Multilayered 2D Cesium-Based Hybrid Perovskite with Strong Polarization Sensitivity: Dimensional Reduction of CsPbBr3

3D perovskite CsPbBr₃ has recently taken a blooming position for optoelectronic applications. However, due to the lack of natural anisotropy of optical attributes, it is a great challenge to fulfil polarization-sensitive photodetection. Here, for the first time, we exploited dimensionality reduction of CsPbBr₃ to tailor a 2D-multilayered hybrid perovskite, (TRA)₂CsPb₂Br₇ ( 1 , in which TRA is (carboxy)cyclohexylmethylammonium), serving as a potential polarized-light detecting candidate. Its unique quantum-confined 2D structure results in intrinsic anisotropy of electrical conductivity, optical absorbance, and polarization-dependent responses. Particularly, it exhibits remarkable dichroism with the photocurrent ratio (I_pc/I_pa) of ≈2.1, being much higher than that of the isotropic CsPbBr₃ crystal and reported CH₃NH₃PbI₃ nanowire (≈1.3), which reveals its great potentials for polarization-sensitive photodetection. Further, crystal-based detectors of 1 show fascinating responses to the polarized light, including high detectivity (>10¹⁰ Jones), fast responding time (≈300 μs), and sizeable on/off current ratios (>10⁴). To our best knowledge, this is the first study on 2D Cs-based hybrid perovskite exhibiting strong polarization-sensitivity. The work highlights an effective pathway to explore new polarization sensitive candidates for hybrid perovskites and promotes their future electronic applications.     

A Narrow Bandgap of 2D Ruddlesden-Popper Bilayer Perovskite with Giant Entropy Change and Photoluminescence

The multifunctional two-dimensional (2D) organic-inorganic hybrid perovskites have potential applications in many fields, such as, semiconductor, energy storage and fluorescent device etc. Here, a 2D Ruddlesden-Popper (RP) perovskite (IPA)₂(FA)Pb₂I₇ ( 1 , IPA⁺=C₃H₉NI⁺, FA⁺=CN₂H₅⁺) is determined for its photophysical properties. Strikingly, 1 reveals a solid reversible phase transition with T_c of 382 K accompanied by giant entropy change of 40 J mol⁻¹ K⁻¹. Further optical investigations indicate that 1 reveals a narrow direct bandgap (2.024 eV) attributed to the slight bending of I−Pb-I edge and inorganic [Pb₂I₇]_n layer and a superior photoluminescence (PL) emission with super long lifetime of 0.1607 ms. It is believed that this work will pave an avenue to further design multifunctional semiconductors that combines energy storage and photoelectric materials.     

Ion‐Exchange‐Induced 2D–3D Conversion of HMA1−xFAxPbI3Cl Perovskite into a High‐Quality MA1−xFAxPbI3 Perovskite

High‐quality phase‐pure MA_1?xFA_xPbI₃ planar films (MA=methylammonium, FA=formamidinium) with extended absorption and enhanced thermal stability are difficult to deposit by regular simple solution chemistry approaches owing to crystallization competition between the easy‐to‐crystallize but unwanted δ‐FAPbI₃/MAPbI₃ and FA_xMA_1?xPbI₃ requiring rigid crystallization conditions. Here A 2D–3D conversion to transform compact 2D mixed composition HMA_1?xFA_xPbI₃Cl perovskite precursor films into 3D MA_1?xFA_xPbI₃ (x=0.1–0.9) perovskites is presented. The designed Cl/I and H/FA(MA) ion exchange reaction induced fast transformation of compact 2D perovskite film, helping to form the phase‐pure and high quality MA_1?xFA_xPbI₃ without δ‐FAPbI₃ and MAPbI₃ impurity. In all, we successfully developed a facile one‐step method to fabricate high quality phase‐pure MA_1?xFA_xPbI₃ (x=0.1–0.9) perovskite films by 2D–3D conversion of HMA_1?xFA_xPbI₃Cl perovskite. This 2D–3D conversion is a promising strategy for lead halide perovskite fabrication.     

