Search query: Stabilizing heterostructures of soft perovskite semiconductors

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abstract: Strong perovskite interfaces The weak bonding in the crystal lattice of hybrid perovskites used in solar cells promotes surface decomposition and interferes with the formation of stable heterostructures with the charge carrier layers. Y. Wang et al. show that strong bonds are formed between lead and both chlorine and oxygen atoms in a film with a lead rich surface and a chlorinated graphene oxide layer. This interface was used with common hole transporting materials to fabricate solar cells that maintained 90% of their initial efficiency of 21% after operation at 60degC for 1000 hours. Science, this issue p. 687 Chlorinated graphene oxide forms a stable interface with hybrid perovskites that have a lead rich surface. Here we report a solution processing strategy to stabilize the perovskite based heterostructure. Strong Pb Cl and Pb O bonds formed between a [CH(NH2)2]x[CH3NH3]1 xPb1+yI3 film with a Pb rich surface and a chlorinated graphene oxide layer. The constructed heterostructure can selectively extract photogenerated charge carriers and impede the loss of decomposed components from soft perovskites, thereby reducing damage to the organic charge transporting semiconductors. Perovskite solar cells with an aperture area of 1.02 square centimeters maintained 90% of their initial efficiency of 21% after operation at the maximum power point under AM1.5G solar light (100 milliwatts per square centimeter) at 60degC for 1000 hours. The stabilized output efficiency of the aged device was further certified by an accredited test center.
author_names: Yanbo Wang

Tianhao Wu

Julien Barbaud

Weiyu Kong

Danyu Cui

Han-Hsu Chen

Xudong Yang

Liyuan Han
title: Stabilizing heterostructures of soft perovskite semiconductors
venue: Science
year: 2019

abstract: Epitaxial heterostructures based on oxide perovskites and III V, II VI and transition metal dichalcogenide semiconductors form the foundation of modern electronics and optoelectronics 1 7 Halide perovskites an emerging family of tunable semiconductors with desirable properties are attractive for applications such as solution processed solar cells, light emitting diodes, detectors and lasers 8 15 Their inherently soft crystal lattice allows greater tolerance to lattice mismatch, making them promising for heterostructure formation and semiconductor integration 16 17 Atomically sharp epitaxial interfaces are necessary to improve performance and for device miniaturization. However, epitaxial growth of atomically sharp heterostructures of halide perovskites has not yet been achieved, owing to their high intrinsic ion mobility, which leads to interdiffusion and large junction widths 18 21 and owing to their poor chemical stability, which leads to decomposition of prior layers during the fabrication of subsequent layers. Therefore, understanding the origins of this instability and identifying effective approaches to suppress ion diffusion are of great importance 22 26 Here we report an effective strategy to substantially inhibit in plane ion diffusion in two dimensional halide perovskites by incorporating rigid p conjugated organic ligands. We demonstrate highly stable and tunable lateral epitaxial heterostructures, multiheterostructures and superlattices. Near atomically sharp interfaces and epitaxial growth are revealed by low dose aberration corrected high resolution transmission electron microscopy. Molecular dynamics simulations confirm the reduced heterostructure disorder and larger vacancy formation energies of the two dimensional perovskites in the presence of conjugated ligands. These findings provide insights into the immobilization and stabilization of halide perovskite semiconductors and demonstrate a materials platform for complex and molecularly thin superlattices, devices and integrated circuits. An epitaxial growth strategy that improves the stability of two dimensional halide perovskites by inhibiting ion diffusion in their heterostructures using rigid p conjugated ligands is demonstrated, and shows near atomically sharp interfaces.
author_names: Enzheng Shi

Biao Yuan

Stephen B Shiring

Yao Gao

Yunfan Guo

Cong Su

Minliang Lai

Peidong Yang

Jing Kong

Brett M Savoie

Yi Yu

Letian Dou
title: Two dimensional halide perovskite lateral epitaxial heterostructures
venue: Nature
year: 2020

abstract: Formation of heterostructures is often inevitable in two dimensional (2D) halide perovskites and band alignment in 2D perovskite heterostructures is of central importance to their applications. However, controversies abound in literature on the band alignment of the 2D perovskite heterostructures. While external factors have been sought to reconcile the controversies, we show that the 2D perovskite heterostructures are in fact intrinsically prone to band "misalignment" driven by thermal fluctuations. Owing to the "softness" of inorganic layers in the perovskites, electron phonon coupling at room temperature could be strong enough to override band offsets at zero temperature, leading to oscillational band alignment between type I and type II at 300 K. We further demonstrate that by tuning the inorganic layers, one can increase the band offsets and stabilize the band alignment, paving the way for optoelectronic applications of the 2D perovskite heterostructures.
author_names: Linghai Zhang

