报告人：冷凯 Atomic Imaging and Device application in Molecularly Thin 2D Hybrid Perovskites
时间：2023年4月12日下午15：30
地址：沧海校区致腾楼223室
Abstract
2D Organic-Inorganic Hybrid perovskites (OIHPs) possess alternating layers of organic molecules and inorganic quantum wells. By tuning the interaction between organic and inorganic layers, very interesting properties can be introduced. The successful isolation of hybrid perovskite monolayers with clean and flat surfaces are particularly suitable for atomic structure characterization and optoelectronic device fabrication. In this talk, I will present recent results on the excitonic properties and atomic structure of molecularly thin OIHPs1,2. We found that a reversible shift in excitonic energies can be induced upon laser irradiation in large-sized 2D hybrid perovskite monolayers which is attributed to the reversible structural reorientation of the surface BA cations in the easily deformable lattice3. The photodetection performance of monolayer, bilayer and thicker OIHPs were compared. The internal quantum efficiency was measured to be 34% for a monolayer (BA)2(MA)3Pb4I13 and 19% for the bulk crystal. In addition, 2D heterostructures of molecularly thin OIHPs/graphene were constructed which exhibited a lower barrier than gold for carrier injection, enabling applications in field effect transistors (FETs)4. Electron tunneling occurs across the interface of organic molecular layers on 2D perovskite and graphene, while photoinduced charge transfer occurs at femtosecond timescale (~50 fs).
Resolving the atomic structure of 2D hybrid perovskite is a challenging task because it is easily damaged by electron beam. Here we use scanning tunneling microscopy (STM) & Qplus AFM to directly visualize surface octahedral tilt in freshly exfoliated 2D Ruddlesden-Popper perovskites (RPPs)5. The experimentally determined octahedral tilts from n = 1 to n = 4 RPPs from STM images are found to agree very well with out-of-plane surface octahedral tilts predicted by density functional theory calculations. The surface-enhanced octahedral tilt is correlated to excitonic redshift observed in photoluminescence (PL) and promotes Rashba spin splitting for n > 1. Our studies demonstrate a protocol to investigate structure-property correlations in low dimensional 2D OIHPs, which will pave the way to better material design and device performance.
References
1. K. Leng, W. Fu, Y. Liu, M. Chhowalla & KP Loh* “From Bulk to Molecularly Thin Hybrid Perovskites” Nature Reviews Materials, 5, 482-500 (2020).
2. C. Zhao, KP Loh, K. Leng* “Organic-inorganic hybrid perovskites and their heterostructures” Matter, 5, 4153-4169 (2022).
3. K. Leng, I. Abdelwaha, I. Verzhbitskiy, M. Telychko, L. Chu, W. Fu, X. Chi, N. Guo, Z. Chen, Z. Chen, C. Zhang, Q. Xu, J. Lu, M. Chhowalla, G. Eda, KP Loh* “Molecularly thin two-dimensional hybrid perovskites with tunable optoelectronic properties due to reversible surface relaxation” Nature Materials, 17, 908-914 (2018).
4. K. Leng, L. Wang, Y. Shao, I. Abdelwahab, G. Grinblat, I. Verzhbitskiy, Y. Cai, X. Chi, W. Fu, P. Song, G. Eda, S. A. Maier & KP Loh* “Electron Tunneling at the Molecularly Thin 2D Perovskite and Graphene Van der Waals Interface” Nature Communications, 11, 5483 (2020).
5. Y Shao, W. Gao, H. Yan, R. Li, I. Abdelwahab, L. Zhuang, W. Fu, SP Lau, SF YU, Y. Cai, KP Loh, K. Leng* “Unlocking Surface Octahedral Tilt in Two-dimensional Ruddlesden-Popper Perovskites” Nature Communications, 13, 138 (2022).
冷凯，香港理工大学校长青年助理教授，应用物理学系。2018年毕业于新加坡国立大学，获物理化学博士学位。2018-2020年在新加坡国立大学和剑桥大学先后从事博士后研究。2020年10月加入香港理工大学，入选香港研究资助局杰出青年学者计划。在国际著名学术期刊发表论文50余篇，其中以第一作者/通讯作者身份发表高质量SCI论文10篇，包括Nat. Mater. (1篇)，Nat. Commun. (2篇)，Nat. Rev. Mater. (1篇)，Matter (1篇)，Trends Chem. (1篇)等，7篇论文入选ESI高被引。论文共计他引6000余次，h-index 34. 作为香港理工大学唯一候选人入选2023年裘槎基金-前瞻科研大奖（Croucher Tak Wah Mak Innovation Awards）面试。荣获2020年度新加坡国际化学会 (SNIC) “李秀英教授早期职业研究奖” 金奖（1人）；2018年度国家优秀自费留学生奖学。主要研究方向为二维有机无机杂化钙钛矿和新型器件。
欢迎各位老师同学参加！
