Two-dimensional Hybrid Organic-inorganic Perovskites Research Articles

Organic Ligand Engineering for Tailoring Electron-Phonon Coupling in 2D Hybrid Perovskites.

In the emerging two-dimensional organic-inorganic hybrid perovskites, the electronic structures and carrier behaviors are strongly impacted by intrinsic electron-phonon interactions, which have received inadequate attention. In this study, we report an intriguing phenomenon of negative carrier diffusion induced by electron-phonon coupling in (2T)2PbI4. Theoretical calculations reveal that the electron-phonon coupling drives the band alignment in (2T)2PbI4 to alternate between type I and type II heterostructures. As a consequence, photoexcited holes undergo transitions between the organic ligands and inorganic layers, resulting in abnormal carrier transport behavior compared to other two-dimensional hybrid perovskites. These findings provide valuable insights into the role of electron-phonon coupling in shaping the band alignments and carrier behaviors in two-dimensional hybrid perovskites. They also open up exciting avenues for designing and fabricating functional semiconductor heterostructures with tailored properties.

The effect of organic ligand length on structural, vibrational and electrical properties of low-dimensional cobalt hybrid perovskites

Recently, two-dimensional hybrid organic–inorganic perovskites (2D-HOIPs) have emerged in popularity due to ease of tunability in terms of the structure and properties. However, a systematic chemistry and physical description of cobalt-based system is lacking. In this study, we employ X-ray diffraction, Raman spectroscopy and electrochemical impedance spectroscopy (EIS) techniques to investigate the effect of the organic ligand length on the structural, vibrational, and electrical properties of A2CoCl4 [A = methylammonium (MA), ethylammonium (EA) and butylammonium (BA)] perovskite. Results from the measurements showed a noticeable difference and showed potential usage in future applications in the field of electronics.

Carrier Transport in 2D Hybrid Organic-Inorganic Perovskites: The Role of Spacer Molecules.

Two-dimensional organic-inorganic hybrid perovskites (2D HOIPs) have been widely used for various optoelectronics applications owing to their excellent photoelectric properties. However, the selection of organic spacer cations is mostly qualitative without quantitative guidance. Meanwhile, the fundamental mechanism of the carrier transport across the organic spacer layer is still unclear. Here, by using the first-principles nonadiabatic molecular dynamics (NAMD) method, we have studied the transport process of excited carriers between 2D HOIPs separated by a spacer cation layer in real time at atomic levels. We find that the excited electrons and holes can transfer from single-inorganic-layer 2D HOIP to bi-inorganic-layer 2D HOIP on a subpicosecond to picosecond scale. Moreover, we have developed a new method to capture the electron-hole interaction in the frame of NAMD. This work provides a promising direction to design new materials toward high-performance optoelectronics.

Stable and Highly Efficient Photocatalysis with Two-Dimensional Organic-Inorganic Hybrid Perovskites.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) have excellent photoelectric properties, such as high charge mobility and a high optical absorption coefficient, which have attracted enormous attention in the field of optoelectronic devices and photochemistry. However, the stability of 2D OIHPs in solution is deficient. In particular, the lack of stability in polar solutions hinders their application in photochemistry. In this work, (iso-BA)2PbI4 was used as a model to explore the three possibilities of the stable existence of a 2D perovskite in aqueous solution. And two of these systems that stabilize the presence of (iso-BA)2PbI4 were further investigated through electrochemical testing. Moreover, (iso-BA)2PbI4 2D hybrid perovskites exhibited an outstanding degradation rate. The chiral perovskite (R/S-MBA)2PbI4 is able to degrade a 30 mg/L methyl orange solution completely within 5 min, making it one of the fastest catalysts for this particular organic reaction. Further, based on the electron spin resonance test, a degradation mechanism by the halide perovskite was proposed. Based on the great catalytic performance as well as good reusability and stability, (R/S-MBA)2PbI4 perovskites are expected to be a new generation of catalysts, making a great impact on the application of asymmetrically catalyzed photoreactions.

