【20th.June】Ultrafast Charge Carrier Dynamics in Low Dimensional Energy-related Materials and Interfaces
日期：2019-06-20
阅读：780
TOPIC：Ultrafast Charge Carrier Dynamics in Low Dimensional Energy-related Materials and Interfaces
SPEAKER：王海 研究员，Max Planck Institute for Polymer Research, Mainz, Germany
TIME：June 20 (Thursday) 10:00 am
LOCATION：化学A楼518会议室
INVITER：麦亦勇 教授
Ultrafast Charge Carrier Dynamics in Low Dimensional Energy-related Materials and Interfaces
Dr. Hai Wang
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
Email: wanghai@mpip-mainz.mpg.de
Abstract
In photovoltaic or photochemical cells, charge carriers are generated and transported in the photo-active materials and collected at the materials/electrode or electrolyte interfaces. Understanding and eventually controlling the generation, transport, and collection of charge carriers are therefore crucial for improving the energy conversion efficiency of devices. In this talk, I will present our recent advances in this field using terahertz (THz) spectroscopy.1-10, 13
In the first part of the talk, we will present our recent work on exploring interfacial charge transfer process in model quantum dot (QD)-sensitized oxide system. Throughout a series of systematic work1-6 (e.g. exploring QD-oxide coupling strength1, QD surface stoichiometric2, and the hot carrier3 on the charge transfer process), besides our scientific finding, we establish THz spectroscopy as a powerful tool not only for investigating the fundamental interfacial charge transfer mechanism but also for quantifying the efficiency of the process. These fundamental findings have led to a collaborative effort that set a by-then new world record efficiency for quantum dot solar cells.6
The second part of the talk will focus on the fundamentals of charge carrier dynamics in graphene and graphene nanoribbons relevant for optoelectronics and electrochemical energy conversion. Thanks to its outstanding electrical properties, graphene finds widespread use in various electrochemical applications. Although the presence of electrolytes is known to strongly affect graphene’s conductivity, the underlying mechanism has remained elusive.
We employ terahertz spectroscopy to investigate the impact of ubiquitous cations in aqueous solution on the electronic properties of SiO2-supported graphene. We find that cations can induce a positive shift in Fermi energy of 200 meV in graphene, which can be kinetically controlled by cation size and concentration. Combined with theoretical calculations, the ionic doping effect is found to involve cationic permeation through defects in graphene.
These insights are crucial for graphene device processing and further developing graphene as an ion sensing material.7-8 Furthermore, recent advances in bottom-up synthesis allow atomic control of graphene nanoribbons (GNRs) with well-defined bandgap and optical properties.9-12 I will present some our recent ultrafast conductivity studies on GNRs using THz spectroscopy, which demonstrates the strong exciton effect in GNRs owing to the reduced charge screening effect.13
Reference
1. Wang, H. et al., Nano Lett 2013, 13, 5311-5315.
2. Wang, H et al., Nano Lett 2014, 14, 5780-5786.
3. Wang, H. et al., Nano Lett 2018, 18, 5111-5115.
4. Wang, H. et al., ACS Nano 2017, 11, 4760-4767.
5. Wang, H. et al., J Phys Chem Lett. 2017, 8, 2654-2658.
6. Zhao, K. et al., J. Am. Chem. Soc. 2015, 137, 5602-5609.
7. Jia X. Y.; Wang, H.; et al. submitted.
8. Liu, Z.; Wang, H.; et al., J. Am. Chem. Soc. 2017, 139, 9443–9446;
9. Chen, Z. P.; Wang, H.; et al. J. Am. Chem. Soc. 2017, 139, 3635-3638;
10. Chen, Z. P.; Wang, H.; et al. J. Am. Chem. Soc. 2017, 139, 9483–9486;
11. Cai, J.; et al., Nature 2010, 466, 470–473;
12. Huang, Y.; Mai, Y.; et al., J. Am. Chem. Soc. 2018, 140, 10416–10420.
13. Tries, A.;Wang, H.; et al. to be submitted.
Biography
Dr. Hai Wang studied materials science at Zhejiang University and obtained his degree in 2007. Between 2009 and 2011, he finished a joint master program in nanoscience at University of Leuven (2009-2010) in Belgium and Delft University of Technology in the Netherlands (2010-2011), supported by the Erasmus Mundus fellowship. From 2012, following his research interests in optoelectronic materials, he started his Ph.D at Max Planck institute for polymer research (MPIP) in Mainz with the support of a fellowship from MAINZ (graduate school of excellence, materials science in Mainz). In his PhD, Hai worked with Prof. dr. Mischa Bonn on investigating ultrafast charge transfer process at quantum dot and oxide interfaces, and graduated with Summa Cum Laude (with the highest honor) in 2016. After that, After 1.5 year postdoc training in the group of Prof. dr. Mathias Kläui at Mainz university, Hai started his group “Nano-optoelectronic materials” in the Molecular Spectroscopy department at MPIP from August of 2017.
