光子能量上转换复合TiO2微/纳米分等级结构的染料敏化太阳能电池研究

The preparation of TiO2 photoanode materials with high conversion efficiency has been the research frontier and one of the hot topics owing to their important influences on the photovoltaic performances of dye-sensitized solar cells (DSSCs). In this project, morphology-controlled TiO2 hierarchical micro/nanostructures will be prepared by exploring new synthetic methods. And rare-earth upconversion luminescent materials with high luminous intensity will be fabricated through reducing host phonon energy, optimizing rare earth ion doping and sensitization. Then, the synthesized luminescent materials will be hybridized with different TiO2 hierarchical structures to fabricate novel composite photoelectrodes with upconversion luminescent property, thus to replace traditional nanocrystalling film electrodes. The advantages of such composite TiO2 film electrodes of DSSC are as follows. Firstly, the light harvesting ability will be significantly enhanced due to the increased dye adsorption of TiO2 hierarchical structures with high surface area, as well as the novel microstructure for strong light scattering. Secondly, the response range of DSSCs can be extended to the infrared region owing to the ability of upconversion luminescent materials, to convert infrared radiation to visible light that can be absorbed by the dyes. Thirdly, the heterojunction formed at the interfaces of luminescent materials and TiO2 hierarchical structures can retard the photogenerated charge recombination. Therefore, the photovoltaic performances of DSSCs will be remarkably enhanced by the synergic action of upconversion luminescent materials and TiO2 hierarchical structures. Carrying out this project will provide both practical and theoretical guidance for the development of high-efficiency photoelectrodes and thus the high-performance DSSCs.

具有高光电转换效率的光阳极材料的制备是染料敏化太阳能电池（DSSC）的前沿和热点之一。本项目通过探索新的合成方法以实现不同形貌TiO2微/纳米分等级结构的可控制备；通过降低基质声子能量、优化稀土离子掺杂及敏化，制备出较高发光强度的上转换荧光材料。然后，将上转换荧光材料与TiO2微/纳米分等级结构复合，制备具有光子能量上转换TiO2薄膜电极，替代传统纳米晶电极，研究该DSSC的光电性能。该复合薄膜电极的优点在于：综合利用TiO2分等级结构大比表面积，高的染料吸附量，以及对光的强散射提高太阳光的捕获能力；上转换荧光材料吸收红外光转换成染料可以吸收的可见光，拓宽其吸光范围；而且上转换材料与TiO2微结构之间形成异质结，抑制光激发电子复合；光子能量上转换与TiO2分等级结构协同作用，有望显著提高DSSC的光电转换效率。该项目的实施将为高效光阳极的研究和应用提供依据，进一步提高DSSC的总效率。

作为最具有代表性的染料敏化太阳能电池（DSSC）光阳极材料，纳米TiO2存在太阳光吸收范围窄，电子在传输过程中易与空穴复合等问题。本项目通过新的合成方法以实现不同形貌TiO2微/纳分等级结构的可控制备；通过优化稀土离子掺杂及敏化，制备出与太阳能光谱匹配且较高发光强度的上转换荧光材料。然后，将上转换荧光材料与TiO2微/纳分等级结构复合，制备具有光子能量上转换TiO2薄膜电极，替代传统纳米晶电极，研究该DSSC的光电性能。结果发现：（1）TiO2空心球、微球、花状TiO2等分等级结构大比表面积，高的染料吸附量，以及对光的强散射提高太阳光的捕获能力；（2）La(OH)3:Yb3+/Er3+、NaLuF4:Er3+/Yb3+和NaYbF4:Ho3+等这些上转换荧光材料吸收红外光转换成染料N719可以吸收的红光和绿光，拓宽电池对光响应范围，从而提高电池的光电流密度；（3）这些纳米上转换材料与TiO2微结构之间形成异质结，抑制光激发电子复合，提高了电子的寿命； （4）纳米上转换材料在TiO2光阳极薄膜中掺入有一个最佳添加范围，过量的加入反而成为电子和空穴复合的中心；（5）光子能量上转换技术与TiO2微/纳分等级结构协同作用，显著提高DSSC的光电转换效率。该项目的研究，不仅会推动高效太阳能电池的发展，也为日益严峻的环境与能源问题的解决，提供了新的思路。