Properties and applications of microcrystalline organic thin films

摘要：非技术：随着一些有机电子设备在市场上站稳脚跟，有机电子产品对我们的技术生态系统产生积极影响的能力越来越明显。然而，当今有机电子设备中使用的无序薄膜阻碍了美国在科学和工业上的发展。共轭有机分子单晶的研究对于推动我们理解和测试有机半导体的各种特性的极限至关重要，例如迁移率，激子扩散长度等。尽管这些研究非常有前景，但高度无序的非晶态薄膜目前正在使用和研究应用，因为这些无序薄膜可以重现地形成无针孔薄膜。晶体异质结结合了高激子扩散长度和载流子迁移率，当用于垂直异质结器件时，晶体薄膜可以显着扩展有机电子学的应用领域。该项目将1)实现有机电子器件的重要技术和工业突破，2)加强美国的技术领先地位，并为下一代STEM毕业生（包括女性和代表性不足的群体）做好准备，以从事STEM职业。PI将与公众和学生接触，并特别参与主动学习活动，以建立跨越代沟的榜样。在这个项目中，PI将研究有机半导体薄膜和异质结，其晶体域尺寸高达1毫米，与目前使用的非晶或纳米晶体薄膜相比，非常有序。值得注意的是，这将在保持低表面粗糙度和无针孔覆盖的情况下完成。事实上，有机单晶在无序薄膜方面显示出高度吸引人的特性，这意味着有机半导体比今天的无序薄膜具有更大的前景。这是在电荷和激子传输方面，对有机电子设备的操作至关重要。与无序薄膜相比，晶体中的电荷载流子迁移率高达两个数量级（高达20 Vs . 0.1-1 cm2/Vs），并伴有带输运的证据，而激子扩散长度高达2微米Vs . 5-30纳米。无序薄膜和单晶之间的这些巨大差异被认为来自于晶界和结构的无序。未来应用的两个科学目标是：1)展示大大降低能量损失的高性能晶体异质结太阳能电池；2)揭示了晶界在激子和电荷输运中的作用。

Abstract:Nontechnical: With some organic electronic devices now firmly established in the marketplace, it is becoming clear that organic electronics has the capacity to positively influence our technological ecosystem. However, the disordered films used in today's organic electronic devices hold the U.S. back in science and industry. Studies on single crystals of conjugated organic molecules have been critical in driving our understanding and testing the limits of various properties of organic semiconductors, such as mobility, exciton diffusion length, etc. Despite the very promising implications of such studies, highly disordered amorphous films are currently used and studied for applications, because these disordered films can be reproducibly formed into pinhole free films. Crystalline heterojunctions promise combined high exciton diffusion lengths and carrier mobilities and, when used in vertical heterojunction devices, crystalline films can dramatically expand the application domain of organic electronics. This project will 1) enable important technological and industrial breakthroughs in organic electronic devices, and 2) strengthen technological leadership of the U.S. and prepare the next generation of STEM graduates, including women and underrepresented groups, to follow a STEM career. The PI will engage with the public and students, and is particularly involved in active learning activities to establish role models across generational gaps.In this project, the PI will study organic semiconductor films and heterojunctions with crystal domain sizes of up to 1 mm, very ordered when compared to amorphous or nanocrystalline films employed today. Notably, this will be accomplished while still maintaining a low surface roughness and pinhole free coverage. The fact that organic single crystals reveal highly attractive properties with respect to disordered films means that organic semiconductors hold significantly more promise than what can be realized with the disordered films of today. This is in terms of charge and exciton transport, central to the operation of organic electronic devices. Charge carrier mobility is up to two orders of magnitude more in crystals compared to disordered films (up to 20 vs. 0.1-1 cm2/Vs) along with evidence of band transport, whereas exciton diffusion lengths are up to 2 microns vs. 5-30 nm. These large differences between disordered films and single crystals are thought to source from grain boundaries and structural disorder. Two scientific goals that will allow for future applications are: 1) demonstrate high-performance crystalline heterojunction solar cells with greatly reduced energy losses; 2) unveil the role of grain boundaries on exciton and charge transport.