Introducing Intermolecular Cation-π Interactions for Water-Stable Low Dimensional Hybrid Lead Halide Perovskites

Revival of Degraded CsPbI3 Nanocrystals by Diselenide Ligand and Nanocrystal Self-Assembly on Nanofibrilar Ligand Template

Among the lead halide perovskite (LHP) family, CsPbI3 is known to be significantly vulnerable to moisture, which hinders its use in real device applications. It is reported that chalcogen-based ligands can better stabilize CsPbI3 and revive nanocrystals (NCs). Here, diphenyl diselenide (DPhDSe) ligand is used to revive the degraded CsPbI3 NCs through a post-synthetic treatment of adding a small amount of DPhDSe in the degraded NC dispersion. DPhDSe in the dispersion formed nanofibrillar crystals at a low temperature through the π-π stacking of the phenyl ring. The nanofibrils played as a template on which the NCs self-assembled and they are attached side-by-side to form microfibers. The microfiber powder containing the NCs is optically stable at ambient conditions and morphologically self-healable by mild thermal annealing due to the dynamic Se─Se bond. The mechanism of the structural changes, optical transitions, and chemical changes has been systematically characterized through electron microscopy, diffraction, spectroscopy, and elemental analysis.

One-Dimensional Red Light-Emissive Organic Manganese(II) Halides as X-Ray Scintillators

Although metal halide-based X-ray scintillators have obtained significant development with adjustable radioluminescent spectral range, the red light-emitting scintillator has been sparsely reported and remains a great challenge until now. To remedy this research blank, we investigated the scintillating property of red light-emissive one-dimensional (1D) organic manganese halide of (MBIZ)(MnCl3H2O)·H2O (MBIZ = 2-methyl-1H-benzoimidazolium) with a high PLQY of 71% under UV light excitation. Remarkably, this manganese halide single crystal exhibits a compelling X-ray scintillating property in the red light spectral range with a light yield of 19 600 photons MeV-1 and detection limit of 0.204 μGy/s, which is significantly better than the standard dosage for X-ray diagnostics. Furthermore, this manganese halide also exhibits excellent radiation resistance ability toward long-term continuous irradiation of high-dose X-ray with stable radiophotoluminescence intensity. Benefiting from the abovementioned combined merits, (MBIZ)(MnCl3H2O)·H2O demonstrates high-performance X-ray imaging with an outstanding spatial resolution of 11.1 lpmm-1. As far as we know, this is an infrequent red-emissive X-ray scintillator in metal halide materials, which highlights a successful structural design concept to explore new manganese halides as more desirable scintillators and expand the application field in medical diagnosis.

Conjugated diamine cation based halide perovskitoid enables robust stability and high photodetector performance

Low-dimensional lead halide materials have proved to be intrinsically stable semiconductor materials. However, the development of one-dimensional (1D) perovskites or perovskitoids with both robust water stability and high optoelectronic performance still faces significant challenges. Here, we report a new class of 1D (TzBIPY)Pb2X6 (X = Cl, Br, I) perovskitoids featuring a π-conjugated diamine cation (TzBIPY = 2,5-di(pyridin-4-yl)thiazolo[5,4-d]thiazole). The TzBIPY2+ cation with delocalized electrons directly contributes to the electronic structure and hence reduces the band gap. Especially, the Br-based material exhibits enhanced carrier separation and transport capacity, benefiting from the improved electronic conjugation together with a type II intramolecular heterojunction between conjugated organic cations and Pb-X octahedra. The (TzBIPY)Pb2Br6 photodetector exhibits an impressive photocurrent on/off ratio of 8.1 × 105, which is much superior to the previous three-dimensional (3D) perovskite benchmark. Additionally, the π-conjugated cations serve as dense protective shields for vulnerable Pb-X inorganic lattice against being attacked by water, thus demonstrating exceptional stability even immersed in water for over 3000 h.

Organic-Inorganic Hybrid Halide X-ray Scintillator with High Antiwater Stability

In recent years, low-dimensional organic-inorganic hybrid metal halides have garnered significant attention for optoelectronic applications due to their exceptional photophysical properties, despite their persistent challenge of low stability. Addressing this challenge, our study introduces 1-[5-(trifluoromethyl)pyridin-2-yl]piperazinium (TFPP) as a cation, harvesting a novel one-dimensional hybrid cadmium-based halide semiconductor (TFPP)CdCl4, which exhibits intense blue-light emission upon UV excitation. Additionally, (TFPP)CdCl4 demonstrates a high scintillation performance under X-ray excitation, producing 16600 ± 500 photons MeV-1 and achieving a low detection limit of 0.891 μGyair s-1. Notably, (TFPP)CdCl4 showcases remarkable stability against water, intense light sources, heating, and corrosive environments, positioning it as a promising candidate for optoelectronic applications. Through a blend of experimental techniques and theoretical analyses, including density functional theory calculations, we elucidate the unique photophysical properties and structural stability of (TFPP)CdCl4. These findings significantly contribute to the understanding of low-dimensional hybrid halide semiconductors, offering valuable insights into their potential application in advanced optoelectronic devices and paving the way for further research in this field.

