Bulletin of the American Physical Society
Joint Meeting of the Four Corners and Texas Sections of the American Physical Society
Volume 61, Number 15
Friday–Saturday, October 21–22, 2016; Las Cruces, New Mexico
Session B5: Condensed Matter |
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Chair: Kathryn Ross, Colorado State University Room: Meeting Room 1 |
Friday, October 21, 2016 10:00AM - 10:24AM |
B5.00001: Exciton spin dynamics in hybrid organic-inorganic perovskites Invited Speaker: Yan (Sarah) Li The hybrid organic-inorganic perovskites have emerged as a new class of semiconductors which make excellent solar cells with an efficiency over 20\%. They are also highly promising semiconductors for the field of spintronics due to their large and tunable spin-orbit coupling, spin dependent optical selection rules, and predicted electrically tunable Rashba spin splitting. I will present our latest study of exciton spin dynamics on the solution processed polycrystalline methylammonium lead iodide films. With time-resolved Faraday rotation (TRFR) and optical Hanle measurements, we demonstrate the optical orientation and quantum beating of excitons in the perovskites, which confirms the spin-dependent optical transitions. The energy dependence of the Faraday rotation follows the exciton absorption band at low temperatures, confirming its excitonic origin. The TRFR in zero field reveals unexpected long spin lifetimes exceeding 1 ns at 4 K, given that Pb and I exhibit large spin-orbit coupling, and usually lead to fast spin relaxation. Application of a transverse magnetic field causes quantum beating at two distinct frequencies, and the approximate linear relationships give two g-factors, which we assign to electrons and holes as $g_e = 2.63$, and $g_h = -0.33$. These results provide a basic picture of the exciton states in the hybrid perovskites, and suggests their great potential in spintronic applications. [Preview Abstract] |
Friday, October 21, 2016 10:24AM - 10:48AM |
B5.00002: Role of Interface in Stability of Perovskite Solar Cells. Invited Speaker: Alex Zakhidov Perovskite solar cells (PSC) are promising devices for help meeting future energy challenges due to their low cost and comparable efficiencies with other PV technologies. However, long term stability of PSCs remains the major roadblock for large scale commercialization. In my talk, I will review and discuss different device layouts and summarize their progress on performance and stability. In particular, I will discuss the mechanism of perovskite thermal decomposition on ZnO electron transport layer and possible mitigation strategies. I will also present theoretical results of our recent study, where we have predicted the existence of self-trapped polarons in the organohalide lead perovskites using DFT$+$U methodology. The plethora of materials and interfaces between materials available for PSC obscures the larger challenge in PSCs, long term stability. Future research should focus on fundamental understanding of the interfaces not only for charge transport, but for the long term reliability of PSC if these devices are to move from laboratory settings to industrial production. [Preview Abstract] |
Friday, October 21, 2016 10:48AM - 11:00AM |
B5.00003: Microstructure and Optical Properties of Perovskite Solar Materials Nicholas Allen, Heather Browning, Andrew Sandoval, Meagan Parker, Charles Smith, Colin Inglefield, Brandon Burnett, Kristin Rabosky Traditional silicon solar cells are costly and require much energy to refine the silicon. A developing alternative technology which shows great promise are perovskite solar cells; the active layer being made of CH$_{3}$NH$_{3}$PbI$_{3}$. We created perovskite samples using a spin-coating technique. After the samples were created, they were examined under an SEM to verify that they had a homogeneous amorphous structure. The sample thickness was determined using an AFM and an ellipsometer. A UV-Vis setup was also built using a monochromator, a series of lenses, and a detector in order to test the bandgap of the samples. By varying our material deposition techniques, we were able to create an amorphous sample with a bandgap of about 1.6 eV, which closely matches the solar spectrum. We will discuss our perovskite deposition process at WSU. [Preview Abstract] |
Friday, October 21, 2016 11:00AM - 11:12AM |
B5.00004: Quantum Dot Band Gap Measurements J. Ryan Peterson Quantum dot solar cells have become one of the fastest emerging solar cell technologies to date. In order to raise their efficiency, a combination of materials with varying band gaps can be used to capture more energy from each photon. Our group has synthesized lead sulfide quantum dots with varying band gaps with and without the help of the protein ferritin. The use of ferritin provides a structural template, in addition to protecting against photodegredation. The radius and therefore band gap of the quantum dots were controlled by varying reactant concentration in solution. The resulting quantum dots had band gaps ranging from 1.33 eV to below 1.0 eV. [Preview Abstract] |
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