【作者】 池玉娟；

【导师】 付宏刚；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2008， 博士

【摘要】 作为太阳电池光阳极的半导体材料TiO₂由于带隙宽、量子效率低而限制了其实际应用。本文制备了ITO/TiO₂多孔纳米晶薄膜,然后以ITO/TiO₂多孔纳米晶薄膜为基底,利用阴极恒电位沉积法,分别沉积窄带隙半导体CdS和CdSe,制备出ITO/TiO₂/CdS和ITO/TiO₂/CdSe纳米半导体复合薄膜,并研究了不同实验条件对半导体复合薄膜中沉积物粒子的平均粒径、组成及薄膜表面形貌的影响,同时将以上各半导体复合薄膜制备成太阳电池的光阳极,考察了各半导体复合薄膜电极的光电性能。研究中分别以TiO₂溶胶、TiO₂纳米粒子、TiO₂溶胶与TiO₂纳米粒子混合的分散体系为前躯体,利用浸渍-提拉技术或涂敷技术制备了TiO₂溶胶膜、TiO₂粒子膜和TiO₂溶胶-粒子膜三类薄膜。通过XRD和Raman光谱确定了所制备TiO₂的晶相结构,利用SEM和AFM观察了TiO₂薄膜的表面形貌,计算了TiO₂粒子尺寸,通过氮气吸附-脱附实验表征了TiO₂溶胶-粒子薄膜的孔道结构及薄膜的比表面积,并使用紫外吸收光谱及光电性能测试手段分析了各类TiO₂薄膜的光吸收特征及光电化学性能。结果表明,TiO₂溶胶-粒子薄膜是一类多孔纳米晶薄膜,由锐钛矿相的TiO₂粒子构成,TiO₂粒子的平均粒径约10 nm,且粒子分布均匀,薄膜表面具有较高的粗糙度,比表面积为123 m 2 ? g?1,薄膜中较丰富的孔道结构,增加了光生载流子的分离效率,该类薄膜对紫外光有较强的吸收,其光电化学性能明显好于TiO₂溶胶膜和TiO₂粒子膜。采用阴极恒电位沉积方法,以ITO/TiO₂多孔纳米晶薄膜为基底,在含有CdCl2和Na2S3O2的酸性混合水溶液中沉积CdS,制备了ITO/TiO₂/CdS纳米半导体复合薄膜,并利用XRD和XPS表征了沉积物CdS的晶相结构与组成,通过SEM观察薄膜的表面形貌、粒子尺寸及膜厚。根据本文实验数据及前人研究工作讨论了CdS的电沉积过程与机理。实验中,也研究了沉积电位、沉积时间、电解液的组成、实验温度等实验条件对CdS平均粒径及ITO/TiO₂/CdS纳米半导体复合薄膜表面形貌的影响。研究结果表明,在ITO/TiO₂表面沉积的CdS粒子具有六方结构为主的混合晶相结构,球形粒子均匀沉积于ITO/TiO₂多孔纳米晶薄膜的内部及表面。在40℃、-1.00 V、沉积20 min条件下制备的ITO/TiO₂/CdS薄膜形成菜花状的表面形貌,CdS粒子的平均粒径约8 10 nm,沉积层厚度约为1.885μm,薄膜中镉硫元素的原子比接近1:1。通过控制实验的沉积电位由-0.80 V负移至-1.40 V,CdS粒子的平均粒径由15.0 nm减小至6.2 nm,薄膜中硫镉元素的原子含量也由硫富集变为镉富集,且薄膜厚度增加。沉积时间为5 min的薄膜中CdS的平均粒径约5 nm,形成网络状的表面形貌,薄膜厚度约为1.40μA。实验中,还利用光电流-电势曲线与光电流作用谱考察了ITO/TiO₂/CdS半导体复合薄膜电极的光电化学性能及实验条件的改变对薄膜电极光电性能的影响。借助于表面光电压谱和瞬态光电流谱探讨了ITO/TiO₂/CdS薄膜电极中电荷传输过程。实验结果表明,窄带隙半导体CdS与宽带隙半导体TiO₂的复合有效地促进了光电子与空穴的分离,增大了薄膜电极的光电流,改善了ITO/TiO₂薄膜电极初始光电流响应,ITO/TiO₂/CdS半导体复合薄膜电极的光电响应拓宽至500 nm的可见光区,在400 nm单色光照射下半导体复合薄膜电极具有约45%的光电转换效率。此外,实验中还利用了阴极恒电位沉积法将窄带隙半导体CdSe沉积于ITO/TiO₂多孔纳米晶薄膜中。通过XRD、SEM等测试手段表征了沉积物CdSe的晶相结构与粒子尺寸、分析了所制备的ITO/TiO₂/CdSe的组成及表面形貌。讨论了在不同沉积电位下CdSe的沉积机理。利用紫外-可见吸收光谱、表面光电压谱、电流-电势曲线及瞬态光电流谱等考察了ITO/TiO₂/CdSe薄膜的光电性能。实验结果表明,窄带隙半导体CdSe纳米粒子以球体较均匀地分布形成较致密、平整的表面形貌,粒子的粒径分布较宽,控制CdSe沉积电位不同时CdSe的沉积按不同的沉积机理进行;窄带隙半导体CdSe与宽带隙半导体TiO₂的复合有效抑制了光生电子与空穴复合的机会,将ITO/TiO₂薄膜的光吸收和光电响应范围覆盖了400 nm至700 nm的可见光区。更多还原

