    Ku, Z.4    Liu, T.5    Rong, Y.6    Xu, M.7    Hu, M.8    Chen, J.9    Yang, Y.10    Grätzel, M.11    Han, H.12
  • 4
    • 84868195671 scopus 로고    scopus 로고
    • Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites
    • Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites Science 2012, 338, 643-647 10.1126/science.1228604
    • (2012) Science , vol.338 , pp. 643-647
    • Lee, M.M.1    Teuscher, J.2    Miyasaka, T.3    Murakami, T.N.4    Snaith, H.J.5
  • 5
    • 84900642672 scopus 로고    scopus 로고
    • A Perspective of Mesoscopic Solar Cells Based on Metal Chalcogenide Quantum Dots and Organometal-Halide Perovskites
    • Rhee, J. H.; Chung, C.-C.; Diau, E. W.-G. A Perspective of Mesoscopic Solar Cells Based on Metal Chalcogenide Quantum Dots and Organometal-Halide Perovskites NPG Asia Mater. 2013, 5, e68 10.1038/am.2013.53
    • (2013) NPG Asia Mater. , vol.5 , pp. e68
    • Rhee, J.H.1    Chung, C.-C.2    Diau, E.W.-G.3
  • 7
    • 84928485608 scopus 로고    scopus 로고
    • Inorganic p-Type Contact Materials for Perovskite-Based Solar Cells
    • Li, M.-H.; Shen, P.-S.; Wang, K.-C.; Guo, T.-F.; Chen, P. Inorganic p-Type Contact Materials for Perovskite-Based Solar Cells J. Mater. Chem. A 2015, 3, 9011-9019 10.1039/C4TA06425A
    • (2015) J. Mater. Chem. A , vol.3 , pp. 9011-9019
    • Li, M.-H.1    Shen, P.-S.2    Wang, K.-C.3    Guo, T.-F.4    Chen, P.5
  • 8
    • 84923319912 scopus 로고    scopus 로고
    • Perovskite-Based Solar Cells: Impact of Morphology and Device Architecture on Device Performance
    • Salim, T.; Sun, S.; Abe, Y.; Krishna, A.; Grimsdale, A. C.; Lam, Y. M. Perovskite-Based Solar Cells: Impact of Morphology and Device Architecture on Device Performance J. Mater. Chem. A 2015, 3, 8943-8969 10.1039/C4TA05226A
    • (2015) J. Mater. Chem. A , vol.3 , pp. 8943-8969
    • Salim, T.1    Sun, S.2    Abe, Y.3    Krishna, A.4    Grimsdale, A.C.5    Lam, Y.M.6
  • 9
    • 84903544471 scopus 로고    scopus 로고
    • The Emergence of Perovskite Solar Cells
    • Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of Perovskite Solar Cells Nat. Photonics 2014, 8, 506-514 10.1038/nphoton.2014.134
    • (2014) Nat. Photonics , vol.8 , pp. 506-514
    • Green, M.A.1    Ho-Baillie, A.2    Snaith, H.J.3
  • 10
    • 84928951451 scopus 로고    scopus 로고
    • Solvent Engineering for High-Performance Inorganic-Organic Hybrid Perovskite Solar Cells
    • Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Solvent Engineering for High-Performance Inorganic-Organic Hybrid Perovskite Solar Cells Nat. Mater. 2014, 13, 897-903 10.1038/nmat4014
    • (2014) Nat. Mater. , vol.13 , pp. 897-903
    • Jeon, N.J.1    Noh, J.H.2    Kim, Y.C.3    Yang, W.S.4    Ryu, S.5    Seok, S.I.6
  • 15
    • 84893824650 scopus 로고    scopus 로고
    • 3 Solar Cells: Charge Transport, Recombination, and Diffusion Length
    • 3 Solar Cells: Charge Transport, Recombination, and Diffusion Length J. Phys. Chem. Lett. 2014, 5, 490-494 10.1021/jz500003v
    • (2014) J. Phys. Chem. Lett. , vol.5 , pp. 490-494
    • Zhao, Y.1    Nardes, A.M.2    Zhu, K.3
  • 18
    • 84922586427 scopus 로고    scopus 로고
