Low-dimensional Perovskites Research Articles

Role of Hydrogen Bonding on the Design of New Hybrid Perovskites Unraveled by Machine Learning.

Selecting a set of reactants to accurately design a new low dimensional hybrid perovskite could greatly accelerate the discovery of materials with great potential in photovoltaics, or solid-state lighting. However, this design is challenging as most hybrid metal halides are not perovskites and no feature is clearly associated to the structural characteristics of the inorganic metal halide network. This work first demonstrates that the organic molecules are key parameters to determine the structure type of the inorganic network (i.e., perovskite versus non-perovskite). Then, machine learning (ML) algorithms are used to identify the key features of the organic cations leading to the perovskite structure type. Using a large dataset of hybrid metal halides, this work extracts the organic molecules of all hybrid lead halide compounds, calculates 2756 molecular descriptors and fingerprints for each of these molecules, and are able to predict through ML techniques if a specific organic amine will lead to the perovskite type with an accuracy up to 88.65%. Descriptors related to hydrogen bonding are identified as important features. Thus, a simple but reliable design principle could be demonstrated: the presence of primary ammonium cation is the primary condition to prepare hybrid lead halide perovskites regardless of their dimensionalities.

Temperature and frequency dependent dielectric capacitance and polarization performances of low dimensional perovskite based manganese stannate

Manganese stannate perovskite nanoparticles were synthesized by applying a complexation mediated approach. Rietveld refinement of the XRD data exhibited orthorhombic structure with space group of Pnma. The structure included eightfold coordinated Mn2+ cation, surrounded by eight O2− anions and formed MnO8 polyhedra unit. Each polyhedra unit interconnected through the corner-sharing SnO6 octahedra with the formation of a cage-like network. The temperature and frequency dependent dielectric performances of manganese stannate were measured in the form of a device, which exhibited maximum dielectric constant value ~ 3445. The high dielectric constant value was originated due to the contribution of space charge polarization and orientation polarization of dipoles within the measured frequency ranges. Temperature and frequency dependent AC-conduction mechanism of the manganese stannate-based device involved both overlapping large polarons and non-overlapping small polarons. Electric field-dependent of polarization hysteresis loop of the device exhibited the maximum polarization value 1.5 µC/cm2 under the electric field of 3 kV/mm. Under the applied field of 2 kV/mm, the device exhibited a fatigue-free polarization with a maximum value of 0.92 µC/cm2, sustained for 103 cycles under ambient temperature condition.

Origin of Broad Emission Induced by Rigid Aromatic Ditopic Cations in Low-Dimensional Metal Halide Perovskites.

The development of broadband emitters based on metal halide perovskites (MHPs) requires the elucidation of structure-emission property correlations. Herein, we report a combined experimental and theoretical study on a series of novel low-dimensional lead chloride perovskites, including ditopic aromatic cations. Synthesized lead chloride perovskites and their bromide analogues show both narrow and broad photoluminescence emission properties as a function of their cation and halide nature. Structural analysis shows a correlation between the rigidity of the ditopic cations and the lead halide octahedral distortions. Density functional theory calculations reveal, in turn, the pivotal role of octahedral distortions in the formation of self-trapped excitons, which are responsible for the insurgence of broad emission and large Stokes shifts together with a contribution of halide vacancies. For the considered MHP series, the use of conventional octahedral distortion parameters allows us to nicely describe the trend of emission properties, thus providing a solid guide for further materials design.

