Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G21: Perovskites and Chalcopyrites for Energy Applications |
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Sponsoring Units: GERA Chair: Matthew Sheldon Room: 302 |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G21.00001: Chemical trends of absolute volume deformation potentials of all-inorganic ABX3 halide perovskites Shanshan Wang, Menglin Huang, Shiyou Chen The absolute volume deformation potential (AVDP) is an important physical quantity that describes the energy level shift under pressure, which, however, has not been investigated for halide perovskites. We systematically calculate the valence band maximum (VBM) and conduction band minimum (CBM) AVDPs of all-inorganic ABX3-type perovskites (where A = K, Rb, Cs; B = Ge, Sn, Pb; X = Cl, Br, I) in cubic structure using ab-initio calculation methods. Although it was shown that spin-orbit coupling played an important role in the band structure calculation of ABX3 perovskite, we prove that it has negligible effect on AVDP calculation. We show that the AVDPs of VBM are all negative and large, indicating the energy level will shift down when the volume increases, while AVDPs of CBM are mostly positive and small. There are clear trends in the calculated AVDPs of both VBM and CBM which will be discussed. Our results suggest that strain is an effective way to adjust the energy level of valence band edge in ABX3, which may be of great significance to design optoelectronic devices. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G21.00002: Relative stability of perovskite and non-perovskite phases of
inorganic trihalogeno germanates. Walter Lambrecht, Santosh Kumar Radha One of the main problems of halide perovskites is the existence of competing non-perovskite phases. Here we focus on (Cs,Rb)GeX3 compounds which exist either in a rhombohedrally distorted ferroelectric perovskite phase exhibiting cornersharing octahedra or a monoclinic and various orthorhombic phases with edge-sharing octahedra. We show that the GeX3 tetrahedral building blocks are arranged antiferroelectrically (AFE) in he monoclinic phase and ferroelectrically (FE) in the perovskite phase. The electrostic dipole interaction favors the AFE arrangement but the additional bond formation favors the perovskite. A spin model and first-principles calculations explain why the Rb based compounds prefer the monoclinic and Cs compounds prefer the perovskite form. Similar phases exist for CsSnX3 .The different structural arrangement is accompanied by a large change in band structure with a much larger gap and flat bands in the monoclinic form, which is unsuitable for photovoltaic applications. This new insight in the stability of these phases suggests the use of an electric field to control the phase transition. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G21.00003: Contrasting GGA and hybrid functionals description of dynamic properties of CsPbI3 Ali Kachmar, Marcelo Carignano Caesium lead iodide perovskite exhibit similar structural properties than methylammonium (MA) lead iodide, in particular with respect to the inorganic cage. Both systems show anharmonic behavior in the halide dynamics. Having Cs instead of MA as the cation allows for a study based on expensive hybrid functionals. Considering that most of the reported first principles molecular dynamics simulations were performed using GGA functionals, it becomes pertinent to question what are the corresponding results when the forces are accounted for using the more accurate hybrid functionals. In this work we present a comparison between PBE and HSE functionals for the anharmonicity of the halide atoms at high temperature. Our study is based on first principles molecular dynamics simulations on large 444 supercells and trajectories extending up to 40 ps. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G21.00004: Carrier Dynamics and Recombination in Low-Dimensional Halide Perovskites: Role of Structural Fluctuations Dibyajyoti Ghosh, Amanda Neukirch, Sergei Tretiak Low-dimensional halide perovskites have demonstrated promising luminescence properties for light-emitting diodes due to their high radiative recombination rate.[1] However, the lack of a complete understanding of the structure-property relationship hinders the systematic design of these materials to enhance their luminescence efficiency. Combining state-of-the-art nonadiabatic molecular dynamics and time-domain density functional theory, we explore the substantial effects of structural fluctuations on the excited state dynamics and carrier recombination in these perovskites. Here, I will demonstrate how structurally rigid perovskites experience weaker electron-phonon interactions, resulting in suppressed non-radiative carrier recombination and enhanced photoluminescence quantum yield (PLQY).[2,3] Our work revealed that stacking of the spacer cations, and halogen composition of the inorganic layers substantially tune the PLQY of these materials. Based on these understanding, we further propose a combination of suitable spacer cations and inorganic layer compositions to improve the PLQY of low-dimensional halide perovskites. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G21.00005: Tailoring structural transitions in layered 2D perovskites using light Wenbin Li, Hao Zhang, Siraj Sidhik, Mercouri Kanatzidis, Jacky Even, Jean-Christophe Blancon, Aditya Mohite Organic-inorganic (hybrid) perovskite have recently emerged as a new semiconductor platform for next generation optoelectronics devices. These perovskite solids feature weak bonds between their organic and inorganic building blocks, which results in an intrinsic softness and dynamics disorder of the lattice and an acute sensitivity to external stimuli. For example, our group demonstrated that continuous sunlight illumination leads to a uniform expansion of the perovskite lattice, which impact the optoelectronic properties of the three-dimensional perovskites. In particular, this effect is beneficial as it helps cure electronics impurities and lowers energetic barriers near the surface/interface. Here, we present comprehensive in-situ light induced structural dynamics to layered two-dimensional (2D) hybrid perovskites. We correlate the changes in the structure of the 2D perovskite to modification of both the physical properties and the figures of merit in solar cells. We propose a new microscopic model to explain the evolution of the structure and optoelectronic properties under an external stimulus. These results demonstrate that structural characterization of hybrid perovskite under external perturbation is key in unraveling the fundamental physics of these materials. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G21.00006: Optimization of recombination region within inorganic perovskite light emitting diodes Lindsey Gray, Xiaoheng Yan, Xiang Zhang, David Carroll Recent advances in metal halide perovskite-based LEDs have included high brightness, extended lifetimes, and excellent color saturation in comparison with other thin film light sources such as OLEDs. We have shown that many of these properties can be traced to nanoscale sub-phase formation within the larger perovskite matrix, which leads to exciton self-trapping. However, since such phase formation modifies carrier mobility, a significant challenge in per-LEDs is optimizing device design such that the driving voltage, sensitive of recombination zone formation and position within the emitting layer, is overcome. In this work we examine the use of various organic layers, such as poly-TPD, in barrier formation and recombination zone stability. We show that interface preparation between the perovskite and transport layers can play a major role in barrier formation. Focusing on the correlation of brightness and efficiency with device structure modification, we demonstrate that optimized carrier balance can allow for maintained efficiency over a wide range of driving voltages and brightnesses. |
Tuesday, March 3, 2020 12:27PM - 12:39PM |
G21.00007: Origin of Anomalous Capacitive Behaviour in Perovskite Light Emitting Diodes Ramesh Kumar, Jitendra Kumar, Priya Srivastava, Monojit Bag Owing to the exceptional optoelectronic properties, Hybrid halide perovskites (HHPs) have attracted great attention leading to the variegated application in optoelectronic devices 1. Study of carrier kinetics in perovskite solar cells using Impedance Spectroscopy (IS) has been the topic of research since the last few years2. But, research in Perovskite LEDs (PeLEDs) is still sparse. |
Tuesday, March 3, 2020 12:39PM - 12:51PM |
G21.00008: Identifying electronic descriptors to predict work functions of perovskite electrodes Yihuang Xiong, Weinan Chen, Wenbo Guo, Hua Wei, Ismaila Dabo The ability to predict work functions of semiconductor electrodes is critical to the development of photocatalytic and electrocatalytic systems. Understanding the compositional and structural dependence of the interfacial electronic structure of semiconductors could enable us to screen and select appropriate functional materials for electronic applications. We address this problem with a focus on perovskite oxides (ABO3) in the metastable cubic phase by enumerating the possible compositions for A- and B-site cations. We analyze the computed work functions by means of statistical learning using elemental and bulk chemical descriptors. The resulting descriptor-based model not only delivers accurate predictions of computed work functions using a limited number of features, but also allows us to interpret the complex correlations between electronic levels and surface structure across a vast chemical space. |
Tuesday, March 3, 2020 12:51PM - 1:03PM |
G21.00009: Modeling the dynamics of interacting defects, charge carriers, and excitons in perovskite solar cells Barbara Sanborn, Abdul Shaik, Dragica Vasileska This talk presents calculations based on a theoretical model that includes the dynamics of excitons, free charge carriers, and electrically active defects, to study the stability of perovskite solar cells. Previously, the PVRD-FASP tool was developed and released for public use (www.pvrdfasp.com) to model metastability and reliability issues of solar cells. In the model, charge carriers and electrically active defect centers are treated on an equal footing, as both obey the same reaction-kinetic equations: the continuity, drift-diffusion, and the Poisson equations. The rate terms in these equations are highly non-linear and require solution of a system of stiff partial differential equations. To efficiently solve such systems, a reaction solver based on the forward Euler method implicit in time with a Newton step was proposed and implemented. The Jacobian for the Newton step was analytically calculated. The PVRD-FASP tool was used successfully to study the role of Cu migration in CdTe solar cells. In current work, the theoretical model of the tool is expanded to include the dynamics of excitons. The expanded solver is used to study the stability of perovskite solar cells in the presence of light-induced formation