Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D69: Fundamental Properties of Metal Halide Perovskites IIFocus Recordings Available
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Sponsoring Units: DMP Chair: Nicholas Weadock, University of Colorado Boulder Room: Hyatt Regency Hotel -Jackson Park A |
Monday, March 14, 2022 3:00PM - 3:36PM |
D69.00001: Exciton polarons in Ruddlesden Popper metal halides - lessons from coherent spectroscopy Invited Speaker: Ajay Ram Srimath Kandada Two-dimensional Ruddlesden-Popper metal halides (2D-RPMHs) are materials composed of quasi-2D layers of metal-halide octahedra separated by long (~1nm) organic cationic layers. The latter facilitate electron and hole quantum confinement within the metal-halide layers resulting in a quantum-well like structure. Properties of excitons (electron-hole bound states) in such structures are characterized by strong binding energy (>200 meV) arising from the dynamically screened Coulomb interactions. We have experimentally observed that polaronic effects arising from the lattice dressing of the carriers, are not only active but that they fundamentally define excitons in 2D-RPMHs. We thus refer to such excitons as the exciton-polarons, with properties that are measurably distinct from those of free excitons in semiconductors. We will discuss the quantum dynamics of exciton-polarons and provide spectroscopic insights into the peculiar phonon-phonon, exciton-phonon and exciton-exciton interactions. We will present our perspective on how the coherent optical response of 2D-RPMHs can be effectively rationalized within the "exciton-polaron" framework, in which lattice dressing of photo-carriers constitute an integral component of excitonic wavefunction, with consequences on exciton recombination dynamics and diffusion. |
Monday, March 14, 2022 3:36PM - 3:48PM |
D69.00002: Coherent Hopping Transport and Giant Negative Magnetoresistance in Epitaxial CsSnBr3 Liangji Zhang, Isaac King, Kostyantyn Nasyedkin, Pei Chen, Brian Skinner, Richard R Lunt, Johannes Pollanen Single-crystal inorganic halide perovskites are attracting interest for quantum device applications. Here we present low-temperature quantum magnetotransport measurements on thin film devices of epitaxial single-crystal CsSnBr3, which exhibit two-dimensional Mott variable range hopping and giant negative magnetoresistance. These findings are described by a model for quantum interference between different directed hopping paths, and we extract the temperature-dependent hopping length of charge carriers, their localization length, and a lower bound for their phase coherence length of ~100 nm at low temperatures. These observations demonstrate that epitaxial halide perovskite devices are emerging as a material class for low-dimensional quantum coherent transport devices. |
Monday, March 14, 2022 3:48PM - 4:00PM |
D69.00003: Data-driven design of halide perovskites using high-throughput computations and machine learning Jiaqi Yang, Panayotis Thalis Manganaris, David Enrique Farache, Arun Kumar Mannodi Kanakkithodi Halide perovskites are highly desirable for optoelectronic applications due to their extraordinary tunability, especially via composition engineering and octahedral rotation and distortion. However, significant challenges arise when exploring combinatorial possibilities for atoms, compositions and structures, which results in a computationally and experimentally intractable problem. In this work, we address this issue using a combination of high-throughput density functional theory (DFT) and machine learning (ML). We generate a DFT dataset of ~ 550 perovskite alloys based on a selected set of A, B, and X atoms and arbitrary mixing at each site, calculating several critical properties using standard GGA-PBE and hybrid HSE06 functionals, including band gap, decomposition energy, photovoltaic absorption, and vacancy formation energy. Predictive models are trained from this dataset using descriptors that encode compositional, elemental, and octahedral information, and applying state-of-the-art ML regression techniques such as random forests and neural networks. These DFT-surrogate models are used for screening of thousands of promising new candidates and combined with a genetic algorithm framework for inverse design of new compositions with multiple targeted properties, which are validated with additional computations and recommended for experimental synthesis and characterization. The large datasets and AI-based prediction and optimization schemes resulting from this work are promising for the accelerated design of novel halide perovskites for solar cells, photodiodes, electronics, infrared sensors, and other related applications. |