Orange-emitting zero-dimensional Te4+-Doped Cs2ScCl5·H2O perovskite microcrystals

Low-dimensional metal halide perovskites have gained the favor of many researchers for their potential applications in solid-state lighting due to their excellent optoelectronic properties. Herein, Te4+ doped Cs2ScCl5·H2O, a novel orange-emitting zero-dimensional scandium halide perovskite microcrystal was synthesized by hydrothermal method. Cs2ScCl5·H2O is isomorphic to Cs2InCl5·H2O with the space group Pnma. Under UV excitation, Cs2ScCl5·H2O:Te4+ exhibits a bright orange emission at 620 nm with a full width at half maximum (FWHM) of 170 nm, which is related to the formation of self-trapping excitons (STEs) in the zero-dimensional Te4+ doped Cs2ScCl5·H2O soft lattice. The fluorescence lifetime of Cs2ScCl5·H2O:Te4+ microcrystals are highly temperature-dependent with significant changes from microseconds (5.352 μs) at 110 K to nanoseconds (252 ns) at 298 K. The microcrystal-based white LED and thin film were initially explored for their potential application. These findings provide new insights into the excited state dynamics of Te4+ in Cs2ScCl5·H2O and demonstrate the potential application prospect for lead-free scandium halides doped by ns2 metal ions.

Accurate Dimension Prediction for Low-Dimensional Organic-Inorganic Halide Perovskites via a Self-Established Machine Learning Strategy.

Low-dimensional perovskites (LDPs) have enormous potential for the development of advanced optoelectronic devices and tackling the stability issue for the commercial application of perovskites. However, quantified structural dimensionality prediction for LDPs is still an intractable issue. Herein, we develop a self-established machine learning (ML)-assisted approach to predict the dimensionality of LDPs based on 195 reported amines that are classified as two-dimensional, one-dimensional, and zero-dimensional. The optimal K-nearest neighbor model allows us to realize an accuracy rate of 92.3% for the test data set containing 39 reported amines. Two features, i.e., ATSC1pe and SlogP_VSA2, associated with polarity and electrostatic potential on the van der Waals surface of an organic spacer, are identified from >1800 descriptors as key controlling factors determining the structure dimensionality. This work develops a typical paradigm for the application of a multiple-classification strategy of ML with an extremely high accuracy rate, which would thereby motivate the development of new types of LDPs.

Difluorine-substituent tailored roles of aromatic monoammonium cations on the perovskite surface

Aromatic monoammonium cations (AMCs) have been widely used to ameliorate the perovskite surface by interacting with defects or constructing low-dimensional perovskites, yet ignoring substituent effects on the working principle of AMCs. Here, we demonstrated that benzylammonium cation (BA) and difluorinated BA (DFBA) AMCs play different roles on the perovskite surface. BA can transform three-dimensional (3D) perovskite into two-dimensional (2D) ones on perovskite surface, but the 2D perovskites with random orientation impede charge extraction and increase nonradiative charge recombination. As a comparison, DFBA cannot form 2D perovskites, while directly interacting with the perovskite surface, simultaneously improving the contact between the perovskite and “2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9′- spirobifluorene (Spiro-OMeTAD) layer, promoting interfacial charge extraction, thus boosting the efficiency to 20.29 % and 24.02 % for (CH3NH3)PbI3 (MAPbI3) and (CH(NH2)2)PbI3 (FAPbI3) based perovskite solar cells (PSCs), respectively. Our finding provides a distinctive understanding on the roles of AMCs on the perovskite surface for PSCs.

Layered Low-Dimensional Ruddlesden-Popper and Dion-Jacobson Perovskites: From Material Properties to Photovoltaic Device Performance.

Layered low-dimensional halide perovskites (LDPs) with multiple quantum well structure have shown increasing research interest in photovoltaic solar cell applications owing to their intrinsic moisture stability and favorable photophysical properties in comparison with their three-dimensional (3D) counterparts. The most common LDPs are Ruddlesden-Popper (RP) phases and Dion-Jacobson (DJ) phases, both of which have made significant research advances in efficiency and stability. However, distinct interlayer cations between RP and DJ phase lead to disparate chemical bonds and different perovskite structures, which endow RP and DJ perovskite with distinctive chemical and physical properties. Plenty of reviews have reported the research progress of LDPs but no summary has elaborated from the perspective of the merits and drawbacks of the RP and DJ phases. Herein, in this review, we offer a comprehensive expound on the merits and promises of RP and DJ LDPs from their chemical structure, physicochemical properties, and photovoltaic performance research progress aiming to provide a new insight into the dominance of RP and DJ phases. Then, we reviewed the recent progress on the synthesis and implementation of RP and DJ LDPs thin films and devices, as well as their optoelectronic properties. Finally, we discussed the possible strategies to resolve existing toughs to realize the desired high-performance LDPs solar cells.

