In this thesis, generation of point defects in TMDs and utilization plans of defects for target-specific applications were discussed. Furthermore, the physicochemical properties modulated TMDs was successfully applied to the target-specific application including electrocatalysts, optoelectronic devices, and Li-metal batteries.
In chapter 3, we demonstrate one-step modulation of chalcogen vacancy concentrations during the CVD synthesis of MoSe2 for application in hydrogen production. We demonstrate for the first time that the Volmer-Tafel reaction can be activated through the one-step vacancy-engineered MoSe2, resulting in enhanced overall electrochemical activity including onset potential and an unprecendented low Tafel slope, which presents one of the lowest values reported for TMDs-based electrocatalysts to date.
Theoretical calculations revealed that coalesced vacancy reduced the hydrogen adsorption free energy and diffusion barrier, leading to activate the Tafel reaction. Our approach could suggest a facile method to mimic the noble metal-based electrocatalysts through defect engineering of transition metal-based electrocatalysts.
In chapter 4, we propose a facile liquid-phase organometallic approaches for large-scale, uniform, and vacancy-tunable synthesis of TMDs thin films. Controlling the molar ratio of the chalcogen to transition metal precursors enabled the one-step modulation of the chalcogen vacancy concentrations without necessitating additional post-treatments. When applied as the electrocatalysts for hydrogen production, the vacancy-induced TMDs, exhibiting a synergetic effect on the optimized energy level with the water reduction potential and minimized free energy differences in the HER pathways, presented a significant improvement in the HER through the reduced charge transfer resistance and increased active sites. The proposed approach for synthesizing tunable vacancy-modulated TMDs with wafer-scale synthesis capability is, therefore, promising for better practical applications of TMDs.
In chapter 5, we suggested a facile chemical doping approach to modulate the electrical properties of TMDs. The carrier concentrations control through the chemical doping suppresses the ambipolar characteristics of WSe2, inducing the formation of p-type unipolar WSe2. When fabricating PN junction devices, ambipolar-suppressed WSe2 enhanced the Schottky barrier which could improve the diode characteristics of PN junction devices. The improved diode characteristics could increase the
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photovoltaic effect of TMDs up to 2.12% under white light illumination. Our results suggest a method that can be applied to various advanced optoelectronic devices by controlling the electrical properties of TMDs through molecular doping methods.
In chapter 6, we applied vacancy-induced MoS2 as the host materials for Li-metal anodes. The MoS2
host layer not only attracts the Li-ion but also increase the Li-ion flux by phase the transition from semiconducting 2H MoS2 to metallic 1T LixMoS2. In addition, chalcogen vacancy in MoS2 breaks the symmetric structure, leading to activating the piezoelectric properties. These piezoelectric properties attract Li-ion stronger, inducing lateral growth of the Ni-metal layer. By applying the MoS2 layer, thereby increasing the Li-ion flux and binding energy, thermodynamics, and kinetics of the Li-metal deposition were significantly enhanced for stable Li-metal batteries. Our study revealed that vacancy- induced MoS2 could induce uniform film formation by controlling the kinetics of Li-ions.
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Acknowledgments
학부생활 4년 대학원 생활 7년 총 11년, 저의 20대를 함께한 UNIST에서 이제 박사 학 위를 마무리하고 사회에 나갈 준비를 하고 있습니다. 돌이켜 생각해보면 제가 무사히 학 위를 마칠 수 있었던 것은 학위 과정 중에 많은 분들의 크고 작은 도움이 있었기 때문입 니다.
과학과 연구에 관심이 있던 저에게 UNIST로의 진학은 저의 진로를 정하는데 가장 큰 도움을 주었습니다. 그러던 와중에 대학원으로 진학하기로 결심을 하고 지도교수님이신 박혜성 교수님을 알게 된 것은 학위기간 중 저에게 가장 큰 행운이었던 것 같습니다. 당 시 부족했던 저를 물심양면으로 지원해주시고 바른길로 나아갈 수 있게 지도해주신 덕분 에 제가 하고 싶었던 연구를 하면서 무사히 학위를 마칠 수 있었습니다. 짧다고 하면 짧 고 길다고 하면 길수 있는 7년간 교수님께서 베풀어 주신 은혜에 감사드립니다. 사회에 나가서도 교수님 명성에 누가되지 않게 항상 발전하는 제자가 되도록 하겠습니다.
