Atomically Thin Photovoltaics

原子薄太阳能电池：可持续发展是能源部门保护地球的主要理念，包括英国在内的许多国家都设定了到2050年实现“净零”碳排放的目标。可再生能源是指不直接排放碳基温室气体的能源生产方式，包括：风能、水力发电和太阳能。利用太阳能电池板可以在不给地球带来直接成本的情况下获取太阳能。这是一种将太阳光转化为电能的装置。太阳能电池，也称为光伏（PV）电池，是组成太阳能电池板的单元。光伏电池的效率量化了它将光能转化为电能的效率——目前基于硅（Si）的商业太阳能电池板的效率达到25%左右，这是行业标准。探索硅的替代材料，以便它们可以用于硅的性质可能限制基于它们的设备的应用。例如，传统的光伏电池在变薄的过程中效率会下降，通常不会降低到0.1-0.4mm以下。这些都是由硅和金属制成的，使得它们很重，不灵活，而且肉眼可见，限制了它们的应用。在这个项目中研究的替代材料可以缩小到只有几个原子的厚度（因此被称为原子薄），使它们变得更轻，更灵活，肉眼看不见，比硅器件薄10万倍。想象一下，将光伏应用于服装、手机或建筑涂层等新领域。不幸的是，从原子薄的光伏电池中获得的最佳效率要比硅电池差5-10%，但如果它们可以被放置在新的位置，这可能不是可行性的最终因素。光伏电池只能在太阳光照下工作，而由于地球上的时间或天气，太阳能照明并不总是可用的，因此，它们一直在探索在地球外的使用，以绕过这一点。空间应用的一个重要考虑因素是航天器发射成本，主要取决于质量和体积。由于原子薄材料的质量和体积小，它有几个主要的优点。它们已被证明能够承受太空中的强烈辐射，而且它们的灵活性将允许在航天器上发电。这可以补充航天器现有的太阳能电池板，而不会增加其体积。这可能导致在太空中使用的高度适用性。目的：本项目旨在通过高反射镜的新应用来增加光子吸收，优化材料选择和电池尺寸，提高原子薄PV电池的效率。这些装置用于聚光太阳能电池的可行性将被研究，这将带来另一个新颖的元素。在这些电池中，光的强度通过聚焦在电池上来增加，以达到更高的效率。这种增加的强度可能会损坏细胞，类似于通过放大镜的光引起的火灾，因此必须表明它们没有损坏，以证明它们的适用性。方法：光伏电池将通过分离过渡金属二硫化物和黑磷等材料层来生产。这可以做到，直到它们只有一个原子层厚，因为这些材料的层只是弱结合。不同的材料层可以随意堆叠在一起，就像堆叠乐高一样，产生具有特定属性的新材料。然后，这些装置可以用原子力显微镜来表征它们的厚度，用拉曼光谱来表征它们的化学成分。它们的效率是通过测量当设备被太阳能光模拟器照射时产生的电流来确定的，然而，当设备上的特定位置被照射时，激光可以用来确定响应。

Atomically Thin Solar Cells: Sustainability is a predominant idea in the energy sector to protect the planet going forward, with many countries including the U.K. setting "net-zero" carbon emission targets by 2050. Renewables are methods of energy generation which do not directly emit carbon-based greenhouse gases, these include: wind, hydropower, and solar power. The sun's energy can be harvested at no direct cost to the planet using a solar panel. This is a device which converts the energy from the sun's light to electricity. Solar cells, alternatively called photovoltaic (PV) cells are the units which make up solar panels. The efficiency of a PV cell quantifies how effective it converts energy from the light to electricity - current commercial solar panels based on silicon (Si) achieve ~25% efficiency, which is the industry's standard. Alternative materials to Si are explored so that they can be used where silicon's properties may restrict the applications of devices based upon them. For example, traditional PV cells suffer decreasing efficiency as they become thinner, typically not reduced below 0.1-0.4mm. These are made from Si and metals, rendering them heavy, non-flexible, and visible to the eye, restricting their applications. The alternative materials investigated in this project may be scaled down to just a few atoms in thickness (hence are called atomically thin), rendering them light, flexible, invisible to the eye and ~100,000 times thinner than Si devices. Imagine placing PV in new places like clothing, your phone, or coating buildings. Unfortunately, the best achieved efficiencies from atomically thin PV cells are comparably worse than Si at ~5-10%, but this may not be the ultimate factor for viability if they can be placed in new locations. PV cells only function under solar illumination which is not always available due to time of day or weather on Earth, therefore, they have always been explored for extra-terrestrial use to circumvent this. An important consideration for space applications is spacecraft launch costs, mainly depending on mass and volume. Atomically thin materials have several main advantages here due to their low mass and volume. They have been proven to withstand the harsh radiation found in space, and their flexibility would allow electricity generation on the body of the spacecraft. This could supplement the craft's existing solar panels, without increasing its volume. This may lead to high suitability for use in space. Aims: This project aims to increase the efficiency of atomically thin PV cells through the novel application of highly reflective mirrors to increase photon absorption, optimum material choices, and sizing of the cells. The feasibility of these devices for concentrator solar cells will be investigated which will bring another element of novelty. These are cells where the intensity of light is increased by focusing it upon the cell to achieve higher efficiency. This increased intensity may damage the cells, akin to fire starting due to light through a magnifying glass, therefore it must be shown that they are undamaged for to demonstrate their suitability. Methodology: The PV cells will be produced by cleaving apart the layers of materials known as transition metal dichalcogenides, and black phosphorus. This can be done until they are only one atomic layer thick because these materials' layers are only bound weakly. Layers of different materials can then be stacked on each other however you choose, analogous to how one stacks Lego, to produce new materials with specific properties. These devices can then have their thickness characterised by atomic force microscopy, and their chemical composition by Raman spectroscopy. Their efficiency is determined by measuring electrical current generated when the devices are illuminated by a solar light simulator, however a laser can be used to determine the response when specific positions on the device are illuminated.