Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K20: Solar Energy Conversion: Perovskite MaterialsFocus Prize/Award
|
Hide Abstracts |
Sponsoring Units: GERA Chair: Michelle Johannes, Naval Research Lab Room: LACC 308B |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K20.00001: Stanford R. Ovshinsky Sustainable Energy Fellowship Talk: Materials for applications in solar energy conversion, thermoelectrics, batteries, and electronics Invited Speaker: Luisa Whittaker-Brooks The Whittaker-Brooks group aims to address important challenges related to the understanding of the relationships among the composition, structure, electronic structure, and properties of inorganic and organic nanomaterials, as well as their composites. Our efforts are focused on three different directions in the areas of materials chemistry and nanotechnology, i.e., synthetic inorganic-organic chemistry, spectroscopy, and nanofabrication of functional devices. Specifically, our group is driven by two of the greatest challenges of our time –sustainable energy and low cost electronics for daily use applications. We plan to embark in these new endeavors by synthesizing and elucidating the functional properties of well-defined and high-quality materials for applications in photovoltaics, thermoelectrics, batteries, spintronics, and electronics. In this talk, we will discuss our recent findings toward generating practical structure-property-function relationships in nanostructured materials for energy conversion and storage. |
Wednesday, March 7, 2018 8:36AM - 8:48AM |
K20.00002: Abstract Withdrawn
|
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K20.00003: Modeling Advanced Halide Perovskite Materials for Solar Energy Harvesting and Optoelectronics Oleksandr Kobryn Thin film morphology is a key factor determining the performance of bulk heterojunction organic solar cells through its influence on charge separation, transport and recombination losses in donor-acceptor blends. With this respect, both descriptive and predictive modeling of structural properties of blends of PCBM or hybrid perovskites of the type CH3NH3PbX3 (X=Cl, Br, I) with P3HT, P3BT and SQ2 dye sensitizer, including adsorption on TiO2 clusters having rutile (110) surface, is presented with the use of a methodology that allows computing the microscopic structure of blends on the nanometer scale and getting insight on miscibility of its components at various thermodynamic conditions. The methodology is based on the integral equation theory of molecular liquids and the density functional theory. A remarkably good agreement with available experimental data and results of alternative modeling is observed for PCBM in P3HT system. We interpret this as a validation of our approach for organic photovoltaics and support of its results for new systems that do not have reference data for comparison or calibration. The calculated nanoscale morphologies of blends of P3HT, P3BT or SQ2 with perovskites and TiO2 are all new and guide the rational design of organic/hybrid photovoltaics. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K20.00004: Manipulation of Cation Combination and Configuration of Halide Double Perovskites for Solar Cell Absorbers Peng Zhang, Suhuai Wei Pb-free halide double perovskites, A2B+B3+X6 (A = Cs, B+/B3+ = metal cation, X = halogen anion) have been proposed to replace hybrid halide perovskites (e.g., CH3NH3PbI3) as stable, Pb-free materials for high efficiency solar cell absorbers. Here, using first-principles density functional theory calculations and symmetry analysis we show that the overall electronic properties of A2B+B3+X6 depend strongly on the atomic orbitals and site occupation of the B+ and B3+ cations. For the ordered A2B+B3+X6 compounds, in order to have a direct band gap with allowed optical transitions, both of the B+ and B3+ cations should possess the lone-pair s state. Thus, only the family of compounds stratifies this criterion. On the other hand, we reveal that the electronic structures of A2B+B3+X6 can be greatly tuned by controlling the site occupation ordering parameter of the B+ and B3+ cations. Compared to their ordered counterparts, the band gaps of the disordered A2B+B3+X6 alloys can be reduced significantly and the band gap character can be switched from indirect to direct, which greatly expanded the possible candidates for solar cell applications. Our results thus set a new direction and guidelines for the design of Pb-free halide double perovskites for solar cells. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K20.00005: Origin of Long Lifetime of Band-Edge Charge Carriers in Organic-Inorganic Lead Iodide Perovskites Tianran Chen, Wei-Liang Chen, Benjamin Foley, Jooseop Lee, Jacob Ruff, J. Y. Peter Ko, Craig Brown, Leland Harriger, Depei Zhang, Changwon Park, Mina Yoon, Yu-Ming Chang, Joshua Choi, Seunghun Lee Long carrier lifetime is what makes hybrid organic-inorganic perovskites high performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photo-excited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.