또한 함께 연구실 생활을 함께 시작하였고, 함께 많은 프로젝트를 수행하고 추억을 쌓 았던 승온이형, 웅수형, 윤성이, 지형이에게도 감사의 말을 전합니다. 저와 함께 졸업하고 맏형으로서 연구실을 위해 많은 노력을 한 남근이형, 연구실 친구인 동환이, 항상 열심히 연구실에서 연구에 매진 중인 후배 규정이, 형민이, 은빈이, 지하, 지후 그리고 졸업 후 사회에 나가 사회생활중인 상현이, 민성이에게도 감사의 인사드립니다. 많이 부족했던 동 료이고 선배였던 저를 믿고 함께해준 연구실 동료들에게 다시한번 정말 감사합니다.
또한 연구실 생활하면서 힘든 일이 있거나 어려운 부분이 있을 경우, 항상 조언을 해 주고 위로를 해주면서 힘들 대학원 생활을 견딜 수 있게 해주었던 김남우 박사님, 허정 우 박사님, 윤영진 박사님께도 감사인사를 드립니다.
학위논문을 심사하는데 시간을 할애해주시고 연구 및 향후 진로관련해서 소중한 조언 을 아끼지 않으신 정후영 교수님, 이창영 교수님, 이준희 교수님, 그리고 서준기 교수님 께도 감사드립니다. 그리고 항상 저를 응원해줬던 UNIST 18조 친구들, 전우조 친구들, 소 정이, 소현이, 정환이, 덕재, 영훈이, 재웅이형에게도 감사인사를 드립니다.
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마지막으로, 저를 항상 믿어 주시고 제가 타지 생활을 하면서도 아무런 걱정없이 학업 이 집중할 수 있게 도움을 주신 아버지, 어머니, 그리고 동생인 종민이에게도 감사 인사 를 드립니다.
만약 저 혼자서 대학원 학위를 하였다면 무사히 학위를 받지 못했을 수도 있을 것입니 다. 많은 분들의 도움이 있었기 때문에 이렇게 무사히 길고 긴 대학원 생활을 끝마칠 수 있었습니다. 사회에 나가서도 많은 도움을 주신 분들에게 부끄럽지 않은 사람으로 살아 갈 수 있도록 노력하겠습니다. 다시한번 도움을 주신분들께 감사의 인사를 드리면 마치 도록 하겠습니다. 감사합니다.
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Curriculum Vitae
Junghyun Lee
Department of Materials Science and Engineering
Ulsan National Institute of Science and Technology (UNIST) 50, UNIST-gil, Ulsan, 44919, Republic of Korea
Birth: 1992.06.04 / Sex: Male Tel: (+82) 52-217-2580 Phone: (+82) 10-2914-6199
E-mail: jhlee92@unist.ac.kr / j_lee92@naver.com
Education
• M.S. and Ph.D. Combined Degree 2015.03. – 2022.02.
Department of Materials Science and Engineering
Ulsan National Institute of Science and Technology (UNIST) Advisor: Prof. Hyesung Park / E-mail: hspark@unist.ac.kr
Project: Modulation of Material Properties in Two-Dimensional Semiconductors via Defect Engineering
• Bachelor’s Degree 2011.03. – 2015.02.
Department of Chemical Engineering for 1st track Department of Biomedical Science for 2nd track
Ulsan National Institute of Science and Technology (UNIST)
Publications
SCI(E) publications [†equally contribution]
1. Song, G.; Hwang, C.; Song, W.-J.; Lee, J.; Lee, S.; Han, D.-Y.; Kim, J.; Park, H.; Song, H.-K.; Park, S.
Breathable Artificial Interphase for Dendrite-Free and Chemo-Resistive Lithium Metal Anode. Small 2021, in press.