    • Compositional Engineering of Perovskite Materials for High-Performance Solar Cells
    • Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Compositional Engineering of Perovskite Materials for High-Performance Solar Cells Nature 2015, 517, 476-480 10.1038/nature14133
    • (2015) Nature , vol.517 , pp. 476-480
    • Jeon, N.J.1    Noh, J.H.2    Yang, W.S.3    Kim, Y.C.4    Ryu, S.5    Seo, J.6    Seok, S.I.7
  • 19
    • 84897879784 scopus 로고    scopus 로고
    • Organolead Halide Perovskite: New Horizons in Solar Cell Research
    • Kim, H. S.; Im, S. H.; Park, N. G. Organolead Halide Perovskite: New Horizons in Solar Cell Research J. Phys. Chem. C 2014, 118, 5615-5625 10.1021/jp409025w
    • (2014) J. Phys. Chem. C , vol.118 , pp. 5615-5625
    • Kim, H.S.1    Im, S.H.2    Park, N.G.3
  • 24
    • 84954199152 scopus 로고    scopus 로고
    • 2 Aggregates with Diameter of 100 nm for Efficient Mesoscopic Perovskite Solar Cells
    • 2 Aggregates with Diameter of 100 nm for Efficient Mesoscopic Perovskite Solar Cells Nano Energy 2016, 20, 272-282 10.1016/j.nanoen.2015.12.031
    • (2016) Nano Energy , vol.20 , pp. 272-282
    • Yang, I.S.1    You, J.S.2    Sung, S.D.3    Chung, C.W.4    Kim, J.5    Lee, W.I.6
  • 25
    • 84905438646 scopus 로고    scopus 로고
    • 2 Photoelectrodes by Block Copolymer-Induced Sol-Gel Assembly for Inorganic-Organic Hybrid Perovskite Solar Cells
    • 2 Photoelectrodes by Block Copolymer-Induced Sol-Gel Assembly for Inorganic-Organic Hybrid Perovskite Solar Cells J. Phys. Chem. C 2014, 118, 16688-16693 10.1021/jp412655p
    • (2014) J. Phys. Chem. C , vol.118 , pp. 16688-16693
    • Sarkar, A.1    Jeon, N.J.2    Noh, J.H.3    Seok, S.I.4
  • 29
    • 84874923445 scopus 로고    scopus 로고
    • Large-Pore Ordered Mesoporous Materials Templated from Non-Pluronic Amphiphilic Block Copolymers
    • Deng, Y.; Wei, J.; Sun, Z.; Zhao, D. Large-Pore Ordered Mesoporous Materials Templated from Non-Pluronic Amphiphilic Block Copolymers Chem. Soc. Rev. 2013, 42, 4054-4070 10.1039/C2CS35426H
    • (2013) Chem. Soc. Rev. , vol.42 , pp. 4054-4070
    • Deng, Y.1    Wei, J.2    Sun, Z.3    Zhao, D.4
  • 30
    • 84930506160 scopus 로고    scopus 로고
    • Ordered Mesoporous Titania from Highly Amphiphilic Block Copolymers: Tuned Solution Conditions Enable Highly Ordered Morphologies and Ultra-Large Mesopores
    • Stefik, M.; Song, J.; Sai, H.; Guldin, S.; Boldrighini, P.; Orilall, M. C.; Steiner, U.; Gruner, S. M.; Wiesner, U. Ordered Mesoporous Titania from Highly Amphiphilic Block Copolymers: Tuned Solution Conditions Enable Highly Ordered Morphologies and Ultra-Large Mesopores J. Mater. Chem. A 2015, 3, 11478-11492 10.1039/C5TA02483H
    • (2015) J. Mater. Chem. A , vol.3 , pp. 11478-11492
    • Stefik, M.1    Song, J.2    Sai, H.3    Guldin, S.4    Boldrighini, P.5    Orilall, M.C.6    Steiner, U.7    Gruner, S.M.8    Wiesner, U.9
  • 31
    • 84907855737 scopus 로고    scopus 로고
    • Molecular Design of the Amphiphilic AB Diblock Copolymer Toward One-Step Synthesis of Amino-Group Functionalized Large Pore Mesoporous Silica
