利用协同效应在导电玻璃上生长高比表面积超长单晶TiO2纳米线阵列及制备高效染料敏化太阳电池

Vertically aligned single crystal TiO2 nanowire array grown directly on transparent conductive oxide glass is considered as a kind of very promising nanostructure for dye-sensitized solar cells (DSCs) because it ensures rapid collection of charge carriers generated throughout the cells. However, there are at least three major challenges in the fabrication of such nanowires on conductive glass for highly efficient DSCs. The first challenge is that, the most commonly reported length of nanowires on conductive glass is only 2-5 μm. The second challenge is that the specific surface area of the single crystal nanowires is very low (3-11 m2/g). Thirdly, conductive glass will be destroyed by hydrochloric acid during hydrothermal conditions, which results in a decrease of the cell performance. Therefore, we will develop a mild solvothermal approach that involves the synergistic interaction of self-supplied chloride ion from titanium precursor and lauric acid for synthesizing single crystal TiO2 nanowire arrays on conductive glass, instead of participation of strong acids, to overcome the challenges mentioned above. The direct growth of TiO2 nanowire arrays with length up to tens of micrometers and high surface area would be desirable for highly efficient solar cells. The initial results show that single-crystal TiO2 nanowire arrays possess a large surface area of 95 m2/g and a controlled length in the range of 10-46 μm. Future work will be focused on improving the adhesion properties of longer nanowire film on substrate as well as controlling length, length-diameter ratio and pore size distribution of nanowires. It is expected to fabricate low cost DSCs by further growing nanowires in low temperature. Based above experiments, we will propose a growth kinetics mechanism of nanowires. The length of TiO2 nanowire films can be tuned in the range of 10-100 μm to meet the requirement of light absorption. By applying these long nanowire arrays with high surface area for DSCs, an overall photoconversion efficiency of 7-11 % is expected to be achieved.

在导电玻璃上直接生长有序单晶TiO2纳米线阵列制备染料敏化太阳电池可以获得更好的电子传输性能并减小复合损失。文献报道的应用这类材料迫切需要解决的难题是：长度太短(2-5 μm)；比表面积小(3-11 m2/g)；所用盐酸破坏基底的导电性。温和条件下在导电玻璃上生长高比表面积、更长的单晶TiO2纳米线阵列是进一步提高电池效率的关键。本课题提出通过含氯的钛前驱体和月桂酸的协同效应在导电玻璃上直接生长高比表面积、超长的单晶TiO2纳米线阵列并制备染料敏化太阳电池。本课题的前期实验已经实现了在导电玻璃上生长10-46 μm，比表面积95 m2/g的单晶TiO2纳米线，月桂酸是有机弱酸，制备条件温和。我们将进一步研究纳米线与导电基底的界面结合问题；调控长度、长径比和孔径分布；实现低温制备降低成本及探明生长动力学机理，并制备10-100 μm的单晶纳米线电池，预期制备的电池效率达到7-11%。

本项目围绕利用含氯的钛前驱体和有机弱酸的协同效应替代传统盐酸水热法制备单晶TiO2纳米线阵列展开研究。在研究中发现利用长碳链饱和脂肪酸的特殊热物性和分子结构，可以在常压玻璃容器中利用限域空间低温(60-150℃)条件下生长TiO2纳米线阵列。并将制备纳米线的机理由我们最初提出的月桂酸（十二烷酸）扩展到丁酸，戊酸，己酸，庚酸，辛酸，壬酸，十四烷酸，十六烷酸和十八烷酸等不同直线碳链的有机弱酸上及正二十烷，使其成为一种通用合成方法，且用有机弱酸合成纳米线是一种制备条件温和的绿色合成工艺。通过改变生长温度、时间和不同碳链长的饱和脂肪酸的种类，实现了纳米线长度在10-50 µm和比表面积在60-95 m2/g可控制备。以具有弯曲碳链的不饱和脂肪酸（油酸）作为对比实验讨论了其生长机理，发现油酸条件下生成的是TiO2颗粒聚集体，我们提出直线性碳链结构在生长纳米线阵列中起了决定性作用。并发展了用其它链状分子结构（如聚乙烯亚胺、壳聚糖、聚丙烯酰胺、葡萄糖）定向吸附金属离子制备金属氧化物一维结构的通用方法，合成了石墨烯包裹的ZnO纳米管、超长TiO2纳米纤维、纳米晶互连的TiO2微米管、CuO纳米棒和ZnxCo3-xO4纳米纤维等，拓展了本项目提出的生长机理在合成一维纳米结构中的应用。通过在导电玻璃上制备TiO2种子层实现界面晶格匹配生长TiO2纳米线阵列，并通过对界面处局部微小缝隙真空吸附TiO2稀溶液以填塞超小TiO2纳米颗粒，解决了TiO2纳米线阵列与基底的界面结合问题。并将这一机理延伸发展了通过浓氨水热法在钛片上原位溶解-结晶制备TiO2“粘结”界面，使暴露MoS2(002)面边的纳米片阵列垂直取向地生长在钛片基底上。对在导电玻璃上直接生长的20 μm 厚单晶TiO2纳米线阵列制备染料敏化太阳电池，标准条件下测试得到了7.86%的光电转换效率，实现了预期的目标。在本国家自然科学基金资助下在Journal of Materials Chemistry A等国际期刊上发表论文15篇，授权国家发明专利4件。