2. Choi, Y.; Koo, D.; Jeong, M.; Jeong, G.; Lee. J.; Lee, B.; Choi, K. J.; Ynag, C.; Park, H. Toward All-Vacuum- Processable Perovskite Solar Cells with High Efficiency, Stability, and Scalability Enabled by Fluorinated Spiro-OMeTAD through Thermal Evaporation. Sol. RRL 2021, 5, 2100415.
3. Oh, N. K.; Seo, J.; Lee, S.; Kim, H.-J.; Kim, U.; Lee, J.; Han, Y.-K.; Park, H. Highly efficient and robust noble-metal free bifunctional water electrolysis catalyst achieved via complementary charge transfer. Nat.
Commun. 2021, 12, 4606.
4. Koo, D.; Kim, U.; Cho, Y.; Lee, J.; Seo, J.; Choi, Y.; Choi, K. J.; Baik, J. M.; Yang, C.; Park, H. Graphene- Assisted Zwitterionic Conjugated Polycyclic Molecular Interfacial Layer Enables Highly Efficient and Stable Inverted Perovskite Solar Cells. Chem. Mater. 2021, 33, 5563-5571.
5. Kim, M.; Seo, J.; Kim, J.; Moon, J. S.; Lee, J.; Kim, J.-H.; Kang, J.; Park, H. High-Crystalline Monolayer Transition Metal Dichalcogenides Films for Wafer-Scale Electronics. ACS Nano 2021, 15, 3038-3046.
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6. Lee, J.; Heo, J.; Lim, H. Y.; Seo, J.; Kim, Y.; Kim, J.; Kim, U.; Choi, Y.; Kim, S. H.; Yoon, Y. J.; Shin, T. J.;
Kang, J.; Kwak, S. K.; Kim, J. Y.; Park, H. Defect-Induced in Situ Atomic Doping in Transition Metal Dichalcogenides via Liquid-Phase Synthesis toward Efficient Electrochemical Activity. ACS Nano 2020, 14, 17114-17124.
7. Koo, D.; Cho, Y.; Kim, U.; Jeong, G.; Lee, J.; Seo, J.; Yang, C.; Park, H. High-Performance Inverted Perovskite Solar Cells with Operational Stability via n-Type Small Molecule Additive-Assisted Defect Passivation. Adv. Energy Mater. 2020, 10, 2001920.
8. Park, S.; Kim, C.; Park, S. O.; Oh, N. K.; Kim, U.; Lee, J.; Seo, J.; Yang, Y.; Lim, H. Y.; Kwak, S. K.; Kim, G.; Park, H. Phase Engineering of Transition Metal Dichalcogenides with Unprecedentedly High Phase Purity, Stability, and Scalability via Molten-Metal-Assisted Intercalation. Adv. Mater. 2020, 32, 2001889.
9. Koo, D.; Jung, S.; Seo, J.; Jeong, G.; Choi, Y.; Lee, J.; Lee, S. M.; Cho, Y.; Jeong, M.; Lee, J.; Oh, J.; Yang, C.; Park, H. Flexible Organic Solar Cells Over 15% Efficiency with Polyimide-Integrated Graphene Electrodes. Joule 2020, 4, 1021-1034.
10. Jeong, G.; Koo, D.; Seo, J.; Jung, S.; Choi, Y.; Lee, J.; Park, H. Suppressed Interdiffusion and Degradation in Flexible and Transparent Metal Electrode-Based Perovskite Solar Cells with a Graphene Interlayer. Nano Lett. 2020, 20, 3718-3727.