All-optical passive photonic diodes based on perovskite and transparent conducting oxide material

Low dimensional perovskite emerging as a highly promising class of functional materials for semiconductor optoelectronic applications have drawn great attention. Here, we report the nonlinear absorption of low-dimensional perovskite PEA2PbI4 and transparent conducting oxide material Aluminum-doped zinc oxide (AZO) with operating spectral window in telecommunications. Then we fabricate all-optical diodes with nonreciprocity factor of 10.1 dB based on the reverse saturable absorber (PEA2PbI4) and the saturable absorber (AZO). The results show the potential applications of perovskite-based materials in all-optical diode, and may pave way for the development of high-performance photonic devices.

A Multifunctional Additive Strategy Enables Efficient Pure-Blue Perovskite Light-Emitting Diodes.

Lead halide perovskites have shown exceptional performance in light-emitting devices (PeLEDs), particularly in producing significant electroluminescence in sky-blue to near-infrared wavelengths. However, PeLEDs emitting pure-blue light at 465-475 nm are still not satisfactory. Herein, efficient and stable pure-blue PeLEDs are reported by controlling phase distribution, passivation of defects, as well as surface modifications using multifunctional phenylethylammonium trifluoroacetate (PEATFA) in reduced-dimensional p-F-PEA2 Csn-1 Pbn (Br0.55 Cl0.45 )3n+1 polycrystalline perovskite films. Compared with 4-fluorophenylethylammonium (p-F-PEA+ ) in the pristine films, phenylethylammonium (PEA+ ) has lower adsorption energy while interacting with perovskites, resulting in large-n low-dimensional perovskites, which can greatly facilitate charge transport within the low-dimensional perovskite films. The interaction between the CO group in trifluoroacetate (TFA- ) and perovskites significantly reduces defects in the perovskite films. Additionally, the electron-giving CF3 group in TFA- uplifts surface potential in the films, resulting in smooth electronic injection in devices. The multifunctional additive strategy leads to elevated radiative recombination and efficient carrier transport in the films and devices. As a result, the devices exhibit a maximum external quantum efficiency (EQE) of 11.87% at 468 nm with stable spectral output, the highest reported to date for pure-blue PeLEDs. Thus, this study extends the way for high-efficiency pure-blue LED with perovskite polycrystal films.

Understanding optical and structural properties of the CH3NH3PbI3 nanocrystal thin films under humidity conditions

Low-dimensional organic-inorganic hybrid perovskite materials have drawn a lot of interest in optoelectronic applications because of their unique optoelectronic performance in comparison to their bulk counterparts. There is an influence of humidity conditions on the stability of perovskite in both positive and negative ways. The passivation of surface and bulk defects in the thin film of perovskite by the H2O molecules is a positive way. The negative way is that the material's stability will hinder the commercialization of perovskite-based devices. Herein, CH3NH3PbI3 nanocrystals are synthesized by the hot-injection method. The optical and structural properties of the thin film of the synthesized nanocrystals under different humidity conditions are studied through photoluminescence (PL), TRPL, Raman, X-ray diffraction (XRD), UV–Vis, spectroscopic ellipsometry, and FTIR techniques for 4 weeks. The redshift in the PL spectra of the thin film with an increase in PL intensity and carrier lifetime is caused by the shallow trap-assisted radiative recombination and localization of the charge carriers at the interface of the CH3NH3PbI3/water. The XRD, Raman, and FTIR peaks of the thin film are also shifted due to defect formation and structure distortion of the CH3NH3PbI3 crystal lattice. The thin films of these nanocrystals exhibit very high PLQY of 56% and 60% after 5 h and 1 week respectively. The results pave the way to analyse the stability of CH3NH3PbI3 nanocrystals through their optical and structural behaviour under different humidity conditions. The results also reflect that the photoemission of the synthesized material can be tuned by regulating the defect density and the structural deformation of the nanocrystals under controlled humidity conditions.

