Polyoxometalate-Based Sensitizers for p-Type Dye-Sensitized Solar Cells

光子材料以有趣和有用的方式与光相互作用。它们对许多现有和新兴技术至关重要，如生物成像、光学数据处理、电信和太阳能。该项目将研究一种有前途但很少探索的光子材料的特性，并将其作为提高新兴太阳能电池-p型染料敏化光电阴极（p-DSSC）性能的一种手段进行测试。因此，我们的长期目标是开发低成本、高效率的太阳能设备，这将有助于减少碳排放和对进口化石燃料的依赖。 基于染料敏化n型二氧化钛光阳极的染料敏化太阳能电池（DSSC）有望成为传统半导体光伏（PV）材料（如硅）的低成本替代品。它们在北欧低光条件下运行良好，但其峰值功率转换远远落后于最好的半导体设计，后者结合了联合收割机几种不同的半导体，优化吸收太阳光谱的不同部分。DSSC的性能可以通过类似的方法来改善-串联DSSC，其将通常的染料敏化光电阳极（n-DSSC）与染料敏化光电阴极（p-DSSC）配对。在互补吸收曲线的情况下，n-和p-DSSC在串联DSSC中一起吸收的阳光比单独吸收的阳光多。然而，目前，p-DSSC的效率（创纪录的1.3%）远远不能与n-DSSC的效率（10 - 15%）相匹配。这意味着串联DSSC本身的性能比n-DSSC差，而p-DSSC必须显著改善才能使串联DSSC成为可行的器件。n-DSSC实现了有用的效率，因为光导致染料快速将电子注入n型（电子传输）金属氧化物。电子通过金属氧化物的传输，以及来自氧化还原电解质的电子对染料中形成的“空穴”的填充，比从金属氧化物到染料的复合（电子返回）快得多。p-DSSC以相反的方式工作，将空穴注入p型（空穴传输）金属氧化物中，氧化还原电解质从染料中获取电子。p-DSSC的问题是空穴通过氧化物的传输是缓慢的，并且从染料和电解质的复合是快速的。在本项目中，我们将基于电子接受多金属簇（聚氧乙烯酸盐，POM）与有机基团的连接，合成一类用于p-DSSC的新型染料。通过保持电子远离金属氧化物表面，POM电子受体基团将减缓复合并改善性能。所提出的基于POM的敏化剂具有有利于电荷分离的电子结构，并且预计在稳定性和快速将电子转移到氧化还原电解质的能力方面具有重要的优势-超过目前的纯有机材料。

Photonic materials interact with light in interesting and useful ways. They are vital to many current and emerging technologies, such as biological imaging, optical data processing, telecommunications and solar energy. This project will investigate the properties of a promising, but little explored class of photonic materials and test them as a means to improve the performance of an emerging type of solar cell - the p-type dye sensitized photocathode (p-DSSC). In this way, our long-term goal is to develop low cost, high-efficiency solar energy devices which will help reduce carbon emissions and dependence on imported fossil fuels. Dye-sensitized solar cells (DSSCs), based on a dye-sensitized n-type titanium dioxide photoanode, promise a low-cost alternative to conventional semiconductor photovoltaic (PV) materials like silicon. They function well in northern-European, low-light conditions but their peak power conversion lags far behind that of the best semiconductor designs, which combine several different semiconductors optimized to absorb different portions of the solar spectrum. DSSC performance may be improved through an analogous approach - tandem DSSCs which pair the usual dye-sensitized photoanode (n-DSSC) with a dye-sensitized photocathode (p-DSSC). With complementary absorption profiles, the n- and p-DSSCs absorb more sunlight together in the tandem DSSC than either can alone. Currently, though, the efficiency of the p-DSSC (record 1.3%) is far from matching that of n-DSSCs (10 to 15%). This means that tandem DSSCs perform worse than n-DSSCs by themselves, and p-DSSCs must improve dramatically for the tandem DSSC to become a viable device.Both n- and p-DSSCs depend on efficient charge separation at the interface between a dye and a metal oxide support to generate electricity. n-DSSCs achieve useful efficiencies because light causes the dyes to rapidly inject electrons into an n-type (electron transporting) metal oxide. Transport of electrons through the metal oxide, and filling of "holes" formed in the dyes by electrons from a redox electrolyte, is much faster than recombination (return of electrons) to the dye from the metal oxide. p-DSSCs work in the opposite sense, injecting holes into a p-type (hole transporting) metal oxide, with the redox electrolyte taking electrons from the dyes. The problem for p-DSSCs is that transport of holes through oxides is slow, and recombination from the dye and electrolyte is fast. This leads to low efficiency.In this project, we will synthesize a novel class of dye for the p-DSSC, based on connection of electron accepting multi-metallic clusters (polyoxometalates, POMs) to organic groups. By holding electrons away from the metal oxide surface, the POM electron acceptor groups will slow recombination and improve performance. The proposed POM-based sensitizers have an electronic structure that will favour charge separation, and are expected to have important advantages - in stability and ability to rapidly transfer electrons to the redox electrolyte - over the current purely organic materials.