Monday, March 14, 2022 4:00PM - 4:12PM |
D69.00004: Structure and optical properties of Tl2LiYCl6 : A new phosphor scintillator material for gamma ray and neutron detection Shivani Srivastava, Mauro Del Ben, Jaroslaw Glodo, Mark D Asta, Andrew M Canning Tl based double halide perovskites are emerging as promising candidates for commercial scintillator applications such as gamma ray and neutron detection. They offer increased detection efficiency for applications such as gamma rays detection due to the increased stopping power with high Z Tl (Z=81) and good detection efficiency for thermal neutrons due to the presence of Li. |
Monday, March 14, 2022 4:12PM - 4:24PM |
D69.00005: Resolving discrepancies in mechanical properties of hybrid perovskites: a DFT study Kuntal Talit, David A Strubbe The mechanical properties of hybrid perovskite materials are important for the behavior of flexible devices, resistance to fracture, epitaxial growth, surface energetics of quantum dots, and induction or relief of stress in thin films due to thermal expansion and phase changes. These issues are particularly salient for solar cells in space applications. Nonetheless few studies are available on the mechanical properties of CH3NH3PbI3 (MAPI). Experimental results are only available for the room-temperature tetragonal phase, which have significant variation. Results from density functional theory (DFT) are available for all three phases but have even larger discrepancies from each other and from experiments. To bring order to the confusion in the literature, we have studied the elastic properties of all three phases in detail with DFT calculations. We have examined the effect of different aspects such as structure, exchange-correlation functionals, van der Waals corrections, pseudopotentials, and other considerations in calculation methodology. Our results provide accurate reference values and an appropriate general methodology for elastic properties of metal halide perovskites. |
Monday, March 14, 2022 4:24PM - 4:36PM |
D69.00006: Composition-dependent phase transitions and superlattice ordering in lead-iodide perovskite nanocrystals Julian A Vigil, Joseph M Luther, Michael F Toney Confinement of lead-iodide perovskites to nanoscale dimensions via colloidal synthesis has enabled several emergent properties, notably including the stabilization of crystallographic phases known to be thermodynamically unstable in the bulk. Further, these halide perovskite quantum dots exhibit desirable optoelectronic properties for light emission and quantum optics applications, including efficient photoluminescence and superfluorescence arising from coherent coupling between neighboring nanocrystals. |
Monday, March 14, 2022 4:36PM - 4:48PM |
D69.00007: Defect Calculation by Combined SCAN and Hybrid Functional in γ-CsPbI3 Shengyuan Wang, Kin Fai Tse, Alena Boyko, Junyi Zhu γ-CsPbI3 solar cells have achieved promising efficiencies, yet the quantitative understanding of their defect properties is limited due to severe computational challenges of hybrid functionals. We have discovered an algorithm to improve the convergence speed by a combination of structural relaxation with strongly constrained and appropriately normed (SCAN) Meta-generalized-gradient approximation (Meta-GGA) functional and further ionic and electronic calculations with Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. The static HSE calculation with SCAN results as inputs is qualitatively reliable in defect calculations, different from one-ionic step HSE calculation based on GGA inputs. Contradictory to previous GGA defect results, a suppressed bipolar conductivity by p-type VCs and VPb, and n-type CsI is found. Additionally, stable bipolar defects Iint and CsPb, featured by strong bond orbital coupling or structural deformation, detrimentally serve as carrier-traps. Such a strengthened bond orbital coupling in γ-CsPbI3 causes more defect charge states than organic perovskites with larger lattice constants. |
Monday, March 14, 2022 4:48PM - 5:00PM Withdrawn |