Dynamics of self-hybridized exciton–polaritons in 2D halide perovskites

Excitons, bound electron–hole pairs, in two-dimensional hybrid organic inorganic perovskites (2D HOIPs) are capable of forming hybrid light-matter states known as exciton-polaritons (E–Ps) when the excitonic medium is confined in an optical cavity. In the case of 2D HOIPs, they can self-hybridize into E–Ps at specific thicknesses of the HOIP crystals that form a resonant optical cavity with the excitons. However, the fundamental properties of these self-hybridized E–Ps in 2D HOIPs, including their role in ultrafast energy and/or charge transfer at interfaces, remain unclear. Here, we demonstrate that >0.5 µm thick 2D HOIP crystals on Au substrates are capable of supporting multiple-orders of self-hybridized E–P modes. These E–Ps have high Q factors (>100) and modulate the optical dispersion for the crystal to enhance sub-gap absorption and emission. Through varying excitation energy and ultrafast measurements, we also confirm energy transfer from higher energy E–Ps to lower energy E–Ps. Finally, we also demonstrate that E–Ps are capable of charge transport and transfer at interfaces. Our findings provide new insights into charge and energy transfer in E–Ps opening new opportunities towards their manipulation for polaritonic devices.

Mechanochemically-induced glass formation from two-dimensional hybrid organic-inorganic perovskites.

Hybrid organic-inorganic perovskites (HOIPs) occupy a prominent position in the field of materials chemistry due to their attractive optoelectronic properties. While extensive work has been done on the crystalline materials over the past decades, the newly reported glasses formed from HOIPs open up a new avenue for perovskite research with their unique structures and functionalities. Melt-quenching is the predominant route to glass formation; however, the absence of a stable liquid state prior to thermal decomposition precludes this method for most HOIPs. In this work, we describe the first mechanochemically-induced crystal-glass transformation of HOIPs as a rapid, green and efficient approach for producing glasses. The amorphous phase was formed from the crystalline phase within 10 minutes of ball-milling, and exhibited glass transition behaviour as evidenced by thermal analysis techniques. Time-resolved in situ ball-milling with synchrotron powder diffraction was employed to study the microstructural evolution of amorphisation, which showed that the crystallite size reaches a comminution limit before the amorphisation process is complete, indicating that energy may be further accumulated as crystal defects. Total scattering experiments revealed the limited short-range order of amorphous HOIPs, and their optical properties were studied by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy.

Dopant effect on the optical and thermal properties of the 2D organic-inorganic hybrid perovskite (HDA)2PbBr4.

Lead-based two-dimensional organic-inorganic hybrid perovskites (2D HOIPs) are popular materials with various optical properties, which can be tuned through metal ion doping. Due to the size and valence misfit, metal ion dopants in 2D lead-based HOIPs are still limited. In this work, Mn2+, Sb3+ and Bi3+ are doped into 2D (HDA)2PbBr4 (HDA = protonated dopamine) successfully. As a result, the dopants in 2D (HDA)2PbBr4 can induce their characteristic optical spectra, which is studied at different temperatures and excitation powers. The temperature-dependent energy transfer in the Mn-doped sample has been clarified, in which abnormal phenomena including negative thermal quenching have been observed. In addition, the dopant ions can impact the phase transition temperatures of the samples, especially lowering their crystallization temperatures greatly. The mussel-inspired organic cation, feasible metal ion regulation, and superior stability provide (HDA)2PbBr4 potential for further applications.

Fluorination and Conjugation Engineering Synergistically Enhance the Optoelectronic Properties of Two-Dimensional Hybrid Organic-Inorganic Perovskites.

