Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F63: Transport and Device Physics of Halide PerovskitesFocus
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Volker Blum, Duke University Room: Mile High Ballroom 4D |
Tuesday, March 3, 2020 8:00AM - 8:12AM |
F63.00001: Temperature and Phase Dependence of Carrier Diffusion in Single Crystal MAPbI3 Perovskite Microstructures Luke McClintock, Rui Xiao, Yasen Hou, Henry Travaglini, David Abramovitch, Liang Tan, Dong Yu Understanding and improving carrier transport in photovoltaic materials is crucial to developing high quality solar energy harvesting devices. Here, we have investigated carrier diffusion lengths in single crystal methylammonium lead iodide (MAPbI3) microstuctures via scanning photocurrent microscopy. Carrier diffusion lengths were found to increase abruptly once below the transition temperature from the tetragonal to the orthorhombic phase and reached 200 ± 50 μm at 80 K. Enormous mobility values of 3 x 104 cm2 / V s were extracted at 80 K using these long diffusion lengths in combination with transient photocurrent lifetime measurements. We attributed the increased diffusion lengths to the emergence of an excitonic nature to the transport in the orthorhombic phase. Our findings provide significant fundamental insights on the temperature and phase-dependent charge transport properties of halide perovskites. |
Tuesday, March 3, 2020 8:12AM - 8:24AM |
F63.00002: Quantifying exciton heterogeneities in mixed-phase organometal halide multiple quantum wells via Stark spectroscopy studies Eric Amerling, Sangita Baniya, Evan Lafalce, Steve Blair, Zeev Valy Vardeny, Luisa Whittaker-Brooks Solution processable organic-inorganic hybrid perovskite (OIHP) quantum wells naturally self-assemble through weak van der Waals forces. In this study, we investigated the structural and optoelectronic properties of (C4H9NH3)2(CH3NH3)n-1PbnI3n+1, varying n from 1 to 4. Through conventional structural characterization, the thin films showcase high-quality phase purity. However, while investigating the optoelectronic properties, it was clear that these van der Waals heterostructures consist of multiple quantum well thicknesses coexisting within a single thin film. We utilized modulation spectroscopy, electroabsorption, and Liptay theory analysis to deconvolute the different excitonic features arising from different quantum well thicknesses (n). Rather than merely identifying what quantum well heterostructures are present within a thin film, this novel method of analysis provides powerful insight into the exact exciton composition in the thin film and can be utilized to analyze the optoelectronic properties of many other mixed-phase quantum well heterostructures beyond those formed by OIHPs. |
Tuesday, March 3, 2020 8:24AM - 8:36AM |
F63.00003: Angle-Resolved Time-Resolved Microwave Conductivity Shirsopratim Chattopadhyay, John Labram The contactless electronic characterization technique time resolved microwave conductivity (TRMC) provides a very convenient way of quickly evaluating carrier mobilities and lifetimes for a variety of semiconducting materials. However, the technique has one notable limitation in that it can conventionally only be used to resolve carrier mobilities in the plane of substrate (lateral mobility). |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F63.00004: Peculiar Defects Behavior in Charge Recombination of Metal Halide Perovskites Weibin Chu, Wissam A Saidi, Jin Zhao, Oleg Prezhdo Defects are inevitably introduced in the near room-temperature and solution-based growth of metal halide perovskites (MHPs) thin films for solar cell devices. However, the astonishing improvements in the efficiency of the corresponding solar cells indicate that MHPs have a strong defect tolerance. Motivated by the recent experimental demonstration of a new state-of-art β phase CsPbI3 with a stable and impressive efficiency reaching 18.4% at ambient conditions, we investigate the non-radiative recombination processes in CsPbI3 using ab initio non-adiabatic molecular dynamics within real-time time-dependent Kohn-Sham formalism and surface-hopping framework. Regardless of their nature, we find that the native defects in CsPbI3 do not accelerate the charge recombination process. We show that the strong tolerance of electron-hole recombination against defects is explained due to the combination of having low-frequency lattice phonons and weakly overlapping electron and hole states. The deep-level defect becomes tolerant owing to the strong covalency, which contrary to predictions from SRH theory in previous work. Considering similar results found in MAPbI3, we propose that the strong defect tolerance is general to the metal halide perovskites. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F63.00005: Small Urbach energies in halide perovskites due to anharmonicity and short-range correlated disorder Christian Gehrmann, David A. Egger Halide perovskites (HaPs), a class of up-and-coming solar absorber materials, feature small Urbach energies and sharp optical absorption edges. These characteristics render the fabrication of efficient HaP based solar-cell devices possible. But they also indicate a low amount of disorder, which is seemingly in contrast with the complex nuclear dynamics and structural effects known for HaPs. Here, we present our findings on spatial correlations in the disorder potential induced for electronic states due to nuclear dynamics in several HaPs. Our theoretical results are based on density functional theory (DFT) calculations and DFT-based molecular dynamics [1]. With this approach, anharmonicity in the nuclear dynamics is accounted for up to all orders in the Taylor expansion of the crystal potential. We find that correlations in the disorder potential are dynamically shortened. The mechanism responsible for this shortening is found to be the nuclear motion of A-site and X-site ions. We conclude that sharp optical absorption edges and small Urbach energies in HaPs are possible due to the dynamical shortening of correlations in the disorder potential. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F63.00006: The evolution of ultrafast carrier dynamics in situ perovskite solar cells Exian Liu, Jinhui Tong, Kanishka Kobbekaduwa, Pan P Adhikari, Kai Zhu, Jianbo Gao Photoelectric performances of perovskite solar cells (PSC), such as photovoltage, short-circuit current density, fill factor and power-conversation-efficiency are determined by the charge carrier dynamics, especially the early-stage processes including charge generation, recombination and interface transfer. These photophysics dynamics, which are within pico- to nano-second timescale, directly relate to the PSC working mechanism. However, the study on the ultrafast photophysics dynamics in situ PSC is still in infancy although considerable works were performed on the performance improvement at steady-state condition. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F63.00007: Defects in polymorphous cubic halide perovskites: coexistence of shallow and deep vacancy transition levels Gustavo Dalpian, Xingang Zhao, Alex Zunger Halide perovskites are usually said to be defect tolerant materials suggesting a possible explanation for being good solar compounds. Molecular dynamics (MD) simulations of Cohen et al revealed that the orbital energy of the Br-vacancy in CsPbBr3 resides deep in the gap (i.e., not defect tolerant) and can considerably fluctuate on the time scale of the MD trajectories. Recently, it was pointed out that the static structure of cubic halide perovskites involves a distribution of different local environments such as tilting and atomic displacements, being a polymorphous network [Zhao, X., Dalpian, G. M., Wang, Z. & Zunger, A. The polymorphous nature of cubic halide perovskites. arXiv:1905.09141 (2019)]. We have studied anion vacancies in different, inequivalent lattice sites in the polymorphous network of CsSnI3, CsPbI3, MaPbI3, and CsPbBr3, finding that all except CsPbBr3 have shallow transition levels whereas the latter has a bimodal distribution with some deep levels (mostly shallow). We show how these results correlate with the local geometric deformations of the various sites in the polymorphous network. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F63.00008: Hot Carrier Dynamics in Bulk and 2D Perovskites Shashi Sourabh, Vincent R. Whiteside, Hamidreza Esmaielpour, Brandon Durant, Giles E. Eperon, Matthew C Beard, Ian R Sellers A comparison of the effect of carrier-carrier and carrier-phonon interactions in 2D (BA)2PbI4 Ruddlesden-Popper (n=1) and conventional bulk MAPbI3 perovskite thin films is presented. It is shown that the nature and strength of the exciton binding energy strongly mediate the nature of their interaction with phonons. Specifically, more strongly coupled excitons manifest themselves in the formation of small polarons that interact with lattice via the emission of LO-phonon replicas, while weakly bound (or free) excitons interact with phonons to form large polarons resulting in large LO-phonon broadening and strong carrier-phonon scattering. These results suggest that the unusual hot carrier thermalization observed in the perovskites is dominated by the strength and nature of the exciton-phonon interaction and subtlety different from more conventional semiconductors. To support this hypothesis, comparisons of the hot carrier dynamics and electron-phonon interaction in a number of stable and well-studied perovskites are also presented. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F63.00009: Unravelling free carrier and exciton dynamics in hybrid organic-inorganic perovskites using transient absorption spectroscopy Chang Qing, Daming Zhao, Hongwei Hu, Yeng Ming Lam, Ee Min Chia Mixed-cation lead mixed-halide perovskites have been shown to good photostability, thermal stability and high power conversion efficiency, proving to be good candidates as energy harvesting materials [1]. Transient absorption spectroscopy is a powerful tool to study the response of free carriers and excitons upon photoexcitation in the perovskites [2]. Here, we excite FA0.85 Cs0.15 PbI2.9 Br0.1 thin films with bandgap and above-bandgap pump pulses, and probe the sample with white light. Our results show that, compared to resonant excitation, shorter-wavelength excitation generates more free carriers, and by increasing the pump fluence, bandgap renormalization and hot-phonon bottleneck can be achieved. