报告题目：Harvesting Solar Energy through Multiexciton Generation（利用激子增值收获太阳能）
报 告 人：王晨博士(西北大学)
报告时间：2016年12月30日（星期五）下午16:00-17:30
报告地点：北区科技园一号楼报告厅（N308）
报告摘要：
A major obstacle that limits the progress of solar cells is the contradiction between the continuous solar spectrum and discrete band structures of photovoltaic materials. One strategy that can overcome this 31% Shockley-Queisser limit for photovoltaic devices with a single junction is to split the energy of a blue photon into two or more low-energy excitons, and make use of the multiplication of charge carriers to avoid energy waste through heat dissipation. Using time-resolved optical spectroscopy, we demonstrate that zeaxanthin, a common carotenoid, can generate two triplet excitons with one absorbed photon through a mechanism called singlet fission. The efficiency of the singlet fission process is closely related to the exciton coupling strength between chromophores. Next, in order to take the advantages of exciton multiplication, it is necessary to extract the multiexciton states from the system before they annihilate each other. In PbS quantum dots (QDs), the extraction of excitons through a resonance energy transfer mechanism is impeded by their slow radiative relaxation rate. We employ the J-aggregate of a cyanine dye to facilitate the exciton extraction from PbS QDs. The rate of the energy transfer from PbS QDs to the J-aggregate is capable of competing with the Auger recombination of the multiexciton state. Employing the J-aggregate as an exciton bridge, we can further accelerate the exciton migration between PbS QDs with different energy levels. These studies provide insights into the design of the new generation of photovoltaic devices.
提高太阳能电池效率的一大障碍在于连续的太阳光谱和不连续的材料能带结构之间的矛盾。对于单结光伏装置，极限效率只能达到31%（Shockley-Queisser limit）。突破这一极限的一种策略是利用激子增值原理，即让每一个高能量的蓝光光子产生多个载流子，从而减少热耗散的能量浪费。运用超快光谱，我们首次在玉米黄质的聚合体中证明了单重态裂分，即吸收一个光子产生两个三重激发态的过程。进一步研究发现单重态裂分的效率与分子间跃迁偶极矩耦合相互作用密切相关。然而要真正利用激子增值的机制，就必须找到迅速从发生体系中移除激子的方法，以避免多激子的湮灭效应。在硫化铅量子点中，我们发现通过共振能量转移来移除激子的速率受到了量子点本身辐射弛豫速率太慢的限制。我们利用染料的J型聚合体作为激子，将提取量子点中激子的速率提高了一到两个数量级，使得激子提取过程有可能与多激子的俄歇湮灭相竞争。并且进一步利用J型聚合体为桥梁，实现了激子在不同能级的硫化铅量子点之间的快速迁移。该研究对于新一代的光伏装置设计具有一定意义。
报告人简历
RESEARCH ACTIVITIES
Feb.2015 Postdoctoral researcher in Prof.Emily A. Weiss group, Department of Chemistry,
Northwestern University
Project: Spatial-Separated Resonance Energy Transfer and Quantum Cutting in
Semiconductor Quanturn Dots
l Synthesis and characterization of semiconductor nanocrystals and their inorganic/organic conjugates
l Transient absorption spectrosecopy
l Time-resolved photoluminescence(TCSPC. Fluorescence upconversion)
Sept.2008-Dec.2014 Graduate researcher in Prof.Michael J. Tauber group. Department of
Chemistry &Biochemistry, University of California, San Diego
Thesis: Spectroscopic Studies of Triplet Excited States in Conjugated
Organic Dyes, and the Singlet Fission Process
l Transient absorption spectroscopy
l Time-resolved resonance Raman (Stokes and Anti-Stokes) spectroscopy
l Microscope resonance Raman spertroscopySept.2004-June 2007 Graduate Researcher. Department of Chemistry, Fudan University
Thesis: Layered Metal Phosphate Materials: Synthesis and Catalytic
Application
l Solvothermal synthesis
l Catalysts characterization: GC, X-ray diffraction. BET surface measurement
Apr. 2003-June 2004 Research Aissistant, Fudan University
Project: Heterogeneous Catalysis and Microporous Layered Materials
EDUCATION
Sept.2008- Dec. 2014 Department of Chemistry & Biochemistry , University of California, San
Diego, Ph. D.in Chemistry
Jul.2007-May 2008 Chemistry Department, Michigan State University
Sept.2004-Jun.2007 Chemistry Department. Fudan University.M.S in Applied Chemistry
Sept.2000-Jun.2004 Chemistry Department. Fudan University.B.S in Applied Chemistry