B.Sc., Saint John's University (2003) Ph.D., University of Minnesota (2009) Postdoctoral Fellow, University of Texas, Austin Postdoctoral Fellow, University of California, Santa Barbara

Physical Chemistry of Optoelectronic Materials

Time Dependent Thermal Deflection

Organic thermoelectrics have already been demonstrated and would provide a cost effective means of serving moderate temperature applications not adequately served by existing technologies. The properties which make an excellent thermoelectric material are high electrical conductivity, low thermal conductivity and a third metric, called the Seebeck coefficient. Time dependent thermal deflection is an excellent way to study the thermal conductivity of thin films and also provides information on the acoustic vibrational modes important in the mechanism of heat transfer. Because the highly doped state is more technologically important, combining electrochemical transistors and thermal deflection measurements allows for systematic investigations to be carried out.

Data in the figure reproduced from the following publication Ezzahri, Y.; Grauby, S.; Rampnoux, J. M.; Michel, H.; Pernot, G.; Claeys, W.; Dilhaire, S.; Rossignol, C.; Zeng, G.; Shakouri, A. Coherent phonons in Si/SiGe superlattices. Phys. Rev. B 2007, 75.

Ion Transport in Electrochemical Devices

Devices using the ionic and electronic conductivity of conjugated organic materials offer many advantages over standard device structures, especially since the advent of ionic liquids. For example, electrochemical transistors, electrochromics, light emitting electrochemical cells, supercapacitors and all-organic batteries. However, in order to leverage these benefits, the problem of ion mobility must be confronted. Although the mechanism of ion movement in an organic semiconductor is mostly understood, very little research exists regarding the structure-property relationship which governs this rate.

Data in the figure reproduced from the following publication Lee, J.; Kaake, L. G.; Cho, J. H.; Zhu, X. Y.; Lodge, T. P.; Frisbie, C. D. Ion Gel-Gated Polymer Thin-Film Transistors: Operating Mechanism and Characterization of Gate Dielectric Capacitance, Switching Speed, and Stability. J. Phys. Chem. C 2009, 113, 8972-8981.

Insulator-Metal Transition and Polyelectrolyte Dielectrics

A metal is defined as a material which has finite conductivity at arbitrarily low temperatures. Although a few organic systems display this behavior, it is not known how general true metallic behavior is in organic materials. Polyelectrolyte dielectric materials will be used to form electrostatic double layers in an organic transistor, inducing large charge densities and probing electronic phase transitions like the insulator-metal transition.

Data in the figure reproduced from the following publication Shimotani, H.; Asanuma, H.; Tsukazaki, A.; Ohtomo, A.; Kawasaki, M.; Iwasa, Y. Insulator-to-metal transition in ZnO by electric double layer gating. Appl. Phys. Lett. 2007, 91.