D69.00008: Photon recycling in CsPbBr3 all-inorganic perovskite nanocrystals Marco van der Laan, Chris de Weerd, Lucas Poirier, Oscar van de Water, Deepika Poonia, Leyre Gomez, Sachin Kinge, Laurens D.A. Siebbeles, A. Femius Koenderink, Tom Gregorkiewicz, Peter Schall Photon recycling, the iterative process of re-absorption and re-emission of photons in an absorbing medium, can play an important role in the power-conversion efficiency of photovoltaic cells. To date, several studies have proposed that this process may occur in bulk or thin films of inorganic lead-halide perovskites, but conclusive proof of the occurrence and magnitude of this effect are missing. Here, we provide clear evidence of photon recycling in CsPbBr3 nanocrystal suspensions by combining measurements of steady-state and time-resolved (TR) photoluminescence (PL) and PL quantum yield with simulations of photon diffusion through the suspension. We observe clear spectral modifications including red shifts and quantum yield decrease, while the TRPL measurements show prolonged PL decay and rise times. Monte Carlo simulations of photons diffusing through the medium account quantitatively for the observed trends and show that up to 5 re-emission cycles are involved. We thus identify 4 quantifiable measures, PL red-shift, PL QY, PL decay-time, and PL rise-time that together all point towards repeated, energy-directed radiative transfer between nanocrystals. These results further establish lead-halide perovskites as strong candidates for optoelectronic applications. |
Monday, March 14, 2022 5:00PM - 5:12PM |
D69.00009: Ultrafast Excited-State Localization and Charge-Carrier Mobility in Cs2AgBiBr6 and Cu2AgBiI6 Adam D Wright Understanding the nature of the charge-lattice coupling in Ag-Bi−halide semiconductors is crucial for the optimization of these materials in a variety of optoelectronic applications. In this study, I report on the evolution of photoexcited charge carriers in Cs2AgBiBr6 and Cu2AgBiI6. In both materials, I observe rapid decays in THz photoconductivity transients that reveal an ultrafast, barrier-free localization of free carriers on the time scale of a few ps to an intrinsic small polaronic state. I attribute this to the strong charge-lattice coupling in these Bi-Ag materials, while the temperature-independence of the self-trapping is indicative of low electronic dimensionality due to the electronic isolation of the distinct Ag+ and Bi3+ sites. Through a combination of temperature-dependent photoluminescence and absorption spectroscopy, I identify the electronic states occupied before and after localization, directly tracing the localization of the charge carriers with time and interpreting its influence on the charge-carrier mobility in terms of a quantitative model. Since the small polaron motion is temperature-activated, I find that their mobility still exceeds 1 cm2 V−1s−1 in both materials, leaving open the prospect of their application in efficient photovoltaic devices. |
Monday, March 14, 2022 5:12PM - 5:24PM |
D69.00010: Vanderwals contact engineering in CsPbBr3 micro crystals for optoelectronic application Gokul M. A The study focuses on the synthesise, transfer and opto electronic properties of a single CsPbBr3 micro crystal. We use vanderwals contact engineering to explore the properties and device perforance of these microcrystals. A new synthesis route for easy fabrication of CsPbBr3 microcrystals and the device fabrication willbe discussed. Theelectrical charecterisation of various vandervals contact and their impact on device performance will be discussed in detail |
Monday, March 14, 2022 5:24PM - 5:36PM |
D69.00011: Lead-tin halide perovskite thin films by chemical vapor deposition Christopher J Arendse, Siphesihle S Magubane, Siphelo Ngqoloda, Stephen C Klue, Suchismita Guha Binary-metal halide perovskites films have attracted considerable attention, in an attempt to reduce the toxic lead (Pb) content in the perovskite thin films, while improving the charge transport properties without distorting the structure of the material. Chemical vapor deposition (CVD) has been successfully used to deposit Pb-only based perovskites with improved stability, but has limitation in controlling Sn-content when depositing Pb-Sn perovskites. We report on a two-step CVD method to synthesize methylammonium lead-tin triiodide perovskite films (MAPb1-xSnxI3, x= 0 to 1), where the Sn-content, probed by Rutherford backscattering spectroscopy (RBS), is controlled. The perovskite films exhibit the characteristic tetragonal structure, independent of the Sn-loading. The inclusion of Sn in the structure has a direct influence on the optical properties of the films, manifested by the decrease in band gap from about 1.59 eV for MAPbI3 to 1.26 eV for MAPb0.4Sn0.6I3 and an increased defect density in the band gap that is associated with the increased oxidation of Sn2+ to Sn4+. In addition, we will report on the effect of the precursor material (SnI2/PbI2 and SnCl2/PbCl2) on the resultant structure and optical properties. |
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