Photoluminescence analysis of CsPb2Cl5 and CsPbCl3 perovskite films doped with Yb3+ deposited by aerosol-assisted CVD

Low-dimensional all-inorganic metal halide perovskites (MHPs) have attracted attention due to their promising advantages as semiconductor materials for optoelectronic applications. However, obtaining a low-dimensional MHPs pure phase has been difficult due to its high ionic nature. Here, the one-step in-situ deposition of CsPb2Cl5 films by Aerosol Assisted Chemical Vapor Deposition (AACVD) is reported for the first time. An analysis of the effects of precursor concentrations, using ethanol (EtOH) as antisolvent, and Yb3+ doping on the resulting three-dimensional and/or two-dimensional perovskite phase films is presented. It was found that a lead rich precursor (PbCl2:CsCl = 2:1) was necessary to promote the formation of the CsPb2Cl5 phase, in addition, the use of EtOH and doping with hetero-valent Yb3+ ions was required to attain this phase successfully. The excitation and emission photoluminescence spectra analysis for these films is focused on the three principal emissions: i) a narrow emission peak around 418 nm from the CsPbCl3 phase, ii) a dual broad emission around 550 nm from the CsPb2Cl5 phase, and iii) an emission at 984 nm associated with the Yb3+ ions introduced as dopants in the MHPs lattice. A possible mechanism is proposed for the observed energy transfer from the CsPb2Cl5 matrix to the ytterbium ions and for the interactions between Yb3+ and the excitonic emissions.

Three Semiconductive 1D Naphthalene Diimide/Iodoplumbate Perovskites with High Moisture Tolerance and Long-Lived Charge Separation States.

Low-dimensional inorganic-organic hybrid perovskites with high moisture tolerance and long-lived charge separation states have captured significant attention in the field of optoelectronic devices. To further achieve the relationship between crystal structures and stability, as well as charge separation behaviors, three one-dimensional hybrid perovskites containing electron-deficient naphthalene diimide ammonium (NDIEA) and electron-rich iodoplumbate chains, [(H2NDIEA)Pb2I6]·2DMF (1), [(H2NDIEA)2Pb5I14·(DMF)2]·4DMF (2), and [(HNDIEA)2Pb2I6]·3H2O (3), were synthesized. Crystal structure determinations revealed various synthesis conditions leading to different stacking modes, especially the inorganic lead iodide fraction, which resulted in different water resistances and charge-separated behaviors. The comprehensive analysis found that strong intermolecular interactions (anion-π interactions and π-π interactions), and matching energy levels between protonated NDIEA and iodoplumbate chains, can facilitate the generation of long-lived charge separation states and extraordinary moisture stability, even in the water environment. In addition, the conductivity behavior of 3 was also explored in detail.

Mn Doping in Low-Dimensional Perovskites: A Switch for Controlling Dopant and Host Emission

The growth of solid-state photonics relies on the design of highly efficient devices with tunable photoluminescence (PL) based on thermally stable phosphors. In this study, a room-temperature, all-ambient synthesis of Mn-doped hybrid lead halide perovskite phosphors is presented. By applying temperature-dependent (4.2–300 K) steady-state and transient PL measurements, the photophysical pathways of the hybrid system were identified and the carrier recombination processes at play were defined. At higher Mn-doping concentrations (>4%), the excitonic white light host emission nearly disappears, and a bright Mn transition appears at ∼650 nm with a record PL quantum yield of ∼87.4%. The intense sensitized Mn luminescence results from rapid and efficient exciton-to-dopant energy transfer, as evidenced by time-gated and femtosecond fluorescence upconversion measurements. A millisecond PL decay time attributed to the Mn dopant and a microsecond PL decay time associated with the excitonic emission of the host were found, indicating energy and reverse energy transfer in the system. These findings provide unique insights into the chemical tailoring of the Mn-dopant emission by investigating the coupling between the host semiconductor and the dopant ion, a stepping stone toward the development of high-performance solid-state light-emitting diodes and scintillators.

