【作者】 唐爱伟；

【导师】 侯延冰； 滕枫；

【作者基本信息】 北京交通大学 ， 光学， 2009， 博士

【摘要】 金属硫族化合物半导体纳米材料由于其具有一系列优异的物理和化学特性以及在光电子器件和生物医学领域所存在的巨大的应用前景,目前已经发展成为物理学、化学以及材料学等许多学科最活跃的研究领域之一。系统地开发新型金属硫族半导体纳米晶以及深入研究它们的光学、电学和磁学等性质具有十分重要的意义,将有利于充分发挥这一类材料的最大潜能。本论文选取CdSe纳米晶,Cu₂S-In₂S₃异质结纳米晶以及掺杂Cu（I）离子的CdS纳米晶等作为研究对象,系统的研究了水溶性的CdSe纳米晶在电致发光器件中的应用和Cu₂S-In₂S₃异质结纳米晶在光伏器件中的应用,以及掺杂Cu（I）离子的CdS纳米晶的制备和自组装成为超晶格的性质和发光性质的研究。首先,采用巯基水相法制备了CdSe半导体纳米晶,利用季铵盐类表面活性剂借助于静电相互作用将CdSe纳米晶从水相转移到油相中,并将其与聚合物聚乙烯咔唑（PVK）按照一定的质量比例混合作为发光层制备了多层电致发光器件,研究了不同驱动电压下以及不同CdSe纳米晶和PVK的质量比例和不同粒径的CdSe半导体纳米晶对CdSe:PVK复合电致发光器件的发光特性的影响,并对比了CdSe:PVK复合薄膜电致发光和光致发光特性的区别。并在此基础之上探究了CdSe:PVK复合电致发光器件的发光机理,发现在不同驱动电压以及不同的CdSe纳米晶的粒径情况下,CdSe纳米晶和PVK之间的能量传递以及载流子的直接注入所起的作用并不相同。其次,采用简单的高温热解反应,通过一步合成法制备了球形的Cu₂S纳米晶,并在此基础之上采用分步注射的方法合成了具有火柴棒状的Cu₂S-In₂S₃异质结纳米晶和棒状的In₂S₃纳米晶。将Cu₂S,Cu₂S-In₂S₃和In₂S₃三种不同组分的半导体纳米晶与聚合物MEH-PPV按照相同的比例混合,将其作为活化层制备了纳米晶/聚合物异质结光伏器件,对比了三种器件的光伏性能,发现Cu₂S-In₂S₃/MEH-PPV光伏器件的能量转换效率较单组分的Cu₂S/MEH-PPV和In₂S₃/MEH-PPV光伏器件提高了3-5倍,这主要是因为半导体异质结纳米晶更加有利于激子离化和电荷传输。因此,半导体异质结纳米材料将会成为一种新型的光伏材料。最后,采用高温热解一步合成法在十二硫醇中制备了CdS和掺杂Cu（I）离子的CdS半导体纳米晶。考查了掺杂不同Cu（I）离子浓度的CdS纳米晶的光学性质,并将其与未掺杂的CdS纳米晶进行了对比,发现在CdS纳米晶中掺杂Cu（I）离子后,CdS纳米晶的发光随着掺杂Cu（I）离子比例的增加逐渐由表面缺陷态的发光变化为掺杂在CdS纳米晶中Cu（I）离子的红色发光,掺杂Cu（I）离子的CdS纳米晶的荧光量子产率最高可达15.8%。同时,通过改变Cu（I）离子的不同掺杂比例,CdS:Cu（I）纳米晶在所掺杂的Cu（I）离子浓度合适时自组装成为二维或三维的超晶格结构。通过对比掺杂不同比例的Cu（I）离子的CdS:Cu（I）纳米晶的粒径分布范围、制备条件以及形貌变化,我们将单分散的CdS:Cu（I）纳米晶自组装成为超晶格的原因归于掺杂进入CdS纳米晶中过多的Cu（I）离子能够在纳米晶的表面形成一种极化体系,这种极化作用促使了纳米晶自发形成了超晶格结构。同时过多的Cu（I）离子还可以在十二硫醇体系中形成Cu₂S纳米晶。这种合成方法还可以推广到制备其它类型的金属硫系半导体纳米材料中去。更多还原

