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이번 학기 콜로퀴움은 학교의 권고를 따라, 사회적 거리두기 단계와 연계하여 온라인 혹은 오프라인(온라인 방송 병행)으로 운영될 예정입니다.
열번째 강연에는 이화여자대학교 조윌렴 교수님을 모시고 콜로퀴움을 개최하오니, 학과 구성원 여러분의 많은 참여를 부탁 드립니다.
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1. Title: Halide Perovskite Single Crystals and Thin Films for Solar Cells and Optoelectronics
2. Speaker: 조 윌 렴 교수님 (이화여자대학교)
3. Date & Time: Dec. 1(Wed.) 2021. 4:30 PM
4. Place: Natural Science 1, Room No. 31214
5. Abstract: Hybrid perovskite is one of the most promising materials for solar cells and photonic devices owing to its outstanding absorption coefficient, long carrier lifetime, direct bandgap, and low trap density. Recently, perovskite single crystals have attracted a great attention to understand the intrinsic properties of perovskite material without the grain boundary issues. We have synthesized CH3NH3PbX3 (X= I, Br, and Cl) perovskite single crystals. X-ray diffraction and Raman scattering spectra confirmed the crystallinity of the grown crystals and phase transition depending on the temperature. The temperature dependent photoluminescence and the spatial surface potential analyses helped us to visualize the band structure of the material itself and apprehend the local degradation. Anomalous photoluminescence peaks at low temperatures were proportional to the power of the excitation intensity, indicating that the excitonic transition, which was formed by the trapped photoexcited carriers, could affect the photoluminescence at the orthorhombic phase. On the other hand, SnO2 is widely used as an electron transport layer (ETL) in hybrid perovskite planar solar cells because of its good transparency, band alignment to perovskite, and stability. But it has issues at the interface between perovskite and ITO substrate that electron recombination and current saturation by their surface defects as cracks and pinholes. Surface treatment of SnO2, such as UV ozone (UVO) treatment, is shown to improve the efficiency and reduce junction issues as the ETL. In addition, we used a NH4Cl for passivation of SnO2. Herein, we propose an UVO treatment of SnO2 and then NH4Cl passivation (UVOSnO2-Cl) as an excellent alternative to ETL at a low temperature process of 150 °C. We determined the resistance, mobility, conductivity and carrier concentration of UVOSnO2-Cl based solar cells by an electrical measurement. After passivation with NH4Cl, the current density increased at an active area and the grain size of perovskite films also increased. In addition, it can promote the electron transfer, and suppress the interface recombination rather than SnO2 alone. The band structure and the carrier transport mechanism at perovskite/UVOSnO2-Cl interface was explained by conductive atomic force microscopy, Kelvin probe force microscopy. The UVOSnO2-Cl based H-PSCs has been found to eliminate severe current leakage inside the device, reducing interface defects and hysteresis.
 Y. Cho, H. R. Jung, Y. S. Kim, Y. Kim, S. Yoon, Y. Lee, M. Cheon, S.-Y. Jeong, and W. Jo, “High speed growth of MAPbBr3 single crystals via low-temperature inverting solubility: enhancement of mobility and trap density for photodetector applications”, Nanoscale 13, 8275 (2021).
 J. H. Kim, Y. S. Kim, H. R. Jung, and W. Jo, “Chlorine-passivation of the ozone-treated SnO2 thin films: occurrence of oxygen vacancies for manipulation of conducting states and bipolarities in resistive switching”, Applied Surface Science 555, 149625 (2021).
 H. R. Jung, M. Bari, Y. Cho, Y. C. Jo, J. H. Kim, S. Yuldashev, Z.-G. Ye and W. Jo, “Exotic Optoelectronic Behaviors in CH3NH3PbCl3 Perovskite Single Crystals: Interplay of Free and Bound Excitons along with Structural Phase Transitions”, Applied Physics Letters 118, 143301 (2021).
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