【作者】 陈杰；

【导师】 张红星；

【作者基本信息】 吉林大学 ， 物理化学， 2012， 博士

【摘要】 染料敏化太阳能电池具有良好的光学性质，不但有很高的光电转化效率，同时兼具良好的热稳定性、低成本、制备简单等突出的优点，已经被作为传统能源的替代品，特别广泛地应用于机械、仿生、航天等领域，有望成为传统硅基太阳能电池的有力竞争者。通过近二十年的研究与优化改良，染料敏化太阳能电池的实验室效率已经超过了11%。因此，对于染料敏化太阳能电池体系实验和理论研究一直以来是学术界的前沿热点，实验上主要关注于电池材料效率的提高，包括染料分子的设计和器件的制作；而理论上对于分子结构和光电性质的分析和模拟更加感兴趣。本论文对一类以过渡金属Ru配合物作为染料敏化分子的太阳能电池体系作了系统的研究，得到了染料分子单体以及染料分子吸附在二氧化钛晶体之后的异质界面几何构型,电子结构和光谱性质.通过对以上诸方面的深入探索,拓宽了调控染料分子自身吸收光谱性质的操作空间并深入了对于涉及异质界面吸附模型的认识。全文共分为七章：第一章为前言，概述了染料敏化太阳能电池材料体系工作原理、影响电池效率的因素，以及当前实验和理论研究在此方向的研究进展和本文研究的理论意义；第二章为本研究涉及到的理论方法和技术细节；第三章至第五章对几类染料分子光电性质的理论研究；第六章和七章研究染料敏化太阳能电池中染料和二氧化钛晶体之间异质界面的几何和电子结构性质,进一步探讨提升电池效率的调控窗口。具体研究内容介绍如下：1.由于含不同的杂环的钌敏化剂拥有较母体N3更高的光电转换效率和更低的电荷重组能，此类物质被广泛设计和合成。正因如此，基本结构为Ru (辅助配体) (附着配体)的敏化分子引起了科研工作者的很大兴趣，其中C101和J13比较具有代表性。通过模拟不同质子化程度的敏化分子的吸收光谱性质来模拟不同pH值下的染料分子的吸收性能。应用密度泛函和含时密度泛函分别研究基态和激发态几何结构，并对电子结构和光谱性质进行计算研究。所有化合物在乙腈溶液中的吸收和发射光谱都是使用B3LYP泛函进行预测。计算结构表明，辅助配体对于分子整体的能级分布和吸收光谱有很大贡献。值得注意的是，作为修饰的而连接在辅助配体的噻吩基团可以有效的提高染料分子在380–450 nm范围内的吸收强度。尽管去质子化可以使染料分子的整体前线轨道不稳定，但是对于非占据轨道的影响要更大。因此随着去质子程度的加剧，吸收和发射都呈现出蓝移。最终，得到C101和J13最优去质子化程度。我们对染料分子的结构和光谱加以分析，期望能够获得更高效的染料敏化分子，并且让人们在对于染料敏化太阳能电池体系的效率有更全面的认知。2.本文在理论上设计了一系列染料敏化分子。把唑和其类似物作为修饰基团引入N3的辅助配体上，以期使N3具有更符合DSSC应用要求的光电性质。根据密度泛函理论（DFT）计算，含有1, 2, 4-三唑基团的敏化分子在可见光区具有强吸收带，可见辅助配体对于分子轨道和吸收光谱是有决定性的影响。另外，配体去质子化程度不仅能影响具体的前线轨道分布，而且能控制HOMO和LUMO之间的能隙以及LUMO和LUMO+1的能级差。如果LUMO和LUMO+1的的能级差足够小，那么就有望获得具有更宽阔的吸收谱带的染料分子。3.我们一直致力于提高AR20在可见区域的光吸收强度的研究工作。密度泛函理论的方法也被应用于探索AR20和它的衍生物的电子结构性质的研究中。TDDFT的结果暗示了辅助配体控制着分子轨道能级并决定了吸收跃迁的类型。敏化分子的去质子化作用不仅影响了分子轨道能级的分布，还决定了LUMO-HOMO和LUMO-LUMO+1的能量差。将噻吩基团引入到辅助配体中的行为，能增强染料敏化太阳能电池（DSSC）的效率。噻吩取代的AR20衍生物的吸收强度与周围环境的变化有关，如pH值。这个特殊的性质预示了噻吩修饰的AR20衍生物可能在DSSC的实际应用中发挥良好的作用。4.光激发后，电子由染料敏化分子注入二氧化钛纳米晶体导带的电荷转移过程决定着DSSC光电转化效率的高低。通过设计的合理二氧化钛表面模型（取自锐钛矿的101表面和取自金红石的110表面），借助DFT方法深入探究了C101，J13，N749等在不同吸附模型下的光谱性质。根据计算，我们获得了详细的轨道能级分布和吸收跃迁特征，进而可以很细致的确认激发态快速电子注入或发射机制。一般来说，不同的二氧化钛的表面模型和敏化分子自身的去质子化程度可以对体系的吸收光谱产生深远的影响。我们的计算表明提高共轭染料分子的共轭性质,可以强化可见光区乃至红外区域的吸收强度,提高对太阳能的利用率,进而提升DSSC的总观光电转化效率。5.基于染料敏化分子N749的DSSC在长波长范围内有出色的光电转化效率。基于二氧化钛(101)表面模型和N749与二氧化钛薄膜之间不同的连接类型的合理设计，我们在理论上成功模拟了吸附体系宏观光谱性质。采用TDDFT方法得到前线分子轨道能量分布和吸收光谱与实验吸收峰形和特征吻合。当前的研究表明,染料分子和二氧化钛晶体之间的异质界面的微观构型直接影响最终DSSC的宏观光电转化效率。DSSC中的电子注入方式可以通过激发过程中电荷转移的结果加以区别。此外，染料分子去质子化的程度也强烈影响着吸收光谱的具体形态。结果表明，高效的染料敏化太阳能电池应含有低能量、密集、易于部分轨道耦合的非占据分子轨道。更多还原

【Abstract】 Due to the high incident photo-to-current efficiency （IPCE） and unique thermalstability, dye-sensitised solar cell （DSSC） have been widely used in mechanica, bionic,aerospace and other fields. Compared with the traditional silicon solar cell. DSSCs arelower in cost, simpler in preparation. Though lower in efficiency, DSSCs wouldchallenge the market of traditional silicon cells with further increasing in efficiency.The remarkable improvements in DSSCs’s overall efficiency contributed by thechemistry commucity from every corner of the world have been enlargeing thispossibility in the last two decades. In experiment, the attentions are focused onincreasing efficiency, synthesizing dye molecule and optimizing device structure,while physical chemist devote more effort on the electronic structure of molecule andsimulation of photoelectric