    • Xu, D.; Yao, Y.; Han, L.; Che, S. Molecular Design of the Amphiphilic AB Diblock Copolymer Toward One-Step Synthesis of Amino-Group Functionalized Large Pore Mesoporous Silica RSC Adv. 2014, 4, 43047-43051 10.1039/C4RA05790B
    • (2014) RSC Adv. , vol.4 , pp. 43047-43051
    • Xu, D.1    Yao, Y.2    Han, L.3    Che, S.4
  • 32
    • 84915818902 scopus 로고    scopus 로고
    • Amphiphilic ABC Triblock Terpolymer Templated Large-Pore Mesoporous Silicas
    • Xu, D.; Huang, Z.; Han, L.; Yao, Y.; Che, S. Amphiphilic ABC Triblock Terpolymer Templated Large-Pore Mesoporous Silicas Mater. Lett. 2015, 141, 176-179 10.1016/j.matlet.2014.11.064
    • (2015) Mater. Lett. , vol.141 , pp. 176-179
    • Xu, D.1    Huang, Z.2    Han, L.3    Yao, Y.4    Che, S.5
  • 33
    • 84888989052 scopus 로고    scopus 로고
    • Synthesis of Non-Siliceous Mesoporous Oxides
    • Gu, D.; Schuth, F. Synthesis of Non-Siliceous Mesoporous Oxides Chem. Soc. Rev. 2014, 43, 313-344 10.1039/C3CS60155B
    • (2014) Chem. Soc. Rev. , vol.43 , pp. 313-344
    • Gu, D.1    Schuth, F.2
  • 34
    • 84942163788 scopus 로고    scopus 로고
    • Colloidal Amphiphile-Templated Growth of Highly Crystalline Mesoporous Nonsiliceous Oxides
    • Liu, B.; Luo, Z.; Federico, A.; Song, W.; Suib, S. L.; He, J. Colloidal Amphiphile-Templated Growth of Highly Crystalline Mesoporous Nonsiliceous Oxides Chem. Mater. 2015, 27, 6173-6176 10.1021/acs.chemmater.5b02248
    • (2015) Chem. Mater. , vol.27 , pp. 6173-6176
    • Liu, B.1    Luo, Z.2    Federico, A.3    Song, W.4    Suib, S.L.5    He, J.6
  • 35
    • 84942781749 scopus 로고    scopus 로고
    • Ordered Mesoporous Particles in Titania Films with Hierarchical Structure as Scattering Layers in Dye-Sensitized Solar Cells
    • Xiong, Y.; He, D.; Jin, Y.; Cameron, P. J.; Edler, K. J. Ordered Mesoporous Particles in Titania Films with Hierarchical Structure as Scattering Layers in Dye-Sensitized Solar Cells J. Phys. Chem. C 2015, 119, 22552-22559 10.1021/acs.jpcc.5b06977
    • (2015) J. Phys. Chem. C , vol.119 , pp. 22552-22559
    • Xiong, Y.1    He, D.2    Jin, Y.3    Cameron, P.J.4    Edler, K.J.5
  • 37
    • 0034617265 scopus 로고    scopus 로고
    • Synthesis of Highly Ordered Mesoporous Silica Materials Using Sodium Silicate and Amphiphilic Block Copolymers
    • Kim, J. M.; Stucky, G. D. Synthesis of Highly Ordered Mesoporous Silica Materials Using Sodium Silicate and Amphiphilic Block Copolymers Chem. Commun. 2000, 1159-1160 10.1039/b002362k
    • (2000) Chem. Commun. , pp. 1159-1160
    • Kim, J.M.1    Stucky, G.D.2
  • 39
    • 84901679124 scopus 로고    scopus 로고
    • Thermally Induced Structural Evolution and Performance of Mesoporous Block Copolymer-Directed Alumina Perovskite Solar Cells
    • Tan, K. W.; Moore, D. T.; Saliba, M.; Sai, H.; Estroff, L. A.; Hanrath, T.; Snaith, H. J.; Wiesner, U. Thermally Induced Structural Evolution and Performance of Mesoporous Block Copolymer-Directed Alumina Perovskite Solar Cells ACS Nano 2014, 8, 4730-4739 10.1021/nn500526t
    • (2014) ACS Nano , vol.8 , pp. 4730-4739
    • Tan, K.W.1    Moore, D.T.2    Saliba, M.3    Sai, H.4    Estroff, L.A.5    Hanrath, T.6    Snaith, H.J.7    Wiesner, U.8
  • 40
