Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T41: Low-Dimensional Halide Perovskites |
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Sponsoring Units: DMP Chair: Ross Kerner, National Renewable Energy Laboratory; Barry Rand, Princeton University Room: Room 319 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T41.00001: Surface Effects on Anisotropic Photoluminescence in One-Dimensional Halide Perovskites Luke McClintock, Long Yuan, Ziyi Song, Michael T Pettes, Dmitry A Yarotski, Rijan Karkee, David A Strubbe, Liang Tan, Azza Ben Akacha, Biwu Ma, Yunshu Shi, Valentin Taufour, Dong Yu One-dimensional (1D) hybrid organic-inorganic perovskites exhibit strongly anisotropic optical properties, highly efficient light emission, and large Stokes shift, holding promises for novel photo-detection and lighting applications. However, the fundamental mechanisms governing their unique optical properties and in particular the impacts of surface effects are not understood. Here, we investigate C4N2H14PbBr4 by polarization dependent time-averaged and time-resolved PL (TRPL) spectroscopy, as a function of photoexcitation energy. Surprisingly, we found that the emission under photoexcitation polarization parallel to the 1D molecular chain can be either stronger or weaker than that under perpendicular polarization, depending on the excitation energy. We attribute the excitation energy dependent anisotropic PL to fast nonradiative surface recombination, as supported by TRPL measurements and first principles calculations. Our comprehensive studies provide a more complete picture for a deeper understanding of the optical anisotropy in 1D perovskites. |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T41.00002: Anisotropy and exciton self-trapping in the 1D perovskite C4N2H14PbBr4 from first principles Rijan Karkee, David A Strubbe Low-dimensional organic-inorganic metal halide hybrids have remarkable optical and electronic properties and better stability against heat and moisture. We study a 1D perovskite of formula C4N2H14PbBr4, consisting of PbBr chains separated by organic cations. Experiments showed a large Stokes shift (0.83 eV) with broadband emission [Nat Commun 8, 14051 (2017)] which hints at interesting photo-physics involving self-trapped excitons. We calculate the highly anisotropic optical, bandstructure, vibrational, and transport properties of this 1D perovskite, which could be used for polarized photodetectors and LEDs. The bands are highly dispersive along PbBr chains and nearly flat along other directions, leading to a factor of 100 in conductivity as calculated by Boltzmann transport. We find an indirect gap and a direct gap which is just slightly higher in energy. Our GW/Bethe-Salpeter equation calculations using BerkeleyGW show strong anisotropy in absorption, especially in the lowest exciton which has a binding energy of about 1 eV. We calculate excited-state forces based on these results and our vibrational calculations to find the coupling of excitons and phonons, from which we can predict exciton self-trapping and mechanisms of broadband emission. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T41.00003: A 2D lead halide hybrid system with the lowest bandgap and exciton binding energy Debasmita Pariari, Sakshi Mehta, Sayak Mandal, Arup Mahata, Titas Pramanik, Sujit Kamilya, Trupthi D Chonamada, Arya Vidhan, Pralay K Santra, Shaibal K Sarkar, Filippo De Angelis, Abhishake Mondal, Dipankar Das Sarma Despite the rapid developments of hybrid lead halide perovskites as light harvesters and hole-transport materials, the inadequate environmental stability of these materials imposes an obstruction on the way to its commercialization. Insertion of large, hydrophobic cations at the A-site enhances the environmental stability at the cost of breaking 3D structure to obtain its 2D derivatives, resembling quantum well type structures with high bandgap (Eg) as well as large exciton binding energy (Eb), detrimental to the photovoltaic performances. In this work, a new 2D hybrid system is synthesised with a new organic spacer molecule. Unlike other n=1 2D systems reported in the literature, the Pb-I-Pb angle of the synthesized material is 180º, which implies an absence of any inter-octahedral tilt distortions in the inorganic lattice, leading to the smallest (2.19 eV) amongst the series of (A)nPbI4 (where n = 1 or 2) with any organic spacer molecule (A). The estimated (~50 meV) from a series of temperature dependent absorption measurements is close to that of the 3D limit of the hybrid perovskites. Moreover, the material exhibits exceptional water stability, making it an excellent candidate for photovoltaic applications. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T41.00004: Charge Transfer in Organo-metallic Halide Perovskite Thin Film/Quantum Dot Heterostructures Jorge Arteaga, William Delmas, Melissa Guarino-Hotz, Jin Zhang, Sayantani Ghosh Organo-metallic Halide Perovskite (OMHP) thin films have been of great interest for photovoltaics due to the rate at which their power conversion efficiency (PCE) has increased, as well as for their low production cost. Perovskite quantum dots (PQDs) have also garnered interest for similar applications. However, thin films have stability issues in the presence of moisture or oxygen, and PQDs have not demonstrated high enough PCE. Some of these issues could be addressed by combining the two to form a heterostructure of PQDs layered atop an OMHP thin film. We investigated charge transfer mechanisms between spin-coated methylammonium lead iodide (MAPI) thin films and PQDs. We varied the PQD composition and surface ligands for a systematic study where the PQDs all had band gaps larger than that of MAPI, allowing for multiple routes of energy and charge transfer. Using photoluminescence (PL) spectroscopy, we found that the emission from PQDs functionalized with aliphatic ligands, was quenched while the MAPI emission intensity was increased indicating energy or charge transfer between the PQD and thin film layer. When varying the excitation energy to above and below PQD band gap, we found charge carrier recombination lifetimes were affected by the excitation energy only for films with PQDs with conducting ligands, indicating ligands played a role in the charge transfer mechanism. In addition to these studies, further investigations are in progress to better quantify the effect of charge transfer between PQDs and thin films on the electronic properties of the heterostructures. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T41.00005: Density Functional Theory Treatment of Site-Disordered Silver Iodo-Bismuthate Semiconductors Victor T Barone, Blair Tuttle Silver iodo-bismuthates, a class of derivative metal-halide perovskite materials, are promising candidates for applications including indoor photovoltaics, radiation detectors, and flexible electronics. Their large degree of site-disorder has prevented first principles calculations of all but the simplest material structures. In this study, we use a cluster expansion description of the total energy and a simulated annealing minimization routine to determine low-energy structures of the NaVO2-like Ag-Bi-I materials. It is found that 92 clusters are capable of describing greater than 1017 possible cell configurations to an average accuracy of 11 meV/atom. With the low-energy cells, we employ density functional theory to calculate optoelectronic properties such as the effective masses and absorption spectra. It is found that fundamental properties, such as the experimental band gaps, only agree with experimental values for the lowest-energy structures, indicating a need for the proposed efficient ground-state search method. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T41.00006: Amplified Spontaneous Emission in Facet Engineered Metal Halide Perovskite Nanocrystals Santu K Bera, Suman Bera, Narayan Pradhan, K. V. Adarsh Lead halide perovskite nanocrystals exhibiting rich chemical, structural, and optical tunability are at the forefront of current research due to their defect-tolerant electronic structure, extremely narrow absorption and emission line widths, and ability to control their surface or facet chemistry. Significant advances have been achieved in improving device efficiencies by varying ligand, precursor, size of the NCs, and cation-anion compositions, etc. However, all these studies are confined to a six-faceted hexahedron (cube/platelet) shape. In contrast, for the first time, we studied a new design strategy of facet engineering to reduce the gain threshold of amplified spontaneous emission by many-folds in NCs of the same concentration and edge length. We achieved this hallmark result by controlling the Auger recombination rates dominated by processes involving NC volume and thermalization time to the emitting states by optimizing the number of facets from 6 (cube) to 12 (rhombic dodecahedron) and 26 (rhombicuboctahedrons) in CsPbBr3 NCs. For instance, we demonstrate a two-fold reduction in Auger recombination rates and thermalization time with increased number of facets. The gain threshold can be further reduced ∼ 50% by decreasing sample temperature to 4K. Our systematic studies offer a new method to reduce the gain threshold that ultimately forms the basis of nanolasers. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T41.00007: Circular and linear polarized reflectivity of intra-plane and inter-plane excitons in 2D phenethylammonium lead iodide single crystal Xiaomei Jiang 2D phenethylammonium lead iodide (2D-PEPI), being an exemplary 2D hybrid organic-inorganic perovskites having Ruddlesden-Popper structure, has attracted substantial research interest. Having a natural multiple quatum well (MQW) structure with interdigitated organic and inorganic layers, 2D-PEPI has tunable band structure. 2D-PEPI also possesses strong spin-orbit coupling (SOC) owing to the inclusion of the ‘heavy atom’ lead (Pb), with the presence of inversion symmetry breaking that may originate from structural imperfections and interfaces, giant Rashba splitting was reported by spin related circular photogalvanic effect (CPGE). Due to quasi-2D quantum and dielectric confinements, the excitons in 2D-PEPI are tightly bound with binding energy on the order of a few hundreds meV. Two types of excitons co-exist in 2D-PEPI, namely the free exciton and bound exciton associated with edge states. In this work, we measure polarized photoluminescence and reflectivity and CPGE of 2D-PEPI single crystal and confirm that the free exciton is in the MQW plane, whereas the bound exciton possesses an out-of-plane dipole moment. By comparing the results from circular polarized reflectivity with the CPGE current, we show that the spin-polarized current in 2D-PEPI originates from the interplane bound exciton, while the intraplane free exciton does not produce such current. Our finding is important to guide the design of a cost-effective MQW spintronic devices made from solution process. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T41.00008: Electro-Absorption Spectroscopy of Hybrid Organic-Inorganic Perovskites Heshan S Hewa Walpitage, Dipak Khanal, Zeev V Vardeny The method of Electro Absorption (EA) related to the third-order nonlinear optical susceptibility allows probing electronic states of semiconductors better than linear absorption since it is a modulation technique. Using the EA spectroscopy in two-dimensional (2D)- and three-dimensional (3D)-hybrid organic-inorganic perovskites (HOIP) at various temperatures, we obtained the optical band gap, the 1s exciton energy, and the exciton binding energy (Eb) in these materials. We found that whereas Eb is of the order of 20 meV in 3D-HOIP, it is of the order of 250 meV in 2D-HOIP due to dielectric and dimensionality enhancement. We also found the signature of internal fields in some 2D-HOIP that indicates the existence of ferroelectricity in these compounds. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T41.00009: Studying the Effect of Solvent Interactions in Fabricating High Purity 2D Perovskites for Optoelectronic Applications Mohammad Hossein Khalili Samani, Siraj Sidhik, Amanda B Marciel, Aditya Mohite, Shahryar Ramezani Bajgiran 2D perovskites have attracted attention due to their higher stability in comparison their 3D counterparts. However, attaining phase-pure 2D perovskites has been a challenge. Recently, our group showed an efficient way to make high phase purity (>95%) 2D Ruddlesden-Popper (RP) perovskite films that achieve solar cells with efficiencies greater than 17%. To extend our processing method to other 2D perovskites (Dion-Jacobson, alternating cation), a detailed study of solvent interactions with synthesized crystals/precursors is required. The solvent-3D perovskite interactions have been well studied to provide criteria for solvents that can produce high quality 3D perovskite films for solar cells. However, solvent interactions with the 2D perovskite are poorly understood. In this study, we investigate the influence of solvent dielectric constant, donor number, and Hansen parameter to predict interactions between 2D perovskite precursors/crystals and the solvent. We perform dynamic light scattering (DLS) correlated with microscopy, absorption, and GIWAXS measurements. Our initial results show a strong effect of various solvents on the 2D perovskites, building towards our end goal of fabricating phase-pure films of RP, DJ, and ACI for LED, and solar cells applications. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T41.00010: Revealing Electronic Properties in Template-Grown Perovskite CsPbBr3 Nanorods Yize Stephanie Li, Eduardo Avila-Lopez, Shuang Liang, Isaac Elias, Zhiqun Lin We develop a general and vibrant bottlebrush-like block copolymer nanoreactor platform to craft a library of one-dimensional (1D) all-inorganic perovskite CsPbBr3 nanorods (NRs) [1]. We capitalize on contactless dielectric force microscopy (DFM), a novel contactless scanning probe microscopy (SPM)-based imaging technique, to probe electronic properties in these templated CsPbBr3 NRs. It is found that all freshly prepared CsPbBr3 NRs samples exhibit ambipolar behaviors, indicating an improved control of their electronic properties over their nanowire (NW) counterparts synthesized via the conventional hot-injection method [2]. Moreover, template-grown CsPbBr3 NRs demonstrate better nanoscale electronic homogeneity than conventional ones [2]. As such, templated CsPbBr3 NRs represent promising building blocks for electronic and optoelectronic applications that require uniform polarity and nanoscale electronic homogeneity. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T41.00011: Rationally-Designed Organic Ligands for Water-Proofed 2D Perovskites Zih-Yu Lin, Stephen B Shiring, Yao Gao, Letian Dou, Brett M Savoie Two-dimensional (2D) halide perovskites have attracted considerable attention as semiconducting materials due to their broader design space of organic ligands compared to their 3D counterparts while retaining favorable properties such as solution-processable, long carrier diffusion length and lifetime, high carrier mobility, etc. However, perovskites suffer from environmental stability issues, particularly intolerance to moisture, that limit their device applications. Here, the role of organic ligands in improving the water-proofing ability of perovskite is interrogated by a joint computational and experimental study: free energy (FE) calculations for water penetration and the synthesis and characterization of down-selected ligands. The FE curves and the subsequent experimental synthesis on investigated aliphatic and conjugated ligands with systematically varied length, bulkiness, and backbone rigidity revealed two chief components for effective water-proofing: (1) ligands length; (2) small free volume, i.e., a large cross-section, which can be realized by increasing terminal bulkiness or modifying backbone torsion. These findings pave the way for the use of π-conjugated molecules with water-proofing while retaining desirable optoelectronic properties and functions. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T41.00012: Biexcitons in lead halide perovskite nanocrystals Yoonjae Park, David T Limmer Lead halide perovskite nanocrystals are the subject of great interest owing to the unique photophysical properties of perovskites combined with the controllable properties. The complex structure and anharmonic nature of perovskites make theoretical study challenging, and a number of experimental observations have defied analysis. For example, recent reports of exciton-exciton interactions in perovskite nanocrystals have reported a potential antibinding behavior. However, the large variance in the size of nanocrystals, spectral drift, and thermal broadening of spectral lines render these reports controversial. Using quasiparticle-based path integral molecular dynamics within the effective mass approximation, we have studied the interplay of anharmonic lattice degrees of freedom, dielectric confinement, and electronic correlation to understand the multiparticle excitations over a range of nanoparticle sizes. These detailed molecular models are compared with simplified harmonic models. |
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