Franz-Keldysh and Stark Effects in Two-Dimensional Metal Halide Perovskites

Hansen, Kameron R.; McClure, C. Emma; Colton, John; Whittaker‐Brooks, Luisa

doi:10.1103/prxenergy.1.013001

Cited by 15 publications

(48 citation statements)

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“…In contrast, continuum states respond via the Franz–Keldysh (FK) effect to produce an interband feature at the band gap and FK oscillations above the band gap, as shown in Figure 5D. [ 25,47 ] As discussed in greater detail below, each of these features (Stark, interband, and FK oscillation) is present to varying degrees in the 2D MHP EA spectra. The measured EA spectra are shown in Figures 5E–H for PEA 2 PbI 4 , PEA 2 SnI 4 , BA 2 PbI 4 , and BA 2 SnI 4 at room temperature (≈300 K) and in Figures 5I–L for the corresponding spectra at low temperature (<50 K).…”

Section: Resultsmentioning

confidence: 99%

“…For absorbance and electroabsorption measurements, perovskite thin films were spin‐coated on an array of interdigitated gold electrodes which were deposited via photolithography onto a quartz substrate. [ 25,63 ] The small distance between opposing electrode fingers ( d = 45 μm) allowed for the generation of large electric fields (11 – 77 kV/cm) using modest voltages (50 – 350 V). Thin copper wires were soldered to the opposing electrode stripes and samples were mounted in a cryostat for low temperature measurements.…”

Section: Methodsmentioning

confidence: 99%

“…[ 12,23 ] However in 2D MHPs, bulky organic cations occupy the A‐site; this separates the metal halide octahedra into layers (shown in Figure A) and results in quantum confinement, dielectric confinement, and a lower bulk dielectric constant. [ 24 ] These three factors produce exciton binding energies ( E B ) that are an order of magnitude greater than their 3D counterparts (≈250 meV vs 10 meV), [ 25–27 ] allowing for clear spectroscopic isolation of the exciton state. We compare the spectral structure of the exciton peak in tin versus lead 2D MHPs, using photoluminescence (PL), absorption, and electroabsorption (EA) to measure Stark shifts, Franz–Keldysh effects, and the exciton's spectral fine structure.…”

Section: Introductionmentioning

confidence: 99%

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Low Exciton Binding Energies and Localized Exciton–Polaron States in 2D Tin Halide Perovskites

Hansen

McClure

Powell

et al. 2022

Advanced Optical Materials

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Aside from band gap reduction, little is understood about the effect of the tin‐for‐lead substitution on the fundamental optical and optoelectronic properties of metal halide perovskites (MHPs), especially when transitioning from 3D to lower dimensional structures. Herein, we take advantage of the spectroscopic isolation of excitons in 2D MHPs to study the intrinsic differences between lead and tin MHPs. The exciton's spectral fine structure indicates a larger polaron binding energy in tin MHPs. Additionally, the electroabsorption responses of the 2D MHPs demonstrates that tin MHPs have exciton binding energies 1.5–2× lower than that of their lead counterparts. Despite the lower binding energy, the excitons in tin MHPs are more Frenkel‐like with small radii, small polarizabilities, and large dipole moments. These results are interpreted as consequences of small polaron formation and disorder‐induced dipole moments. This work highlights the wide range of intrinsic differences between lead and tin MHPs as well as the complexity of excited states in these systems.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low Exciton Binding Energies and Localized Exciton–Polaron States in 2D Tin Halide Perovskites

Hansen

McClure

Powell

et al. 2022

Advanced Optical Materials

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“…This investigation of 3D perovskites reveals the interplay between composition and morphology in dictating charge migration pathways . Hansen, K.; McClure, C. E.; Colton, J.; Whittaker-Brooks, L. Franz–Keldysh and Stark effects in two-dimensional metal halide perovskites. arXiv.org 2021 , arXiv:2109.09021 Amerling, E.; Baniya, S.; Lafalce, E.; Blair, S.; Vardeny, Z. V.; Whittaker-Brooks, L. Quantifying exciton heterogeneities in mixed-phase organometal halide multiple quantum wells via Stark spectroscopy studies.…”

Section: Key Referencesmentioning

confidence: 99%

“…Hansen, K.; McClure, C. E.; Colton, J.; Whittaker-Brooks, L. Franz–Keldysh and Stark effects in two-dimensional metal halide perovskites. arXiv.org 2021 , arXiv:2109.09021 …”

Section: Key Referencesmentioning

confidence: 99%

Traversing Excitonic and Ionic Landscapes: Reduced-Dimensionality-Inspired Design of Organometal Halide Semiconductors for Energy Applications

et al. 2021

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Conspectus At the very heart of the global semiconductor industry lies the omnipresent push for new materials discovery. New materials constantly rise and fall out of fashion in the scientific literature, with those passing an initial phase of research scrutiny becoming hotbeds of characterization and optimization efforts. Yet, innumerable hours of painstaking research have been devoted to materials that have ultimately fallen by the wayside after crossing over an indefinable threshold, whereupon historical optimism is met with newfound skepticism. Materials have to perform well, and they have to do it quickly. In the past decade, metal-halide perovskites (MHPs) have garnered widespread attention. The hegemonic view in both academic and industrial circles is that these materials could be engineered to meet the demands of the semiconductor industry. Their promise as inexpensive solar cell devices is highly attractive, and it has been nothing short of remarkable that efficiencies have risen from 3.8% in 2009 to more than 25.5% in 2021. Moreover, MHPs are poised to be revolutionary materials in more ways than one. The highest MHP LED efficiency was recently reported (23.4%), and MHPs have demonstrated promise in photodetectors, memristors, and transistors. However, the many excellent properties of MHPs are contrasted by longstanding stability and reproducibility limitations that have hindered their commercialization. Overcoming the limitations of MHPs is ultimately a materials engineering problem, which should be solved by mapping more precise relationships between structure, composition, and device performance. In 1958, Francis Crick famously developed the central dogma of molecular biology which describes the unidirectional flow of information in biological systems. In the words of Crick, “nature has devised a unique instrument in which an underlying simplicity is used to express great subtlety and versatility.” In this Account, taking inspiration from the hierarchical organization of nature, we describe a hierarchical approach to materials engineering of organic metal-halide semiconductors. We demonstrate that organo-metal halide semiconductors’ dimensionality, composition, and morphology dictate their optoelectronic properties and can be exploited in defining more explicit relationships between structure and function. Here, we traverse three-dimensional (3D), two-dimensional (2D), and one-dimensional (1D) organo-metal halide semiconductors, detailing the morphological and compositional differences in each and the implications that can be drawn within each domain on the engineering process. Control over ion migration pathways via morphology engineering as well as control over charge formation in organic–inorganic semiconductors is demonstrated. Fundamental insights into the amount of static and dynamic disorder in the MHP lattice are provided, which can be continuously tuned as a function of composition and morphology. Using electroabsorption spectroscopy on 2D MHPs, a disorder-induced dipole moment in the excito...

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Measuring the Exciton Binding Energy: Learning from a Decade of Measurements on Halide Perovskites and Transition Metal Dichalcogenides

Hansen,

Colton,

Whittaker‐Brooks

2023

Advanced Optical Materials

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The exciton binding energy (Eb) is a key parameter that governs the physics of many optoelectronic devices. At their best, trustworthy and precise measurements of Eb challenge theoreticians to refine models, are a driving force in advancing the understanding of a material system, and lead to efficient device design. At their worst, inaccurate Eb measurements lead theoreticians astray, sow confusion within the research community, and hinder device improvements by leading to poor designs. This review article seeks to highlight the pros and cons of different measurement techniques used to determine Eb, namely, temperature‐dependent photoluminescence, resolving Rydberg states, electroabsorption, magnetoabsorption, scanning tunneling spectroscopy, and fitting the optical absorption. Due to numerous conflicting Eb values reported for halide perovskites (HP) and transition metal dichalcogenides (TMDC) monolayers, an emphasis is placed on highlighting these measurements in an attempt to reconcile the variance between different measurement techniques. It is argued that the experiments with the clearest indicators are in agreement on the following values: ≈350–450 meV for TMDC monolayers between SiO2 and vacuum, ≈150–200 meV for hBN‐encapsulated TMDC monolayers, ≈200–300 meV for common lead‐iodide 2D HPs, and ≈10 meV for methylammonium lead iodide.

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Franz-Keldysh and Stark Effects in Two-Dimensional Metal Halide Perovskites

Cited by 15 publications

References 73 publications

Low Exciton Binding Energies and Localized Exciton–Polaron States in 2D Tin Halide Perovskites

Low Exciton Binding Energies and Localized Exciton–Polaron States in 2D Tin Halide Perovskites

Traversing Excitonic and Ionic Landscapes: Reduced-Dimensionality-Inspired Design of Organometal Halide Semiconductors for Energy Applications

Measuring the Exciton Binding Energy: Learning from a Decade of Measurements on Halide Perovskites and Transition Metal Dichalcogenides

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