First-principles and machine learning modeling on adsorption of atmospheric gases on two-dimensional Ruddlesden–Popper halide perovskite surface

The interactions between the atmospheric gases and the halide perovskite materials are receiving attention in these years before the extensive industrial deployment of halide perovskite materials. In this manuscript, we combine first-principles calculation and machine learning techniques to evaluate the interactions between the atmospheric gas molecules and a two-dimensional Ruddlesden–Popper halide perovskite Cs2PbBr4 surface based on the adsorption energies and automatically design advanced molecular descriptors for the target output. The impacts of density functionals are considered while an accurate machine learning model (r = 0.954 and R 2 = 0.951) is obtained based on the XGBRF ensemble algorithm. Importantly, the symbolic regression automatically finds an effective hybrid descriptor that exhibits high correlation with the target output that is comparable with the machine learning model; the symbolic regression-derived descriptor is mathematically simple and chemistry-aware, which complements the debatable ‘black-box’ machine learning model. Both feature importance ranking and symbolic regression indicate the importance of the functional-dependent energy levels of the perovskite systems and the amide/hydroxyl functional groups of the molecules. The present study highlights the viability of combining density functional theory and machine learning techniques to model the low-dimensional perovskite structures under the atmospheric conditions.

Modulation of Colloidal Assembly Behavior Enables Printable Low-Dimensional Perovskite Photovoltaics.

The multiple quantum wells (QWs) distribution in low-dimensional perovskite films hinders charge transport due to the fundamental difficulty of controlling crystal growth from precursor solutions, yielding poorly homogeneous low-dimensional perovskite solar cells (PSCs), especially in upscaling fabrication. Here, efficient low-dimensional PSCs are realized by modulating the colloidal assembly behavior in the precursor solution to induce intermediate structures. In combination with in situ liquid time-of-flight secondary ion mass spectrometry, the assembly behavior of organic cations involved lead iodide-dominated colloidal soft framework is visualized by investigating the precursor species differences under hydrogen bonding interactions. Subsequently, solid-state reactions emerge and the formamidine (FA)-based perovskite films exhibit significantly suppressed multiple QWs distribution. Encouragingly, the FA device (n = 9, by meniscus-assisted coating) achieves a power conversion efficiency (PCE) of 20.28% for a size of 0.04 cm2 and a PCE of 15.35% for a mini-module of 16.94 cm2 with superior stability.

Temperature Dependent Hydrogen Bond Toward High Emission in an Emerging Indium-Based Perovskite.

Low-dimensional organic-inorganic hybrid perovskites (OIHPs) with broadband emission attract immense scientific interest due to their potential application for the next generation of solid-state lighting. However, due to low exciton utilization, organic cations generally adjust structure rather than contribute the band edge to affect optical properties. Based on this, OIHPs are usually allowed to obtain a low photoluminescence quantum yield (PLQY). Herein, a good charge transfer carrier (p-phenylenediamine, PPDA) as organic cation is rationally employed and a novel indium-based perovskite is synthesized. By coupling with H2 O molecules, a strong interaction between organic and inorganic components is realized by hydrogen bonding, which has good transportability and greatly improves the exciton utilization. The regions of hydrogen bonding show high electron mobility, combined with the induced recombination center, improving the progress of charge relaxation. As a result, the regulation of hydrogen bond strength based on the microstructure optimization directly determines the optical emission intensity, realizing nearly 100% PLQY. Further, the polyhydrogen bond structure makes each component a stronger interaction, showing high stability in polar, organic, and acidic solvent, as well as long-term storing, which represents one of the highest overall performances for lighting in OIHPs.

