Query: From bulk to molecularly thin hybrid perovskites

Candidate papers:

abstract: Organic inorganic hybrid perovskites have been intensively researched in the past decade for their optoelectronic properties. The emergence of Ruddlesden Popper perovskites, which have mixed dimensionality, has heralded new opportunities for tailor made semiconductors that combine enhanced stability with useful properties between those of 2D and 3D systems. Inspired by advances in 2D materials research, there is growing interest in molecularly thin versions of these hybrid perovskites, owing to their ease of incorporation into electronic devices. There is, thus, a need to understand thickness dependent electrical, excitonic and phononic properties that go beyond quantum confinement effects. Recent studies have shown that, apart from tuning the dimensionality of the system, fine tuning its thickness also helps to optimize performance in different applications, ranging from third harmonic generation to photodetectors and spintronics. Owing to their layered structure, the properties of 2D perovskites can be controlled by tuning their thickness. This Review surveys how fine tuning the thickness of 2D perovskites from the sub micrometre to the molecularly thin regime helps to optimize their electrical and optical properties for use in different applications.
author_names: Kai Leng

Wei Fu

Yanpeng Liu

Manish Chhowalla

Kian Ping Loh
title: From bulk to molecularly thin hybrid perovskites
venue: Nature Reviews Materials
year: 2020

abstract: Due to their layered structure, two dimensional Ruddlesden Popper perovskites (RPPs) composed of multiple organic/inorganic quantum wells, can in principle be exfoliated down to few and single layers. These molecularly thin layers are expected to present unique properties with respect to the bulk counterpart, due to increased lattice deformations caused by interface strain. Here, we have synthesized centimetre sized, pure phase single crystal RPP perovskites (CH3(CH2)3NH3)2(CH3NH3)n 1PbnI3n+1 (n 1 4) from which single quantum well layers have been exfoliated. We observed a reversible shift in excitonic energies induced by laser annealing on exfoliated layers encapsulated by hexagonal boron nitride. Moreover, a highly efficient photodetector was fabricated using a molecularly thin n 4 RPP crystal, showing a photogain of 105 and an internal quantum efficiency of ~34% Our results suggest that, thanks to their dynamic structure, atomically thin perovskites enable an additional degree of control for the bandgap engineering of these materialsReversible structural surface relaxation under laser exposure is observed for monolayers of 2D metal halide perovskites. These structural changes also induce reversible shifts in the photoluminescence peaks of these materials.
author_names: Kai Leng

Ibrahim Abdelwahab

Ivan A Verzhbitskiy

Mykola Telychko

Leiqiang Chu

Wei Fu

Xiao Chi

Na Guo

Zhihui Chen

Zhongxin Chen

Chun Zhang

Qing-Hua Xu

Jiong Lu

Manish Chhowalla

Goki Eda

Kian Ping Loh
title: Molecularly thin two dimensional hybrid perovskites with tunable optoelectronic properties due to reversible surface relaxation
venue: Nature Materials
year: 2018

abstract: In layered hybrid perovskites like (BA) 2 PbI 4 (BA C 4 H 9 NH 3 electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Our experimental findings suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical and optoelectronic properties of these technologically important materials.
author_names: Tariq Sheikh

Vaibhav V Nawale

Nithin Pathoor

Chinmay Phadnis

Arindam Chowdhury

Angshuman Nag
title: Molecular Intercalation and Electronic Two Dimensionality in Layered Hybrid Perovskites.
venue: Angewandte Chemie
year: 2020

abstract: Abstract Organic inorganic hybrid perovskites have potential applications in flexible electronics based on solution processing polycrystalline thin films. This article reports an emerging phenomenon: mechanically tunable spin orbit coupling (SOC) in flexible perovskite solar cells under elastic bending. Polarization dependent photocurrent studies show that mechanical bending increases the orbit orbit interaction, shown as an enhanced SOC, and consequently boosting the intersystem crossing to convert optically generated bright states (which are allowed to recombine) into dark states (which are forbidden to recombine) in flexible perovskite solar cells [PET/ITO/PEDOT:PSS/MAPbI3 xClx/PCBM/PEI/Ag] Simultaneously, the photocurrent is increased from 15.39 mA/cm2 to 22.0 mA/cm2 by 43% upon such elastic bending with the curvature radius of 4.2 mm. It is further found that introducing mechanical stress leads to both grain boundary interaction and grain deformation shown as the decreased defects at grain boundaries through thermal admittance spectroscopy and the elastic strain verified by X ray diffraction measurement. The capacitance frequency characteristics indicate that applying this mechanical stress causes an increase on the bulk polarization by introducing grain boundary interaction and grain deformation. This provides necessary condition to realize mechanically tunable SOC effects in perovskites via electric magnetic coupling. Essentially, mechanically tunable SOC effects present new mechanisms to control the optoelectronic properties in flexible perovskite electronic devices.
author_names: Haomiao Yu