11. Kim, U.; Cho, Y.; Jeon, D.; Kim, Y.; Park, S.; Seo, J.; Lee, J.; Oh, N. K.; Lee, G.; Ryu, J.; Yang, C.; Park, H.
Zwitterionic Conjugated Surfactant Functionalization of Graphene with pH‐Independent Dispersibility: An Efficient Electron Mediator for the Oxygen Evolution Reaction in Acidic Media. Small 2020, 16, 1906635.
12. Seo, J.; Lee, J.; Kim, Y.; Koo, D.; Lee, G.; Park, H. Ultrasensitive Plasmon-Free Surface-Enhanced Raman Spectroscopy with Femtomolar Detection Limit from 2D van der Waals Heterostructure. Nano Lett. 2020, 20, 1620-1630.
13. Choi, J. H.; Lee, J.†; Byeon, M. Hong, T. E.; Park, H.; Lee, C. Y. Graphene-Based Gas Sensors with High Sensitivity and Minimal Sensor-to-Sensor Variation. ACS Appl. Nano Mater. 2020, 3, 2257-2265.
14. Jung, S.; Lee, J.†; Kim, U.; Park, H. Solution‐Processed Molybdenum Oxide with Hydroxyl Radical‐Induced Oxygen Vacancy as an Efficient and Stable Interfacial Layer for Organic Solar Cells. Sol. RRL 2019, 4, 1900420.
15. Kumar, S.; Choi, Y.; Kang, S.-H.; Oh, N. K.; Lee, J.; Seo, J.; Jeong, M.; Kwon, H. W.; Seok, S. I.; Park, H.
Multifaceted Role of Dibutylhydroxytoluene Processing Additive in Enhancing Efficiency and Stability of Planar Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2019, 11, 38828-38837.
16. Lee, J.†; Kim, C.†; Choi, K.†; Seo, J.; Choi, Y.; Choi, W.; Kim, Y.-M.; Jeong, H. Y.; Lee, J. H.; Kim, G.; Park, H. In-Situ Coalesced Vacancies on MoSe2 Mimicking Noble Metal: Unprecedented Tafel Reaction in Hydrogen Evolution. Nano Energy 2019, 63, 103846.
17. Jung, S.; Yoon, H. H.; Jin, H.; Mo, K.; Choi, G.; Lee, J.; Park, H.; Park, H. Reduction of Water-Molecule- Induced Current-Voltage Hysteresis in Graphene Field Effect Transistor with Semi-Dry Transfer Using Flexible Supporter. J. Appl. Phys. 2019, 125, 184302.
18. Kim, U.; Choi, K.; Park, K. H.; Lee, J.; Choi, Y.; Seo, J.; Oh, N. K.; Jung, S.; Yang, H.; Lee, J. H.; Yang, C.;
Park, H. Size Fractionation of Graphene Oxide via Solvent‐Mediated Consecutive Charge Manipulation and Investigation of the Size Effect as Hole Transporting Layer in Perovskite Solar Cells. ChemNanoMat 2019, 5, 776-783.
19. Choi, Y.; Jung, S.; Oh, N. K.; Lee, J.; Seo, J.; Kim, U.; Koo, D.; Park, H. Enhanced charge transport via metallic 1T phase transition metal dichalcogenides-mediated hole transport layer engineering for perovskite solar cells. ChemNanoMat 2019, 5, 1050-1058.
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20. Oh, H. K.; Kim, C.; Lee, J.; Kwon, O.; Choi, Y.; Jung, G. Y.; Lim, H. Y.; Kwak, S. K.; Kim, G.; Park, H. In- situ Local Phase-Transitioned MoSe2 in La0.5Sr0.5CoO3-δ Heterostructure and Stable Overall Water Electrolysis over 1000 hours. Nat. Commun. 2019, 10, 1723.
21. Seo, J.; Lee, J.; Jeong, G.; Park, H. Site-Selective and van der Waals Epitaxial Growth of Rhenium Disulfide on Graphene. Small 2019, 15, 1804133.
22. Jeong, G.; Jung, S.; Choi, Y.; Lee, J.; Kim, D. S.; Park, H. Highly Robust and Stable Graphene-Encapsulated Cu-Grid Hybrid Transparent Electrode Demonstrating Superior Performance in Organic Solar Cells. J. Mater.
