High-Field, High-Temperature, and Higher Permittivity Polymer Multilayer Dielectrics via Distributed Charge-Trapping Electroactive Organic Crystallites
Abstract
This project tests the hypothesis that dilute electron-donating and electron-accepting crystallites of conjugated organic molecules in dielectric polymers will serve as improved charge traps to increase breakdown field(dielectric strength) for high energy density storage applications. There are multiple precedents for molecular additives doing so in polymer dielectrics, but their use in micro/nano crystallite form has never been reported. Using trapping additives in crystallite form allows more stable interception of undesired charge carriers and a larger total molecule concentration in the dielectric, with average distances between crystallites being larger than the distances between molecules present as unaggregated dispersions. This increases charge trapping capacity while decreasing formation of current pathways that cause catastrophic degradation. Effects of crystallites on improving high-temperature dielectric breakdown strength in a series of polymers along the dielectric constant-bandgap continuum will be determined. We will start with styrene polymers slightly more polarizable than polypropylene and for which preliminary observations have been made. We will then investigate polypropylene as the established low-dielectric constant/high bandgap standard and the higher-dielectric constant/lower bandgap/higher-Tg bisphenol A polycarbonate (PC), poly (ethylene naphthalate) (PEN, a polyester), polyether ether ketone (PEEK) and poly (ether imide) (ULTEM, a bisphenol A-based polyimide) will be used as matrix polymers for higher temperature application. Modifications of these polymers to promote desired crystallite morphologies will be done, based on preliminary observations. Electron donating and accepting molecules that constitute the crystallites will be selected for their trap energy levels relative to transport levels of the dielectric polymers to perform their intended function, and relative to redox potentials of environmental oxygen and water for stability. They will also be tuned for preferred miscibility in dielectric polymers and their spin coating solutions to promote micro/nano crystallization. Crystallite molecule selection will leverage the vast literature and extensive experience of the Katz group in synthesizing and processing such molecules for organic transistor (OFET) applications, especially thienyl oligomers and tetracarboxylic diimides. Molecular assembly strategies for tuning the crystallite size distributions will be developed. The crystallites will be placed in different positions of multilayer films to minimize direct charge injection and maximize effectiveness in trapping incidentally generated charges. Accepted polymer film characterization in capacitor geometries, including frequency-dependent capacitance/tan delta, discharge energy efficiency, unipolar and bipolar P-E loops and statistical breakdown (Weibull) analyses will be performed. Activities of crystallites as charge traps will be compared using pairs of crystallite compositions grown simultaneously in the same dielectric films, using a combination of scanning probe electrostatic measurements and microscopic elemental analysis. Optimization of trapping effectiveness versus resistance to charge injection from electrodes, and the tradeoffs among elevated temperature, dielectric strength, and dielectric constant, will be achieved. A combined breakdown voltage of 10 MV/cm, dielectric constant of 3.5, and operating temperature >200 degrees C for solution-processable polymer dielectrics, with >90% discharge energy efficiency, will be achieved. This combination of performance metrics is aimed to surpass those of biaxially oriented polypropylene (BOPP).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 06, 2023
- Source ID
- N000142312273
Entities
People
- Howard E Katz
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy