Understanding mechanical behavior and reliability of organic electronic materials
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Introduction Stretchable and flexible electronic devices require both structural and active electronic materials that are compliant and able to withstand mechanical deformation without damage. Often, it is desirable that the active electronic materials also act as structural elements—resistant to damage processes such as buckling and fracture without the need for supporting structures. Engineering reliable, flexible, and stretchable devices requires characterizing thermomechanical properties, including strength, stiffness, and ductility of the constituent materials. In addition, the fracture energy, Gc (J/m2), quantifies the adhesion of interfaces or cohesion of constituent layers and is one of the most fundamental metrics of reliability. Organic electronic materials have Gc values that are often much lower than those of conventional engineering materials, and strategies for improvements are required for thermomechanically reliable technologies.1 Characterizing salient mechanical properties of organic charge-transport layers and semiconducting materials used in
organic logic devices, displays, and organic or even recent perovskite photovoltaic solar cells have provided essential lessons for the development of mechanically reliable, electronically active, and flexible technologies.
Mechanical properties important for reliability Adhesive or cohesive failure may result from residual or applied mechanical stresses introduced during device processing, handling, packaging, and operation.2,3 Mechanical stresses provide the driving force for damage and can vary markedly with thermal cycling or device application, particularly for stretchable and wearable devices subject to significant deformation from physiological motion. The driving force for failure processes like film cracking or interface debonding can be quantified in terms of the strain-energy release rate, G (J/m2), which is a function of the previously discussed mechanical stresses. Fracture occurs when G ≥ Gc. Gc values of representative organic electronic materials can be accurately measured and recently characterized ranges
Jae-Han Kim, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, South Korea; [email protected] Inhwa Lee, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, South Korea; [email protected] Taek-Soo Kim, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, South Korea; [email protected] Nicholas Rolston, Department of Applied Physics, Stanford University, USA; [email protected] Brian L. Watson, Department of Materials Science and Engineering, Stanford University, USA; [email protected] Reinhold H. Dauskardt, Department of Materials Science and Engineering, Stanford University, USA; [email protected] doi:10.1557/mrs.2017.3
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