Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J15: Halide Perovskites I: Excitons and Charge CarriersFocus Live
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Sponsoring Units: DMP Chair: Ram Seshadri, University of California, Santa Barbara |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J15.00001: Efficient Interlayer Exciton Transport in Two-Dimensional Metal-Halide Perovskites Alvaro J Magdaleno, Michael Seitz, Michel Frising, Ana Herranz de la Cruz, Antonio I. Fernández-Domínguez, Ferry Prins Two-dimensional (2D) metal-halide perovskites have emerged as a more robust alternative to their three-dimensional counterparts. Due to quantum and dielectric confinement effects, excitons dominate the energy transport characteristics in the thinnest members of the 2D perovskites family. Recently we have reported on the in-plane exciton diffusion using transient photoluminescence microscopy, where high diffusivities were found (0.2 cm2/s for PEA2PbI4). Using the same technique, here, we will show that this material exhibits remarkably efficient out-of-plane exciton transport (0.06 cm2/s) as well. This out-of-plane diffusivity translates to a diffusion length that exceeds 100 nm, making it relevant to device design. Moreover, we show that the energy transfer steps that underly the out-of-plane transport occur on a sub-ps timescale. Such ultrafast timescales are over two orders of magnitude faster than predictions using Förster theory. We will discuss the shortcomings of Förster theory for the 2D perovskites. Our results show that the excitonic energy transport is considerably less anisotropic than charge-carrier transport for 2D perovskites. |
Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J15.00002: Exciton Propagation in Two-Dimensional Hybrid Perovskites Barbara Meisinger, Jonas-David Ziegler, Jonas Zipfel, Matan Menahem, Xiangzhou Zhu, Takashi Taniguchi, Kenji Watanabe, Omer Yaffe, David Egger, Alexey Chernikov Layered hybrid perovskites are a highly interesting class of materials with intriguing fundamental properties and emerging potential for optoelectronic applications. Conceptually, they represent natural quantum well systems composed of nanometer-thin sheets of inorganics separated by organic spacer molecules. Due to enhanced Coulomb interaction 2D perovskites host tightly-bound electron-hole pairs, known as excitons, dominating their optical response. While the properties of these quasiparticles have been broadly studied, their spatial behavior remains barely explored so far. Here, we report the results of our study of exciton diffusion in hBN-encapsulated 2D perovskites, monitored from liquid helium up to room temperature conditions [1]. We find efficient propagation of long-lived excitons at all temperatures above 50 K with characteristic features of free-particle transport. At lower temperatures we observe a non-trivial behavior of a rapidly expanding exciton population followed by a slow and even negative effective diffusion. We discuss our results in the context of efficient exciton-phonon coupling in a simplified framework of a semi-classical model and outline general considerations of exciton transport in these systems. |
Tuesday, March 16, 2021 3:24PM - 3:36PM Live |
J15.00003: Terahertz Phonons and Electron–Phonon Interactions in Two-Dimensional Lead Halide Perovskites Andrey Baydin, Fuyang Tay, Nolan Bitner, Jin Hou, Hao Zhang, Fumiya Katsutani, Nicolas Marquez Peraca, Jean-Christophe Blancon, Aditya Mohite, Junichiro Kono While Ruddlesden–Popper halide perovskites have attracted much attention in recent years due to their promising properties for applications in optoelectronics, they are also known to possess novel phononic properties due to the soft lattice as well as strong electron-phonon interactions. The lowest-frequency optical phonon modes in these materials lie in the terahertz (THz) frequency range. It has previously been demonstrated that in bulk perovskites both free carriers and optical phonons contribute to the THz optical conductivity with intriguing interterplay between them. Here, we used THz time-domain spectroscopy to study optical phonon modes in (BA)2(MA)n-1PbnI3n-1 samples with different values of n (1 to 5). We observed pronounced resonances in the 0.3-2.5 THz range and systematically studied them as a function of temperature, including the temperature range where a structural phase transition occurs in these compounds. Further, we performed optical-pump/THz-probe spectroscopy measurements, which elucidated the nonequilibrium dynamics and interactions of free charge carriers and phonons. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J15.00004: Plasmonically Enhanced Perovskite Quantum Dot Based Luminescent Solar Concentrators Albert DiBenedetto, Benaz Mendewala, Sayantani Ghosh Luminescent solar concentrators (LSCs) are attractive alternatives to solar energy harvesting, especially as they can capture both direct and diffuse sunlight. However, LSCs experience losses in efficiency with increasing size. To reduce these losses, plasmonic nanoparticles have been incorporated into quantum dot and dye based LSCs to enhance absorption, photoluminescence (PL) and efficiency, with varying degrees of success. Perovskite quantum dots (PQDs) are great candidates for LSCs due to their high absorption coefficient, high PL quantum yield and facile incorporation into planar structures. In this talk, we present a systematic study of CH3NH3PbBr3 PQDs incorporated with 5 and 10 nm gold nanoparticles (AuNPs) in LSCs. We fabricate both small scale (1.5 cm x 1.5 cm x 0.2 cm) and large scale LSCs (10 cm x 10 cm x 0.2 cm) via a dip coating