Room-Temperature Ferroelectric Material Composed of a Two-Dimensional Metal Halide Double Perovskite for X-ray Detection

Although two-dimensional (2D) metal–halide double perovskites display versatile physical properties due to their huge structural compatibility, room-temperature ferroelectric behavior has not yet been reported for this fascinating family. Here, we designed a room-temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)₄AgBiBr₈, using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm⁻², triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr₆/BiBr₆ octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility-lifetime product (μτ=1.0×10⁻³ cm² V⁻¹) for detecting X-ray photons, which is almost tenfold higher than that of CH₃NH₃PbI₃ wafers. As far as we know, this is the first study on an X-ray-sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.     

Room‐Temperature Ferroelectric Material Composed of a Two‐Dimensional Metal Halide Double Perovskite for X‐ray Detection

Although two‐dimensional (2D) metal–halide double perovskites display versatile physical properties due to their huge structural compatibility, room‐temperature ferroelectric behavior has not yet been reported for this fascinating family. Here, we designed a room‐temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)₄AgBiBr₈, using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm^?2, triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr₆/BiBr₆ octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility‐lifetime product (μτ=1.0×10^?3 cm² V^?1) for detecting X‐ray photons, which is almost tenfold higher than that of CH₃NH₃PbI₃ wafers. As far as we know, this is the first study on an X‐ray‐sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.     

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(O₂C−(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(O₂C−(CH₂)₃−NH₃)₂]PbBr₄ single-crystal device can reach a record charges/ions collection ratio of 1.69×10¹⁸±4.7 % μGy_air⁻¹ s, and exhibit a large sensitivity of 1.14×10⁵±7% μC Gy_air⁻¹ cm⁻² with the lowest detectable dose rate of 56 nGy_air s⁻¹ under 120 keV X-rays irradiation. In addition, [Cu(O₂C−(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.     

Steric Mixed‐Cation 2D Perovskite as a Methylammonium Locker to Stabilize MAPbI3

The reduced dimension perovskite including 2D perovskites are one of the most promising strategies to stabilize lead halide perovskite. A mixed‐cation 2D perovskite based on a steric phenyltrimethylammonium (PTA) cation is presented. The PTA‐MA mixed‐cation 2D perovskite of PTAMAPbI₄ can be formed on the surface of MAPbI₃ (PTAI‐MAPbI₃) by controllable PTAI intercalation by either spin coating or soaking. The PTAMAPbI₄ capping layer can not only passivate PTAI‐MAPbI₃ perovskite but also act as MA⁺ locker to inhibit MAI extraction and significantly enhance the stability. The highly stable PTAI‐MAPbI₃ based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion PCE of 21.16 %. Such unencapsulated devices retain 93 % of initial efficiency after 500 h continuous illumination. This steric mixed‐cation 2D perovskite as MA⁺ locker to stabilize the MAPbI₃ is a promising strategy to design stable and high‐performance hybrid lead halide perovskites.     

Near IR Bandgap Semiconducting 2D Conjugated Metal-Organic Framework with Rhombic Lattice and High Mobility

Two-dimensional conjugated metal–organic frameworks (2D c-MOFs) are emerging as a unique class of electronic materials. However, 2D c-MOFs with band gaps in the Vis-NIR and high charge carrier mobility are rare. Most of the reported conducting 2D c-MOFs are metallic (i.e. gapless), which largely limits their use in logic devices. Herein, we design a phenanthrotriphenylene-based, D_2h-symmetric π-extended ligand ( OHPTP ), and synthesize the first rhombic 2D c-MOF single crystals ( Cu₂(OHPTP) ). The continuous rotation electron diffraction (cRED) analysis unveils the orthorhombic crystal structure at the atomic level with a unique slipped AA stacking. The Cu₂(OHPTP) is a p-type semiconductor with an indirect band gap of ≈0.50 eV and exhibits high electrical conductivity of 0.10 S cm⁻¹ and high charge carrier mobility of ≈10.0 cm² V⁻¹ s⁻¹. Theoretical calculations underline the predominant role of the out-of-plane charge transport in this semiquinone-based 2D c-MOF.     

Synergistic Surface Passivation of CH3NH3PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3-Aminopropyl)triethoxysilane

CH₃NH₃PbBr₃ perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9–4.2 nm) and excitonic absorption band positions (λ=488–525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46–83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb²⁺ and CH₃NH₃⁺ surface defects are passivated by R−PO₃²⁻ or R−PO₂(OH)⁻, whereas Br⁻ surface defects are passivated by R−NH₃⁺ moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding.     