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are expected to be a viable alternative to three-dimensional (3D) analogs in solar cells (SCs) and optoelectronic devices due to their high stability, diverse composition, and physical properties. However, unsuitable band alignment and large bandgaps limit the power conversion efficiency (PCE) improvement of SCs based on 2D HOIPs. Here, we report a molecular design strategy that combines fluorination and conjugation engineering to tune the electronic structure and optimize the PCE of 2D HOIPs. Our results show that type IIa band alignment and tunable bandgaps can be achieved in 2D Dion-Jacobson (DJ) HOIPs by H/F substitution of organic cations with different degrees of conjugation. In general, the bandgap of 2D DJ-HOIPs decreases monotonously with the increase of the number of F atoms, which is due to the gradual decrease of the lowest unoccupied molecular orbitals (LUMO) of organic cations. In addition, the enhanced interlayer charge transfer and higher dielectric constant suggest that the fluorination-induced dielectric limitations are weakened. The estimated PCE of 2D DJ-HOIPs is exponentially increased and positively correlated with the degree of conjugation and fluorination of organic cations, with a PCE approaching 29% under their synergistic effect. Our results not only provide promising candidates for photovoltaic device applications but also provide an effective method for PCE optimization.

Intrinsic Ferromagnetic Semiconductors with High Saturation Magnetization from Hybrid Perovskites.

Ferromagnetic semiconductors (FMS) enable simultaneous control of both charge and spin transport of charge carriers, which have emerged as a class of highly desirable but rare material for applications in spin field-effect transistors and quantum computing. Organic-inorganic hybrid perovskite with high compositional adjustability and structural versatility can offer unique benefits in the design of FMS but has not been fully explored. Here we demonstrate a series of molecular FMSs based on two-dimensional organic-inorganic hybrid perovskite structure, namely (2ampy)CuCl4 , (3ampy)CuCl4 and (4ampy)CuCl4 , which exhibits high saturation magnetization, dramatic temperature-dependent conductivity change and tunable ferromagnetic resonance. Magnetic measurements revealed high saturation magnetization up to 18.56 emu/g for (4ampy)CuCl4 , which is one of the highest value among reported hybrid FMSs to date. Conductivity studies of the three FMSs demonstrate that the smaller adjacent octahedron distance in the two-dimensional layer results in higher conductivity. Systematic ferromagnetic resonance investigation shows that the gyromagnetic ratio and Landau factor values are strongly dependent on the types of organic cations used. This work demonstrates that two-dimensional hybrid perovskite materials can simultaneously possess both tunable long-range ferromagnetic ordering and semiconductivity, providing a straightforward strategy for designing and synthesizing high-performance intrinsic FMSs. This article is protected by copyright. All rights reserved.

Friction Characteristics of Two-Dimensional Hybrid Organic-Inorganic Perovskites

Friction Characteristics of Two-Dimensional Hybrid Organic-Inorganic Perovskites

Surface engineering of lead-free two-dimensional organic-inorganic hybrid perovskite by laser interference lithography

Laser interference patterning of environment-friendly material with micro/nanoscale surface structures is in high demand for applications. We demonstrated the fabrication of periodic structure in copper-based organic-inorganic hybrid perovskite thin film by 532 nm laser two-beam interference. The extinction coefficient and index of refraction of the copper-based perovskite thin film were characterized by spectroscopic ellipsometry. The morphology of laser-induced structure was investigated by a combination of optical microscopy, scanning electron microscopy, and atomic force microscopy. In addition, the mechanism of the interaction between laser and copper-based perovskite thin film was discussed. This investigation expands the materials selection in laser fabrication and paves the way for optimization towards obtaining micro/nano features for applications in diffractive optics.

Spin-orbit-coupling-induced band splitting in two-dimensional hybrid organic-inorganic perovskites: Importance of organic cations

We investigate how the spin-orbit-coupling-induced lifting of the spin degeneracy depends indirectly on constituting organic motifs in two-dimensional hybrid organic-inorganic perovskites. We examine experimentally synthesized structures using first-principles electronic structure theory. In particular, the effect of the organic spacer cation packing and of the methyl ammonium orientation within the inorganic layer are elucidated. Both the organic spacer packing and subtle changes in methyl ammonium orientations can cause enough distortions of lead iodide octahedral cages to induce the spin splitting. Interestingly, the momentum-independent persistent spin texture splitting rather than the traditional Rashba/Dresselhaus splitting is observed for a structure in which organic spacer molecules are modified with fluorine substitution. Our calculation on these experimentally reported structures highlights the important role of the organic constituents in these hybrid organic inorganic perovskites for the spin splitting.