Chem. A 2018, 6, 24805-24813.
23. Koo, D.; Jung, S.; Oh, N. K.; Choi, Y.; Seo, J.; Lee, J.; Kim, U.; Park. H. Improved Charge Transport via WSe2-Mediated Hole Transporting Layer toward Efficient Organic Solar Cells. Semicond. Sci. Technol. 2018, 33, 125020.
24. Jung, S.†; Kim, H†.; Lee, J.†; Jeong, G.; Kim, H.; Park, J.; Park, H. Bio-Inspired Catecholamine-Derived Surface Modifier for Graphene-Based Organic Solar Cells. ACS Appl. Energy Mater. 2018, 1, 6463-6468.
25. Lee, J.; Seo, J.; Jung, S.; Park, K.; Park, H. Unveiling the direct correlation between the CVD-grown graphene and the growth template. J. Nanomater. 2018, 7610409.
26. Chung, K.; Lee, J. S.; Kim, E.; Lee, K.-E.; Kim, K.; Lee, J.; Kim, D.; Kim, S. O.; Jeon, S.; Park, H.; Kim, D.-W.; Kim, D. H. Enhancing the Performance of Surface Plasmon Resonance Biosensor via Modulation of Electron Density at the Graphene–Gold Interface. Adv. Mater. Interfaces 2018, 5, 1800433.
27. Oh, N. K.; Lee, H. J.; Choi, K.; Seo, J.; Kim, U.; Lee, J.; Choi, Y.; Jung, S.; Lee, J. H.; Shin, H. S.; Park, H.
Nafion-Mediated Liquid-Phase Exfoliation of Transition Metal Dichalcogenides and Direct Application in Hydrogen Evolution Reaction. Chem. Mater. 2018, 30, 4658-4666.
28. Jung, S.; Lee, J.; Seo, J.; Kim, U.; Choi, Y.; Park, H. Development of Annealing-Free, Solution-Processable Inverted Organic Solar Cells with N-Doped Graphene Electrodes using Zinc Oxide Nanoparticles. Nano Lett.
2018, 18, 1337-1343.
29. Kim, Y.-T.; Min, H.; Lee, J.; Park, H.; Lee, C. Y. Probing sub-diffraction optical confinement via polarized Raman spectroscopy of a single-walled carbon nanotube. Nanoscale 2018, 10, 1030-1037.
30. Park, W. K.; Yoon, Y.; Song, Y. H.; Choi, S. Y.; Kim, S.; Do, Y.; Lee, J.; Park, H.; Yoon, D. H.; Yang, W. S.
High-efficiency exfoliation of large-area mono-layer graphene oxide with controlled dimension. Sci. Rep.
2017, 7, 16414.
31. Choi, Y.†; Lee, J.†; Seo, J.†; Jung, S.; Kim, U.; Park, H. The Effect of the Graphene Integration Process in the Performance of Graphene-based Schottky Junction Solar Cells. J. Mater. Chem. A 2017, 5, 18716-18724.
32. Jung, S.; Lee, J.; Choi, Y.; Lee, S. M.; Yang, C.; Park, H. Improved Interface Control for High-Performance Graphene-based Organic Solar Cells. 2D Mater. 2017, 4, 045004.
33. Seo, J.; Lee, J.; Jang, A.-R.; Choi, Y.; Kim, U.; Shin, H. S.; Park, H. Study of Cooling Rate on the Growth of Graphene via Chemical Vapor Deposition. Chem. Mater. 2017, 29, 4202-4208.
34. Choi, J. H.; Lee, J.; Moon, S. M.; Kim, Y.-T.; Park, H.; Lee, C. Y. A Low-Energy Electron Beam Does Not Damage Single-Walled Carbon Nanotubes and Graphene. J. Phys. Chem. Lett. 2016, 7, 4739-4743.