Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D63: Theory and Computation of Hybrid PerovskitesFocus
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Sponsoring Units: DMP Chair: Aron Walsh, National Renewable Energy Laboratory Room: Mile High Ballroom 4D |
Monday, March 2, 2020 2:30PM - 2:42PM |
D63.00001: A Theoretical Study of Structure Property Relations in Photovoltaic Perovskites Jordan Cowell, Nicholas C. Bristowe Perovskite materials are a great example of systems with a multitude of structure-property relationships. For example, metal insulator transitions in the nickelates and manganites can be linked to breathing and Jahn-Teller distortions which allow for charge and orbital ordering, respectively. This study examines the relationship between atomic structure and electrical band-gaps in the promising photovolatics material A2Au2X6 (A = Cs, Rb, K, X = I, Cl), through first principles calculations based on DFT. We find that there is a complex competition between various structural degrees of freedom in the material, which can be manipulated through chemistry and pressure, and that each of the structural modes can strongly tune the band gap. For example, in the Rb2Au2I6 double perovskite, we predict that, contrary to expectation, hydrostatic pressure produces a polar phase. We argue that this is due to a) the cooperative coupling of the Jahn-Teller and tilt modes which are both reduced with pressure, and b) the competitive coupling of tilting and polar modes. We finally discuss the effect of each of these modes and chemical changes on the band gap, and how the polar mode could be helpful to separate photo-excited carriers via the photoferroic effect. |
Monday, March 2, 2020 2:42PM - 2:54PM |
D63.00002: Improved Accuracy Tight Binding Model for Finite Temperature Electronic Structure Dynamics in Methyl Ammonium Lead Iodide (MAPbI3) David Abramovitch, Liang Tan Halide perovskites are promising photovoltaic and optoelectronic materials. However, computing electronic properties and dynamics at finite temperature is challenging due to nonlinear lattice dynamics and prohibitive computational costs for ab initio methods. Tight binding models decrease computational costs, but current models lack the ability to accurately model instantaneous atom displacement and reduced symmetry at finite temperature. We present a parameterized tight binding model for MAPbI3 capable of predicting instantaneous electronic structures for large systems based on atomic positions extracted from classical molecular dynamics. Our tight binding Hamiltonian predicts instantaneous atomic orbital onsite energies and hopping parameters accurate to 0.1 to 0.01 eV compared to DFT across the orthorhombic, tetragonal, and cubic phases, including effects of temperature, reduced symmetry, and spin orbit coupling. This model allows for efficient calculation of instantaneous and dynamical electronic structure at the length and time scales required to address coupled electronic and ionic dynamics, as required for predicting temperature dependence of carrier mass, band structure, free carrier scattering, and polaron transport and recombination. |
Monday, March 2, 2020 2:54PM - 3:06PM |
D63.00003: Materials Property Database for Hybrid Organic-Inorganic Perovskites and Application to Stability and Electronic Structure of (PEA)2PbI4 Xixi Qin, Xiaochen Du, Svenja Janke, Raul Laasner, Tianyang Li, Manoj Kumar Jana, Connor Clayton, Chi Liu, Sampreeti Bhattacharya, Juliana Mendes, Jun Hu, Dovletgeldi Seyitliyev, Ruyi Song, Matti Ropo, Franky So, Kenan Gundogdu, Wei You, Yosuke Kanai, David B. Mitzi, Volker Blum Hybrid organic-inorganic perovskites (HOIPs) are attracting significant attention as new semiconductor materials, due to their inherent tunability by varying both the organic and the inorganic components. However, keeping track of the dramatically increasing volume of materials data related to HOIPs is challenging. We here present an open database, "HybriD3" (Design, discovery and dissemination (D3) of data related to hybrid materials, https://materials.hybrid3.duke.edu), aiming to collect, curate, and make available materials data related to HOIPs. The database is open to the community and designed to accept community input for a broad set of data, i.e., experimental and computational, related to in principle any materials property. We demonstrate the use of the database for the widely investigated material pheneythylamine lead iodide, (PEA)2PbI4, for which several crystal structure refinements have been reported in past work. Using density functional theory including van der Waals effects, we identify the lowest-energy structure among them and provide the electronic band structure at a high level of theory (hybrid density functional theory including spin-orbit coupling). |
Monday, March 2, 2020 3:06PM - 3:18PM |
D63.00004: First-principles Study of Water Insertion Process on MAPbI3 Surface Md. Abdullah Asad, Masaki Hada, Kyosuke Sato, Yoichi Hasegawa, Ryota Nagaoka, Ryuji Mishima, Takeshi Nishikawa, Yoshifumi Yamashita, Yasuhiko Hayashi, Kenji Tsuruta We computationally investigate an insertion process of water into the methylammonium lead halide perovskite (MAPbI3), which has been attracting considerable interest during recent years due to its high performance in solar-cell application [1]. The rapid decomposition of MAPbI3 reaction with water has been recognized to be a major obstacle to outdoor applications [2]. To overcome this drawback process, it is important to identify the initial stage of water insertion into the MAPbI3. The first-principles calculation based on the density-functional theory is performed to investigate the water insertion process on outer surface layer of MAPbI3 slab model. Using the Nudged Elastic Band method, we find that the initial insertion process follows the three steps; approaching, re-orienting and finally sinking into the perovskite layer. This process requires approximately 0.60 eV to overcome an energy barrier, which agrees with an in situ X-ray diffraction (XRD) measurement of the reaction threshold of water molecules with the MAPbI3 crystal at room temperature [3]. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D63.00005: Theory of Layer Edge States in 2D Halide-Perovskites Jisook Hong, David Prendergast, Liang Tan Halide perovskites are one of the most promising candidate materials for photovoltaic and optoelectronic applications. Compared to the 3D organic-inorganic hybrid perovskites, the 2D layered perovskites exhibit greater tunability of band gaps and exciton binding energies, while solving the well-known stability issue of hybrid perovskites at the same time. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D63.00006: Calculating band gap distributions of halide perovskites with a first-principles tight-binding approach Maximilian Schilcher, Matthew Z. Mayers, Liang Tan, David Reichman, David Alexander Egger
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Monday, March 2, 2020 3:42PM - 3:54PM |
D63.00007: Calculations on shallow defect levels in CsPbBr3 Jun Kang It is well known that in metal-halide perovskite the dominant defects are shallow. However, accurately prediction of the shallow defect level from DFT calculation is still challenging due to two reasons. One is that the defect state wave function could be quite delocalized, thus a very large supercell is necessary to get converged results, which is beyond the capacity of traditional DFT method. The other one is that the band gap error of DFT would also affect the accuracy. Here we proposed a method to calculate the shallow defect levels combining the potential patching and the LDA-1/2 approaches (PP+LDA-1/2). The potential patching method allows the calculation of 105-atom supercells, and the LDA-1/2 method overcomes the band gap problem. We apply this method to calculate the shallow levels of the dominant intrinsic defects (VPb, VCs, VBr) in CsPbBr3. It is found supercells with over 104-atom needed to get converged energy. The predicted defect levels are only 15-70 meV away from the band edge, much smaller than previously reported results obtained from small supercell calculations. These results highlights the importance of large-supercell calculations in predicting shallow defect levels. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D63.00008: Structural and transport studies from air-stable hybrid perovskite thin films Randy Burns, Siphelo Ngqoloda, Christopher Arendse, Theophillus Muller, Sorb Yesudhas, Deepak K Singh, Suchismita Guha Traditionally, MAPbX3 (X = Br, I, or Cl) hybrid organic-inorganic perovskite films have been deposited with spin coating techniques which cause degradation under ambient atmospheric conditions. We demonstrate the feasibility of stable MAPbI3 thin films grown by a facile two-step low-pressure vapor deposition process in a single reactor. Absorption measurements confirm excellent stability after three weeks. In confluence with the absorption data, synchrotron x-ray diffraction experiments reveal good structural stability on the timescale of several months. Temperature dependent transport measurements show sharp inflection points of the resistance curve at distinct temperatures. One inflection point occurs precisely at the expected tetragonal to orthorhombic transition, however, another inflection deviates significantly from the expected tetragonal to cubic transition. Consequently, we conducted temperature dependent laboratory-based x-ray diffraction measurements that also suggest a transition below the commonly reported tetragonal/cubic transition temperature. Concerning device application, the MAPbI3 films were incorporated into solar cells that maintained the majority of their efficiency and energy yield on the timescale of weeks. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D63.00009: Frenkel-Holstein Hamiltonian Applied to Quaterthiophene-based 2D Hybrid Organic-Inorganic Perovskites Svenja Janke, Mohammad B. Qarai, Volker Blum, Frank Spano In two-dimensional hybrid organic-inorganic perovskites (HOIPs), both the organic and inorganic components can contribute to the electronic properties at the electronic frontier levels and hence open up a wide area for design of new materials with high tunability. For development of new devices like solar cells or light emitting diodes, the understanding of electronic excitations and their photophysical signatures plays a fundamental role. Here, we show by the example of quaterthiophene-based lead-halide HOIPs that the organic contribution to 2D HOIP absorption spectra can be theoretically appreciated employing a Frenkel-Holstein Hamiltonian that treats electronic coupling and electron-phonon coupling on equal footing. We relate changes in the spectra to structural changes in the organic layer that in turn are caused by variation of the halide anion. Specifically, we find that the strength of the excitonic coupling on the organic component decreases when the halide anion is varied from Cl to Br to I. Our research opens up a potential pathway for predicting optoeletronic properties of newly designed 2D HOIPs. |
Monday, March 2, 2020 4:18PM - 4:54PM |
