分等级锐钛矿TiO2多孔纳米管阵列的制备及其在染料敏化太阳电池中的应用

The hierarchical anatase TiO2 porous nanotube arrays on conductive glass substrate have attracted considerable attention due to high density photon absorption, long-range order carrier transport channel and multi-channel electrolyte diffusion, which are the ideal photoanode materials. It is difficult to directly grow anatase TiO2 nanoarrays on FTO glass substrate because of a large lattice mismatch of 19% between FTO and anatase TiO2. In this project, anatase TiO2 nanowire arrays on conductive glass substrate are fabricated by a facile solvothermal method. The resulting TiO2 nanowire arrays serve as the skeleton for controllable preparation of hierarchical TiO2 nanowire arrays. In terms of an in situ hydrothermal corrosion method, the as-prepared hierarchical TiO2 nanowire arrays are transformed into hierarchical TiO2 porous nanotube arrays. The interface problem between nanoarrays and FTO glass substrate is discussed. It is demonstrated that the FTO glass substrate pre-treatment conditions such as concentration of seed, spin coating times and substrate annealing treatment have their respective influence on the structure and properties of TiO2 nanoarrays. From the reaction kinetics and thermodynamics, the formation and evolution mechanism of TiO2 nanoarrays are interpreted. By changing the experiment conditions, the length, aspect ratio and number of pore are tunable, and the relationship between structure and performance of the dye-sensitized solar cells is studied. Furthermore, the internal mechanism of interfacial electron transfer, recombination, collection and kinetics process are investigated by electrochemical technology and the intensity-modulated photocurrent (photovoltage) spectroscopy (IMPS and IPVS). The mechanism for improving efficiency of DSSCs is clarified by summarizing relationship between structure and performance.

分等级锐钛矿TiO2多孔纳米管阵列具有高密度光子吸收、长程有序载流子传输通道和多通道电解液扩散等优点，是理想的光阳极材料。由于FTO玻璃与锐钛矿TiO2晶格失配，很难直接生长锐钛矿TiO2纳米阵列。本项目运用溶剂热法在FTO玻璃上可控制备锐钛矿TiO2纳米线阵列的基础上，以TiO2纳米线阵列为骨架，制备分等级TiO2纳米线阵列，然后采用水热原位腐蚀法，可控制备分等级TiO2多孔纳米管阵列。研究纳米阵列与FTO玻璃的界面结合问题。揭示种子浓度、旋涂次数和热处理对TiO2纳米阵列的结构和性能的影响。从反应动力学和热力学的角度对TiO2纳米阵列的形成和演化机制进行诠释，实现TiO2纳米阵列的可控合成与生长。通过改变实验条件，控制长度、长径比和孔的数量，并研究其对染料敏化太阳电池的性能影响。借助于电化学和强度调制光电流（电压）谱，研究电子传输、复合和收集的动力学过程，总结结构与性能之间的构效关系。

多级纳米阵列光阳极具有多重功能，一方面，主干能够为光生电子提供直接的传输路径，加快电子的传输，减小电子复合的机率；另一方面，分支能够增大表面积，提高染料吸附量和增强光散射能力。本项目讨论材料的尺寸、形貌等结构参数与实验条件之间的联系，并探明形貌控制的要素，实现材料的可控制备，深入理解材料制备过程中生长规律，研究材料微结构参数与光伏性能之间的相关性，探索电子传输动力学过程，明晰其电子传输和复合机理。通过研究，我们取得了一些研究成果。（1）筛选出低温简易的制备单分散致密种子层的方法。（2）以草酸钛钾、水和二甘醇为原料，运用水热反应在FTO玻璃上制备了超长锐钛矿TiO2纳米线阵列。（3）多步水热反应制备了分等级锐钛矿TiO2纳米线阵列；在草酸钛钾、水和二甘醇体系基础上，添加少量的食盐，一步法制备了分等级锐钛矿TiO2纳米阵列。（4）TiO2双纳米线阵列的制备。（5）以锐钛矿TiO2纳米线阵列为模板，自模板法制备分级TiO2纳米管阵列，研究纳米管的形成过程。（6）以乙醇取代二甘醇，一步法制备分级二氧化钛纳米管阵列，电池的光电转换效率达到了9.89%，IMPS和IMVS研究表明，二氧化钛纳米管阵列具有优越的电子传输和较慢的电子复合，表现出较高的电子收集效率。