Long-Range Charge and Energy Transfer at Heterojunctions for Photovoltaics Beyond the Shockley-Queisser Limit

开发高效、低成本的可再生能源是当今最紧迫的研究挑战之一。这一领域的两项有前途的技术是光伏发电和太阳能燃料发电系统。光伏发电通过吸收阳光产生电荷，然后在外部电路中收集。太阳能燃料系统的工作原理是吸收阳光，然后利用产生的电荷驱动氧化还原化学反应，从现成的原料中生产化学燃料，例如分解水产生氢，这是一种强大的燃料。但目前这两种技术的成本效率比都过高。为了将这些技术的价格降低到与化石燃料相当的水平，这些系统利用太阳能的方式需要取得根本性的突破。该项目旨在通过建立对有机半导体量子力学过程的最新见解来解决这一挑战，以提高当前和未来光伏系统的效率，并为高效太阳能燃料发电系统制定新的设计规则。在许多光伏和太阳能燃料系统的核心是有机和无机半导体之间的界面。这些界面的作用，被称为异质结，是分开相反的电荷，空穴和电子，从彼此，并防止它们的重新组合。我们将利用超快激光光谱学的最新突破来研究这些界面，并开发有效分离电荷的新型结构。PV中最大的能量损失是一个被称为热化的过程。这指的是这样一个事实，即吸收高能光子产生一个电子-空穴对，就像吸收低能光子一样。在带隙以上的高能光子的额外能量以热量的形式损失掉。这个问题影响着当今所有商业部署的光伏发电，长期以来一直被认为是根本性的损失。事实上，它导致了所谓的肖克利-奎瑟效率极限，即带隙1.1eV的理想PV为33%。在这里，我们将在有机半导体中使用一种独特的量子力学过程，称为单线态激子裂变，来克服这种损失。当光子被吸收时，单线态裂变允许在某些有机材料中产生两个电子-空穴对。我们将设计新的方法，通过这些电子-空穴对可以在有机/无机界面上收获，从而提高效率。我们将利用这一过程开发的方法和结构将与当前和未来的光伏技术兼容，使它们能够克服Shockley-Queisser对效率的限制。这将大大提高光伏发电的效率，并有助于实现其大规模部署。

The development of high-efficiency low-cost renewable energy sources is one of the most pressing research challenges today. Two promising technologies in this area are photovoltaics (PV) and Solar Fuel generation systems. PV work by absorbing sunlight to generate electrical charges that are then collected in an external circuit. Solar Fuel systems work by absorbing sunlight and then using the charges produced to drive redox chemistry to produce chemical fuels from readily available starting materials, for example splitting water to produce H2, which is a powerful fuel. But the cost to efficiency ratio of both these technologies is too high currently. In order to drive the price of these technologies down to match fossil fuels, fundamental breakthroughs are required in the way these systems harness solar energy. This project seeks to tackle this challenge by building on recent insights into quantum mechanical processes in organic semiconductors to improve the efficiency both of current and future PV systems as well as put in place new design ruled for high-efficiency solar fuel generation systems.At the heart of many kinds of PV and Solar Fuel systems are interfaces between organic and inorganic semiconductors. The role of these interfaces, known as heterojunctions, is to separate opposite charges, hole and electrons, from each other and prevent their recombination. We will use the latest breakthroughs in ultrafast laser spectroscopy to study these interfaces and develop novel structure that efficiently separate charges. The biggest energy loss in PV is a process known as thermalization. This refers to the fact that the absorption of a high-energy photon generates one electron-hole pair just as the absorption of a low-energy photon does. The extra energy of high-energy photons above the bandgap is lost as heat. This problem affects all commercially deployed PV today and has long been considered a fundamental loss. Indeed it leads to what is known as the Shockley-Queisser limit on efficiency, which is 33% for an idea PV of bandgap 1.1eV. Here we will use a unique quantum mechanical process in organic semiconductors called Singlet Exciton Fission, to overcome this loss. Singlet Fission allows two electron-hole pairs to be generated in certain organic materials when a photon is absorbed. We will design new ways by which these electron-hole pairs can be harvested at the organic/inorganic interface, leading to improved efficiencies. The methods and structures we will develop using this process would be compatible both with current and future PV technologies, allowing them to over come the Shockley-Queisser limit on efficiency. This could dramatically improve the efficiency of PV and help bring about their wide scale deployment.