Properties and applications of microcrystalline organic thin films

摘要：非技术：随着一些有机电子设备现在市场上站稳脚跟，有机电子有能力积极影响我们的技术生态系统，这一点变得越来越明显。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方面的发展。对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各种性质的极限，如迁移率、激子扩散长度等至关重要。尽管这些研究具有非常有希望的意义，但目前高度无序的非晶薄膜被用于应用和研究，因为这些无序薄膜可以重复形成无针孔的薄膜。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，晶体薄膜可以极大地扩展有机电子的应用领域。该项目将1)在有机电子设备方面实现重要的技术和工业突破，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)从事STEM职业做好准备。PI将与公众和学生接触，并特别参与积极的学习活动，以建立跨越代沟的榜样。在这个项目中，PI将研究晶区尺寸高达1毫米的有机半导体薄膜和异质结，与目前使用的非晶态或纳米晶膜相比，这是非常有序的。值得注意的是，这将在保持低表面粗糙度和无针孔覆盖的同时实现。有机单晶相对于无序薄膜显示出极具吸引力的性质，这一事实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，这是有机电子设备运行的核心。与无序薄膜相比，晶体中的载流子迁移率高达两个数量级(高达20比0.1-1 cm2/vs)，并有能带传输的证据，而激子扩散长度高达2微米比5-30 nm。无序薄膜和单晶之间的巨大差异被认为源于晶界和结构无序。未来应用的两个科学目标是：1)展示高性能晶体异质结太阳能电池，大大减少能量损失；2)揭示晶界对激子和电荷传输的作用。

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.