technique and demonstrate low self-absorption losses despite a small Stokes Shift. Our devices exhibit optical efficiencies of 68% (small-scale) and 2.87% (the large-scale), which compare most favorably with previously tested, similarly scaled silicon quantum dot LSCs (2.86%). |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J15.00005: Polaronic Biexcitons in Metal Halide Perovskite Quantum Dots Ajay K. Poonia, MEGHA SHRIVASTAVA, Angshuman Nag, K V Adarsh Strong exciton-phonon interactions in the soft-polar lattice of metal halide perovskites result in large polaron formation, which profoundly dominates the optical and electronic properties. Quantum confinement further fosters the exciton-phonon coupling and leads to the exciton-polaron formation in the low dimension structures. Here, we study the exciton-exciton interactions in the background of lattice coupling in the CsPbBr3 quantum dots (QDs) using temperature and polarization-dependent transient absorption spectroscopy. We find that intervalley polaron pairing of charge carriers derives an unusually strong exciton-exciton interaction and leads to the occurrence of polaronic biexciton, a strongly coupled system of biexciton and polarons. It is observed that the ratio of biexciton to exciton binding energy (Haynes factor) is near unity for the CsPbBr3 QDs, which is one order larger than the bulk semiconductor and more than five times compared to 2D and quantum well semiconductors. It will pave the way for the creation of room-temperature quantum droplets and Bose-Einstein condensates of biexcitons. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J15.00006: Excitons in lead-halide perovskite nanocrystals from tight-binding GW/BSE approach Giulia Biffi, Yeongsu Cho, Roman Krahne, Timothy Berkelbach Lead-halide perovskite nanocrystals constitute a flourishing field of investigation due to their potential technological applications as tunable high-quantum-yield emitters[1]. Concerted research effort from both experimental and theoretical sides has helped in gaining a deeper understanding of the underlying parameters that play a role in determining the electronic and optical properties of these materials, such as the chemistry of the “A-site” cation or spin-orbit coupling[2]. Nevertheless, some fundamental quantities like the exciton binding energy and the multiplicity of the excited state are still a topic of debate. We addressed these issues with a tight-binding model parametrized on first-principle calculations and corrected within the GW approximation, and making use of the Bethe-Salpeter equation for the evaluation of the excitonic states[3]. This approach allows us to obtain the absorption spectra of methylammonium lead iodide nanocrystals of different dimensions and in different dielectric environments while retaining an atomic orbital description at each step. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J15.00007: Novel Absorption Feature due to Intrinsic Quantum Confinement in FAPbI3 Adam Wright, George Volonakis, Juliane Borchert, Christopher Davies, Feliciano Giustino, Michael B Johnston, Laura Herz In this study[1], I report the discovery of intrinsically-occurring nanostructures in FAPbI3, which exhibit quantum confinement effects manifested as an oscillatory absorption feature above the band gap. These features are present at room temperature but sharpen and become more apparent as the temperature is lowered. I demonstrate that the energetic spacings and temperature-dependence of the peaks vary in a manner consistent with quantum confinement intrinsically associated with the lattice of the material. I suggest the origin of this confinement to be nanodomains with an extent of approximately 10-20 nm. This interpretation is supported by correlating absorption spectra against ab initio calculations based on the bandstructure of FAPbI3 in the presence of infinite barriers, and simulations for superlattices with moderate barrier heights. I further explore ferroelectricity/ferroelasticity and delta-phase twin boundaries as two possible causes of these domains. Altogether, such absorption peaks present a novel and intriguing quantum electronic phenomenon in a nominally bulk semiconductor, offering intrinsic nanoscale optoelectronic properties without necessitating cumbersome additional processing steps. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J15.00008: Optical Phonon Assisted Carrier Dynamics in APbBr3 Single Crystals MEGHA SHRIVASTAVA, Abhinav Kala, Dmitry Dirin, Maryna I. Bodnarchuk, Maksym V Kovalenko, Venu Gopal Achanta, Adarsh K. V. The low-frequency phonon modes in lead halide perovskites (LHPs), responsible for intrinsic strong carrier-phonon coupling, has led to the observation of peculiar properties like long carrier-lifetime, long carrier diffusion length, moderate carrier mobility, etc. As the phonon population strongly governs the carrier dynamics, the fundamental understanding of the role of carrier-phonon coupling on carrier dynamics is crucial for the potential application of LHPs in optoelectronics. Herein, using steady-state photoluminescence (PL) and time-resolved spectroscopy, we demonstrate temperature-dependent carrier dynamics in APbBr3 (A= MA/Cs) single crystals. Strikingly, moving from cryogenic to room temperature, we observe an unusual blue-shift of PL and long carrier-lifetime on the order of ns. The PL blue-shift with temperature is in stark contrast to the red-shift observed in conventional semiconductors and is attributed to thermal expansion in the lattice. Whereas, the long carrier-lifetime at room temperature is ascribed to the dominance of optical phonon mediated polaron formation. The long-lived carrier at room temperature promotes the candidature of LHPs in photovoltaics. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J15.00009: Hot Carrier Cooling and Recombination Dynamics of Chlorine Doped Hybrid Perovskite Single Crystals La Moyne Mix, Dibyajyoti Ghosh, Jeremy Tisdale, Min Cheol Lee, Ken ONeal, Nicholas Sirica, Amanda Neukirch, Wanyi Nie wanyi@lanl.gov, Antoinette Taylor, Rohit P Prasankumar, Sergei Tretiak, Dmitry Yarotski Controlling the photoexcited properties and behavior of hybrid perovskites by halide doping has the potential to impact a wide range of emerging technologies, including solar cells and radiation detectors. We examined crystalline samples of methyl ammonium lead bromide substituted with chlorine (MAPbBr3-xClx) by transient reflectivity spectroscopy and non-adiabatic molecular dynamics (NAMD) simulations. At picosecond timescales, the addition of chlorine to the perovskite crystal increased the observed rate of hot carrier cooling by approximately 30%. Calculated nonadiabatic electron-phonon coupling constants increased with chlorine doping percentage mimicking the experimental data. At longer times, chlorine doped samples exhibit smaller ambipolar mobility and slower surface recombination velocity which may be a key factor in enhancing perovskite photoelectric devices. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J15.00010: Fine Features in the Photoluminescence of Single Crystal MAPbI3 Matthew Sheffield, Yue Yao, Isaac P Brown Heft, Heshan S.W Hewa Walpitage, Ye Liu, Zhenyi Ni, Jinsong Huang, Yan Li Hybrid organic-inorganic perovskites (HOIPs) have seen promising developments in recent years in photovoltaics, light emitting diodes, and lasing applications. Understanding the photoluminescence (PL) and exciton properties of HOIPs plays a key role in optimizing their performance. PL is an important technique for the investigation of carrier-phonon interactions and quantification of defects in a system. However, these properties are inaccessible when important signatures are masked by the wide inhomogeneous broadening seen in polycrystalline films. Here, we study PL on MAPbI3 single crystals in the low temperature orthorhombic phase. The high crystalline quality and well controlled defect density allow us to obtain PL spectra with narrow features and reveal previously unresolveable emissions. By comparing single crystals with low and moderate defect densities, the temperature and excitation intensity dependence data show evidence of the free exciton, bound excitons, and other defect dependent emissions in this material. The potential origin of these peaks will be discussed, as well as the measured exciton binding and exciton-phonon energies. These fine PL features will allow for further in-depth studies of the intrinsic photophysics and defect properties in HOIPs. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J15.00011: Spatiotemporal Dynamics of Photo-excited Electrons and Holes in Organometal Trihalide Perovskites by Microwave Impedance Microscopy Xuejian Ma, Fei Zhang, Zhaodong Chu, Ji Hao, Xihan Chen, Jiamin Quan, Xiaoqin (Elaine) Li, Kai Zhu, Keji Lai The outstanding performance of organometal trihalide solar cells benefits from the exceptional photo-physical properties of both electrons and holes in the material. Here, we directly probe the spatial diffusion and temporal dynamics of photo-generated free carriers in Cs-doped FAPbI3 thin films by nanoscale microwave impedance microscopy. The sample exhibits two relaxation times on the order of 1 μs and 10 μs, which are uniform across grains and grain boundaries. Using charge transport layers to selectively quench one type of carriers, we are able to attribute the short and long lifetimes to that of electrons and holes, respectively. Both types of carriers display a long diffusion length of 3 ~ 5 μm, indicating that the difference in lifetimes is compensated by their distinct mobility. The spatiotemporal microwave imaging provides the most direct method to accurately determine photo-physical properties, which are crucial for the development of perovskite solar cells. |
Tuesday, March 16, 2021 5:12PM - 5:48PM Live |
J15.00012: Hot Exciton Dynamics in Two-Dimensional Organic-Inorganic Hybrid Perovskites Invited Speaker: Cherie R Kagan Two-dimensional, organic-inorganic hybrid perovskites (2DHPs) are stoichiometric compounds |
Tuesday, March 16, 2021 5:48PM - 6:00PM Live |
J15.00013: Photoluminescence and Time Resolved Photoluminescence of Organic-inorganic Halide Perovskites Giti Khodaparast, Brenden A Magill, Kai Wang, Tao Ye, Carlos G Garcia, Stephen A McGill, Shashank Priya Organic-inorganic halide perovskites (OIHP), where perovskites layers are separated by organic spacers, can be engineered to have photoluminescence (PL) emissions from UV to IR regions, in addition to power conversion efficiencies of more than 24%. This class of materials offers broad tunability through controlling the number of atomic layers in the quantum well via perovskite composition and the spacer thickness depending on what organic groups are incorporated. In this work we present PL and time resolved PL (TRPL) measurements of these materials as a function of temperature and magnetic field, including: BA2PbI4, BA2MA1Pb2I7, and BA2CuCI4 where BA2 represents (CH3(CH2)3NH3)2, and MA: CH3NH3. Both BA2PbI4 and BA2CuCI4 have a single layer of perovskite material separated by an organic cation layer while BA2MA1Pb2I7 has two atomic layers of perovskite. Our observations indicate the existense of both free and trapped excitons. |
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