The Impact of Mechanical Stress and Strains on Organic Semiconductor Thin Films for Flexible Electronic Applications

有机半导体作为生物和化学传感器以及可穿戴电子产品中的活性成分越来越多地被研究，这将刺激对保持我们的繁荣和全球技术领先地位至关重要的新技术。这些应用要求有源部件具有坚固可靠的性能，通常在机械变形的情况下。以往对有机半导体的研究主要集中在其静电性质上。虽然这些研究为下一代材料的设计和合成奠定了基础，但了解这些有机半导体在机械应力和应变下的表现对于改善和控制其在使用过程中与器件相关的性能至关重要。几个重要的应用领域，如柔性，可穿戴传感器和电子产品，要求设备在机械弯曲下运行，并且它们的组成部分具有机械顺应性。本研究评估了机械变形对结构异质有机半导体薄膜电学性质的影响。这项研究将提供一个更好的理解，在这些电活性薄膜导致的方法，以克服减少或消除故障的柔性电子设备，始终经历机械变形的故障模式。通过对薄膜缺陷结构的详细分析，可以提高器件在机械弯曲和负载下的可靠性。本文研究的控制和改善缺陷结构的工艺方法将有助于为柔性有机电子器件的快速发展和大规模应用铺平道路。该项目位于化学，材料科学和几个工程学科的接口，对跨学科团队的需求将汇集不同背景和专业知识的参与者，并对现代工程研究和教育产生积极影响。柔性有机电子产品通常需要薄膜形式的电活性元件。这些有机半导体薄膜是分层结构的，具有跨越纳米到毫米长度尺度的特征，如构象和填充多晶型物、优先分子取向和边界缺陷的存在。这项工作的核心是阐明机械应力和应变如何影响这种薄膜的电性能，在这种结构的异质性的存在下。无定形有机半导体薄膜的沉积后处理将允许这些结构特征的规范和隔离，这将使得能够评估它们对宏观机械性能的贡献，并且因此，它们响应于循环机械变形的电性能。与电化学响应的非晶薄膜的一个极端，和单晶对应物的另一个比较，将阐明边界缺陷和其他结构异质性在机械变形过程中影响电荷输运的作用。该奖项将从表现出优异静电性能的有机半导体开始，为加工提供设计规则，使其薄膜形式可以变形，而不会对电气性能产生不利影响。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Organic semiconductors are increasingly researched as active components in biological and chemical sensors, and wearable electronics which will spur new technologies essential for maintaining our prosperity and global technological leadership. These applications demand robust and reliable performance of the active components, often under mechanical deformation. The majority of previous studies on organic semiconductors have focused their static electrical properties. While such studies form the basis for the design and synthesis of next-generation materials, understanding how such organic semiconductors perform under mechanical stress and strain is critical to improving and controlling their device-related performance during use. Several important application areas, such as flexible, wearable sensors and electronics, require that the devices perform under mechanical flexure and their component parts possess mechanical compliance. This research assesses the effect of mechanical deformation on the electrical properties of structurally heterogeneous organic semiconductor thin films. This study will provide a better understanding of failure modes in these electrically active thin films leading to methods to overcome reduce or eliminate failure in flexible electronic devices that consistently undergo mechanical deformation. The improved reliability of devices under mechanical flexure and load can be achieved through a detailed analysis of the film defect structure. Processing means studied here to control and improve the defect structure will help pave the way for the rapid development and wide-scale deployment of flexible organic electronic devices. This project sits at the interface of chemistry, materials science and several engineering disciplines and the need for an interdisciplinary team will bring together participants of diverse background and expertise, and positively impact modern engineering research and education. Flexible organic electronics often call for electrically-active components in thin-film formats. These organic semiconductor thin films are hierarchically structured, with features, like conformational and packing polymorphs, preferential molecular orientation and the presence of boundary defects, that span nanometric to millimetric length scales. Central to this work is the elucidation of how mechanical stress and strains affect the electrical properties of such thin films in the presence of such structural heterogeneities. Post-deposition processing of amorphous organic semiconductor thin films will allow specification and isolation of these structural features, which will enable assessment of their contributions to the macroscopic mechanical properties, and accordingly, their electrical properties in response to cyclic mechanical deformation. Comparison with the electrochemical response of amorphous thin films on the one extreme, and single-crystal counterparts on the other, will shed light on the role boundary defects and other structural heterogeneities play in impacting charge transport during mechanical deformation. Starting with organic semiconductors that exhibit excellent static electrical properties, this effort will provide design rules for processing so their thin-film formats can be deformed without deleteriously impacting electrical properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.