Bulk Photovoltaic Effect Induced by Non-Covalent Interactions in Bilayered Hybrid Perovskite for Efficient Passive X-Ray Detection

Hydrogen bonding as a multifunctional tool has always influenced the structure of hybrid perovskites. Compared with the research on hydrogen bonding, the study of halogen-halogen interactions on the structure and properties of hybrid perovskites is still in its early stages. Herein, a polar bilayered hybrid perovskite (IEA)2FAPb2I7 (IEA+ is 2-iodoethyl-1-ammonium, FA is formamidinium) with iodine-substituted spacer is successfully constructed by changing the configuration of interlayer cations and regulating non-covalent interactions at the organic-inorganic interface, which shows a shorter interlayer spacing and higher density (ρ = 3.862 g cm-3). The generation of structure polarity in (IEA)2FAPb2I7 is caused by the synergistic effect of hydrogen bonding and halogen-halogen interactions. Especially, as the length of the carbon chain in organic cations decreases, the I---I interaction in the system gradually strengthens, which may be the main reason for the symmetry-breaking. Polarity-induced bulk photovoltaics (Voc = 1.0 V) and higher density endow the device based on (I-EA)2FAPb2I7 exhibit a high sensitivity of 175.6 µC Gy-1 cm-2 and an ultralow detection limit of 60.4 nGy s-1 at 0 V bias under X-ray irradiation. The results present a facile approach for designing polar multifunctional hybrid perovskites, also providing useful assistance for future research on halogen-halogen interactions.

Synchronously Improved Multiple Afterglow and Phosphorescence Efficiencies in 0D Hybrid Zinc Halides With Ultrahigh Anti-Water Stabilities

Zero-dimensional (0D) hybrid metal halides have been emerged as room-temperature phosphorescence (RTP) materials, but synchronous optimization of multiple phosphorescence performance in one structural platform remains less resolved, and stable RTP activity in aqueous medium is also unrealized due to serious instability toward water and oxygen. Herein, we demonstrated a photophysical tuning strategy in a new 0D hybrid zinc halide family of (BTPP)2ZnX4 (BTPP=benzyltriphenylphosphonium, X=Cl and Br). Infrequently, the delicate combination of organic and inorganic species enables this family to display multiple ultralong green afterglow and efficient self-trapped exciton (STE) associated cyan phosphorescence. Compared with inert luminescence of [BTPP]+ cation, incorporation of anionic [ZnX4]2- effectively enhance the spin-orbit coupling effect, which significantly boosts the photoluminescence quantum yield (PLQY) up to 30.66 % and 54.62 % for afterglow and phosphorescence, respectively. Synchronously, the corresponding luminescence lifetime extend to 143.94 ms and 0.308 μs surpassing the indiscernible phosphorescence of [BTPP]X salt. More importantly, this halide family presents robust RTP emission with nearly unattenuated PLQY in water and harsh condition (acid and basic aqueous solution) over half a year. The highly efficient integrated afterglow and STE phosphorescence as well as ultrahigh aqueous state RTP realize multiple anti-counterfeiting applications in wide chemical environments.

Harnessing Pb-S Interactions for Long-Term Water Stability in Cesium Lead Halide Perovskite Nanocrystals

Lead halide perovskite nanocrystals (LHP NCs) have garnered attention as promising light-harvesting materials for optoelectronics and photovoltaic devices, attributed to their impressive optoelectronic properties. However, their susceptibility to moisture-induced degradation has hindered their practical applications. Despite various encapsulation strategies, challenges persist in maintaining their stability and optoelectronic performance simultaneously. Here, a ligand exchange approach is proposed using (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide (MUTAB) to enhance the stability and dispersibility of CsPbBr3 (CPB) NCs in aqueous environments. MUTAB enables effective surface passivation of the CPB NCs via robust Pb-S interactions at the S-terminal while concurrently directing water molecules through the unbound cationic N-terminal or vice versa, ensuring water dispersibility and stability. Spectroscopic analysis confirms retained structural and optical integrity post-ligand exchange. Crucially, MUTAB-bound CPB NCs exhibit sustained charge transfer properties, demonstrated by aqueous colloidal oxidation reactions. This ligand exchange strategy offers a promising pathway for advancing LHP NCs toward practical optoelectronic and photocatalytic applications.