PEA2PbI4: fast two-dimensional lead iodide perovskite scintillator with green and red emission

Among the two-dimensional hybrid organic-inorganic perovskites, PEA2PbBr4 is one of the best scintillators combining high light yield and fast nanosecond decay time. However, it has limited sensitivity to X-ray and positron emission tomography because of insufficient mass density and effective atomic number. In this article, we show that exchanging the halide from bromide to iodide allows to shorten the absorption length as much as two times for X-ray energies. We present a detailed study on scintillation properties of self-grown samples of PEA2PbI4 crystal, which we compare with the previously reported results for PEA2PbBr4 crystal. The synthesis method of PEA2PbI4 crystal is based on dissolving the perovskite precursors in hydroiodic acid, which is then stirred and left for evaporation. Our measurements include the characterizations with optical, X-ray, and γ-ray sources. We observe two emission bands of PEA2PbI4 crystal centered at 532 (green) and 660 (red) nm, and we link them to the scintillation mechanisms involving exciton and surface defect states. We also report the scintillation light yields of 1,000 and 10,000 photons/MeV at room temperature and 10 K, respectively, and the coincidence timing resolution full width at half maximum of 138 ps, and the fast component in scintillation decay curve of 0.5 ns. This fast component is much faster than that of 13.4 ns of PEA2PbBr4 crystal, and with two times shorter absorption length, it secures better opportunities in timing applications in particular time-of-flight positron emission tomography and high energy physics.

Mussel-Inspired Two-Dimensional Halide Perovskite Facilitated Dopamine Polymerization and Self-Adhesive Photoelectric Coating.

Polydopamine (PDA) is a good adhesion agent for lots of gels inspired by the mussel, whereas hybrid organic-inorganic perovskites (HOIPs) usually exhibit extraordinary optoelectronic performance. Herein, mussel-inspired chemistry has been integrated with two-dimensional HOIPs first, leading to the preparation of new crystal (HDA)2PbBr4 (1) (DA = dopamine). The organic cation dopamine can be introduced into PDA resulting in a thin film of (HPDA)2PbBr4 (PDA-1). The dissolved inorganic components of layered perovskite in DMF solution together with H2O2 addition can facilitate DA polymerization greatly. More importantly, PDA-1 can inherit an excellent semiconductor property of HOIPs and robust adhesion of the PDA hydrogel resulting in a self-adhesive photoelectric coating on various interfaces.

Correction: Crystal growth of two-dimensional organic–inorganic hybrid perovskites and their application in photovoltaics

Correction for ‘Crystal growth of two-dimensional organic–inorganic hybrid perovskites and their application in photovoltaics’ by Yuling Zhang et al., J. Mater. Chem. A, 2023, https://doi.org/10.1039/D3TA01496G.

Crystal growth of two-dimensional organic–inorganic hybrid perovskites and their application in photovoltaics

Crystal growth of two-dimensional organic–inorganic hybrid perovskite has attracted much attention toward adjusting the orientation to obtain higher PCE and more lasting operational stability.

Halogen's effect on the photoelectric properties of two-dimensional organic–inorganic hybrid perovskite (MTEA)2MAPb2X7 (X = Cl, Br, I) with a Ruddlesden–Popper structure

Recently, a two-dimensional (2D) Ruddlesden–Popper (RP) organic–inorganic hybrid perovskite material (MTEA)2MAn−1PbnI3n+1 (n = 1–6) has attracted great attention, and experiments have reported that the thicker material (MTEA)2(MA)4Pb5I16 (n = 5) perovskite material has excellent environmental stability and improved photovoltaic stability. However, considering that the thickness of the material and the substitution of halogen anions have influence on photoelectric properties of materials. In this paper, we study the photoelectric properties of 2D RP organic–inorganic hybrid perovskite (MTEA)2MAPb2X7 (X = Cl, Br, I) (n = 2) based on the density functional theory. The calculated results show that as the halogen in (MTEA)2MAPb2Cl7 varies from Cl to I, the bandgap decreases, the absorption intensity increases, and the exciton binding energies decrease, which is significantly higher than that of MAPbI3 crystal photovoltaic materials, indicating that the material (MTEA)2MAPb2X7 (X = Cl, Br, and I) (n = 2) is more suitable as candidates for luminescent devices. Our work provides opportunities and challenges for the application of 2D RP organic–inorganic hybrid perovskites in luminescent devices.