Xu Zhang

Gang Lu
title: Band Alignment in Two Dimensional Halide Perovskite Heterostructures: Type I or Type II?
venue: The journal of physical chemistry letters
year: 2020

abstract: Significance Functional semiconductor heterojunctions are fundamental units for building up advanced optoelectronics and circuits. Halide perovskites, representing a new class of semiconductors with soft and reconfigurable ionic bonding, hold promise for a variety of applications because of their many unusual, tunable physical properties. This paper reports the formation of the current rectifying p n heterojunction in single crystalline CsSnI3 nanowires via localized phase transition between the n type yellow and p type black phases. We attribute the distinction of majority carrier types in these two phases to the different formation energies of the cation and anion vacancies. The present approach to heterojunction formation could inspire deeper understanding of phase transition dynamics and enable precise control over the design of functional heterostructures using halide perovskite building blocks. Semiconductor p n junctions are fundamental building blocks for modern optical and electronic devices. The p and n type regions are typically created by chemical doping process. Here we show that in the new class of halide perovskite semiconductors, the p n junctions can be readily induced through a localized thermal driven phase transition. We demonstrate this p n junction formation in a single crystalline halide perovskite CsSnI3 nanowire (NW) This material undergoes a phase transition from a double chain yellow (Y) phase to an orthorhombic black (B) phase. The formation energies of the cation and anion vacancies in these two phases are significantly different, which leads to n and p type electrical characteristics for Y and B phases, respectively. Interface formation between these two phases and directional interface propagation within a single NW are directly observed under cathodoluminescence (CL) microscopy. Current rectification is demonstrated for the p n junction formed with this localized thermal driven phase transition.
author_names: Qiao Kong

Woochul Lee

Minliang Lai

Connor G Bischak

Guoping Gao

Andrew Barnabas Wong

Teng Lei

Yi Yu

Lin-wang Wang

Naomi S Ginsberg

Peidong Yang
title: Phase transition induced p n junction in single halide perovskite nanowire
venue: Proceedings of the National Academy of Sciences
year: 2018

abstract: A simple method (which could be completed within 60 minutes at 298 K) was developed to transform layered organic inorganic metal halide perovskites into colloidal lyotropic liquid crystalline dispersions with microscopic structural orderliness as well as semiconducting properties and photoluminescence. Experimentally, hexagonal shaped mesogenic nanoplatelets of two dimensional lead iodide perovskites (R NH3)2PbI4 were synthesized by antisolvent induced rapid microcrystallization and stabilized by surfactants, and self assembled into discotic nematic phases with optical anisotropy and greenish blue fluorescence. Combining the stimuli responsive, light interactive, and reconfigurable ordered structures of liquid crystals with the adjustable semiconductivity of hybrid perovskites, these photoluminescent soft anisotropic materials may be used for polarized light emission or detection.
author_names: Pei-Xi Wang
title: Lyotropic liquid crystalline phases of anisotropic nanoparticles of organic inorganic metal halide perovskites: photoluminescence from self assembled ordered microstructures of semiconductors.
venue: Chemical communications
year: 2021

abstract: Halide perovskite (HP) semiconductors exhibit unique strong coupling between the electronic and structural dynamics. The high temperature cubic phase of HPs is known to be entropically stabilized, with imaginary frequencies in the calculated phonon dispersion relation. Similar calculations, based on the static average crystal structure, predict a stable tetragonal phase with no imaginary modes. This work shows that in contrast to standard theory predictions, the room temperature tetragonal phase of CH$_{3} $NH$_{3} $PbI$_{3} is strongly anharmonic. We use Raman polarization orientation (PO) measurements and \textit{ab initio} molecular dynamics (AIMD) to investigate the origin and temperature evolution of the strong structural anharmonicity throughout the tetragonal phase. Raman PO measurements reveal a new spectral feature that resembles a soft mode. This mode shows an unusual continuous increase in damping with temperature which is indicative of an anharmonic potential surface. The analysis of AIMD trajectories identifies two major sources of anharmonicity: the orientational unlocking of the [CH$_{3} $NH$_{3} ions and large amplitude octahedral tilting that continuously increases with temperature. Our work suggests that the standard phonon picture cannot describe the structural dynamics of tetragonal CH$_{3} $NH$_{3} $PbI$_{3}
author_names: Rituraj Sharma

