Exceeding the Shockley–Queisser limit?
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Qds Solar Cells
Type-II core/shell Qd materials may be greatly beneficial for photovoltaic devices, especially with the development of anisotropic materials in which the segregation of charges is directional, which may enhance directional charge transport in future electronic devices.
蚀刻刻制作出所需图 案。此方法相当 费时，无法大量 生产，现已不经 常使用。
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Epitaxy: Patterned Growth


Growth is restricted by coating it with a masking compound (SiO2) and etching that mask with the shape of the required crystal cell wall shape. Disadvantage: density of quantum dots limited by mask pattern.
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Size is comparable to the Bohr radius of the excitons .
量子点（Quantum Dot）的特点之一: 量子尺寸 效应
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特点之二： Quantum confinement
Electrons and holes are confined in all three dimensions. Discrete energy levels (artificial atom).
Nie Shuming-Emory Uni.
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如何提高发光的量子产率？
Organically, Surface passivation by oxygen, ligands, and other molecules in the environment; the static passivation of surface defects by polymers and polar molecules. Photo activation. Photo activated rearrangements of ligand molecules stabilize the surface states and increase the probability of trapped charge carriers thermalizing into emissive states!
Colloidal Synthesis of Quantum dots:
r
Mechanism of colloidal Qds growth by La Mer etc.
晶体从小到大的生长遵循Ostwald生长机 制，即小的颗粒可以重新溶解于溶剂中， 而大颗粒由于溶解的小颗粒的补给而不 断长大。因此，要想达到单分散性，一 方面要控制晶体的生长速率，使大颗粒 的长大速率小于小颗粒的长大速率，另 一方面还要控制生长过程中的团聚和二 次成核现象，因此要加入合适的表面活 性剂来阻止。
H.J. Freund, et al., Angew. Chem. Int. Ed. 2011.
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Fluorescent Gold Nanoclusters-Cellular Imaging

Bovine serum albumin(牛血清蛋白）的Gold Nanocluster (<2nm)
金属有机骨架材料 Metal Organic Frameworks (MOF) -从金属簇合物到高孔隙率单晶
以金属基团作为基本结构单元，以有机分子为 连接分子，形成高孔隙率单晶，在催化、药物 释放、分离和能量存储中具有潜在的应用价值。
Framework structures in which metal oxides clusters act as ‘joints’ and the organic linkers as ‘struts’ to produce highly porous crystals (Max. 2 10,400m /g) with the lowest density ever recorded for a crystalline material.
O.M. Yaghi
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MOF-200
以Zn4O(CO2)6 作为基本结构 单元，以 4,4’,4”[benzene1,3,5-triyltris(ethyne2,1diyl)]tribenzo ate (BTE)等有 机分子为连接 分子。
量子点（Quantum Dots）

定义：量子点是由少量原子组成， 能把导带电子、价带空穴及激子 在三个空间方向上束缚住而导致 量子限域效应的准零维半导体纳 米结构。量子点，电子运动在三 维空间都受到了限制，因此有时 被称为“人造原子” 。

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金属cluster的一般特征
与金属表面的相似性：它的催 化活性部位相当于金属结晶表 面参与反应时的活性中心，即 晶体的顶角、棱角、边，以及 局部缺陷的原子团。 与金属中M-M键有类似性：原 子簇中过渡金属原子数越多， 原子簇越接近晶体。

簇合物举例：
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传统硅电池的转化率限制：
The theoretical limit in Si-based p-n junction solar cell: Shockley–Queisser limit!!! The limit places maximum solar conversion efficiency ~ 33.7%
2012/10/17
零维纳米材料及光电特性 （团簇、量子点、纳米晶） 张加涛 2-3学时
团簇、量子点、纳米晶的尺寸分 布
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How Do We Make Nanostructures ? “Chiseller” meets “Assembler”
Geoffrey Ozin
多伦多大学
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Epitaxial growth mechanism:
1. Lattice mismatch strain is small, the epitaxial growth will occur with a Frank–van der Merwe (FM) mode. 2. Lattice mismatch strain is increased somewhat, the epitaxial growth mode is Stranski– Krastanov (SK) mode. 3. Lattice mismatch is large, the epitaxial growth mode is Volmer–Weber (VW) mode.
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CdSe量子点的不同形貌：
彭笑刚-量子点 牛人
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GaP Qds
举例：CdSe胶体量子点制备方法:
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Low PL quantum efficiencies(10%) of CdSe Qds


The non-radiative exciton recombination at the surface defects. Shallow band gap defects. Terminal dangling states.
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CO Oxidation on Supported Model Catalysts- Heterogeneous Catalysis

STM images of Au big clusters supported on a trilayer of MgO(100)/Ag(100):
Qds core/shell structure
Inorganically,

Over coating Nano-crystallites with higher band gap inorganic materials.
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M.G. Bawendi(MIT)-CdSe/ZnS Qds
Ligand-Stabilized Silver Chalcogenide Clusters
（ 1）
（ 2）
Dieter Fenske, Jiatao Zhang, etc. Angew. Chem. Int. Ed. 2008.
The very edge of molecular chemistry

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Quantum dots applications

Photovoltaic devices: solar cells Biology : biosensors, imaging Light emitting diodes: LEDs Quantum computation Flat-panel displays Photodetectors Lasers