Resistive switching and artificial synaptic performances of memristor based on low-dimensional bismuth halide perovskites

Resistive switching and artificial synaptic performances of memristor based on low-dimensional bismuth halide perovskites

Unveiling the Linear Photogalvanic Effect in a Two-Dimensional Organic Tin Halide Perovskite: (CH3)2NH2SnI3

Hybrid organic–inorganic halide perovskites (HOIPs) with intrinsic noncentrosymmetry are an emerging class of semiconducting materials that has been revolutionizing the field of optoelectronics including second-order nonlinear optics (NLO). Following an upsurge in three-dimensional (3D) perovskites, more recently, low-dimensional perovskite materials have displayed desirable NLO responses attributed to structural diversity, strong quantum confinement, and remarkable exciton effect. Herein, using first-principles methods, we elucidate a linear photogalvanic effect (LPGE) photocurrent (shift photocurrent, SPC) with a maximum amplitude of ∼430 μAV–2 in a quasi-two-dimensional (2D) lead-free HOIP, (CH3)2NH2SnI3 (DMASnI3). The simulated SPC whose prominent peaks occur predominantly in the ultraviolet (UV) range is about 8-fold larger in magnitude compared to its 3D counterpart. From the orbital characteristics of the initial and final states, the calculated SPC is attributed to the contributions from the electronic properties of Sn and I whose p-states control the band edges. The organic-cation orientation indirectly influences the bandgap size, valence and conduction band edge behavior, as well as the position of the Fermi level, slightly altering the LPGE photocurrent spectrum. The findings of this work demonstrate the quasi-2D organic tin triiodide perovskite as a promising lead-free alternative for NLO devices.

Uncovering temperature-dependent exciton-polariton relaxation mechanisms in hybrid organic-inorganic perovskites

Hybrid perovskites have emerged as a promising material candidate for exciton-polariton (polariton) optoelectronics. Thermodynamically, low-threshold Bose-Einstein condensation requires efficient scattering to the polariton energy dispersion minimum, and many applications demand precise control of polariton interactions. Thus far, the primary mechanisms by which polaritons relax in perovskites remains unclear. In this work, we perform temperature-dependent measurements of polaritons in low-dimensional perovskite wedged microcavities achieving a Rabi splitting of {{{hslash }}Omega }_{{Rabi}} = 260 ± 5 meV. We change the Hopfield coefficients by moving the optical excitation along the cavity wedge and thus tune the strength of the primary polariton relaxation mechanisms in this material. We observe the polariton bottleneck regime and show that it can be overcome by harnessing the interplay between the different excitonic species whose corresponding dynamics are modified by strong coupling. This work provides an understanding of polariton relaxation in perovskites benefiting from efficient, material-specific relaxation pathways and intracavity pumping schemes from thermally brightened excitonic species.

Low Bandgap 2D Perovskite Single Crystal with Anomalous-large Charges/ions Collection Ratio for Ultra-sensitive and Stable X-ray Detectors.

The low-dimensional halide perovskites have attracted increasing attention due to their improved moisture stability, reduced defects, and suppressed ions migration in many optoelectronic devices such as solar cells, light-emitting diodes, X-ray detectors, and so on. However, they are still limited by their large band gap and short charge carriers' diffusion length. Here, we demonstrate that the introduction of metal ions into organic interlayers of two-dimensional (2D) perovskite by cross-linking the copper paddle-wheel cluster-based lead bromide ([Cu(O2 C-(CH2 )3 -NH3 )2 ]PbBr4 ) perovskite single crystals with coordination bonds can not only significantly reduce the perovskite band gap to 0.96 eV to boost the X-ray induced charge carriers, but can also selectively improve the charge carriers' transport along the out-of-plane direction and blocking the ions motion paths. The [Cu(O2 C-(CH2 )3 -NH3 )2 ]PbBr4 single-crystal device can reach a record charges/ions collection ratio of 1.69×1018 ±4.7 % μGyair -1 s, and exhibit a large sensitivity of 1.14×105 ±7% μC Gyair -1 cm-2 with the lowest detectable dose rate of 56 nGyair s-1 under 120 keV X-rays irradiation. In addition, [Cu(O2 C-(CH2 )3 -NH3 )2 ]PbBr4 single-crystal detector exposed to the air without any encapsulation shows excellent X-ray imaging capability with long-term operational stability without any attenuation of 120 days.