【作者】 范佳杰；

【导师】 余家国；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2012， 博士

【摘要】 能源与环境的可持续发展是当今世界人类社会的两个重要发展战略。随着全球经济的发展,人们对能源的需求正在不断增长,新能源的发展势在必行。太阳能源源不断的辐照地面,且清洁无任何污染,因而成为最具开发潜力的新能源之一。染料敏化太阳能电池(DSSC)是一种有效利用太阳能的光电器件,它制作工艺简单、成本低廉、性能稳定、对环境无污染,因而具有良好的发展前景。DSSC在实际应用中光电转换效率偏低,纳米二氧化钛薄膜是染料敏化太阳能电池的重要组成部分,如何优化二氧化钛阳极对提高染料敏化太阳能电池的效率有很大影响。本论文着重研究了二氧化钛的纳米结构设计和二氧化钛／碳纳米复合材料的制备,以提高系统的电荷分离效果,从而提高染料敏化太阳能电池的光电性能。具体工作包括以下内容：1)(001)高能面暴露的锐钛矿Ti02纳米片在DSSC中的应用及其增强的光电转换效率。最近大量研究发现,与热力学稳定的(101)晶面相比,(001)晶面的反应活性更强,锐钛矿二氧化钛纳米片为高活性的材料和器件提供了一个新的选择。本文首次研究了(001)高能面暴露的锐钛矿二氧化钛纳米片(Ti02NS)在染料敏化太阳能电池中的应用。同时,对比研究了用(001)高能面暴露的锐钛矿二氧化钛纳米片、二氧化钛纳米颗粒以及商业P25电极制备的染料敏化太阳能电池(DSSC)的光电转化性能,其光电转化效率分别为4.56、4.24和3.64%。锐钛矿二氧化钛纳米片电极制备的染料敏化太阳能电池增强的光电转换效率主要源于其良好的晶化、大的孔体积以及增强的光散射效应。所制备的二氧化钛纳米片膜电极在光催化、催化、电化学、分离以及净化等领域有着广泛的潜在应用价值。2)锐钛矿二氧化钛纳米颗粒和纳米片对N719染料的吸附等温线、吸附动力学和吸附热力学研究。最近,(001)高能面暴露的锐钛矿二氧化钛纳米片(Ti02NS)膜电极已经被制备,且应用于染料敏化太阳能电池。锐钛矿二氧化钛纳米片电极制备的染料敏化太阳能电池增强的光电转换效率主要源于其良好的晶化、大的孔体积以及增强的光散射效应。从另一方面来讲,吸附在二氧化钛表面的染料复合物的吸附特性研究对于深入理解敏化特性以及优化染料敏化太阳能电池的性能有着非常重要的意义。因此,我们首次研究了暴露(001)(Ti02NS)对N719染料分子的吸附等温线、吸附动力学和吸附热力学性能,并对比研究了(101)晶面锐钛矿二氧化钛纳米颗粒(Ti02NP)的吸附性能。用准一级,准二级和颗粒内扩散动力学模型来拟合样品的吸附动力学数据,结果表明,准二级动力学和颗粒内扩散模型能更好地描述样品的吸附动力学。此外,用Langmuir和Freundlich模型来分析所制备样品吸附N719的平衡吸附数据,结果表明,Langmuir模型与实验数据符合得更好。通过Langmuir公式计算得到二氧化钛纳米片在不同温度对N719的最大吸附量(qmax)分别为65.2(30℃)、68.2(40℃)和76.6(50℃)mg g-1,小于二氧化钛纳米颗粒在各个温度对N719的最大吸附量92.4(30℃)、100.0(40℃)和108.2(50℃)mg g-1。与二氧化钛纳米片相比,二氧化钛纳米颗粒对N719的更高的最大吸附量是由于二氧化钛纳米颗粒具有更大的比表面积。进一步研究发现,二氧化钛纳米片在不同温度对N719染料的最大比吸附量(qmax/SBET)分别为1.5(30℃)、1.6(40℃)和1.7(50℃)mg m-2,大于二氧化钛纳米颗粒在各个温度对N719最大比吸附量0.9(30℃)、1.0(40℃)和1.1(50℃)mg m-2。与二氧化钛纳米颗粒相比,二氧化钛纳米片对N719具有更高的最大比吸附量,这是因为,与(101)晶面相比,反应物(吸附剂／吸附质)分子更容易在(001)晶面发生解离吸附。值得注意的是,qmax与qmax/SBET均随着温度的升高而增大,这表明二氧化钛表面对N719的吸附是一个吸热过程,这一点也通过对吸附过程的自由能、焓和熵等热力学参数的计算得到进一步的确认。此研究为二氧化钛纳米片和二氧化钛纳米颗粒对N719分子吸附的过程和机理的理解提供了新的视野,而这对于增强染料敏化太阳能电池的性能也有着重要的意义。3)Ti02纳米片／石墨烯复合膜在DSSC中的应用及其增强的光电性能。最近报道的锐钛矿二氧化钛纳米片电极制备的染料敏化太阳能电池增强的光电转换效率主要源于其良好的晶化、大的孔体积以及增强的光散射效应。特别的,考虑到石墨烯的二维纳米结构及优异的导电性,很多研究者将其与二氧化钛进行复合来提高它们的光催化活性和光电性能。本研究首次制备了染料敏化太阳能电池的Ti02NS/石墨烯复合膜电极,并研究了石墨烯对所制备的DSSC的微结构和光电转换性能的影响。石墨烯含量显著影响Ti02NS/石墨烯复合膜的物理结构和光吸收特性,同时也显著影响Ti02NS/石墨烯复合DSSC中载流子的传输、被陷阱捕获及复合。研究结果表明,石墨烯含量显著影响Ti02NS/石墨烯复合电池的光电转换效率。与纯二氧化钛膜制备的染料敏化太阳能电池相比,含有适量石墨烯(<0.75wt.%)的二氧化钛纳米片／石墨烯复合染料敏化太阳能电池表现出增强的光电转换效率。适量的石墨烯不仅降低二氧化钛膜／电解质界面之间的电子传输电阻、降低光生电子和空穴的复合、增强光生电子从二氧化钛膜到FTO导电玻璃基体的传输。同时,石墨烯的引入还增强光的捕获,从而增加光生电子的数量。此外,Ti02NS/石墨烯复合膜电极的良好的孔结构有利于电解质的扩散,从而有利于染料分子的再生和DSSC光电转换性能的增强。然而,过量的石墨烯(>0.75wt.%)显著降低了二氧化钛纳米片／石墨烯复合DSSC的光电性能。这是因为过量的石墨烯不仅降低了半导体半导体复合膜的晶化,同时也屏蔽了染料分子对光的捕获,减少了光生电子的数量。本研究将为高性能染料敏化太阳能电池的制备和结构设计提供新的视野。4)基于锐钛矿Ti02空心球／碳纳米管复合膜的染料敏化太阳能电池的研究。最近,锐钛矿Ti02空心结构材料由于其大的比表面和分等级纳米孔结构,以及其增强的光催化性能和光电转换效率而引起了越来越多的关注。进一步的,考虑到碳纳米管(CNT)的一维纳米结构和良好的导电性,我们有理由推断CNT/TiO2复合物应该有利于二氧化钛膜中电子的传输,有利于增强其光催化性能和光电转换效率。本研究首次制备了锐钛矿二氧化钛空心球(Ti02HS)/多壁碳纳米管(CNT)复合膜,并将其应用于染料敏化太阳能电池(DSSC)。同时,对比研究了相同厚度的TiO2HS/CNT与P25/CNT复合膜电极制备的染料敏化太阳能电池的光电转换效率。研究结果表明,碳纳米管含量显著影响TiO2HS/CNT复合电池的光电转换效率。少量的碳纳米管(<0.1wt.%)能够增强TiO2HS/CNT复合电池的光电转换效率,而过量的碳纳米管(>0.1wt.%)反而降低了其光电性能。前者是因为碳纳米管对电子的快速传输使得电子快速从二氧化钛膜转移到FTO导电玻璃基体。后者是因为过量的碳纳米管屏蔽了染料分子对光的捕获,减少了光生电子的数量,同时碳纳米管的引入也降低了半导体复合膜的晶化,从而增加了二氧化钛膜／染料／电解质界面之间的界面传输电阻,使得电池的性能降低。本研究将为高性能染料敏化太阳能电池的制备和结构设计提供新的视野。更多还原