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F63.00010: Observation of large negative thermo-optic coefficients in lead halide perovskites Taketo Handa, Hirokazu Tahara, Yoshihiko Kanemitsu Lead halide perovskites are a new class of semiconductor materials for photonic devices [1]. Despite intensive research in the last decade, some of their fundamental physical properties still remain unclear. Here, we report that the halide perovskite CH3NH3PbCl3 shows a large negative thermo-optic coefficient, i.e., a distinct decrease of the refractive index upon temperature rise [2]. We demonstrate that this unique response provides new photonic applications [2,3]. Furthermore, the negative thermo-optic property indicates unusual thermally-induced changes in the electronic states. We investigated the origin of the negative coefficient through the temperature dependence of the absorption spectra of a CH3NH3PbCl3 thin film. With increasing temperature, a slight blueshift in the absorption peak energy was observed. Our analysis suggests that both the absorption blueshift and large thermal expansion contribute to the large negative thermo-optic coefficients of halide perovskites. |
Tuesday, March 3, 2020 10:00AM - 10:36AM |
F63.00011: Breaking the Defect Bottleneck in Halide Perovskite Semiconductors Invited Speaker: Aron Walsh The physical properties of semiconducting solids depend on the imperfections they contain[1]. Defects come in a few flavours: conductivity-promoting defects create free carriers that enable electronics; killer defects (deep centres) trigger recombination; and charge scattering defects reduce mobility. Our understanding of halide perovskites is limited in comparison to inorganic semiconductors. I will discuss recent progress, from theory and experiment, to identify, characterise and control point defects and defect processes in this family of compounds. I will cover charge compensation mechanisms [2], carrier trapping phenomena[3], the effect of grain boundaries[4], and how this understanding can be applied to engineer defect populations and distributions. The use of `defect tolerance` as a metric to develop and screen post-perovskite materials will be critically addressed. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F63.00012: Electrohydrodynamically Assisted Deposition of organo-metallic hybrid perovskite thin films for Photovoltaics applications Albert DiBenedetto, William Delmas, Sayantani Ghosh The creation of lightweight and high efficiency photovoltaic devices is challenging, especially for deployment under extreme conditions, such as in outer space. Deposition techniques like drop casting or spin coating produce nonuniform films and are only useful under the influence of gravity. We have developed an alternative technique to prepare thin films via electrohydrodynamically (EHD) assisted deposition. Using Marangoni flow, this process allows precursors of different vapor pressures to be guided (via an applied electric field) onto a substrate in order to self-organize and produce uniform thin films while minimizing the amount of waste solution. In this talk, we will present different perovskite solar cell prototypes with different space qualified substrates that were prepared via EHD assisted deposition. To compare each prototype, we use characterization using photoluminescence (PL), spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). As a final goal, we aim to develop and optimize perovskite solar cell prototypes from inks of high wettability and space qualified substrates. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F63.00013: Coupling Alkali Metal and Organic Cations to Form Oriented Quasi-2D Perovskite for High-performance Solar Cells Qin Hu, Jingnan Song, Feng Liu, Thomas Russell Two-dimensional (2D) perovskite solar cells that boast of high stability and high efficiency have attracted significant attention. A systematically static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is applied, in which the synergic efforts of alkali metal cation and polar solvent lead to high quality 2D perovskite thin film with well orientation. The novel structure can induce high quality 2D slab growth as well as reduce internal and surface defects, thus resulting in a high device efficiency of 13.65%. Steady-state and transient absorption spectra reveal the carrier transporting from low n to high n species of different kinetics. An [PbI6]4- octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed, which then subjects to solvent vapor annealing to recrystallize and reorient 2D perovskite slabs to form an ideal structure to give rise to the improvement of device efficiency and stability. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700