Electronic properties of metal halide perovskites and their interfaces: the basics

Adding a 2D character to halide perovskite (HaP) active layers in ambientprotected cells can improve their stability drastically, which is not obvious from the hydrophobicity of the large cations that force the HaP into a 2D structure. Results of two-photon confocal microscopy are reported to study inherent photo-stability of 2D Pb iodide HaPs in the interior of single crystals. Compared to 3D HaP crystals, 2D ones have higher photo-stability and, under a few sun-equivalent conditions, self-heal efficiently after photo-damage. Using both photoluminescence (PL) intensities (as function of time after photo-damage) and spectra, self-healing dynamics of 2D HaP (C 4 H 9 NH 3 ) 2 PbI 4 , 2D/3D (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 2 Pb 3 I 10 and 3D MAPbI 3 are compared. Differences in response to photo-damage and selfhealing ability from different degrees of photo-damage are found between these HaPs. Based on the findings, a possible chemical mechanism for photo-damage and self-healing of the 2D HaPs is suggested: the layered lattice arrangement limits out-diffusion of degradation products, facilitating damage reversal, leading to better 2D HaP photo-stability and self-healing uniformity than for 2D/3D HaPs. One implication of the layered structures' resilience to photo-damage is transfer of their increased stability to devices made with them, such as photovoltaic solar cells and light-emitting diodes.

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“…As was suggested earlier by us (and supported by Zu et al), [ 21,35 ] at this point the well‐known PbI 2 photolysis [ 36 ] can take place:

\begin{matrix} {PbI}_{2 (s)} \overset{h ν_{400 n m}}{\to} {Pb}_{(normals)}^{0} + {normalI}_{2 (s)} \end{matrix}

…”

Section: Resultssupporting

confidence: 74%

2D Pb‐Halide Perovskites Can Self‐Heal Photodamage Better than 3D Ones

Aharon

Ceratti

Jasti

et al. 2022

Adv Funct Materials

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“…We would like to mention that the determination of the valence band onset values for 3D perovskites is done on a logarithmic intensity scale in order to accurately infer the topmost band edge. [ 41,52,53 ] In contrast, the band edges for 2D MHPs can be directly obtained by extrapolating the photoelectron intensity on a linear intensity scale toward the background because of their non‐dispersive top valence bands, [ 54,55 ] similar to what is conventional for organic semiconductors. [ 56,57 ] The observation of valence features of MAPbI 3 in the heterostructure spectra indicates indeed a sub‐monolayer coverage of PEA 2 PbI 4 on the surface, given the very surface sensitive nature of UPS with an electron inelastic mean free path of ≈1–2 nm.…”

Section: Resultsmentioning

confidence: 99%

“…[ 22 ] While the incremental removal of material by sputtering with cluster ions is more gentle than sputtering with conventional atomic ions, it is still challenging to explore the original energy level at the unperturbed interface, because composition changes induced by the depth profiling process cannot be readily excluded, which could influence the electronic structure. It has been acknowledged in this context that the energy levels of 3D MHP films can undergo drastic changes depending on the stoichiometry, the substrate work function, [ 39–43 ] and sample preparation/handling conditions. [ 39,40,44 ] Therefore, thorough and systematic investigations of the electronic properties of 2D MHPs and their interfaces are still highly desirable.…”

Section: Introductionmentioning

confidence: 99%

The Electronic Properties of a 2D Ruddlesden‐Popper Perovskite and its Energy Level Alignment with a 3D Perovskite Enable Interfacial Energy Transfer

Shin

Nandayapa

et al. 2022

Adv Funct Materials

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The success of using 2D Ruddlesden-Popper metal halide perovskites (MHPs) in optoelectronic devices has ignited great interest as means for energy level tuning at the interface with 3D MHPs. Inter alia, the application of 2D phenylethylammonium lead quaternary iodide (PEA 2 PbI 4 )/3D MHPs interfaces has improved various optoelectronic devices, where a staggered type-II energy level alignment is often assumed. However, a type-II heterojunction seems to contradict the enhanced photoluminescence observed for 2D PEA 2 PbI 4 /3D MHP interfaces, which raises fundamental questions about the electronic properties of such junctions. In this study, using direct and inverse photoelectron spectroscopy, it is revealed that a straddling type-I energy level alignment is present at 2D PEA 2 PbI 4 /3D methylammonium lead triiodide (MAPbI 3 ) interfaces, thus explaining that the photoluminescence enhancement of the 3D perovskite is induced by energy transfer from the 2D perovskite. These results provide a reliable fundamental understanding of the electronic properties at the investigated 2D/3D MHP interfaces and suggest careful (re)consideration of the electronic properties of other 2D/3D MHP heterostructures.

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“…It should be noted that, even though the energy level splitting values could be obtained from the multiple Gaussian fitting of the CD spectrum, just similar to the previous works did, , we still expect that an accurate measurement could be performed to determine the electronic band structure of chiral perovskites in the future. For instance, the angle-resolved photoelectron spectroscopy is capable of delivering the valence-band dispersion of conventional halide perovskites. − Large Rashba splitting at the valence-band maximum in conventional halide perovskites have been observed. , Good practice for photoelectron spectroscopy and data analysis have to be followed. , …”

Section: Resultsmentioning

confidence: 99%

Circularly Polarized Photoluminescence of Chiral 2D Halide Perovskites at Room Temperature

Yang

Lin

Hua

et al. 2022

ACS Appl. Mater. Interfaces

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Chiral halide perovskites have attracted considerable attention because of their chiroptical, second-harmonic generation, and ferroelectricity properties and their potential application in chiroptoelectronics and chiral spintronics. However, the fundamental research of these properties is insufficient. In this work, chiral perovskites were synthesized using precursor solutions with various stoichiometric ratios ⟨n⟩. The chiral perovskite film prepared from the solution with ⟨n⟩ = 1 is composed of (R-/S-/rac-MBA) 2 PbBr 4 , whereas the films prepared from the solutions with ⟨n⟩ larger than 1 are a mixture of (R-/S-/rac-MBA) 2 (CsMA) n−1 Pb n Br 3n+1 with n = 1 and large n values. A photoluminescence quantum yield of approximately 90 was obtained. Symmetric circular dichroism (CD) spectra were observed without an external magnetic field. Under various magnetic fields, magnetic field-induced CD features are superimposed with the intrinsic chirality-induced CD features. For the ⟨n⟩ = 1 chiral perovskite film, the energy level splitting induced by chiral molecules are a few 10 μeV, whereas the energy level splitting induced by magnetic fields are at the range of ∼−250 to ∼250 μeV. Circularly polarized photoluminescence spectra were observed at room temperature and associated with the spin-preserved energy funneling from highly energetic phases to the lower energetic phases.

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Electronic properties of metal halide perovskites and their interfaces: the basics

Abstract: We have witnessed tremendous progress of metal halide perovskite (MHP)-based optoelectronic devices, especially in the field of photovoltaics. Despite intensive research in the past few years, questions still remain regarding...

Cited by 16 publications

References 56 publications

2D Pb‐Halide Perovskites Can Self‐Heal Photodamage Better than 3D Ones

2D Pb‐Halide Perovskites Can Self‐Heal Photodamage Better than 3D Ones

The Electronic Properties of a 2D Ruddlesden‐Popper Perovskite and its Energy Level Alignment with a 3D Perovskite Enable Interfacial Energy Transfer

Circularly Polarized Photoluminescence of Chiral 2D Halide Perovskites at Room Temperature

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