Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E34: Hybrid Organic-Inorganic Halide Perovskites IIIFocus
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Sponsoring Units: DMP Chair: Oana Jurchescu, Wake Forest University Room: 297 |
Tuesday, March 14, 2017 8:00AM - 8:36AM |
E34.00001: Halide Perovskites: New Science or ``only'' future Energy Converters? Invited Speaker: David Cahen Over the years many new ideas and systems for photovoltaic, PV, solar to electrical energy conversion have been explored, but only a few have really impacted PV's role as a more sustainable, environmentally less problematic and safer source of electrical power than fossil or nuclear fuel-based generation. Will Halide Perovskites, HaPs, be able to join the very select group of commercial PV options? To try to address this question, we put Halide Perovskite(HaP) cells in perspective with respect to other PV cells. Doing so also allows to identify fundamental scientific issues that can be important for PV and beyond. What remains to be seen is if those issues lead to new science or scientific insights or additional use of existing models. Being more specific is problematic, given the fact that this will be 4 months after writing this abstract. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 9:12AM |
E34.00002: Confinement Effects in Corner-, Edge- and Face-sharing Iodine-based Hybrids Invited Speaker: Thomas Palstra We investigate organic-inorganic hybrids that combine electronic functionality of the perovskite structures and structural flexibility of metal-organic framework compounds. The chemistry of inorganic materials offers a wide range of band gaps or bandwidths with high carrier density and mobility, magnetic interactions, ferroelectric transitions and thermal stability. On the other hand, organic solids provide nearly unlimited flexibility in structural diversity, good polarizability and they can also be made conductive. The aim of investigating these hybrid materials is to utilize the chemical diversity of the organic moieties with the physical properties of the inorganic moieties to produce useful combinations or even completely new phenomena. We illustrate the opportunities by showing that the structure and properties of the inorganic block can be controlled by using different organic moieties, without the need for substitutions or dopants. References: ``Confinement Effects in Low-Dimensional Lead Iodide Perovskite Hybrids'' by Kamminga, ME, Fang, HH, Filip, MR, Giustino, F, Baas, J, Blake, GR, Loi, MA, Palstra, TTM, Chem.Mater. vol.28, p4554, 2016. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E34.00003: Dynamic elasto-plastic behavior of lead-halide perovskite single crystals Marcos Reyes-Martinez, Ahmed Abdelhady, Makhsud Saidaminov, Duck Young Chung, Osman Bakr, Mercouri Kanatzidis, Wole Soboyejo, Yueh-Lin Loo The ease of processing hybrid organic-inorganic perovskite (HOIPs; having the general composition of ABX$_{\mathrm{3}})$ films from solution and at mild temperatures promises the use of their unique optoelectronic properties in deformable technologies, including flexible sensors and displays. To successfully apply these materials in deformable devices, knowledge of their mechanical response to dynamic strain is necessary. We elucidate the time- and rate-dependent mechanical properties of HOIPs and an inorganic perovskite (IP) single crystal by measuring nanoindentation creep and stress relaxation. The observation of pop-in events and slip bands on the surface of the indented crystals demonstrate dislocation-mediated plastic deformation. The magnitudes of creep and relaxation of both HOIPs and IPs are similar, negating prior hypothesis that the presence of organic A-site cations alters the mechanical response of these materials. Moreover, these samples exhibit a pronounced increase in creep and stress relaxation as a function of indentation rate whose magnitudes reflect differences in the rates of nucleation and propagation of dislocations within the crystal structures of HOIPs and IP. This contribution provides understanding that is critical for designing perovskite devices capable of withstanding mechanical deformations. [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E34.00004: Continuous-wave exciton-polariton lasing in cesium lead bromide perovskite microcrystal cavities Tyler Evans, Andrew Schlaus, Yongping Fu, Xinjue Zhong, Timothy Atallah, Louis Brus, Song Jin, Xiaoyang Zhu Lead halide perovskite microcrystals (MCs) have been demonstrated in pulsed lasing with high quantum yields, low thresholds, and broad wavelength tunability. However, continuous-wave (CW) lasing, which is essential to a wide range of applications, has not been possible to date. This is due to the difficulty in achieving a steady-state population inversion without catastrophic thermal damage. Here we demonstrate coherent light emission from polariton condensates formed in perovskite MC cavities under CW conditions. Analysis of the nonlinear polariton dispersion reveals exceptionally strong light-matter interaction characterized by a vacuum Rabi splitting of 0.20$\pm$ 0.02 eV. These findings suggest that lead halide perovskite MCs may serve as low-power coherent light sources and as model systems for polaritonics. They also provide insight into the nature of excitations in lead halide perovskites for solar energy conversion. [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E34.00005: Enhanced Piezoelectric Response in Hybrid$_{\, }$Perovskite$_{\, }$via Interfacing with Ferroelectric Pb(Zr,Ti)O$_{3}$ Jingfeng Song, Zhiyong Xiao, Bo Chen, Spencer Prockish, Xuegang Chen, Dong Wang, Jinsong Huang, Xia Hong In this work, we have carried out a comprehensive study of the piezoelectric properties of polycrystalline hybrid perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ (MAPbI$_{3})$ thin films on two types of substrates. We spin coated 20-100 nm MAPbI$_{3}$ thin films on gold and ferroelectric Pb(Zr,Ti)O$_{3}$ (PZT), and characterized their piezoelectric coefficient d$_{33}$ using piezoresponse force microscopy (PFM). The MAPbI$_{3}$ thin films on gold showed a d$_{33}$ of \textasciitilde 0.4 pm/V. The epitaxial PZT films (\textasciitilde 50 nm) were deposited on (La,Sr)MnO$_{3}$/SrTiO$_{3}$ substrates, with polarization uniformly oriented in the up direction. For MAPbI$_{3}$ films on PZT, there are regions showing clear PFM phase response, suggesting that MAPbI$_{3}$ is polar with out-of-plane polarization. The PFM amplitude image of MAPbI$_{3}$ indicated the existence of both constructive and destructive piezoresponse with that of PZT. The extracted d$_{33\, }$is$_{\, }$4 pm/V, 10-fold higher than that on gold. The enhanced piezoresponse is attributed to the dipole-dipole interaction between MAPbI$_{3}$ and PZT. Our study points to an effective route to engineer the piezoelectric properties MAPbI$_{3}$ for applications such as mechanical actuators and energy harvesting. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E34.00006: Unconventional Nanoscale Photoresponse and Degradation Process in Hybrid Organic-inorganic Perovskites. Zhaodong Chu, Mengjin Yang, Philip Schulz, Di Wu, Kai Zhu, Xiaoqin Li, Keji Lai The remarkable performance of organic-inorganic perovskite solar cells (PSCs) is challenging the dogma that solution-processed thin films are inevitably associated with inferior energy conversion efficiencies. The surprisingly low impact of polycrystallinity on the film quality highlights the unusual photo-response of intrinsic defects and grain boundaries in these materials. Here, we report the first quantitative nanoscale photoconductivity imaging on methylammonium lead triiodide (MAPbI$_{\mathrm{3}})$ thin films by microwave impedance microscopy with light stimulation. The local photoconductivity as a function of the above-gap laser power is consistent with the high carrier mobility and long lifetime of MAPbI$_{\mathrm{3}}$. The photo-response is largely uniform across grains and grain boundaries, which is direct evidence on the inherently benign nature of microstructures in the perovskite thin films. For encapsulated MAPbI$_{\mathrm{3}}$ films, the observed long-term degradation in photoconductivity begins with the disintegration of large grains due to the diffusion of water molecules through the capping layer. Our work suggests that the striking PSC performance is deeply rooted in the nanoscale optoelectronic properties of MAPbI$_{\mathrm{3}}$. [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E34.00007: Valence Band Dispersion of Perovskite Single Crystal Observed by Angle-resolved Photoemission Spectroscopy Congcong Wang, Benjamin Ecker, Yongli Gao, Haotong Wei, Jinsong Huang, Jian-Qiao Meng The electronic structure of the cleaved perovskite (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbBr$_{\mathrm{3}})$ single crystal was studied in an ultra-high vacuum (UHV) system by angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with nice symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be about 0.73 eV and 0.98 eV along the $\Gamma X$ and $\Gamma M$ directions, respectively. The measured band dispersions correspond to an effective hole mass as about 0.59$ m_{0}$ and a lower limit of the hole mobility of 33.90 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$ from the tight-binding fitting. The quality of the surface was verified by atomic force microscopy (AFM) and scanning electron microscope (SEM). The elemental composition was investigated by high resolution x-ray photoelectron spectroscopy (XPS). The experimental electronic structure shows a good agreement with the theoretical calculation. [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E34.00008: Electron phonon couplings in 2D perovskite probed by ultrafast photoinduced absorption spectroscopy. Uyen Huynh, Limeng Ni, Akshay Rao We use the time-resolved photoinduced absorption (PIA) spectroscopy with 20fs time resolution to investigate the electron phonon coupling in the self-assembled hybrid organic layered perovskite, the hexyl ammonium lead iodide compound (C$_{6}$H$_{13}$NH$_{3})_{2}$ (PbI$_{4})$. The coupling results in the broadening and asymmetry of its temperature-dependence photoluminescence spectra. The exact time scale of this coupling, however, wasn't reported experimentally. Here we show that using an ultrashort excitation pulse allows us to resolve from PIA kinetics the oscillation of coherent longitudinal optical phonons that relaxes and self-traps electrons to lower energy states within 200 fs. The 200fs relaxation time is equivalent to a coupling strength of 40meV. Two coupled phonon modes are also identified as about 100 cm$^{-1}$ and 300 cm$^{-1}$ from the FFT spectrum of the PIA kinetics. The lower energy mode is consistent with previous reports and Raman spectrum but the higher energy one hasn't been observed before. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E34.00009: Origins of Multivalley Electronic Transitions in Hybrid Perovskites Revealed by Transient Spectroscopy K. Appavoo, W. Nie, J.C. Blancon, J. Even, A.D. Mohite, M.Y. Sfeir Mapping complex electronic excitations to the intricate lattice structure of hybrid organic-inorganic perovskites is critical to understand charge separation and hot-carrier extraction, processes that dictate energy-conversion and optoelectronic technologies. Here, we highlight how the dipolar CH3NH3$+$ organic molecule interacts with the inorganic PbI6- octahedral cage to impact the multiband, multivalley electronic structure of this halide perovskite. This is achieved by tracking the transient broadband optical spectra while tuning the structural lattice of the hybrid perovskite via its reversible temperature-dependent phase transition (PT). These temperature-dependent optical snapshots, here captured at 5 ps, reveal exquisite details of those bands, reporting for the first time a degeneracy lifting in the tetragonal state at 2.6 eV that increases as the organic molecule rotational degrees of freedom are suppressed in the orthorhombic state. Plotting this dispersion relation, along with a symmetry analysis of the PT, we describe how the electronic states evolve from the tetragonal to orthorhombic phase and ascribe the splitting to the nearly degenerate transitions at the R and M points of the Brillouin zone. Furthermore, a zone folding in the orthorhombic state explains other salient features of our experiments, such as the emergence of other allowed transitions near 2 eV and a decrease in hot carrier lifetime. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E34.00010: Non-linear optical spectroscopy of organic-inorganic-lead-halide perovskites Sandip Aryal, Evan Lafalce, Sangita Baniya, Chuang Zhang, Yaxin Zhai, Zeev Valy Vardeny We present an investigation of the nonlinear optical properties of organic-inorganic-lead-halide perovskite films and single crystals by a variety of optical techniques including two-photon absorption (2P-PA), two-photon photoluminescence (2P-PLE) and two-photon photocurrent (2P-PC). We found that the 2P-PL and 2P-PC excitation spectra are similar indicating that the two-photon absorption process results in generation of electron-hole pairs. However, comparison to one-photon excitation suggests the role of states other than those of the direct band gap transition. Additionally, we extend previous studies using electro-absorption (EA) spectroscopy to characterize third-order Kerr susceptibility. For both EA and two-photon excitation and absorption we found that the observed response is strong, highlighting the potential of these materials for non-linear optical applications. [Preview Abstract] |
Tuesday, March 14, 2017 10:48AM - 11:00AM |
E34.00011: Photoexcitations Spectroscopy of 2D Hybrid Lead Iodide Perovskites Yaxin Zhai, Chuan-Xiang Sheng, Chuang Zhang, Sangita Baniya, Sandip Aryal, Zeev Valy Vardeny Quantum and dielectric confinement effects in Ruddlesden-Popper 2D hybrid perovskites give rise to unique properties such as large exciton binding energies and anisotropic charge transport. We have studied the ultrafast transient response of photoexcitations in hybrid lead iodide 2D perovskite films, (C$_{6}$H$_{5}$C$_{2}$H$_{2}$NH$_{3}$)$_{2}$PbI$_{4}$ using broadband pump-probe spectroscopy in the spectral range of 0.25–2.7 eV with 300 fs time resolution. We found a strong mid-IR photoinduced absorption (PA) band that is due to photogenerated excitons that decays within 20 ps. This PA is correlated with a derivative-like spectral feature in the visible spectral range close to the absorption band edge. The steady-state properties of the 2D perovskites films have also been investigated by cw-PA and nonlinear optics spectroscopies. [Preview Abstract] |
Tuesday, March 14, 2017 11:00AM - 11:12AM |
E34.00012: Formation and diffusion of metal impurities in perovskite solar cell materials CH3NH3PbI3: implications on the choice of the electrode and the solar cell degradation Wenmei Ming, Mao-Hua Du Hybrid organic-inorganic lead halide perovskite CH3NH3PbI3 has emerged as a high efficiency solar absorber material. However, there are rising concerns on the chemical and electrical instabilities of CH3NH3PbI3 and the resulting device degradation. Recently, it was shown both experimentally and theoretically that Au ions can diffuse into the perovskite layer from the electrode causing device degradation even if there is a hole transport layer that separates the two. It is therefore important to understand the effects of the metal electrode on the performance and the stability of the CH3NH3PbI3 solar cell. Although many metal electrodes (e.g., Au, Ag, Cu, Al) have been studied experimentally, the nature of their interaction with CH3NH3PbI3 remains controversial. Here, we report first-principles calculations of a wide range of metal impurities in CH3NH3PbI3. The metal impurities were chosen based on whether their bulk forms have acceptable resistivities and work functions to be used as electrodes in CH3NH3PbI3 solar cells. The goal is to understand the stability and diffusivity of various metal impurities and their effects on carrier transport in CH3NH3PbI3. The implications of our results on the choice of electrodes in CH3NH3PbI3 solar cells are discussed. [Preview Abstract] |
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