475884 Functional Polymers for Energy Generation and Storage: Donor-Acceptor Block Copolymers for Photovoltaics and Functional Polyimides for Dielectric Materials

Sunday, November 13, 2016
Continental 4 & 5 (Hilton San Francisco Union Square)
Youngmin Lee, Chemical Engineering, The Pennsylvania State University, University Park, PA

Research Interests:

My research program will develop conjugated block copolymers for power generation and polymer dielectrics for energy storage. We will leverage expertise in polymer and organic chemistry as well as advanced characterization techniques, such as resonant soft X-ray scattering (RSOXS) and energy filtered TEM (EF-TEM). Our unique set of skills are crucial to develop new classes of materials that can serve as (1) model platforms for fundamental studies of optoelectronic and dielectric properties and (2) for demonstrations of breakthrough performance in device applications, furthermore, investigate fundamental structure-property relationship.

Wearable electronics utilized in health care, military, and communication applications require the development of a portable electrical power source. Flexible and light-weight organic photovoltaics are one of the most promising solutions, but challenges remain in performance and stability. My approach will develop a new class of active layer materials capable of exceeding the performance of state-of-the-art blend organic solar cells with improved stability. Donor-acceptor fully conjugated block copolymers (D-A BCPs) will be synthesized as single active layer materials, and their morphologies and solar cell performances will be investigated. Current synthetic approaches, including step-growth polymerization, leads to a mixture of products such as unreacted homopolymers, diblock and triblock copolymers. A focus of my group will be on developing polymerization strategies based on chain-growth mechanisms to prepare well-defined architectures and low dispersities. These well-defined D-A BCPs are expected to enable finer control of the microstructure. In organic electronics, donor/acceptor interfaces are crucial to overall performance, and block copolymers provide a unique approach to control such interfaces. D/A interfaces will be modified with a single bridge unit between donor and acceptor blocks. Furthermore, new chemical structures will be explored for the development of high performance D-A BCPs. Proposed chemical structures for new D-A BCPs are based on thieno-thiophene and cyclopentadithiophene donor blocks with naphthalene diimide acceptor blocks.

Polymeric dielectric materials suitable for electrical energy storage applications are promising because of the potential for flexible, lightweight, photo-patternable, scalable and robust properties compared to ceramic counterparts. But, polymeric dielectric materials have limited impact in various applications, such as hybrid and electric vehicles and aerospace power electronics, due to limited working temperatures. My approach will develop functional polymers to demonstrate improved dielectric properties for high temperature and high electric field applications. Two new diamine monomers of polyimide will be prepared associated with methyl sulfonyl and semi-fluoro alkyl groups. Methyl sulfonyl group is known as one of the strongest polar groups and is expected to enhance the dielectric constant. Semi-fluoro alkyl groups are expected to increase the break-down strength and provide stability in humid environments. A key strategy will be to prepare random copolymers consisting of diamine monomers with both methyl sulfonyl and semi-fluoro alkyl group and corresponding dianhydride monomers to optimize the performance in capacitors. Furthermore, crosslinking of functional polyimdes will enhance thermal stability.

My group will focus on the development of large-scale coating techniques for organic electronics and capacitors. My approach will fabricate solar cells and capacitors through blade or slot-die coating to capture the essential physics of roll-to-roll printing and we will investigate the microstructure within cast polymer films using in-situ X-ray scattering.

Teaching Interests:

I believe it is my responsibility to challenge and support my students to reveal their potential and enjoy their studies. Based on my experience as a student, I will pursue three learning goals in my teaching:

Conceptual learning: Establishing a strong foundation of basic concepts is most important, even more so than understanding other derivative content of a class, because students only understand and evaluate following concepts if they understand the fundamentals. Otherwise, students just memorize at best. I will devote more time, in particular at the beginning of the course, to ensure that students understand fundamental concepts.

Experiential learning: Learning needs momentum, and experience offers strong momentum for learning. When I was an undergraduate, I had a chance to observe a scattering experiment in a synchrotron laboratory. Before then, I had only superficial knowledge of X-ray scattering, but after the scattering experiment I was self-motivated to learn more. As a result, my experience at a synchrotron offered me a good chance to develop my passion for X-ray scattering. In experimental classes especially, I will provide opportunities for students to experience and see concrete examples as much as I can.

Stimulating learning: Students learn best when they are engaged in active inquiry. The level of motivation determines the final level of learning or understanding. It is not as exciting to carry out experiments by simply following instructions without sufficient information about the motivation or fundamentals of the experiments. When working with undergraduates for training or research programs during the summer, I tried to devote time to explain why we do undertake specific experiments and what we are expected to see as results. In case of organic reactions or polymerizations, I explained what we were going to do with the resultant materials in the future. In the same manner, I will help students accept the what and why of their studies, and encourage students to become engaged in classes.

As a researcher and a teacher in Chemical Engineering and Materials Science, I will continue to pursue the three learning goals as stated above, and hopefully contribute to the training of the next generation.


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