【Abstract】 Nowadays, the sustainable developments of energy and environment are both of the two important strategies for the development of human society in the world. With the development of the global economy, the demands for energy are growing, and the development of new energy is imperative. The solar energy is one of the most potential because of its continuous irradiation, harmless and inexhaustibility. Dye-sensitized solar cell (DSSC) is one of the effective energy conversion devices. Because of its simple fabrication procedure, low cost, better stability and cleanliness, DSSC has been intensively investigated. The dye-sensitized nanocrystalline porous TiO2film is an important part of the DSSC, and its structure has great impact on cell’s photoelectric performance. In this work, nanostructure design and modification of TiO2with carbon namomaterials favor the separation of photogenerated charge carriers and thus enhance the photoelectric performances of DSSC. The point can be summarized as follows:1) Anatase TiO2nanosheets with exposed (001) facets:improved photoelectric conversion efficiency in dye-sensitized solar cells. Very recently, a lot of studies find that the (001) facets of anatase TiO2nanosheets is much more reactive than the thermodynamically stable (101) facets, the obtained nanosheets would offer a new chance to Design highly active photocatalytic materials and devices. Dye-sensitized solar cells (DSSC) are fabricated based on anatase TiO2nanosheets (TiO2NS) with exposed{001} facets. The photoelectric conversion performances of TiO2NS solar cells are also compared with TiO2nanoparticles (TiO2NP) and commercial-grade Degussa P25TiO2nanoparticles (P25) solar cells at the same film thickness, and their photoelectric conversion efficiencies (η) are4.56,4.24and3.64%, respectively. The enhanced performance of TiO2NS solar cell is due to their good crystallization, high pore volume, large particle size and enhanced light scattering. The prepared TiO2nanosheet film electrode should also find its widely potential applications in various fields including photocatalysis, catalysis, electrochemistry, separation, purification and so on.2) Adsorption of N719dye on anatase TiO2nanoparticles and nanosheets with exposed (001) facets:equilibrium, kinetic, and thermodynamic studies. Very recently, DSSCs based on two-dimensional anatase TiO2nanosheets have been proven to be effective in improving photoelectric conversion efficiency, because their two-dimensional (2D) nano-structures can enhance the light-collection efficiency by multiple light scattering. On the other hand, the characterization of the dye complex adsorption on the titania surface is very important for a deep understanding of the sensitization phenomenon and, then, optimize the performance of the sensitized cells. However, to the best of our knowledge, there are few systematic studies on the adsorption properties of N719molecules on TiO2NS with dominant (001) facets. In this work, the equilibrium, kinetic