[1] |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K20.00006: Crystal Structures and Photoluminescence of a Two-Dimensional Perovskite Depei Zhang, Tianran Chen, Alexander Chen, Wei-Liang Chen, Maiko Kofu, Craig Brown, Leland Harriger, Madhusudan Tyagi, Mina Yoon, Joshua Choi, Seunghun Lee Arguably the biggest challenge of the high-efficiency perovskite solar cells, such as CH3NH3PbI3 and CH(NH2)2PbI3, is their device instability. A recent study of 2D perovskite compounds, butylammonium methylammonium lead iodide perovskite, [CH3(CH2)3NH3]2(CH3NH3)n-1PbnI3n+1, proposed a solution to this problem. This class of materials shows a maximum photovoltaic efficiency of 12.52%, without any obvious degradation over thousands of hours under standard light illumination and humidity test. This talk focuses on the study of temperature-dependent crystal structures, along with the photovoltaic properties of the 2D 1-layer (n = 1) perovskite material. We have performed elastic and inelastic neutron scattering, Raman scattering, and photoluminescence measurements on a powder sample of the 1-layer system ([CH3(CH2)3NH3]2PbI4). Our analysis of the data illuminates the evolution of the lattice structure, rotational and vibrational dynamics with temperature, and their connection to the charge carrier lifetime of the solar cell will be discussed. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K20.00007: Using interface engineering to tune excitonic properties of halide and mix-halide hybrid perovskite thin films Katerina Nikolaidou, Som Sarang, Denzal Martin, Vincent Tung, Jennifer Lu, Sayantani Ghosh ZnO electron transport layers of various morphologies are implemented to modify the exciton binding energy and charge extraction from hybrid perovskite (PVSK) thin films. The ZnO susbtrates employed include single crystalline (SC), micro-structured (MS), and nano-structured (NS) ZnO. Characterization of the PVSK-ZnO interface is achieved via electron microscopy, which is correlated to interfacial charge transfer via temperature, power, and time-resolved photoluminescence (PL) spectroscopy. SC-ZnO is observed to act as an effective electron extraction layer as indicated by PL intensity quenching, reduced recombination lifetime and reduced exciton density in the PVSK thin film. On the other hand, MS- and NS-ZnO result in PL enhancement, while reducing recombination lifetime. These trends change with temperature and can be associated with variations in exciton binding energy of PVSK, underlining the effect of the electron extraction layer on the excitonic properties of the PVSK film. We conclude that while SC-ZnO can be used for electron extraction in photovoltaic devices, MS- and NS-ZnO can be implemented as scaffold in optical devices that require high quantum yield. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K20.00008: The fabrication and the characterization of all inorganic perovskite solar cell with metal oxide charge transport layer Haider Salman, Omar Manasreh Perovskite material have been the focus of researchers for the past few years in photovoltaic applications due to their properties that allow higher power conversion efficiency. Instability and high degradation rate are among the challenges that still face the organic types of perovskite. On the other hand, inorganic perovskites such as cesium lead halide and cesium tin halide have higher stability, but they produce less power conversion efficiency in solar cells. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K20.00009: Air-Stabled All Inorganic Lead-Free Perovskite Solar Cells Xiaojuan Fan, Chance Williams, Evan Kelley Inorganic lead-free perovskite CsSnI3 is an unusual sensitizer that has high electrical conductivity and exhibits near-infrared photoluminescence. However, the lack of chemical stability in air has limited its practical applications because it must be handled in an inert atmosphere when fabricating solar cells. In analogical compound Cs2SnI6, ion Sn in 4+ oxidation state which is stable in atmosphere have attracted great attention for its easy phase transition from CsSnI3. Its direct bandgap at around 1.32 eV has made it a promising sensitizer used in perovskite solar cells (PSC). Both solid state reaction synthesis and solution process can be used. Spin coating Cs2SnI6 on anatase mesoporous TiO2 forms a heterojunction structure followed by a hole transport material and a counter electrode. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K20.00010: Synthesis and characterization of photoferroic BiCoO3 Kaitlin Hellier, Stephan Lany, Sue Carter, David Ginley, Lauren Garten Photoferroics have received increased interest of late, with recent power efficiencies reaching over 8%. However, band gaps of 3 eV or greater in the most common polar materials leaves the room for growth as solar absorbers limited. This has led to further work in the modeling and development of new polar materials, with a focus in band gap tuning. In line with the well-studied BiFeO3, electronic structure calculations were performed on BiMO3 perovskite structures to determine band gaps, dielectric functions, and piezoelectric tensors of the corresponding material. Of those explored, BiCoO3 showed promise as a low band gap semiconductor with a predicted gap of 2.08 eV, a polar P4mm structure, and a predicted relative permittivity of 44.6. To follow up on these predictions, BiCoO3 films were grown via combinatorial pulsed laser deposition, with a multi-target system of Bi2O3 and CoO. The substrate, temperature, chemistry and partial pressure of oxygen were varied to determine the best conditions for achieving a P4mm structure. Epitaxial strain was used to create high quality films with an aligned internal polarization, from which photoferroic testing was performed after completing a metal-semiconductor-metal structure. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K20.00011: Tunable Conductivity of MAPbI3 via Surface Doping from Small Molecules Erin Perry, John Labram, Naveen Venkatesan, Hidenori Nakayama, Michael Chabinyc Lead halide perovskites have gained enormous attention as a low-cost and solution-processable active material for solar cells. The performance of hybrid-halide solar cells is dependent on the nature of interfaces. In order to improve device performance, the physical and chemical properties of these interfaces continue to be explored. Organic hole and electron transport materials are often employed as electron- and hole-blocking layers. In order to optimize charge-extraction in the device, these organic layers can be doped using organic small molecules. However, to date there has been little work carried out on the details of doping at these interfaces. Due to a lack of surface states and undercoordinated Pb2+ ions on the perovskite surface, it is possible for charge transfer to take place from small molecule n-type dopants to MAPbI3. Here we study the change in electrical properties of MAPbI3 by modulation-doping the film with an organic dopant molecule: cobaltocene. By varying the amount of cobaltocene deposited, the conductivity of thin films are observed to be tunable over several orders of magnitude. We observe a tunable shift in the valence band edge of up to 0.7 eV upon doping, illustrating that charge transfer doping allows for control over the interfacial energy levels. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K20.00012: High Resolution X-ray Photoelectron Spectroscopy Study on Stability of MAPbBr3 Single Crystal Congcong Wang, Benjamin Ecker, haotong wei, Jinsong Huang, Yongli Gao Organic-inorganic halide perovskites have emerged as a promising semiconductor family because of their remarkable performance in optoelectronic devices. However, the stability of perovskites remains a critical issue. Here, we quantitatively and systematicly investigated the in-situ cleaved MAPbBr3 single crystal degradation processes in X-ray, N2, O2 and H2O environments. The crystals were monitored by high resolution X-ray photoelectron spectroscopy with careful control of the exposure time and pressure. The detailed electronic structure and compositional changes of the crystal were tracked throughout different exposures, which provided insights into various degradation mechanisms. About 10% of the surface MAPbBr3 degraded into metallic lead under X-ray, while N2 can protect the sample from X-ray for 9 hours under the same condition. The crystal was not sensitive to pure O2, but was susceptible to H2O. A reaction threshold of ~108 Langmuir was found. Below it, H2O only acted as an n-type dopant; above it, the crystal began to decompose. These observations highlight possible future directions to improve the material stability by environmental control. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K20.00013: The Order-Disorder Transition in CH3NH3PbBr3 Katherine Brown, Stewart Parker, Irene Robles GarcĂa, Sanghamitra Mukhopadhyay, Victoria Garcia, Chris Stock Lead-halide organic-inorganic perovskites consist of an inorganic host framework with an organic molecule occupying the interstitial space. The structure and dynamics of these materials have been heavily studied recently due to interest in their exceptional photovoltaic properties[1,2]. We combine inelastic neutron scattering, Raman spectroscopy, and quasielastic neutron scattering to study the temperature dependent dynamics of the molecular cation in CH3NH3PbBr3. By applying high resolution quasielastic neutron scattering, we confirm the [CH3NH3]+ ions are static in the low temperature orthorhombic phase yet become dynamic above 150 K where a series of structural transitions occur. This molecular melting is accompanied by a temporal broadening in the intra-molecular modes probed through high energy inelastic spectroscopy. Simultaneous Raman measurements, a strictly |Q|=0 probe, suggest that this broadening is due to local variations in the crystal field environment around the hydrogen atoms. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700