纳米胶囊包覆的三重态湮灭光子上转换材料的研究及其应用

Upconversion (UC), which is the observation of emission (or population of excited states) at higher energy after excitation at lower energy. The triplet-triplet-annihilation (TTA)-based upconversion has a broad application prospect, such as dye-sensitized solar cells (DSSC) and biological fileds etc., because of its high upconversion efficiency and occurring under sunlight-like condition, namely low-intensity excitation light. The system of TTA-based upconversion consists of triplet sensitizer and acceptor. At present, the TTA-based upconversion mainly occurred in solution not as a single unit, which will significantly limit its applications. It is one of the key problems for the application of TTA based upconversion that how to encapsulate the triplet sensitizer and acceptor and obtain the solid upconversion materials. This project intends to encapsulate the triplet sensitizer and acceptor with inorganic nanocapsules, as well as to explore the variation law of TTA based upconversion in nanocapsules microenvironment. For example, the energy transfer efficiency between sensitizer and acceptors as well as the upconversion quantum yields will be affected in nanocapsules microenvironment. We will investigate these encapsulated TTA upconversion materials in the application of dye-sensitized solar cells to increase the photoelectric conversion efficiency of DSSC.

上转换发光材料是一种能够实现低能量光波向高能量光波转换的发光材料。目前基于三重态-三重态湮灭（TTA）机制上转换，由于其上转换效率高、所需的激发光能量低，在太阳光辐射下即可发生上转换，在染料敏化太阳能电池和生物标记等领域具有广泛的应用前景。基于TTA的上转换体系主要由三重态敏化剂和能量受体两部分组成，该领域面临的难题是，此类机制的上转换主要在溶液中发生，很难作为一个分子整体使用，这将大大限制其应用领域，因此如何将该上转换体系中的敏化剂和受体固载化是应用的关键。本项目拟通过选用二氧化钛等无机非金属纳米胶囊包覆敏化剂和能量受体，并对纳米胶囊微环境下的上转换规律进行探索，即与普通溶液环境相比，处于纳米胶囊微环境下的上转换体系中敏化剂与受体之间的能量传递效率以及上转换发光效率的改变。在应用方面主要研究固载后的上转换材料在染料敏化太阳能电池中的应用，旨在提高染料敏化太阳能电池对长波段太阳光的利用。

基于三重态-三重态湮灭（TTA）机制的上转换，由于其上转换效率高、所需的激发光能量低，在太阳光辐射下即可发生上转换，在太阳能电池和生物标记等领域具有广泛的应用前景。基于TTA 的上转换体系主要由三重态敏化剂和能量受体两部分组成，该领域面临的难题是，此类机制的上转换主要在溶液中发生，很难作为一个分子整体使用，这将大大限制其应用领域。本项目主要从三重态敏化剂的设计和TTA上转换体系包覆方法的探索两个方面入手以解决这个难题：在三重态敏化剂方面，设计合成一系列基于BODIPY（氟硼吡咯）的纯有机三重态敏化剂，其中叠氮基修饰的双碘代BODIPY获得了19.5%的上转换效率，通过实验测试结合理论计算探索了光敏剂具有高效三重态效率的机理，这为如何设计高效的三重态敏化剂提供了理论依据；在TTA上转换体系包覆方面我们采用胶束软模板法分别以聚苯乙烯和二氧化钛为包覆层，成功实现了TTA上转换体系的包覆，通过优化条件，二氧化钛纳米胶囊包覆的TTA上转换体系上转换效率高达6.6%，高于文献报道的数值（~3%），进一步推进了TTA机制的上转换材料在在太阳能电池和生物标记等领域的实际应用。