Improved materials stability and morphology in organic photovoltaic cells

塑料太阳能电池使用有机或聚合物半导体材料，而不是更传统的材料，如硅或碲化镉。 塑料太阳能电池，也被称为有机光伏（OPV），在过去十年中大幅增加，从几个百分点到超过12%，使其性能与更成熟的太阳能电池技术竞争。塑料太阳能电池有可能大大降低太阳能发电的价格，但目前它们的寿命相对较短，低成本生产尚未得到充分证明。短寿命（与20-25年的行业标准相比）是由于使用不稳定的反应性材料，低成本生产需要廉价的半导体材料和制造技术。 该提案旨在通过以下方式解决这些问题：1）设计OPV电气特性的科学模型，以提高我们对OPV操作和局限性的理解。该模型将指导我们在其他两项计划中的材料和器件结构选择，2）开发具有高效率和长期稳定性的太阳能电池的新分子，3）开发使用塑料半导体层压膜的新的低成本制造方法。为了指导我们选择材料和结构，我们必须从第一原理物理学的角度理解OPV技术的操作和基本限制。 多年来，传统太阳能电池的这些问题已经得到了很好的理解，但OPV电池的操作要复杂得多，需要新的模型。 了解这些限制将使我们能够集中精力研究太阳能电池的性能，从而实现最大的改进。每一个高效的OPV电池都使用富勒烯衍生的分子作为“电子受体”。 虽然在早期的器件中使用了一些非富勒烯，但由于其出色的电子传输和高电子亲和力，富勒烯的成功使其应用广泛。 不幸的是，富勒烯不适合成功的商业OPV技术有几个原因。 首先，富勒烯在氧气和光的存在下非常不稳定。 由此产生的光氧化大大降低了它们的电性能，并降低了太阳能电池的效率。 其次，富勒烯需要大量的能量来生产，可持续的太阳能电池技术应该需要尽可能少的能量，以最大限度地减少能量回收时间。 最后，富勒烯对光的吸收非常差，所以我们必须依靠电子供体材料来收集太阳光子。 通过开发非富勒烯受体，我们的目标是生产稳定、更可持续、更高效的塑料太阳能电池。生产OPV电池的最低成本方法是基于溶液的方法，其中使用含有塑料半导体的“油墨”来涂覆电池。 不幸的是，这限制了可以生产的电池的复杂性（以及因此的效率），因为试图在已经涂布的膜的顶部涂布第二种油墨通常会溶解第一种油墨。 我们建议开发新的制造技术，其中复杂的，高效的，多层电池是通过层压半导体薄膜，而不是油墨涂层。 在这个过程中，油墨被用来覆盖一个临时的表面，称为邮票。 油墨干燥，并且膜被转移或层压到包含先前沉积的膜的第二表面上。 这种干转移工艺避免了溶解早期层的问题，并且可以形成复杂的多层膜。 该技术将使高效多层OPV电池的低成本生产成为可能。

Plastic solar cells use organic or polymer semiconductor materials instead of more traditional materials, such as silicon or cadmium telluride. Efficiencies of plastic solar cells, also known as organic photovoltaics (OPV), have increased drastically over the last decade, from a few percent to over 12%, making their performance competitive with more established solar cell technologies. Plastic solar cells have the potential to significantly reduce the price of solar-generated electricity, but they currently suffer from relatively short lifetimes and low-cost production has yet to be fully demonstrated. The short lifetimes (compared to the industry standard of 20-25 years) are due to the use of unstable, reactive materials, and low-cost production would require both inexpensive semiconductor materials and fabrication techniques. This proposal aims to address these issues by 1) designing a scientific model of OPV electrical characteristics to improve our understanding of the operation and limitations of OPV. This model will guide our materials and device structure choices in the other two initiatives, 2) developing new molecules for solar cells that exhibit high efficiencies and long-term stability, and 3) developing new low-cost manufacturing methods using laminated films of plastic semiconductors.**To guide our choices of materials and structures, it is important that we understand, from a first-principles physics point of view, the operation and fundamental limitations of OPV technology. These issues have been well-understood for traditional solar cells for many years, but the operation of OPV cells is significantly more complicated, and new models are required. Understanding these limitations will allow us to focus our efforts on properties of the solar cells where the most improvement can be realized.**Every high-efficiency OPV cell uses a fullerene-derived molecule as the "electron acceptor". Although a few non-fullerenes were used in early devices, the success of fullerenes due to their excellent electron transport, and high electron affinity, has made their use wide-spread. Unfortunately, there are several reasons why fullerenes are not suitable for a successful commercial OPV technology. First, fullerenes are very unstable in the presence of oxygen and light. The resulting photo-oxidation drastically diminishes their electrical properties, and degrades solar cell efficiency. Second, fullerenes require a lot of energy to produce, and a sustainable solar cell technology should require as little energy as possible, to minimize the energy payback time. Finally, fullerenes absorb light very poorly, so we must rely on the electron donor material to harvest the solar photons. By developing non-fullerene acceptors, we aim to produce stable, more sustainable, and more efficient plastic solar cells.**The lowest cost methods for producing OPV cells are solution-based, where an "ink" containing the plastic semiconductor is used to coat the cell. Unfortunately, this limits the complexity (and therefore efficiency) of cells that can be produced, as trying to coat a second ink on top of an already-coated film will typically dissolve the first. We propose to develop new fabrication techniques, where complex, efficient, multilayer cells are produced by laminating semiconductor films, rather than ink-coating. In this procedure, the ink is used to coat a temporary surface called a stamp. The ink dries, and the film is transferred, or laminated, onto a second surface that contains previously deposited films. This dry-transfer process avoids the problems of dissolving earlier layers, and complex multilayer films can be formed. This technology will enable low-cost production of efficient multilayer OPV cells.