Miaosheng Wang

Changfeng Han

Kai Wang

Bin Hu
title: Mechanically tuning spin orbit coupling effects in organic inorganic hybrid perovskites
year: 2020

abstract: Hybrid (organic inorganic) multication lead halide perovskites hold promise for a new generation of easily processable solar cells. Best performing compositions to date are multiple cation solid alloys of formamidinium (FA) methylammonium (MA) cesium, and rubidium lead halides which provide power conversion efficiencies up to around 22% Here, we elucidate the atomic level nature of Cs and Rb incorporation into the perovskite lattice of FA based materials. We use 133Cs, 87Rb, 39K, 13C, and 14N solid state MAS NMR to probe microscopic composition of Cs Rb K MA and FA containing phases in double triple and quadruple cation lead halides in bulk and in a thin film. Contrary to previous reports, we have found no proof of Rb or K incorporation into the 3D perovskite lattice in these systems. We also show that the structure of bulk mechanochemical perovskites bears close resemblance to that of thin films, making them a good benchmark for structural studies. These findings provide fundamental understanding of previously reported excellent photovoltaic parameters in these systems and their superior stability.
author_names: Dominik Jozef Kubicki

Daniel Prochowicz

Albert Hofstetter

Shaik M Zakeeruddin

Michael Gratzel

Lyndon Emsley
title: Phase Segregation in Cs Rb and K Doped Mixed Cation (MA)x(FA)1 xPbI3 Hybrid Perovskites from Solid State NMR
venue: Journal of the American Chemical Society
year: 2017

abstract: Current voltage hysteresis is a major issue for normal architecture organo halide perovskite solar cells. In this manuscript we reveal a several angstrom thick methylammonium iodide rich interface between the perovskite and the metal oxide. Surface functionalization via self assembled monolayers allowed us to control the composition of the interface monolayer from Pb poor to Pb rich, which, in parallel, suppresses hysteresis in perovskite solar cells. The bulk of the perovskite films is not affected by the interface engineering and remains highly crystalline in the surface normal direction over the whole film thickness. The subnanometer structural modifications of the buried interface were revealed by X ray reflectivity, which is most sensitive to monitor changes in the mass density of only several angstrom thin interfacial layers as a function of substrate functionalization. From Kelvin probe force microscopy study on a solar cell cross section, we further demonstrate local variations of the potential on different electron transporting layers within a solar cell. On the basis of these findings, we present a unifying model explaining hysteresis in perovskite solar cells, giving an insight into one crucial aspect of hysteresis for the first time and paving way for new strategies in the field of perovskite based opto electronic devices.
author_names: Johannes Will

Yi Hou

Simon Scheiner

Ute Pinkert

Ilka M Hermes

Stefan A L Weber

Andreas Hirsch

Marcus Halik

Christoph J Brabec

Tobias Unruh
title: Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self Assembled Monolayer.
venue: ACS applied materials interfaces
year: 2018

abstract: Controlling the structure of layered hybrid metal halide perovskites, such as the Ruddlesden Popper (R P) phases, is challenging because of their tendency to form mixtures of varying composition. Colloidal growth techniques, such as antisolvent precipitation, form dispersions with properties that match bulk layered R P phases, but controlling the composition of these particles remains challenging. Here, we explore the microstructure of particles of R P phases of methylammonium lead iodide prepared by antisolvent precipitation from ternary mixtures of alkylammonium cations, where one cation can form perovskite phases (CH3NH3+ and the other two promote layered structures as spacers (e.g. C4H9NH3+ and C12H25NH3+ We determine that alkylammonium spacers pack with constant methylene density in the R P interlayer and exclude interlayer solvent in dispersed colloids, regardless of length or branching. Using this result, we illustrate how the competition between cations that act as spacers between layers, or as grain terminating ligands, determines the colloidal microstructure of layered R P crystallites in solution. Optical measurements reveal that quantum well dimensions can be tuned by engineering the ternary cation composition. Transmission synchrotron wide angle X ray scattering and small angle neutron scattering reveal changes in the structure of colloids in solvent and after deposition into thin films. In particular, we find that spacers can alloy between R P layers if they share common steric arrangements, but tend to segregate into polydisperse R P phases if they do not mix. This study provides a framework to compare the microstructure of colloidal layered perovskites and suggests clear avenues to control phase and colloidal morphology.
author_names: Clayton J Dahlman