Growth of van der Waals Halide Perovskites within the Interlayer Spacings of Mica

Two-dimensional hybrid organic–inorganic perovskites (2D-HOIPs) have been extensively researched for use in solar cells as well as optoelectronic devices over the past few years. Controllable growth of single-crystalline 2D-HOIP thin films has been regarded as a key component for the development of high-performance end devices. Here, we report a solution-based method for the growth of 2D-HOIPs using muscovite mica as a van der Waals substrate that yields millimeter-scale perovskite flakes. Interestingly, the grown 2D-HOIP flakes lie embedded within the interlayer spacings of muscovite mica. We find that such 2D-HOIP flakes buried in mica demonstrate enhanced photostability in comparison to conventional 2D-HOIP flakes. Such liquid-phase growth in the interlayer spacings of van der Waals substrates opens a new avenue for developing novel material structures for designing optoelectronic devices.

Ultrafast Excitonic Response in Two-Dimensional Hybrid Perovskites Driven by Intense Midinfrared Pulses.

Two-dimensional organic-inorganic hybrid perovskites (2DHPs) are natural quantum-well-like materials, in which strong quantum and dielectric confinement effects due to the organic spacers give rise to tightly bound excitons with large binding energy. To examine the mutual interactions between the organic spacer cations and the inorganic charge-residing octahedral framework in 2DHPs, here we perform femtosecond pump-probe spectroscopy by direct vibrational pumping of the organic spacers, followed by a visible-to-ultraviolet probe covering their excitonic resonances. Measurements on prototypical lead-bromide based 2DHP compounds, (BA)_{2}PbBr_{4} and (BA)_{2}(FA)Pb_{2}Br_{7} (BA^{+}=butylammonium; FA^{+}=formamidinium), reveal two distinct regimes of the temporal response. The first regime is dominated by a pump-induced transient expansion of the organic spacer layers that reduces the exciton oscillator strength, whereas the second regime arises from pump-induced lattice heating effects primarily associated with a spectral shift of the exciton energy. In addition, vibrational excitation enhances the biexciton emission, which we attribute to a stronger intralayer exciton confinement as well as vibrationally induced exciton detrapping from defect states. Our study provides fundamental insights regarding the impact of organic spacers on excitons in 2DHPs, as well as the excited-state dynamics and vibrational energy dissipation in these structurally diverse materials.

Scintillation properties of ((CH3)4N)3BiCl6 as a novel lead-free perovskite halide crystal

Two-dimensional hybrid organic-inorganic perovskites (2D-HOIPs) possess intriguing structural properties which makes them promising materials for diverse optical, electronic and scintillation applications. Recently, several classes of hybrid perovskites exhibit potential candidate for radiation detection. However, the scintillation properties of corrugated-type 2D-HOIPs have not been studied so far. In this work, we investigate the scintillation performance of bismuth chloride ((CH3)4N)3BiCl6 perovskites for the lead-free candidate. No strong RL intensity at room temperature is observed due to a strong thermal quenching. A small negative thermal quenching is also observed, which infer the presence of trap states characterized by two activation energies: = 25.71 meV and = 129.27 meV. In addition, low temperature afterglow of ((CH3)4N)3BiCl6 at 10 K is estimated to be 70 s (14.5%) and 1200 s (85.5%). In low temperature thermoluminescence ((CH3)4N)3BiCl6 exhibits a broad band, which is attributed to a quasi-continuous distribution of shallow traps. All these results shed some light on the fundamentals of scintillation properties of bismuth-based perovskites.