【作者】 王凌凌；

【导师】 杨文胜；

【作者基本信息】 吉林大学 ， 物理化学， 2010， 博士

【摘要】 利用太阳能解决能源短缺和环境污染问题是当前国内外的热点课题,而开发高性能的光电功能材料是太阳能有效利用的基础。CdS作为一种典型的Ⅱ-Ⅵ半导体材料,由于具有良好的可见光光电性质而成为太阳能利用研究中的热点。特别是近年来通过对CdS进行修饰和改性构成具有异质界面的复合材料,能够提高光生电荷的分离效率,减缓其光腐蚀,改善其光电性能,而受到了国内外的广泛关注。但是,对于CdS纳米材料及由它构成异质材料的光生电荷行为(光生电荷转移的方向,分离效率和寿命等)却鲜有报道,而这些信息对于构建高效的CdS基光电功能材料却是至关重要的。本论文利用水热合成方法制备了不同形貌的CdS纳米粒子,并以CdS纳米阵列为基础制备了CdS/ZnO和CdS/ZnS异质结构。以表面光伏技术为主要的研究手段,系统研究了它们的光生电荷性质,并取得了一些具有创新意义的研究结果:1、利用水热合成方法制备了CdS纳米粒子、CdS六棱柱体以及CdS纳米柱阵列。表面光伏测试结果显示光伏响应为正值,符合CdS的n-型特征。而长波段的负向响应与亚带隙跃迁相关,属于表面态布居跃迁。首次利用表面光伏相位谱方法对CdS纳米材料的光伏特性进行解析,结果发现:相同的跃迁过程具有相近的光伏相位,不同的跃迁过程其相位值差别较大;当光伏相位发生突变( >100°)时,表明光生电荷扩散方向可能发生反转;可以通过表面光伏相位谱的突变点或拐点估算半导体材料的禁带宽度。2、以CdS六棱柱体和CdS纳米阵列为基础构筑了CdS/ZnO异质结构,并研究了其光生电荷性质,发现CdS/ZnO异质结构材料的表面光伏响应明显降低了,这可能是由于CdS与ZnO之间形成了一个弱的界面电场,在这个界面电场的作用下,CdS带带跃迁的的部分光生电子转移到了ZnO中,抵消了CdS本身带带跃迁的光伏响应。从表面光伏相位谱和瞬态光伏响应结果中可以直接分辩出这种光生电荷转移过程。3、在CdS纳米阵列的基础上,制备了CdS/ZnS异质结构。SPS研究表明:在CdS与ZnS之间存在一个界面电场,由于界面电场的存在消除了光生电子的束缚,导致光生空穴在表面富集。表面光伏相位谱显示CdS纳米阵列在370nm处发生相位突变,而CdS/ZnS异质结构中,没有发生相应的相位突变,这些结果证明异质界面的存在对光生电荷的扩散方向有显著的调控作用。更多还原

【Abstract】 The utilization of the solar energy is a hot and permanent subject. Exploiting photoelectric functional materials with top performance is the foundation for solar energy conversion. As a typicalⅡ-Ⅵsemiconductor, CdS attracts many attentions for its high extinction coefficient in visible spectrum and large intrinsic dipole moment that leads to rapid charge separation. In recent years, many efforts have been focused on the modification of CdS nanostructures by introducing a second semiconductor compound to form heterostructures. It is cognized that the heterogeneous structure can hold up photo corrosion and improve the photoelectric properties of functional materials based on cadmium sulphide. However, few report expounds the behaviors of photogenerated charges (the generation, separation, transportation and recombination) of CdS nanostructrues and its heterostructures. While, this is the basic for developing the advanced materials with photo-to-electric converting function.In this paper, We fabricated large-scale CdS nanorod arrays with different morphologies by hydrothermal approach. And then CdS/ZnO, CdS/ZnS heterostructures was design on that basis. We studied the photoelectric properties of the above systems by surface photovoltage (SPV) technique and the transient photovoltage (TPV) technique and obtained some novel results.1. Well-defined hexangularly faced CdS nanorod arrays with different length-width ratio were fabricated by hydrothermal approach on a FTO substrate. The results shows that a positive response of SPV for CdS band to band transition which is correspond with the characteristics of n-type semiconductor. While the negative response in the lower energy region is correlated to sub-band-gap transitions. We utilized SPV phase for the first time to analyze the photovoltaic properties of CdS nanorod arrays and discovered the following results: The same transition processes have similar SPV phase signals, while different transition processes own their respective SPV phase signals. When the signal exhibits a break (>100°), there is a reversion of photo-generated charges direction. We can assess the band gap of a semiconductor materials by the break-point of SPV phase spectrum.2. The photo-generated charges characteristics of CdS/ZnO heterostructures materials have been studied by means of SPV techniques. The results showed that the photovoltage intensities of CdS/ZnO heterostructures materials decreased comparing with that of CdS. From the results of TPV measurement, the photo-generated electrons of CdS could transfer to ZnO under illumination since an electric field formed on the interface between CdS and ZnO. But this field is too weak to dominate the photo-generated charges characteristics. This result indicates that photo-generated charges characteristics can be clarified furthermore by means of surface photovoltage phase and transient photovoltage techniques.3. The SPV spectra of the CdS/ZnS heterostructures shows that there is a interface electric field between CdS and ZnS. It will counteract the bondage of photogenerated electrons and result in the enrichment of photogenerated holes at the surface. The SPV phase spectrum of bare CdS nanorod arrays has a break-point at 370nm, while in the case of CdS/ZnS, no obvious break-point was observed. These results show that the presence of a heterointerface will adjust the direction of the diffusion of photogenerated charges.更多还原