1D Choline-PbI3-Based Heterostructure Boosts Efficiency and Stability of CsPbI3 Perovskite Solar Cells

Defects in perovskite are key factors in limiting the photovoltaic performance and stability of perovskite solar cells (PSCs). Generally, choline halide (ChX) can effectively passivate defects by binding with charged point defects of perovskite. However, we verified that ChI can react with CsPbI₃ to form a novel crystal phase of one-dimensional (1D) ChPbI₃, which constructs 1D/3D heterostructure with 3D CsPbI₃, passivating the defects of CsPbI₃ more effectively and then resulting in significantly improved photoluminescence lifetime from 20.2 ns to 49.4 ns. Moreover, the outstanding chemical inertness of 1D ChPbI₃ and the repair of undesired δ-CsPbI₃ deficiency during its formation process can significantly enhance the stability of CsPbI₃ film. Benefiting from 1D/3D heterostructure, CsPbI₃ carbon-based PSCs (C-PSCs) delivered a champion efficiency of 18.05 % and a new certified record of 17.8 % in hole transport material (HTM)-free inorganic C-PSCs.     

Dual-Interface Engineering in Perovskite Solar Cells with 2D Carbides

Passivating the interfaces between the perovskite and charge transport layers is crucial for enhancing the power conversion efficiency (PCE) and stability in perovskite solar cells (PSCs). Here we report a dual-interface engineering approach to improving the performance of FA_0.85MA_0.15Pb(I_0.95Br_0.05)₃-based PSCs by incorporating Ti₃C₂Cl_x Nano-MXene and o-TB-GDY nanographdiyne (NanoGDY) into the electron transport layer (ETL)/perovskite and perovskite/ hole transport layer (HTL) interfaces, respectively. The dual-interface passivation simultaneously suppresses non-radiative recombination and promotes carrier extraction by forming the Pb−Cl chemical bond and strong coordination of π-electron conjugation with undercoordinated Pb defects. The resulting perovskite film has an ultralong carrier lifetime exceeding 10 μs and an enlarged crystal size exceeding 2.5 μm. A maximum PCE of 24.86 % is realized, with an open-circuit voltage of 1.20 V. Unencapsulated cells retain 92 % of their initial efficiency after 1464 hours in ambient air and 80 % after 1002 hours of thermal stability test at 85 °C.     

Tailored Engineering of an Unusual (C4H9NH3)2(CH3NH3)2Pb3Br10 Two‐Dimensional Multilayered Perovskite Ferroelectric for a High‐Performance Photodetector

Two‐dimensional (2D) layered hybrid perovskites have shown great potential in optoelectronics, owing to their unique physical attributes. However, 2D hybrid perovskite ferroelectrics remain rare. The first hybrid ferroelectric with unusual 2D multilayered perovskite framework, (C₄H₉NH₃)₂(CH₃NH₃)₂Pb₃Br₁₀ ( 1 ), has been constructed by tailored alloying of the mixed organic cations into 3D prototype of CH₃NH₃PbBr₃. Ferroelectricity is created through molecular reorientation and synergic ordering of organic moieties, which are unprecedented for the known 2D multilayered hybrid perovskites. Single‐crystal photodetectors of 1 exhibit fascinating performances, including extremely low dark currents (ca. 10⁻¹² A), large on/off current ratios (ca. 2.5×10³), and very fast response rate (ca. 150 μs). These merits are superior to integrated detectors of other 2D perovskites, and compete with the most active CH₃NH₃PbI₃.     

Limiting Perovskite Solar Cell Performance by Heterogeneous Carrier Extraction

Although the power conversion efficiency of perovskite solar cells has improved rapidly, a rational path for further improvement remains unclear. The effect of large morphological heterogeneity of polycrystalline perovskite films on their device performance by photoluminescence (PL) microscopy has now been studied. Contrary to the common belief on the deleterious effect of morphological heterogeneity on carrier lifetimes and diffusivities, in neat CH₃NH₃PbI₃(Cl) polycrystalline perovskite films, the local (intra‐grain) carrier diffusivities in different grains are all surprisingly high (1.5 to 3.3 cm² s^?1; comparable to bulk single‐crystals), and the local carrier lifetimes are long (ca. 200 ns) and surprisingly homogenous among grains, and uniform across grain boundary and interior. However, there is a large heterogeneity of carrier extraction efficiency at the perovskite grain–electrode interface. Improving homogeneity at perovskite grain–electrode contacts is thus a promising direction for improving the performance of perovskite thin‐film solar cells.     