process related with DSSC efficiency.The current PhD thesis focuses on the electronic structure and spectral characterof the separate dye molecules and the dye which adsorbed TiO2surface. Based on thetheoretical design and calculation，the dye molecules with strong and wide absorptionband in the visible region were obtained. A small TiO2surface model which can beused to explore the electronic structure and spectral properties of dye onheterogeneous interface contributed by dye and TiO2surface was designed and the rationality has been validated. The detailed findings are summarized in the followingseven chapters. In Chapter 1, we provided the fundmental background about DSSC,the goal of the PhD project, and the principle conclusions I have got. The technicaldetails are summaried in Chapter 2 with possible clarity. The rest of the chapters focuson the exact work I have contributed.1. A variety of heteroleptic ruthenium sensitizers have been widly applied inDSSC due to their higher light-harvesting efficiency and lower charge-recombinationpossibility than the well known homoleptic N3 dye. Hence, a great deal of attentionhas been focused on sensitizers with the general formulaRu（ancillary-ligand）（anchoring-ligand）（NCS）2, for example, Ru（4,4’-bis（5-hexylthio-phen-2-yl）-2,2’-bipyridine）（4,4’-carboxylic acid-4’-2,2’-bipyri-dine）（NCS）2（C101） andRu（N-（4-butoxyphenyl）-N-2-pyridinyl-2-pyridinamine）（4,4’-carboxylic acid-4’-2,2’-bi-pyridine）（NCS）₂（J13）. In order to simulate the real conformation of dye whenadsorbed onto the TiO₂surface under the experimental conditions, thephotosensitizing processes of these sensitizers within different degrees ofdeprotonation （2H, 1H to 0H） have been explored theoretically. The ground/excitedstate geometries, electronic structures and spectroscopic properties are calculatedusing density functional theory （DFT） and time-dependent DFT （TDDFT）. Theabsorption and emission spectra of all the complexes in acetonitrile solution are alsopredicted at the TDDFT （B3LYP） level. The calculated results show that the ancillaryligand contributes to the molecular orbital （MO） energy levels and absorptiontransitions. It is intriguing to observe that the introduction of a thiophene group intothe ancillary ligand increased the absorption transitions in the 380–450 nm region.The calculations reveal that although deprotonation destabilizes the overall frontierMOs of the chromophores, it tends to exert a greater influence on the unoccupiedorbitals than on the occupied orbitals. Consequently, an obvious blue shift wasobserved for the absorptions and emissions from 2H, 1H to 0H. Finally, the optimaldegree of deprotonation for C101 and J13 has been evaluated, which is expected tolead further improvements in the performance of DSSCs coated with these sensitizers. 