D63.00010: Tunable Electronic Structure of 2D Hybrid Organic-Inorganic Perovskites from a First Principles Approach Invited Speaker: Volker Blum Layered (so-called two-dimensional, 2D) hybrid organic-inorganic perovskites (HOIPs) can be created by combining a wide range of possible inorganic components with an even broader range of organic molecules, offering considerable flexibility to fine-tune their synthesizability and properties. This talk focuses on computational predictions of the electronic (carrier, i.e., electron- and hole-like) energy levels of new 2D HOIP materials. Such predictions pose a considerable challenge due to high required levels of theory and large unit cells (hundreds of atoms) associated with typical 2D HOIPs. We here use high-precision, all-electron hybrid density functional theory including spin-orbit coupling, showing that this combination provides descriptions of the quantum-well like energy level alignment in lead halide based oligothiophene perovskites in excellent agreement with experiments. We then employ the same approach to predictively address the electronic properties of a broad range of further 2D HOIPs, including lead-free (Ag-Bi) based ones. As a final point, we show that the details of the atomic structure used to predict electronic properties matter significantly, even in a qualitative sense, by determining energy level alignments and, therefore, which component (organic or inorganic) forms the band edges. A complete structural understanding of a given target 2D HOIP is thus essential for faithfully predicting the properties that can be leveraged within this promising new semiconductor materials space. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D63.00011: Compounds with high macroscopically- averaged symmetries and low local symmetries: The consequence of lone-pair nematicity on electronic properties Xingang Zhao, Zhi Wang, Alex Zunger The knowledge of the appropriate unit cell for a compound is crucial for many physical studies e.g. band structure theory. Traditionally, one prefers to use the smallest cell consistent with the global symmetry, e.g. monomorphous cells containing a single structural motif. It is well known that at high temperatures local displacements have the well-known thermal origin due to dynamically thermal fluctuation. But besides thermal effects, some compounds have non-thermal intrinsic local displacements already at low temperatures (LT) due to the preference of chemical bonding for stabilizing certain low-symmetry structural motifs requiring for their representation larger than minimal unit cells. By calculating in DFT the relaxed total energies of numerous cubic phases of ABX3 compounds (X=oxygen or halogen) we identify special cases where the energy per formula unit decreases due to atomic displacements as the cubic cell size increases. Examples include cubic CsMX3 (M=Sn, Pb; X=Br, I), and PbMO3 (M=Ti, Zr, Hf) etc. These intrinsic, LT polymorphous networks are interesting because their properties (band gaps, etc.,) can be very different than those gleaned from their macroscopic averaged counterparts represented as a minimal unit cell. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D63.00012: Ligand Design Rules for Improving 2-D Organic-Inorganic Hybrid Halide Perovskite Moisture Stability Stephen Shiring, Brett Savoie Organic-inorganic hybrid halide perovskites are promising semiconductor materials due to their long carrier lifetimes, diffusion lengths, and tunable band gap. Two-dimensional (2-D) Ruddlesden-Popper halide perovskites are particularly interesting from an optoelectronics device standpoint due to broad range of organic ligands that can be incorporated into the perovskite lattice and ease of fabrication. However, a major challenge for perovskite optoelectronics is their sensitivity to moisture, leading to chemical instability and device reliability issues. Here, we show that judicious choice in selection of the surface cation for a 2-D perovskite prevents water from penetrating into and dissolving the inorganic layer. We use molecular dynamics simulations to elucidate general design rules for designing water-proofing surface cations, showing that the length/size of the surface ligand alone is not sufficient to suppress water penetration. Our results provide insight into the stability-enhancing mechanism and provide a path for designing perovskites with improved properties. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D63.00013: Interfacial Electromechanics Predict Phase Behavior of 2D Hybrid Halide Perovskites Chris Price, Jean-Christophe Blancon, Aditya Mohite, Vivek Shenoy Quasi - two dimensional mixed-cation hybrid halide perovskites (q-2DPK) have improved structural stability and device lifetime over their 3D perovskite counterparts. The addition of a large organic A’ cation to the bulk AMX3 structure gives the q-2DPK chemical formula A’2AN-1MNX3N+1 and introduces new synthetic degrees of freedom through the composition index N. Ordered lamellar structures form via coordinated M-X bond breaking and peculiar critical phase behavior emerges as a function of N. We propose a thermodynamic model parametrized by first-principles calculations to generate a phase diagram for the q-2DPK. We find that the difficulty in synthesizing phase-pure samples in the high-N composition range arises from the energetic competition between electrostatic interactions of opposing interfacial dipole layers and mechanical relaxation of interfacial stress. Our model shows quantitative agreement with experimental observations and explains the non-monotonic evolution of the lattice parameters with composition index N. This model is generalizable to the entire family of q-2DPK and can guide the design of optoelectronic and photovoltaic materials with enhanced environmental stability and reduced excitonic degradations to carrier transport. |
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