Bulletin of the American Physical Society
Joint Fall 2017 Meeting of the Texas Section of the APS, Texas Section of the AAPT, and Zone 13 of the Society of Physics Students
Volume 62, Number 16
Friday–Saturday, October 20–21, 2017; The University of Texas at Dallas, Richardson, Texas
Session P3: Condensed Matter Physics IV |
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Chair: Alex Zakhidov, Texas State Univ. San Marcos Room: DGAC 1.102C |
Saturday, October 21, 2017 3:45PM - 4:09PM |
P3.00001: Orthogonal patterning and processing of organic perovskite semiconductors. Invited Speaker: Alex Zakhidov Lead halide organic perovskites are promising semiconductors for high-performance, low-cost, printed photonic devices such as solar cells, photodetectors, and light emitting diodes. Organic perovskite inks are made from Earth-abundant, inexpensive precursors and can be printed on plastic foils with resulting the significant reduction of their commercial manufacturing cost. Yet, the progress in organic perovskite photonics is currently hampered by the lack of reliable patterning and processing methods available for other semiconductors such as Si. In this talk, I will present our recent works on patterning and electrochemical processing of methylammonium lead iodide (MAPI) benchmark perovskite using fluorinated, chemically orthogonal solvent class called hydrofluoroether (HFEs). HFEs are non-flammable, non-toxic, green solvents with zero ozone depletion potential. We show that HFE wet processing does not damage the MAPI films and thus enables liquid based processing. We use commercially available HFE-based photoresist to demonstrate high-resolution patterning of MAPI pixels for high-performance photodetectors. We show that isolation of perovskite photodetecting pixels results in a 4.5-fold reduction in the cross-talk between neighboring pixels in the matrix. [1] We also have enabled electrochemical characterization and demonstrated a processing toolset for these materials utilizing HFE based electrolytes solvent. Our results show that chemically orthogonal electrolytes based on HFE solvents do not dissolve organic perovskite films and thus allow electrochemical characterization of the electronic structure, investigation of charge transport properties, and potential electrochemical doping of the films with in situ diagnostic capabilities.[2] \textbf{References.} [1]. D. Lyashenko, A. Perez, and A. Zakhidov, Phys. Status Solidi \textbf{214}, 1600302 (2017). [2]. M. Hasan, S. Venkatesan, D. Lyashenko, J.D. Slinker, and A. Zakhidov, Anal. Chem. \textbf{89}, 9649 (2017). [Preview Abstract] |
Saturday, October 21, 2017 4:09PM - 4:21PM |
P3.00002: Investigating the effect of dielectric constant and ion mobility in light emitting electrochemical cells Lyndon Bastatas, Matthew Moore, Jason Slinker Light emitting electrochemical cells (LEECs) are promising low-cost technologies for display and solid state lighting. A certain type of these devices can be made from a combination of complex emitters made from transition metal complexes and counterions. We investigated the effect of different negative counterions paired with iridium emitters on the performance of the devices. By performing impedance spectroscopy, we were able to estimate the mobility of the ions and the dielectric constant of the film. We complemented the experimental results with simulation studies using a drift-diffusion model where the recombination of electrons and holes is facilitated by a Langevin process. Ultimately, using different counterions yields slightly different values of dielectric constants and ion mobilities that affect their performance. [Preview Abstract] |
Saturday, October 21, 2017 4:21PM - 4:33PM |
P3.00003: Understanding the superior temperature stability of iridium light-emitting electrochemical cells. Melanie Bowler, Tianle Guo, Lyndon Bastatas, Matthew Moore, Anton Malko, Jason Slinker Single-layer light-emitting electrochemical cells from ionic transition metal complexes (iTMCs) are relatively simple to construct and have great potential as cost effective emissive devices. For practical applications, thermal stability is important for environmental robustness, and little has been said about their relative thermal stability. Here, we studied the device performance of iridium and ruthenium iTMCs with temperature to directly compare their stabilities. The thermal onset of radiant flux loss is found to be 67 C (152 F) for iridium devices, 45 C higher than ruthenium iTMCs, a show of their superior thermal stability. We subsequently used temperature-dependent electrochemical impedance spectroscopy, temperature-dependent photoluminescence spectroscopy, time resolved photoluminescence spectroscopy, and photoluminescence quantum yield measurements to understand the physical origin of this substantial temperature stability difference. Prior postulates suggested that films from iridium complexes would yield better thermal stability than those from ruthenium complexes due to details of the orbital energetics. Instead, it is found that this superiority is owed to the details of kinetic effects---the competing kinetics of multiple recombination pathways and the relative rates of radiative to nonradiative processes. Such information guides the design of iTMC emitters for superior light-emitting electrochemical cells. [Preview Abstract] |
Saturday, October 21, 2017 4:33PM - 4:45PM |
P3.00004: Broadband Terahertz Refraction Index Dispersion and Loss of Polymeric Dielectric Materials Elaheh Motaharifar, Rashaunda Henderson, Julia W. P. Hsu, Mark Lee Reliable permittivity data over a broad THz frequency range is important for many dielectric materials of potential use in very high frequency electronics. At THz frequencies, resonant lattice and bond dynamics result directly in dramatic dispersion and large dielectric loss in certain frequency bands in the THz, so it is critical to have quantitative knowledge of a dielectric material's complex index characteristics. $\backslash $pardHere we present broadband measurements (3-75 THz) of the complex index spectra of some polymeric dielectric materials often used in high frequency electronics. Reflection and transmission spectra were made using a Fourier transform spectroscopy on free-standing material samples. Data were analyzed using two different models to extract complex refractive index as a function of frequency. The first model covers frequency regimes away from strong molecular bond where propagation loss is low enough that multiple partial reflections from front and back surfaces contribute to measured reflectance and transmittance. The second model is for frequency ranges spanning infrared active molecular bond resonances where loss and dispersion can become very large, causing zero transmittance. Molecular bond resonances, frequency windows of low loss, and anti-windows of high loss are identified. [Preview Abstract] |
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