2. Azoles and their derivatives were adopted as ancillary ligand to improve theperformance of N3 in DSSC. DFT based approaches were applied to explore theelectronic structures and properties. The calculation reveals that dye molecule with 1,2, 4-triazole groups would show very high intensity of absorption in visible range.TDDFT results indicate that the ancillary ligand dominates the molecular orbital （MO）energy levels and masters the absorption transition nature. The deprotonation ofanchoring ligand not only affects the frontier MO energy levels but also controls theenergy gaps of HOMO–LUMO and LUMO–LUMO+1. Small gap between LUMO–LUMO+1 contributes positively to the overall efficiency of DSSC.3. Special efforts were devoted to improve the absorption behavior of AR20 invisible region. DFT based approaches were applied to explore the electronic structureproperties of AR20 and its derivatives. TDDFT results indicate that the ancillaryligand controls the molecular orbital （MO） energy levels and masters the absorptiontransition nature. The deprotonation of anchoring ligand not only affects the frontierMO energy levels but also determines the energy gaps of highest occupiedMO–lowest unoccupied MO （LUMO） and LUMO–LUMO+1. Introducing thiophenegroups into ancillary ligands would enhance the efficiency of the final DSSC. Theabsorption intensity of the thiophene substituted derivatives of AR20 is irrelevantwith environment circumstance change, such as pH value. This special natureprognosticates the thiophene-substituted derivatives of AR20 which would have abroad application in DSSC.4. Electron injection from a photoexcited chromophore into the surface ofmesoscopic semiconductor TiO₂nanoparticles is one of the key electron transferprocesses for DSSC. A reasonable and reliable TiO₂surface model （taken from theanatase （101） and rutile （110） crystals a slab model） was designed, which wasemployed to investigate the absorption behavior of dye molecules such as C101, J13and N749 on TiO₂surface with under DFT method. According to the calculationresults, the detailed orbital components and absorption transition are obtained;furthermore, the ultrafast, excited-state charge injection and emission charege injection was discriminated. Generally, both the ways by which the dye is adsorbedinto TiO₂and degree of deprotonation of dye molecules could affect absorptionspectrum remarkably. Our calculations show that the more efficient DSSCs shouldhave larger conjugation degree for ancillary ligands or the whole system, which isbeneficial to photon absorption from the visible to near-IR region.5. N749, brings about outstanding IPCE in long wavelength range in DSSC.Depending on rational design of TiO₂（101） surface model and connecting typesbetween N749 and TiO₂film, the experimental absorption peaks have been wellreproduced within DFT and TDDFT approaches. According to the calculations, thedifference in connecting models in DSSC affects the final utilization of solar energydirectly. The way of electron injection in DSSC was discriminated within the resultsof charge-transfer transition. In addition, the degree of deprotonating about dyemolecules could also influence absorption spectrum obviously. It was demonstratedthat the dyes with closely-lying low energy unoccupied orbitals, which are conduciveto orbital-coupling, would improve the overall photo-to-current efficiency in DSSC.更多还原