and annihilation of defects acting as carrier trap states. |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G21.00010: The interplay of bulk and interfacial dynamics in methylammonium lead triiodide perovskite solar cells revealed via current noise spectroscopy Kevin Davenport, Mark Hayward, Andrey Rogachev Hybrid organic-inorganic perovskite solar cells are one of the most promising emerging technologies capable of competing with silicon devices, chief among them those based on methylammonium lead triiodide (MAPbI3). Fundamental understanding of electrical transport and degradation processes in these devices, however, is important for commercial realization. We have performed cross-correlated current noise spectroscopy on a series of MAPbI3 devices. Under illumination, we find near-full-scale shot noise (Fano factor F ~ 1), indicating the dominance of a single element in the device stack. We further observe generation-recombination noise which emerges with illumination and increasing device thickness. This signal is attributed to radiative bimolecular recombination. Finally, we observe a 1/fa flicker noise (a ~ 1.4) which deviates from the expected I2 dependence. This indicates the superposition of canonical resistance fluctuations and a current and/or light-driven source, likely the migration of halide ions through the bulk. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G21.00011: Understanding the role of Sn substitution and Pb vacancy in FAPbBr3 perovskites: A hybrid functional study Manjari Jain, Saswata Bhattacharya Hybrid inorganic-organic perovskites (HIOPs) solar cells have attracted intense attention because of its high carrier lifetime, long diffusion length and low manufacturing cost. Formamidinium Lead Bromide (FAPbBr3), a HIOPs is immensely promising class of material for photovoltaic application. However, due to presence of hazardous Pb, its application to real life is hindered. Therefore, its our profound interest to understand if substitution of adatoms (e.g. Sn, Ge) or creation of Pb-vacancy [Vc] or doing the same simultaneously will be effective considering its efficiency in solar cell devices. |
Tuesday, March 3, 2020 1:27PM - 1:39PM |
G21.00012: Absence of large valence band Rashba splitting in metal halide perovskites Oliver Rader, Maryam Sajedi, Maxim Krivenkov, Dmitry Marchenko, Andrei Varykhalov, Jaime Sánchez-Barriga, Anoop Chandran, Irene Aguilera Organic and inorganic lead halide perovskites share the same properties of high efficiency in energy conversion and high spin-orbit interaction. For both, a large Rashba effect has been invoked to be responsible for the high efficiency by prohibiting direct recombination. In the valence band of methylammonium lead bromide a static Rashba effect has been reported by angle-resolved photoemission (ARPES) and circular dichroism with giant values of 0.7 to 1.1 eV nm [1]. We present precise ARPES band dispersion measurements of methylammonium lead bromide and cesium lead bromide to show that a Rashba effect of the reported size does not exist. Moreover, we use spin-resolved ARPES to confirm the conclusions. We also observe a large circular dichroism effect and demonstrate that this effect does not imply any measurable spin polarization and Rashba effect. Our results exclude a static Rashba effect in the valence band as origin of the high efficiency of metal halide perovskites. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G21.00013: Simulations of the electronic stopping power in perovskites Mario Borunda Electronic stopping power describes the energy transfer rate to electrons in material during ion irradiation. We use time-dependent density functional theory to calculate electronic stopping power in triple-cation perovskites (formamidinium, methylammonium, and cesium). These materials have some of the highest power conversion efficiencies for perovskite-based photovoltaics. From simulations we can estimate the stopping process of ions and this would have implications for the use of photovoltaic devices for space missions. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G21.00014: Role of Cu deficient layer in chalcopyrite based solar cells Abhishek Sharan, Joel Varley, Anderson Janotti Chalcopyrites are a demonstrated material platform for realizing efficient thin-film photovoltaics, with the most well-known Cu(In,Ga)Se2 (CIGS) based solar cells exceeding 23%. The presence a Cu-poor phase layer between the absorber and buffer layers in CIGS solar cells is known to enhance device performance, however, the overall properties and role of very thin layer remain poorly understood. Using first principles calculations based on density functional theory with screened hybrid functionals, we explore the electronic structure and stability of a series ordered vacancy compounds (or OVCs) as a model for the Cu-poor phase layer. We calculate band offsets between the OVCs and defect-free chalcopyrite Cu and Ag based compounds (ABX2 where A = Cu, Ag; B = In, Ga, Al and X = S, Se). Using AB3X5 and AB5X8 stoichiometries as model OVC systems, we report on the variation of the band gap with A/B ratio and discuss the trends in other Cu and Ag-based chalcopyrites beyond CuInSe2. We additionally perform device-level simulations to understand the implications of formation of OVCs, finding that valence band offsets of OVCs are favorable for hole transport, while the conduction band offsets of chalcopyrites beyond CuInSe2-based absorbers may be detrimental to device performance. |
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