and thermodynamic data of the N719dye adsorption on TiO2NS with dominant (001) facets are studied and compared with TiO2NP with dominant (101) facets. Anatase TiO2nanosheets (TiO2NS) with dominant (001) facets and TiO2nanoparticles (TiO2NP) with dominant (101) facets are fabricated by the hydrothermal hydrolysis of Ti(OC4H9)4in the presence and absence of HF, respectively. Adsorption of N719onto the as-prepared samples from ethanol solutions is investigated and discussed. The adsorption kinetic data are modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations, indicating that pseudo-second-order kinetic equation and intra-particle diffusion model can better describe the adsorption kinetics. Furthermore, adsorption equilibrium data of N719on the as-prepared samples are analyzed by Langmuir and Freundlich models, suggesting that the Langmuir model provides the better correlation of the experimental data. The adsorption capacities (qmax) of N719on TiO2NS at various temperatures determined using the Langmuir equation are65.2(30℃),68.2(40℃) and76.6(50℃) mg g-1, which are smaller than that on TiO2NP,92.4(30℃),100.0(40℃), and108.2(50℃) mg g-1, respectively. The larger adsorption capacities of N719for TiO2NP versus NS are attributed to its higher specific surface areas. However, the specific adsorption capacities (qmax/SBET) at various temperatures are1.5(30℃),1.6(40℃) and1.7(50℃) mg m-2for TiO2NS, which are otherwise higher than that for NP,0.9(30℃),1.0(40℃) and1.1(50℃) mg m-2, respectively. The larger specific adsorption capacities of N719for TiO2NS versus NP are because the (001) surface is more reactive for dissociative adsorption of reactant molecules compared with (101) facets. Notably, the qmax and qmax/SBET for both TiO2samples increase with increasing temperature, suggesting that adsorption of N719on TiO2surface is endothermic process, which is further confirmed by the calculated thermodynamic parameters including free energy, enthalpy and entropy of adsorption process. The present work will provide new understanding on the adsorption process and mechanism of N719molecules onto TiO2NS and NP, which should be of great importance for enhancing the performance of dye-sensitized solar cells.3) Enhanced photovoltaic performance of dye-sensitized solar cells based on TiO2nanosheets/graphene composite films. Very recently, DSSCs based on two-dimensional anatase TiO2nanosheets have been proven to be effective in improving photoelectric conversion efficiency, because their two-dimensional (2D) nano-structures can enhance the light-collection efficiency by multiple light scattering. Owing to the2D nano-structures and excellent electronic conductivity of graphene, numerous attempts have been made to combine graphene with TiO2to enhance their photocatalytic and photoelectric performance. In this work, DSSCs based on TiO2NS/graphene nanocomposite films were for the first time fabricated and the effects of graphene on the microstructures and photoelectric conversion performance of the as-fabricated DSSC were investigated. The