Incorporating Guanidinium as Perovskitizer-Cation of Two-Dimensional Metal Halide for Crystal-Array Photodetectors

Two-dimensional (2D) hybrid perovskites are recently emerging as a potential family of semiconductors for versatile optoelectronic applications. Currently, the “perovskitizer” moieties are rigidly limited to small-size cations, while few 2D metal-halides containing guanidinium cations inside perovskite cages have been studied for photodetection. Herein, we present a new 2D hybrid perovskite, (i-BA)₂(G)Pb₂I₇ (where G is guanidinium and i-BA is isobutylammonium), which adopts a bilayered framework of {GPb₂I₇}. Single-crystal structure analyses disclose that G cations act as the perovskitizer, confined in the flexible perovskite cages formed by the distorted PbI₆ octahedra. Such inorganic sheets are crucial to the superior semiconducting properties and optical bandgap, as verified by the density functional theory calculation. Furthermore, its planar crystal-array photodetector shows fascinating photoelectric performance, including a quite low dark current (∼4.6×10⁻¹¹ A), a large current switching ratio (∼1.0×10³), and a notable photo-responsivity of ∼0.72 A W⁻¹, suggesting great potential of (i-BA)₂(G)Pb₂I₇ for photodetection.     

Steric Mixed-Cation 2D Perovskite as a Methylammonium Locker to Stabilize MAPbI3

The reduced dimension perovskite including 2D perovskites are one of the most promising strategies to stabilize lead halide perovskite. A mixed-cation 2D perovskite based on a steric phenyltrimethylammonium (PTA) cation is presented. The PTA-MA mixed-cation 2D perovskite of PTAMAPbI₄ can be formed on the surface of MAPbI₃ (PTAI-MAPbI₃) by controllable PTAI intercalation by either spin coating or soaking. The PTAMAPbI₄ capping layer can not only passivate PTAI-MAPbI₃ perovskite but also act as MA⁺ locker to inhibit MAI extraction and significantly enhance the stability. The highly stable PTAI-MAPbI₃ based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion PCE of 21.16 %. Such unencapsulated devices retain 93 % of initial efficiency after 500 h continuous illumination. This steric mixed-cation 2D perovskite as MA⁺ locker to stabilize the MAPbI₃ is a promising strategy to design stable and high-performance hybrid lead halide perovskites.     

(C6H13NH3)2(NH2CHNH2)Pb2I7: A Two‐dimensional Bilayer Inorganic–Organic Hybrid Perovskite Showing Photodetecting Behavior

Inorganic–organic hybrid perovskites, especially two‐dimensional (2D) layered halide perovskites, have attracted significant attention due to their unique structures and attractive optoelectronic properties, which open up a great opportunity for next‐generation photosensitive devices. Herein, we report a new 2D bilayered inorganic–organic hybrid perovskite, (C₆H₁₃NH₃)₂(NH₂CHNH₂)Pb₂I₇ ( HFA , where C₆H₁₃NH₃⁺ is hexylaminium and NH₂CHNH₂⁺ is formamidinium), which exhibits a remarkable photoresponse under broadband light illumination. Structural characterizations demonstrate that the 2D perovskite structure of HFA is constructed by alternant stacking of inorganic lead iodide bilayered sheets and organic hexylaminium layers. Optical absorbance measurements combined with density functional theory (DFT) calculations suggest that HFA is a direct band gap semiconductor with a narrow band gap (E_g) of ≈2.02 eV. Based on these findings, photodetectors based on HFA crystal wafer are fabricated, which exhibit fascinating optoelectronic properties including large on/off current ratios (over 10³), fast response speeds (τ_rise=310 μs and τ_decay=520 μs) and high responsivity (≈0.95 mA W^?1). This work will contribute to the design and development of new two‐dimensional bilayer inorganic–organic hybrid perovskites for high‐performance photosensitive devices.     

