431586 Dual Conduction Polymers for Energy Conversion and Storage

Sunday, November 8, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Bhooshan C. Popere, Chemical Engineering & Materials, University of California Santa Barbara, Santa Barbara, CA and Rachel Segalman, Departments of Materials and Chemical Engineering, UCSB, Santa Barbara, CA

Organic materials that transport electrons, ions or both are promising candidates for alternative sources of energy. The vast potential of available molecular design principles enables a deeper understanding of how structure at the molecular and mesoscopic length scales affects the macroscopic properties of these functional materials. Despite the recent meteoric progress in the development of high efficiency materials for electron (charge) transport, in general, the fundamental mesoscopic-level understanding of such materials remains somewhat elusive. Drawing on my understanding from physical organic chemistry, polymer physics, self-assembly and transport phenomena in condensed matter, my research has been primarily focused on developing molecular strategies to gain a deeper insight into the structure-property relationships of such functional materials.

During my doctoral research at UMass Amherst (with Prof. Sankaran ‘Thai’ Thayumanavan), I developed a novel class of pi-conjugated polymeric materials, based on the BODIPY core, inspired by optoelectronic applications. These materials possess panchromatic absorption in the visible and near-IR region of the electromagnetic spectrum making them strong light absorbers in photovoltaic devices. Rational molecular design guided by density functional theory calculations enabled us to develop materials with independently tunable frontier molecular orbital energy levels, while retaining the panchromatic absorption and high charge carrier mobility – a highly desirable feature not commonly observed for pi-conjugated polymers. As a postdoc with Prof. Rachel Segalman at UCSB, I am investigating a new set of materials based on polymerized ionic liquids (PILs)viaDielectric Relaxation Spectroscopy with the aim of understanding the fundamental dielectric properties of these systems. An attractive feature of such polymeric materials is their ability to form electrical double layers upon polarization at the interface with an electrode. The large electric fields due to the small electrical double layer (EDL) thickness results in unusually large areal capacitance values in comparison with conventional organic materials. This makes PILs attractive candidates as high k dielectric materials for low-voltage operable field effect transistors (FETs). Our preliminary experiments with using these PILs as gate dielectrics in organic FETs indeed suggest a dependence of operational threshold voltage on the specific capacitance determined at low frequencies. Specifically, for conventional organic semiconducting polymers like P3HT and PBTTT, the threshold voltages with our PILs as gate dielectrics are less than 1V, indicating a true electrolyte gating mechanism.

In the future, my research will focus on understanding the molecular and mesoscopic underpinnings of the next generation of charge transporting materials. Dual-conduction polymeric systems that simultaneously transport ions and electrons are of great interest both, from a fundamental perspective, and as promising materials for energy storage and conversion, electromechanical actuators and biomimetic systems, amongst many others. However, understanding the physics of charge transport through pi-conjugated polymers in the electrochemical milieu is non-trivial. My approach will be based on rational molecular design, guided by theory and simulations to systematically decouple the dynamics of charge transport in these mixed conducting systems.

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