Degradation of Organic Semiconductors: Functional and Mechanistic Descriptions from Macroscale to Nanoscale

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Non-technical AbstractOrganic materials capable of conducting electricity – termed organic semiconductors - are used in many emerging, next-generation technologies including organic light emitting diodes, organic-based solar cells, thermoelectrics, and chemical sensors. The benefits of organic semiconductors include lower cost, improved performance, flexibility, transparency, and lower environmental impact, but concerns persist about their long-term stability and lifetime. The focus of this project – degradation of functional properties – is a fundamental materials chemistry challenge that must be overcome to progress the field of organic electronic devices. With support from the Solid State and Materials Chemistry Program in the Division of Materials Research, the researchers advance the understanding of materials and chemical degradation pathways at a fundamental level, which will eventually facilitate development of new materials design criteria. Hence, this work provides important new insights that drive the creation of new molecules and polymers and contributes to long-term stability and technological relevance of the United States in printable electronic materials and devices. Support from the Solid State and Materials Chemistry program also advances the development of unique capabilities for in operando characterization of organic semiconductor systems that are readily translatable to other active materials chemistry applications and enable identification of the chemical pathways that accompany degradation in materials at length scales from microns to nanometers. This inherently interdisciplinary effort between chemists and engineers is a platform for interdisciplinary training for the graduate and undergraduate students engaged in research. New interdisciplinary graduate- and undergraduate-level laboratory experiences are developed through this effort, and the properties of this important class of materials are explored in K-to-gray public outreach efforts. Technical AbstractPush-pull or donor-acceptor-type molecular and polymeric architectures have become the dominant class of active materials in organic electronics with performance metrics superior to earlier molecular designs. However, little attention has been devoted to understanding long-term stability. This fundamental effort directly examines and compares chemical structure, electronic structure, and charge transport characteristics of complex push-pull organic semiconductor (OSC) architectures as a function of molecular building block composition to understand the chemical, photochemical and photophysical mechanistic origins and functional impacts of degradation. The secondary impact of this effort is formulation of new design criteria for more robust OSCs. This work builds on successful efforts through a previous NSF DMR award (DMR-1608289) in which a collaborative, multi-disciplinary investigation of organic semiconductor degradation was initiated. Previously-demonstrated approaches include surveying functional characteristics under conditions that lead to degradation, coupled with detailed spectroscopic analysis methodologies to understand mechanistic molecular origins. In this project, capabilities are expanded to include local physical structure with site-specific molecular and electronic imaging capabilities, which enables investigation of fundamental materials chemistry across length scales ranging from microns to nanometers. In addition to improving materials design for emerging technologies, the broader impacts of this work manifests through numerous education and outreach activities This collaboration between chemists and engineers is a platform for interdisciplinary training for the graduate and undergraduate students engaged in research. New interdisciplinary graduate- and undergraduate-level laboratory experiences are developed through this effort, and the properties and uses of this important class of materials are explained and explored in K-to-gray outreach efforts.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.