CAREER: Mechanical Behavior of Flexible Electronic Films

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The objective of this Faculty Early Career Development (CAREER) grant is to improve the understanding of the mechanical behavior of organic (polymeric) semiconductor films. Insight into the relationships between mechanical and electrical properties will provide guidelines to achieve mechanically robust flexible electronics for applications such as wearable electronics and low cost solar energy. Organic semiconductors are particularly promising for flexible electronics due to their relatively compliant nature associated with their molecular structure. Mechanical failure in use, primarily due to repeated flexing, has hindered the commercial adoption of organic films for flexible electronic applications. This award provides support to investigate the impact of molecular structure, film microstructure, and device design on performance variation and failure modes of devices under flexure. Research will also include the role of cyclic bending and environmental factors such as moisture on mechanical stability. This research crosses multiple disciplines including mechanics of materials, materials processing, and semiconductor device physics and will provide a stimulating training environment for students. The education plan includes the development of a certificate program in manufacturing and mechanics of emerging thin film electronics to train future leaders in this emerging field. The research objectives will be addressed through the following interrelated tasks: (i) determining the effect of molecular structure and molecular packing characteristics on the mechanical behavior of conjugated polymer films, (ii) establishing the impact of multi-component polymer blend morphology on electrical and mechanical response, (iii) characterizing interfacial features in heterogeneous films, such that delamination and cohesive failure modes can be mitigated, (iv) determining the features that drive performance variation and degradation under sub-critical mechanical loading under various loading protocols and environmental conditions, and (v) developing standardized mechanical test methods for flexible electronics. A focus will be on organic thin film transistors and organic photovoltaic devices that capture unique and fundamental operating characteristics so that the research products may be extrapolated across broad device platforms. Mechanical properties of interest include film stiffness, ductility, fracture strength, and cohesive and adhesive fracture energy that will be measured using four-point bending, double cantilever beam testing, and buckling metrology methods. The intellectual merit of the proposed research is found in the development of a fundamental framework relating polymer semiconductor structure to mechanical and optoelectronic characteristics enabling mechanically robust layered organic and organic-inorganic systems.