Zhenbang Dai

Lingyuan Gao

Thomas M Brenner

Lena Yadgarov

Jiahao Zhang

Yevgeny Rakita

Roman Korobko

Andrew M Rappe

Omer Yaffe
title: The tetragonal phase of CH$_{3}$NH$_{3}$PbI$_{3} is strongly anharmonic
year: 2020

abstract: The recent observation of superconductivity in Nd$_{0.8}$Sr$_{0.2}$NiO$_{2} calls for further investigation and optimization of the synthesis of this metastable infinite layer nickelate structure. Here, we present our current understanding of important aspects of the growth of the parent perovskite compound via pulsed laser deposition on SrTiO$_{3} (001) substrates, and the subsequent topotactic reduction. We find that to achieve single crystalline, single phase superconducting Nd$_{0.8}$Sr$_{0.2}$NiO$_{2} it is essential that the precursor perovskite Nd$_{0.8}$Sr$_{0.2}$NiO$_{3} thin film is stabilized with high crystallinity and no impurity phases; in particular, a Ruddlesden Popper type secondary phase is often observed. We have further investigated the evolution of the soft chemistry topotactic reduction conditions to realize full transformation to the infinite layer structure with no film decomposition or formation of other phases. We find that capping the nickelate film with a subsequent SrTiO$_{3} layer provides an epitaxial template to the top region of the nickelate film, much like the substrate. Thus, for currently optimized growth conditions, we can stabilize superconducting single phase Nd$_{0.8}$Sr$_{0.2}$NiO$_{2} (001) epitaxial thin films up to 10 nm.
author_names: Kyuho Lee

Berit H Goodge

Motoki Osada

Lena F Kourkoutis
title: Aspects of the synthesis of thin film superconducting infinite layer nickelates
year: 2020

abstract: First experimental observations of the ferromagnetic shielding effect in high Tc superconducting coated conductors were carried out. Experimental results were compared to simulations calling upon finite element calculations based on the H formulation of Maxwell equations to model superconducting strips with ferromagnetic shields. Samples of copper stabilized coated conductors were electroplated with nickel shields and afterwards characterized. Both externally applied oscillating transverse magnetic fields as well as transport currents were studied. Having observed promising gains with respect to the reduction of ac losses in both cases, we further investigated the potential of ferromagnetic shielding. The numerical model was able to reproduce and also predict experimental results very well and will serve as an indispensable tool to determine the potential of soft ferromagnetic materials to significantly reduce hysteretic losses.
author_names: Philip J Krueger

Francesco Grilli

Michal Vojenvciak

Victor Manuel Rodriguez Zermeno

Eduard Demencik

Stefania Farinon Karlsruhe Institute of TechnologyGermany

Istituto Nazionale di Fisica NucleareItaly
title: Superconductor/ferromagnet heterostructures exhibit potential for significant reduction of hysteretic losses
year: 2013

abstract: Abstract The effect of growth conditions on interfacial roughness in InAs/GaAs hetcrostructures prepared by molecular beam epitaxy has been investigated using synchrotron radiation. Measurement of grazing incidence X ray reflectivity (GIXR) and total electron yield (TEY) in the soft X ray wavelengths are used for nondestructive characterization of interfacial roughness in these semiconductor heterojunctions. Our results indicate that a smoothing process takes place during epitaxial growth, and that the measured interfacial roughness is lowest for In stabilized deposition on a GaAs substrate at 2deg off (100) and highest with As stabilized overgrowth on GaAs(100) The surface and interfacial roughness are practically independent of the layer thickness in the range investigated (70 600 A)
author_names: Andrzej Krol

C J Sher

D R Storch

S C Woronick

Y H Kao

L L Chang

Hiro Munekata
title: Soft x ray investigation of the effect of growth conditions on InAs/GaAs heterostructures
year: 1990

abstract: Hybrid perovskites have emerged over the past five years as absorber layers for novel high efficiency low cost solar cells combining the advantages of organic and inorganic semiconductors. Unfortunately, electrical transport in these materials is still poorly understood. Employing the linear response approach of density functional theory, we reveal strong anharmonic effects and a double well phonon instability at the center of the Brillouin zone for both cubic and orthorhombic phases of inorganic CsPbI3. Previously reported soft phonon modes are stabilized at the actual lower symmetry equilibrium structure, which occurs in a very flat energy landscape, highlighting the strong competition between the different phases of CsPbI3. Factoring these low energy phonons into electron phonon interactions and band gap calculations could help better understand the electrical transport properties in these materials. Furthermore, the perovskite oscillations through the corresponding energy barrier could explain the underlying ferroelectricity and the dynamical Rashba effect predicted in halide perovskites for photovoltaics.
author_names: Arthur Marronnier

Heejae Lee

Bernard Geffroy

Jacky Even

Yvan Bonnassieux

Guido Roma
title: Structural Instabilities Related to Highly Anharmonic Phonons in Halide Perovskites.
venue: The journal of physical chemistry letters
year: 2017