    • 77949413882 scopus 로고    scopus 로고
    • 2 Films Templated by Graft Copolymers for Dye-Sensitized Solar Cells
    • 2 Films Templated by Graft Copolymers for Dye-Sensitized Solar Cells Chem. Commun. 2010, 46, 1935-1937 10.1039/b919215h
    • (2010) Chem. Commun. , vol.46 , pp. 1935-1937
    • Ahn, S.H.1    Koh, J.H.2    Seo, J.A.3    Kim, J.H.4
  • 41
    • 84880507645 scopus 로고    scopus 로고
    • Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells
    • Burschka, J.; Pellet, N.; Moon, S. J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Gratzel, M. Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells Nature 2013, 499, 316-319 10.1038/nature12340
    • (2013) Nature , vol.499 , pp. 316-319
    • Burschka, J.1    Pellet, N.2    Moon, S.J.3    Humphry-Baker, R.4    Gao, P.5    Nazeeruddin, M.K.6    Gratzel, M.7
  • 42
    • 77953126788 scopus 로고    scopus 로고
    • Amphiphilic Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) Graft Polymer Electrolytes: Interactions, Nanostructures and Applications to Dye-Sensitized Solar Cells
    • Roh, D. K.; Park, J. T.; Ahn, S. H.; Ahn, H.; Ryu, D. Y.; Kim, J. H. Amphiphilic Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) Graft Polymer Electrolytes: Interactions, Nanostructures and Applications to Dye-Sensitized Solar Cells Electrochim. Acta 2010, 55, 4976-4981 10.1016/j.electacta.2010.03.106
    • (2010) Electrochim. Acta , vol.55 , pp. 4976-4981
    • Roh, D.K.1    Park, J.T.2    Ahn, S.H.3    Ahn, H.4    Ryu, D.Y.5    Kim, J.H.6
  • 44
    • 0010146743 scopus 로고    scopus 로고
    • IR Spectroscopy or Hookeâs Law at the Molecular Level-A Joint Freshman Physics-Chemistry Experience
    • Burke, J. T. IR Spectroscopy or Hookeâs Law at the Molecular Level-A Joint Freshman Physics-Chemistry Experience J. Chem. Educ. 1997, 74, 1213 10.1021/ed074p1213
    • (1997) J. Chem. Educ. , vol.74 , pp. 1213
    • Burke, J.T.1
  • 45
    • 77957807643 scopus 로고    scopus 로고
    • 2 Spheres with Hierarchical Pores via Grafting Polymerization and Sol-Gel Process for Dye-Sensitized Solar Cells
    • 2 Spheres with Hierarchical Pores via Grafting Polymerization and Sol-Gel Process for Dye-Sensitized Solar Cells J. Mater. Chem. 2010, 20, 8521-8530 10.1039/c0jm01471k
    • (2010) J. Mater. Chem. , vol.20 , pp. 8521-8530
    • Park, J.T.1    Roh, D.K.2    Patel, R.3    Kim, E.4    Ryu, D.Y.5    Kim, J.H.6
  • 46
    • 70350051149 scopus 로고    scopus 로고
    • Synthesis and Gas Permeation Properties of Amphiphilic Graft Copolymer Membranes
    • Ahn, S. H.; Seo, J. A.; Kim, J. H.; Ko, Y.; Hong, S. U. Synthesis and Gas Permeation Properties of Amphiphilic Graft Copolymer Membranes J. Membr. Sci. 2009, 345, 128-133 10.1016/j.memsci.2009.08.037
    • (2009) J. Membr. Sci. , vol.345 , pp. 128-133
    • Ahn, S.H.1    Seo, J.A.2    Kim, J.H.3    Ko, Y.4    Hong, S.U.5
  • 48
    • 84903954327 scopus 로고    scopus 로고
    • Controllable Self-Induced Passivation of Hybrid Lead Iodide Perovskites toward High Performance Solar Cells
    • Chen, Q.; Zhou, H.; Song, T. B.; Luo, S.; Hong, Z.; Duan, H. S.; Dou, L.; Liu, Y.; Yang, Y. Controllable Self-Induced Passivation of Hybrid Lead Iodide Perovskites toward High Performance Solar Cells Nano Lett. 2014, 14, 4158-4163 10.1021/nl501838y
