Purdue University School of Chemical Engineering Graduate seminar series Prof. Yueh-Lin Loo Theodora D. '78 & William H. Walton III '74 Professor in Engineering Princeton University "Accessing Polymorphism and Tuning Molecular Orientation in Solution-processed Organic Semiconductors" September 30, 2014 9:00-10:15 a.m. FRNY G140 Reception at 10:15-10:45 a.m. in Henson Atrium Abstract: Though both the molecular orientation and crystal structure of molecular semiconductors are known to impact charge transport in thin-film devices, controllably accessing different polymorphs and tuning both the in-plane and out-of-plane molecular orientations remain challenging, requiring careful selection of film deposition conditions, film thickness, and substrate chemistry. Without necessitating any specification of these parameters, we have been able to impose specific polymorphs and/or preferential molecular orientation through post-deposition processing. In the case of contorted hexabenzocoronene (HBC), we can access two distinct polymorphs and independently vary the distributions of its out-of plane molecular orientation. Starting with a thermally evaporated amorphous HBC film, thermal and solvent-vapor annealing induces the thin film to crystallize into distinct polymorphs; we can further transform between the polymorphs with subsequent rounds of processing. Because the molecular orientation distribution is primarily determined during the first processing step, subjecting already crystalline thin films to different post-deposition processing conditions allows us to access different polymorphs without altering the molecular orientation distribution, thus enabling us to decouple the influence of each on charge transport. In the case of solution-processable triethylsilylethnyl anthradithiophene (TES ADT), we have been able to exploit its differential crystallization rates on substrates having different surface energies to guide the in-plane growth direction of neighboring crystals. The systematic engineering of solely low- and high-angle grain boundaries between neighboring crystals have allowed us to elucidate their relative contribution to charge transport. Bio: Lynn Loo is the Theodora D. '78 & William H. Walton III '74 Professor in Engineering at Princeton University. In the Chemical & Biological Engineering Department, her research emphasizes the structure development of complex materials for low-cost, lightweight and scalable plastic circuits and solar cells. With her recent stint at NewWorld Capital Group, a private equity firm that focuses on investments in environmental opportunities, Lynn's research has expanded to include macro-energy-systems analysis and carbon balance for processes that generate liquid fuels. As the Associate Director of External Partnerships at the Andlinger Center for Energy and the Environment, Lynn leads the Princeton Effiliates Partnership that promotes teacher-student-practitioner interactions and fosters collaboration between the private sector and faculty on campus. Lynn received her PhD from Princeton University in 2001. She is a fellow of the American Physical Society and has been recognized as a Top 100 Young Innovator by MIT's Technology Review, with the Alan P. Colburn Award from the American Institute of Chemical Engineers, the John H. Dillon Medal of the American Physical Society and Sloan and Beckman Fellowships. Sincerely, Cindy Waibel Secretary ~ Rm 1144 Forney Hall of Chemical Engineering Purdue University 480 Stadium Mall Drive West Lafayette, IN 47907-2100 765-494-4069 Fax: 765-494-0805 leiklebe@purdue.edu<mailto:leiklebe@purdue.edu> [PurdueEngineeringLogosmall]