π-π Stacking at the Perovskite/C60 Interface Enables High-Efficiency Wide-Bandgap Perovskite Solar Cells

Interface passivation is a key method for improving the efficiency of perovskite solar cells, and 2D/3D perovskite heterojunction is the mainstream passivation strategy. However, the passivation layer also produces a new interface between 2D perovskite and fullerene (C60), and the properties of this interface have received little attention before. Here, the underlying properties of the 2D perovskite/C60 interface by taking the 2D TEA2PbX4 (TEA = C6H10NS; X = I, Br, Cl) passivator as an example are systematically expounded. It is found that the 2D perovskite preferentially exhibits (002) orientation with the outermost surface featuring an oriented arrangement of TEACl, where the thiophene groups face outward. The outward thiophene groups further form a strong π-π stacking system with C60 molecule, strengthening the interaction force with C60 and facilitating the creation of a superior interface. Based on the vacuum-assisted blade coating, wide-bandgap (WBG, 1.77 eV) perovskite solar cells achieved impressive records of 19.28% (0.09 cm2) and 18.08% (1.0 cm2) inefficiency, respectively. This research not only provides a new understanding of interface processing for future perovskite solar cells but also lays a solid foundation for realizing efficient large-area devices.

Exploring the Therapeutic Potential of 5-Fluorouracil-Loaded Calcium Carbonate Nanoparticles Combined with Natural Compound Thymoquinone for Colon Cancer Treatment

Given the need for novel and effective therapies for colon cancer, this study aimed to investigate the effects of 5-fluorouracil-loaded calcium carbonate nanoparticles (5FU-CaCO3np) combined with thymoquinone (TQ) against colon cancer. A shaking incubator and a high-speed homogenizer were used to prepare the optimal 5FU-CaCO3np, with characterizations of physicochemical properties, in vitro drug release profile, and biocompatibility. In vitro experiments and molecular docking were employed to evaluate the therapeutic potential of the combination for colon cancer treatment. Study results revealed that 5FU-CaCO3np with a size of approximately 130 nm was synthesized using the high-speed homogenizer. Its favorable biocompatibility, pH sensitivity, and sustained release properties facilitated reduced toxic side effects of 5-FU on NIH3T3 normal cells and enhanced inhibitory effects on CT26 colon cancer cells. The combination of 5FU-CaCO3np (1.875 μM) and TQ (30 μM) showed significantly superior anti-colon cancer effects to 5FU-CaCO3np alone in terms of cell proliferation and migration inhibition, cell apoptosis induction, and spheroid growth suppression in CT26 cells (p < 0.05), with strong interactions between the drugs and targets (E-cadherin, Bcl-2, PCNA, and MMP-2). These results provide evidence for 5FU-CaCO3np as a novel regimen against colon cancer. Combining 5FU-CaCO3np and TQ may offer a new perspective for colon cancer therapy.

Crystal-Rigidifying Strategy in Hybrid Manganese Halide to Achieve Narrow Green Emission and High Structural Stability

Although organic-inorganic hybrid Mn2+ halides have advanced significantly, achieving high stability and narrow-band emission remains enormously challenging owing to the weak ionic nature and soft crystal lattice of the halide structure. To address these issues, we proposed a cationic engineering strategy of long-range cation π···π stacking and C-H···π interactions to simultaneously improve the crystal structural stability and rigidity. Herein, two organic zero-dimensional (0D) manganese halide hybrids of (BACQ)2MnX4 [BACQ = 4-(butylamino)-7-chloroquinolin-1-ium; X = Cl and Br] were synthesized. (BACQ)2MnX4 display strong green-light emissions with the narrowest full width at half-maximum (fwhm) of 39 nm, which is significantly smaller than those of commercial green phosphor β-SiAlON:Eu2+ and most of reported manganese halides. Detailed Hirshfeld surface analyses demonstrate the rigid environment around the [MnX4]2- units originating from the interactions between [BACQ]+. The rigid crystal structure weakens the electron-phonon coupling and renders narrow fwhm of these manganese halides, which is further confirmed by temperature-dependent emission spectra. Remarkably, (BACQ)2MnX4 realizes outstanding structural and luminescence stabilities in various extreme environments. Benefiting from the excellent performance, these Mn2+ halides are used to assemble light-emitting diodes with a wide color gamut of 105% of the National Television System Committee 1931 standard, showcasing the advanced applications in liquid-crystal-display backlighting.