graphene loading clearly influences the textural properties and the optical absorption properties. Moreover, the charge transfer and transport versus the charge trapping and recombination is also affected by the graphene loading. As a consequence, the photoelectric conversion efficiency of the TiO2NS/graphene nanocomposite film electrodes can be improved to great extent upon graphene loading, which is dependent on the loading amount of graphene. Moderate amount of graphene (<0.75wt.%) obviously enhanced the DSSC efficiency. Graphene not only reduced the electrolyte/electrode interfacial resistance and the charge recombination rate, but also enhanced the transport of electrons from the films to fluorine doped tin oxide (FTO) substrates. Furthermore, the incorporated graphene improved the light harvesting and thus increased the number of the photoinduced electrons. Besides, the modified porous structures of the composite photoanode facilitated the diffusion of electrolyte in the cell, which in turn helped to regenerate the dye. being important to the photovoltatic response of the solar cells. However, excessive graphene loading (>0.75wt.%) largely lowered the DSSC performance. Higher graphene loading not only impaired the crystallinity of the TiO2NS, but also shielded the light adsorption of the dyes and reduced the number of the photogenerated electrons. This study will provide new insight into fabrication and structural design of highly efficient dye-sensitized solar cells.4) Dye-sensitized solar cells based on anatase TiO2hollow spheres/carbon nanotube composite films. Resently, TiO2hollow structured materials have received extensive attention owing to high specific surface areas, hierarchically nanoporous structures, good photocatalytic activity and enhanced photoelectric conversion efficiency. Furthermore, taking account of the1D nano-structures and good electrical conductivity of carbon nanotubes (CNT), it is reasonable to conclude that CNT/TiO2composites are beneficial to transport the electrons within TiO2films and enhance their photocatalytic and photoelectric conversion efficiencies. In this work, the TiO2HS/CNTs composite films are for the first time applied to prepare the photoanodes of DSSCs. The photoelectric conversion performances of the DSSCs based on TiO2HS/CNT composite film electrodes are also compared with commercial-grade Degussa P25TiO2nanoparticles (P25)/CNT composite solar cells at the same film thickness. The results indicate that the photoelectric conversion efficiencies (η) of the TiO2HS/CNT composite DSSCs are dependent on the amount of CNT loading in the electrodes. A small amount of CNT clearly enhances DSSC efficiency, while excessive CNT loading significantly lowers their performance. The former is because CNT enhance the transport of electrons from the films to FTO substrates. The latter is due to high CNT loading shielding the visible light from being adsorbed by dyes.This study will provide new insight into fabrication and structural design of highly efficient dye-sensitized solar cells.更多还原