Electrically Switchable Persistent Spin Texture in a Two-Dimensional Hybrid Perovskite Ferroelectric

As a momentum-independent spin configuration, persistent spin texture (PST) could avoid spin relaxation and play an advantageous role in spin lifetime. Nevertheless, manipulation of PST is a challenge due to the limited materials and ambiguous structure–property relationships. Herein, we present electrically switchable PST in a new 2D perovskite ferroelectric, (PA)₂CsPb₂Br₇ (where PA is n-pentylammonium), which has a high Curie temperature of 349 K, evident spontaneous polarization (3.2 μC cm⁻²) and a low coercive electric field of 5.3 kV cm⁻¹. The combination of symmetry-breaking in ferroelectrics and effective spin-orbit field facilitates intrinsic PST in the bulk and monolayer structure models. Strikingly, the directions of spin texture are reversible by switching the spontaneous electric polarization. This electric switching behavior relates to the tilting of PbBr₆ octahedra and the reorientation of organic PA⁺ cations. Our studies on ferroelectric PST of 2D hybrid perovskites afford a platform for electrical spin texture manipulation.     

A Self-Formed Stable PbI2/NiOx Interface with Increased Ni3+ Centers for Perovskite Photovoltaics

Nickel oxide (NiO_x) is a promising hole transport material (HTM) for perovskite photovoltaics owing to its chemical stability and low cost. However, most NiO_x based solar cells deliver relatively weak performance because of its insufficient electrical property and interfacial contact. In this work, a self-formed PbI₂/NiO_x interface was developed to stabilize the Ni³⁺ centers, which was beneficial for electrical transport and band alignment in perovskite solar cells. Combined with ultraviolet ozone treatment ( UVO ) and sequential deposition, the density of Ni³⁺ centers was greatly increased and could be stabilized by the PbI₂ interface. These merits contributed coordinately to the fast hole extraction and low energy loss across the PbI₂/NiO_x interface, yielding power conversion efficiencies (PCEs) of over 19 %.     

Hybrid Bilayer WSe2–CH3NH3PbI3 Organolead Halide Perovskite as a High‐Performance Photodetector

A high‐performance 2D photodetector based on a bilayer structure comprising a WSe₂ monolayer and CH₃NH₃PbI₃ organolead halide perovskite is reported. High performance is realized by modification of the WSe₂ monolayer with laser healing and perovskite functionalization. After modification, the output of the device was three orders of magnitude better than the pristine device; the performance is superior to that of most of the 2D photodetectors based on transition‐metal‐dichalcogenides (TMDs). This result indicates that combinatory TMDs–halide perovskite hybrids can be promising building blocks in optoelectronics.     

Two-Second-Annealed 2D/3D Perovskite Films with Graded Energy Funnels and Toughened Heterointerfaces for Efficient and Durable Solar Cells

The 2D/3D perovskite heterostructures have been widely investigated to enhance the efficiency and stability of perovskite solar cells (PSCs). However, rational manipulation of phase distribution and energy level alignment in such 2D/3D perovskite hybrids are still of great challenge. Herein, we successfully achieved spontaneous phase alignment of 2D/3D perovskite heterostructures by concurrently introducing both 2D perovskite component and organic halide additive. The graded phase distribution of 2D perovskites with different n values and 3D perovskites induced favorable energy band alignment across the perovskite film and boosted the charge transfer at the relevant heterointerfaces. Moreover, the 2D perovskite component also acted as a “band-aid” to simultaneously passivate the defects and release the residual tensile stress of perovskite films. Encouragingly, the blade-coated PSCs based on only ≈2 s in-situ fast annealed 2D/3D perovskite films with favorable energy funnels and toughened heterointerfaces achieved promising efficiencies of 22.5 %, accompanied by extended lifespan. To our knowledge, this is the highest reported efficiency for the PSCs fabricated with energy-saved thermal treatment just within a few seconds, which also outperformed those state-of-the-art annealing-free analogues. Such a two-second-in-situ-annealing technique could save the energy cost by up to 99.6 % during device fabrication, which will grant its low-coast implementation.