【Abstract】 Recently,metal chalcogenide semiconductor nanomaterials have become an active field among physics,chemistry and materials,because they have unique physical and chemical properties and their wide applications in optoelectronic devices and biological medicine.It is interesting to study and develop new metal chalcogenide semiconductor nanocrystals in combination with their optical,electrical and magnetic properties.In this dissertation,this work is mainly focused on CdSe nanocrystals,Cu₂S-In₂S₃ heterostructure nanocrystals and cuprous ions doped CdS nanocrystals,and the study of their applications in light-emitting diodes,photovoltaic devices,self-assembled into superlattices and their optical properties.Firstly,CdSe nanocrystals were synthesized in aqueous solution by using mercapto molecules as the stabilizer.The nanocrystals were transferred from aqueous solution into organic phase through static effect by using a surfactant with positive charge.The multilayered light-emitting diodes were fabricated using the blends of CdSe and PVK with different mass ratios of CdSe to PVK.The effects of applied voltages,the mass ratios of CdSe to PVK and the particle sizes of CdSe nanocrystals on the electroluminescence（EL） from the devices were studied,and the photoluminescence （PL） and EL from CdSe:PVK blends were compared.The luminescence mechanism of the light-emitting diodes based on CdSe:PVK nanocomposites were proposed based on the above results.It can be found that the energy transfer from PVK to CdSe and the cartier injection play different roles in the luminescence from the devices when the different applied voltages were applied and the different-size CdSe nanocrystals were used in the devices.Secondly,spherical Cu₂S nanocrystals were synthesized through one-pot synthetic method under high temperature,and matchstick-like Cu₂S-In₂S₃ heterostructure nanocrystals and In₂S₃ nanorods were also constructed by multi-injection of precursors. The photovoltaic devices were fabricated by using the blends of the nanocrystals and poly[2-methoxy-5-（2’-ethyl-hexyloxy）-1,4-phenylene vinylene]（MEH-PPV） as active layers.As compared to the photovoltaic performance of the devices based on the blends of Cu₂S or In₂S₃ nanocrystals alone and MEH-PPV,the power conversion efficiency of the photovoltaic device based on the blends of Cu₂S-In₂S₃ and MEH-PPV was enhanced by～3-5 times.This improvement is consistent with the improved exciton dissociation and better charge transport abilities in the semiconducting heterostructure nanocrystals. This method may supply a class of new materials to design high-efficiency nanoerystal/ polymer hybrid photovoltaic devices.Finally,undoped CdS and Cu（Ⅰ） ions doped CdS nanocrystals were successfully prepared in dedocanethiol using one-pot synthetic method under high temperature.The luminescent properties of doped CdS nanocrystals with different concentrations of Cu（Ⅰ） ions.It is found that the emission from surface-related luminescence to the red emission of Cu（Ⅰ） ions in CdS nanocrystals was dominant in the PL spectra with different dopant concentrations.The maximum fluorescence quantum yields of the doped CdS nanoerystals can reach 15.8%.On the other hand,the doped CdS:Cu（Ⅰ） nanocrystals can be self-assembled into highly-ordered 2D or 3D supedattices when the dopant concentration is appropriate.The size-distribution,synthetic condition and morphology of CdS:Cu（Ⅰ） nanocrystals with different dopant concentrations were studied,and we preferred to attribute the superlattiees formation to a polar system created on the nanoerystal surface originating from electric dipole interaction between the adjacent particles,which promoted rapid and spontaneous superlattice formation.Meanwhile, monodispersed Cu₂S nanocrystals were also formed because excess Cu（Ⅰ） ions can react with dodeeanethiol.This method can be extended to prepare other metal chalcogenide semiconductor nanomaterials.更多还原