【Abstract】 The semiconductor TiO₂ was restricted in the application as solar cell materials because of its wide band gap and low quantum efficiency. In present study, porous ITO/TiO₂ nanostructural thin films were prepared, which were further used as substrates for the deposition of narrow band gap semiconductors CdS and CdSe by means of cathode potentiostatic electrodeposition technique for obtaining ITO/TiO₂/CdS and ITO/TiO₂/CdSe nanostructural composite thin film. Furthermore, the effect of different experimental conditions on the composition and surface appearances were investigated. Also, the photoelectric performance of the prepared ITO/TiO₂/CdS and ITO/TiO₂/CdSe thin films was studied as photoanodes of solar cells.Anatase TiO₂ nanoparticles were prepared by hydrothermal method, in which Ti（OBu）4 was used as precursor, while TiO₂ colloids were obtained by Sol-Gel technique. And finally, using obtained nanoparticles and colloids, TiO₂ colloid thin film, TiO₂ particle thin film, and TiO₂ colloid-particle thin film were prepared by as-dipped and coating methods. Subsequently, the crystal structures of the prepared films were characterized by XRD and Raman spectra, and the surface morphologies of thin films were further observed by SEM and AFM techniques. Also, the particle size of TiO₂ was determined based on the XRD and SEM results. Porous structure and specific surface area of the prepared thin films were characterized by means of N2 adsorptiondesorption analysis, while photoelectric performances of different TiO₂ films were investigated by UV absorption spectrum and other photoelectrochemistry measure techniques. The experimental results indicate that the prepared TiO₂ colloid-particle thin films with homogeneous distribution of particles and rough surface as well as large specific surface area possess uniform porous structure, leading to strong absorption for UV radiation. Furthermore, we believe that the better photoelectric performance of the colloid-particle thin films results from the large specific surface area which can effectively decrease the grain boundary resistance and increase the contract district.By means of cathode electrodeposition technique, the ITO/TiO₂/CdS composite films were prepared using the ITO/TiO₂ colloid-particle films as substrate in acid water solution including CdCl2 and Na2S3O2 followed by the characterization for the crystal structures and compositions by XRD and XPS methods and for the surface morphologies, particles sizes, and film thickness by SEM technique. In our experiments, the effects of different experimental conditions, such as deposition potentials and times, electrolyte composition including electrolyte concentrations and addition of EDTA, experimental temperatures, etc., on the sizes of CdS particles and surface morphologies of ITO/TiO₂/CdS films were also evaluated. The results demonstrate that the spherical CdS particles with mixed crystal phase but hexagonal structure as the primary phase were uniformly deposited not only on the ITO/TiO₂/CdS film surface but also inside the ITO/TiO₂ substrate. At the conditions of deposition potential of -1.00 V and deposition time of 20 min, the prepared ITO/TiO₂/CdS thin films possess cauliflower-like morphology and Cd/S atom ratio of near 1:1. By controlling deposition potential and time, the deposition rate can be adjusted, results in high controllabilities for particle size and film thickness.In experiments, the photoelectric performance of the ITO/TiO₂/CdS composite semiconductor thin films and the effect of experimental condition on the photoelectric performance were also discussed photocurrent-potential curve and photocurrent action spectrum techniques, while SPS spectrum was used to estimate charge transfer mechanism of semiconductor film electrodes. The experimental results show that the sensitization of CdS for TiO₂ effectively improves the separation of photogenerated electrons and holes, increases photocurrent, and ameliorates initial photocurrent response, which will result in a high photoelectric transition efficiency within the absorption range of 400 500 nm.Furthermore, we also deposited narrow band gap semiconductor CdSe on the porous ITO/TiO₂ substrate by cathode potentiostatic deposition technique. Whereafter, the crystal structures and particle sizes as well as the film compositions and surface morphologies were analyzed by XRD and SEM techniques. The photoelectric performance of ITO/TiO₂/CdSe films was investigated in detail by UV-Vis, SPS, current-potential, and transient state photocurrent spectra. The results indicate that the sensitization of CdSe for TiO₂ effectively improves the photoabsorption and expand the photoelectric response to the range from 400 nm to 700 nm.更多还原