    • (2014) Nano Lett. , vol.14 , pp. 4158-4163
    • Chen, Q.1    Zhou, H.2    Song, T.B.3    Luo, S.4    Hong, Z.5    Duan, H.S.6    Dou, L.7    Liu, Y.8    Yang, Y.9
  • 49
    • 84871569554 scopus 로고    scopus 로고
    • Size-Controlled Anatase Titania Single Crystals with Octahedron-Like Morphology for Dye-Sensitized Solar Cells
    • Shiu, J.-W.; Lan, C.-M.; Chang, Y.-C.; Wu, H.-P.; Huang, W.-K.; Diau, E. W.-G. Size-Controlled Anatase Titania Single Crystals with Octahedron-Like Morphology for Dye-Sensitized Solar Cells ACS Nano 2012, 6, 10862-10873 10.1021/nn3042418
    • (2012) ACS Nano , vol.6 , pp. 10862-10873
    • Shiu, J.-W.1    Lan, C.-M.2    Chang, Y.-C.3    Wu, H.-P.4    Huang, W.-K.5    Diau, E.W.-G.6
  • 51
    • 85027935402 scopus 로고    scopus 로고
    • Solvent annealing of perovskite-induced crystal growth for photovoltaic-device efficiency enhancement
    • Xiao, Z.; Dong, Q.; Bi, C.; Shao, Y.; Yuan, Y.; Huang, J. Solvent annealing of perovskite-induced crystal growth for photovoltaic-device efficiency enhancement Adv. Mater. 2014, 26, 6503-6509 10.1002/adma.201401685
    • (2014) Adv. Mater. , vol.26 , pp. 6503-6509
    • Xiao, Z.1    Dong, Q.2    Bi, C.3    Shao, Y.4    Yuan, Y.5    Huang, J.6
  • 52
    • 84902125882 scopus 로고    scopus 로고
    • Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells
    • Liang, P.-W.; Liao, C.-Y.; Chueh, C.-C.; Zuo, F.; Williams, S. T.; Xin, X.-K.; Lin, J.; Jen, A. K. Y. Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells Adv. Mater. 2014, 26, 3748-3754 10.1002/adma.201400231
    • (2014) Adv. Mater. , vol.26 , pp. 3748-3754
    • Liang, P.-W.1    Liao, C.-Y.2    Chueh, C.-C.3    Zuo, F.4    Williams, S.T.5    Xin, X.-K.6    Lin, J.7    Jen, A.K.Y.8
  • 53
    • 84905845476 scopus 로고    scopus 로고
    • 4Cl additive
    • 4Cl additive Nanoscale 2014, 6, 9935-9938 10.1039/C4NR02425G
    • (2014) Nanoscale , vol.6 , pp. 9935-9938
    • Zuo, C.1    Ding, L.2
  • 54
    • 84928952050 scopus 로고    scopus 로고
    • 3 planar perovskite hybrid solar cells with 18.1% power conversion efficiency
    • 3 planar perovskite hybrid solar cells with 18.1% power conversion efficiency Energy Environ. Sci. 2015, 8, 1602-1608 10.1039/C5EE00120J
    • (2015) Energy Environ. Sci. , vol.8 , pp. 1602-1608
    • Heo, J.H.1    Han, H.J.2    Kim, D.3    Ahn, T.K.4    Im, S.H.5
  • 55
    • 84871591994 scopus 로고    scopus 로고
    • Characterisation of Electron Transport and Charge Recombination Using Temporally Resolved and Frequency-Domain Techniques for Dye-Sensitised Solar Cells
    • Li, L.-L.; Chang, Y.-C.; Wu, H.-P.; Diau, E. W.-G. Characterisation of Electron Transport and Charge Recombination Using Temporally Resolved and Frequency-Domain Techniques for Dye-Sensitised Solar Cells Int. Rev. Phys. Chem. 2012, 31, 420-467 10.1080/0144235X.2012.733539
    • (2012) Int. Rev. Phys. Chem. , vol.31 , pp. 420-467
    • Li, L.-L.1    Chang, Y.-C.2    Wu, H.-P.3    Diau, E.W.-G.4


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.