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.