Naveen R Venkatesan

Patrick T Corona

Rhys M Kennard

Lingling Mao

Noah C Smith

Jiamin Zhang

Ram Seshadri

Matthew E Helgeson

Michael L Chabinyc
title: Structural Evolution of Layered Hybrid Lead Iodide Perovskites in Colloidal Dispersions.
venue: ACS nano
year: 2020

abstract: In this study, we examine the effects of changing organic cation concentrations on the efficiency and photophysical implications of exciton trapping in two dimensional hybrid lead iodide self assembled quantum wells (SAQWs) We show that increasing the concentration of alkyl and aryl ammonium cations causes the formation of SAQWs at a liquid liquid interface to possess intense, broadband subgap photoluminescence (PL) spectra. Electron microscopy, X ray diffraction, and X ray photoelectron spectroscopic studies suggest that materials formed under these cation concentrations possess morphologies consistent with inhibited crystallization kinetics but exhibit qualitatively similar bulk chemical bonding to nonluminescent materials stabilized in the same structure from precursor solutions containing lower cation concentrations. Temperature and power dependent PL spectra suggest that the broadband subgap light emission stems from excitons self trapped at defect sites, which we assign as edge like, collective I vacancies using a simple model of the chemical equilibrium driving material self assembly. These results suggest that changes to the availability of molecular cations can suitably control the light emission properties of self assembled hybrid organic inorganic materials in ways central to their applicability in lighting technologies.
author_names: Adedayo M Sanni

Aaron S Rury
title: Kinetic Molecular Cationic Control of Defect Induced Broadband Light Emission in 2D Hybrid Lead Iodide Perovskites.
venue: The journal of physical chemistry letters
year: 2020

abstract: Gas induced growth of organic inorganic hybrid perovskites, especially methylammonium lead iodide (MAPbI3) has shown interesting properties and applications in the area of optoelectronics. In this report, we introduce a method of gas induced band gap engineering of thin films of MAPbI3 due to systematic dimensional confinement deconfinement along the crystallographic c axis of growing MAPbI3. Interestingly, such restricted growth phenomenon was observed when hexylammonium lead iodide (2D hybrid perovskite) film was exposed to methylamine gas instead of conventional PbI2 film methylamine gas precursor pair. Hexylamine, formed due to cation exchange reaction interacts selectively with the Pb centres of growing MAPbI3 crystals and this induces an enormous restriction in the growth of MAPbI3 along crystallographic c direction, leading to a unique sheet type MAPbI3 film having a much higher band gap (2.18 eV) compared to conventional bulk MAPbI3. However, careful control of exposure timing gradually evaporates the hexylamine leading to systematic dimensional deconfinement enabling modulation of band gap from 2.18 eV to 1.69 eV. An interplay of adsorption and desorption of hexylamine is also utilized for generating patterns of two different fluorescent hybrid perovskite materials in a single pixel. This new mechanistic investigation highlighting gas induced interplay of dimensional confinement deconfinement associated with band gap tuning provides smooth thin films which can be used to develop optoelectronic devices.
author_names: Sayantan Sasmal

Shilendra Kumar Sharma

Soumyo Chatterjee

Amlan J Pal

Shuvan Prashant Turaga

Andrew A Bettiol

Raj Ganesh S Pala

Sri Sivakumar

Suresh Valiyaveettil
title: Gas Induced Confinement Deconfinement Interplay in Organic Inorganic Hybrid Perovskite Thin Film Results in Systematic Band Modulation.
venue: ACS applied materials interfaces
year: 2019

abstract: Knowledge of the mechanism of formation, orientation, and location of phases inside thin perovskite films is essential to optimize their optoelectronic properties. Among the most promising, low toxicity, lead free perovskites, the tin based ones are receiving much attention. Here, an extensive in situ and ex situ structural study is performed on the mechanism of crystallization from solution of 3D formamidinium tin iodide (FASnI(3) 2D phenylethylammonium tin iodide (PEA(2)SnI(4) and hybrid PEA(2)FA(n) 1)Sn(n)I(3)(n)+1) Ruddlesden Popper perovskites. Addition of small amounts of low dimensional component promotes oriented 3D like crystallite growth in the top part of the film, together with an aligned quasi 2D bottom rich phase. The sporadic bulk nucleation occurring in the pure 3D system is negligible in the pure 2D and in the hybrid systems with sufficiently high PEA content, where only surface crystallization occurs. Moreover, tin based perovskites form through a direct conversion of a disordered precursor phase without forming ordered solvated intermediates and thus without the need of thermal annealing steps. The findings are used to explain the device performances over a wide range of composition and shed light onto the mechanism of the formation of one of the most promising Sn based perovskites, providing opportunities to further improve the performances of these interesting Pb free materials.
author_names: Jingjin Dong

Shuyan Shao

Simon Kahmann

Alexander J Rommens

Daniel Hermida-Merino

Gert H ten Brink

Maria Antonietta Loi

Giuseppe Portale
title: Mechanism of Crystal Formation in Ruddlesden Popper Sn Based Perovskites
year: 2020