Hutnanan, M.P.J., Kaake, L.G. Design principles for block polymer organic double heterojunction solar cells. Mater. Horiz. 2016, 3, 575-580. Kaake, L.G.; Moses, D.; Heeger, A.J.; Charge Transfer from Delocalized Excited States in a Bulk Heterojuction Material. Phys. Rev. B 2015, 91, 075436. Kaake, L.G.; Zhong, C.; Love, J.A.; Nagao, I.; Bazan, G.C.; Nguyen, T.-C.; Huang, F.; Cao, y.; Moses, D.; Heeger, A.J. Ultrafast Charge Generation in an Organic Bilayer Film. J. Phys. Chem. Lett. 2014, 5, 2000-2006. Kaake, L. G.; Moses, D.; Heeger, A. J. Reply to “Comment on ‘Coherence and Uncertainty in Nanostructured Organic Photovoltaics’” J. Phys. Chem. A 2014, 118, 1539-1539. Kaake, L. G.; Moses, D.; Heeger, A. J. Reply to “Comment on ‘Coherence and Uncertainty in Nanostructured Organic Photovolatics’” J. Phys. Chem. A 2013, 117, 10565-10565. Kaake, L. G.; Moses, D.; Heeger, A. J. Coherence and Uncertainty in Nanostructured Organic Photovoltaics. J. Phys. Chem. Lett. 2013, 4, 2264-2268. Kaake, L.; Dang, X. D.; Leong, W. L.; Zhang, Y.; Heeger, A.; Nguyen, T. Q. Effects of Impurities on Operational Mechanism of Organic Bulk Heterojunction Solar Cells. Adv. Mater. 2013, 25,1706-1712. Kaake, L. G.; Sun, Y.; Bazan, G. C.; Heeger, A. J. Fullerene Concentration Dependent Bimolecular Recombination in Organic Photovoltaic Films. Appl. Phys. Lett. 2013, 102, 133302. Jailaubekov, A. E.; Willard, A. P.; Tritsch, J. R.; Chan, W. L.; Sai, N.; Gearba, R.; Kaake, L. G.; Williams, K. J.; Leung, K.; Rossky, P. J.; Zhu, X. Y. Hot Charge-Transfer Excitons Set the Time Limit for Charge Separation at Donor/Acceptor Interfaces in Organic Photovoltaics. Nat. Mater. 2013, 12, 66-73. Kaake, L. G.; Welch, G. C.; Moses, D.; Bazan, G. C.; Heeger, A. J.: Influence of Processing Additives on Charge-Transfer Time Scales and Sound Velocity in Organic Bulk Heterojunction Films. J. Phys. Chem. Lett. 2012, 3, 1253-1257. Leong, W. L.; Welch, G. C.; Kaake, L. G.; Takacs, C. J.; Sun, Y.; Bazan, G. C.; Heeger, A. J.: Role of trace impurities in the photovoltaic performance of solution processed small-molecule bulk heterojunction solar cells. Chem. Sci. 2012, 3, 2103-2109. Chan, W.-L.; Ligges, M.; Jailaubekov, A.; Kaake, L.; Miaja-Avila, L.; Zhu, X.-Y.: Observing the Multiexciton State in Singlet Fission and Ensuing Ultrafast Multielectron Transfer. Science 2011, 334, 1541-1545. Kaake, L. G.; Jailaubekov, A.; Williams, K. J.; Zhu, X. Y.: Probing ultrafast charge separation at organic donor/acceptor interfaces by a femtosecond electric field meter. Appl. Phys. Lett. 2011, 99. Kaake, L. G.; Paulsen, B. D.; Frisbie, C. D.; Zhu, X. Y.: Mixing at the Charged Interface of a Polymer Semiconductor and a Polyelectrolyte Dielectric. J. Phys. Chem. Lett. 2010, 1, 862-867. Kaake, L. G.; Barbara, P. F.; Zhu, X. Y.: Intrinsic Charge Trapping in Organic and Polymeric Semiconductors: A Physical Chemistry Perspective. J. Phys. Chem. Lett. 2010, 1, 628-635. Mills, T.; Kaake, L.; Zhu, X. Y.: Polaron and ion diffusion in a poly(3-hexylthiophene) thin-film transistor gated with polymer electrolyte dielectric. Appl. Phys. A 2009, 95, 291-296. Lee, J.; Kaake, L. G.; Cho, J. H.; Zhu, X. Y.; Lodge, T. P.; Frisbie, C. D.: Ion Gel-Gated Polymer Thin-Film Transistors: Operating Mechanism and Characterization of Gate Dielectric Capacitance, Switching Speed, and Stability. J. Phys. Chem. C 2009, 113, 8972-8981.

Kaake, L. G.; Zhu, X. Y.: Charge Transport, Nanostructure, and the Mott Insulator-to-Metal Transition in Poly(3-hexylthiophene). J. Phys. Chem. C 2008, 112, 16174-16177. Kaake, L. G.; Zou, Y.; Panzer, M. J.; Frisbie, C. D.; Zhu, X. Y.: Vibrational spectroscopy reveals electrostatic and electrochemical doping in organic thin film transistors gated with a polymer electrolyte dielectric. J. Am. Chem. Soc. 2007, 129, 7824-7830.