ARC Centre of Excellence for Electromaterials Science and Intelligent Polymer Research Institute, AIIM Facility, Innovation Campus, University of Wollongong, Wollongong, NSW 2500, Australia.
Chem Commun (Camb). 2012 May 4;48(35):4145-62. doi: 10.1039/c2cc30677h. Epub 2012 Mar 23.
Porphyrin molecules offer immense potential as the light harvesting component of dye-sensitised nanocrystalline TiO(2) solar cells. Synthetic porphyrin dyes were amongst the first dyes trialled for sensitisation of inorganic semiconducting oxides. Today, they exhibit the best performance reported for dye-sensitised solar cells. Accompanying the significant performance improvement over the last two decades is a much improved understanding of efficiency-determining fundamental electron transfer steps, from charge photogeneration to recombination. In this feature article we highlight our recent discoveries of the influence of porphyrin molecule structure on efficiency determining electron transfer kinetics and device performance by systematically changing the molecular structure and observing electron injection and recombination kinetics using time-resolved optical and electrical probes. Despite our observation of ultrafast charge injection for all porphyrin dyes studied by transient absorption spectroscopy, the injection yield estimated using an internal standard remains below 100% and depends strongly on the molecular structure. The observed discrepancy between kinetic competition and the injection yield is attributed to non-injecting dyes, probably arising due to inhomogeneity. A very interesting sub-ns (0.5 ns to 100 ns) charge recombination channel between photo-injected electrons and porphyrin cations is observed, which is found to be more prominent in free-base porphyrin dyes with a conjugated linker. Charge recombination between the acceptor species in the redox containing electrolyte and injected electrons is shown to be an important limitation of most porphyrin-sensitised solar cells, accelerated by the presence of porphyrin molecules at the TiO(2)-electrolyte interface. This recombination reaction is strongly dependent on the porphyrin molecular structure. Bulky substituents, using a porphyrin dimer instead of a porphyrin monomer, a light soaking treatment of freshly prepared films and co-sensitization of TiO(2) with multiple dyes are shown to be successful strategies to improve electron lifetime. Finally, new developments unique to porphyrin dye-sensitised solar cells, including performance enhancements from a light exposure treatment of a zinc porphyrin dye, a significant performance improvement observed after co-sensitisation of TiO(2) with free-base and zinc porphyrin dyes and the use of porphyrin dimers with increased light harvesting in thin-film TiO(2) solar cells are described.
卟啉分子作为染料敏化纳米晶 TiO(2)太阳能电池的光捕获组件具有巨大的潜力。合成卟啉染料是最早用于敏化无机半导体氧化物的染料之一。如今，它们表现出了染料敏化太阳能电池中报道的最佳性能。在过去的二十年中，伴随着性能的显著提高，人们对决定效率的基本电子转移步骤（从电荷光生成到复合）有了更好的理解。在这篇专题文章中，我们通过系统地改变分子结构并使用时间分辨光学和电学探针观察电子注入和复合动力学，突出了我们最近发现的卟啉分子结构对效率决定的电子转移动力学和器件性能的影响。尽管我们通过瞬态吸收光谱观察到所有研究的卟啉染料都具有超快的电荷注入，但使用内部标准估计的注入产率仍低于 100%，并且强烈依赖于分子结构。观察到动力学竞争和注入产率之间的差异归因于非注入染料，可能是由于不均匀性引起的。观察到一个非常有趣的亚纳秒（0.5 ns 至 100 ns）电子注入和卟啉阳离子之间的电荷复合通道，在具有共轭连接体的自由碱基卟啉染料中发现该通道更为突出。在含有氧化还原物质的电解质中，接受体物种与注入电子之间的电荷复合被证明是大多数卟啉敏化太阳能电池的一个重要限制，并且由于 TiO(2)-电解质界面处卟啉分子的存在而加速了该反应。这种复合反应强烈依赖于卟啉分子结构。使用较大的取代基、卟啉二聚体而不是卟啉单体、对新制备的薄膜进行光浸泡处理以及用多种染料共敏化 TiO(2)，被证明是提高电子寿命的有效策略。最后，还描述了卟啉染料敏化太阳能电池的一些新发展，包括锌卟啉染料经过光暴露处理后的性能增强、在 TiO(2)与自由碱基和锌卟啉染料共敏化后观察到的显著性能提高以及在薄膜 TiO(2)太阳能电池中使用具有增加的光捕获能力的卟啉二聚体。