Wafer-Scale Patterning Integration of Chiral 3D Perovskite Single Crystals toward High-Performance Full-Stokes Polarimeter

Chiral three-dimensional (3D) perovskites exhibit exceptional optoelectronic characteristics and inherent chiroptical activity, which may overcome the limitations of low-dimensional chiral optoelectronic devices and achieve superior performance. The integrated chip of high-performance arbitrary polarized light detection is one of the aims of chiral optoelectronic devices and may be achieved by chiral 3D perovskites. Herein, we first fabricate the wafer-scale integrated full-Stokes polarimeter by the synergy of unprecedented chiral 3D perovskites (R/S-PyEA)Pb2Br6 and one-step capillary-bridge assembly technology. Compared with the chiral low-dimensional perovskites, chiral 3D perovskites present smaller exciton binding energies of 57.3 meV and excellent circular dichroism (CD) absorption properties, yielding excellent circularly polarized light (CPL) photodetectors with an ultrahigh responsivity of 86.7 A W-1, an unprecedented detectivity exceeding 4.84 × 1013 Jones, a high anisotropy factor of 0.42, and high-fidelity CPL imaging with 256 pixels. Moreover, the anisotropic crystal structure also enables chiral 3D perovskites to have a large linear-polarization response with a polarized ratio of 1.52. The combination of linear-polarization and circular-polarization discrimination capabilities guarantees the achievement of a full-Stokes polarimeter. Our study provides new research insights for the large-scale patterning wafer integration of high-performance chiroptical devices.

Halide Exchange in Perovskites Enables Bromine/Iodine Hybrid Cathodes for Highly Durable Zinc Ion Batteries

With the increasing need for reliable storage systems, the conversion-type chemistry typified by bromine cathodes attracts considerable attention due to sizeable theoretical capacity, cost efficiency, and high redox potential. However, the severe loss of active species during operation remains a problem, leading researchers to resort to concentrated halide-containing electrolytes. Here, profiting from the intrinsic halide exchange in perovskite lattices, a novel low-dimensional halide hybrid perovskite cathode, TmdpPb2[IBr]6, which serves not only as a halogen reservoir for reversible three-electron conversions but also as an effective halogen absorbent by surface Pb dangling bonds, C─H…Br hydrogen bonds, and Pb─I…Br halogen bonds, is proposed. As such, the Zn||TmdpPb2[IBr]6 battery delivers three remarkable discharge voltage plateaus at 1.21 V (I0/I-), 1.47 V (I+/I0), and 1.74 V (Br0/Br-) in a typical halide-free electrolyte; meanwhile, realizing a high capacity of over 336 mAh g-1 at 0.4 A g-1 and high capacity retentions of 88% and 92% after 1000 cycles at 1.2 A g-1 and 4000 cycles at 3.2 A g-1, respectively, accompanied by a high coulombic efficiency of ≈99%. The work highlights the promising conversion-type cathodes based on metal-halide perovskite materials.

Recent advances in organolead halide crystalline materials for photocatalytic H2 evolution and CO2 reduction applications

The photocatalytic technique has been widely recognized as a feasible technological route for sustainable energy conversion of solar energy into chemical energy. Photocatalysts play a vital role in the whole catalytic process. In particular, organolead halide perovskites have become emerging photocatalysts, owing to their precisely tunable light absorption range, high carrier diffusion mobility, and longer carrier lifetime and diffusion length. Nevertheless, their intrinsic structural instability and high carrier recombination rate are the major bottlenecks for further development in photocatalytic applications. This Frontier is focused on the recent research about the instability mechanism of organolead halide perovskites. Then, we summarize the recently developed strategies to improve the structural stability and photocatalytic activity of organolead halide materials, with an emphasis on the construction of organolead halide crystalline catalysts with high intrinsic structural stability. Finally, an outlook and challenges of organometal halide photocatalysts are presented, demonstrating the irreplaceable role of this class of emergent materials in the field of photo-energy conversion.

Reversible CsPbBr3 ↔ CsPb2Br5 Transformation via Reverse Micellar Aqueous Solution

Lead halide perovskites suffer from water and moisture instability due to the highly ionic nature of the crystal structures, though a few groups took advantage of it for chemical transformation via water-assisted strategy. However, direct exposure of the perovskite to bulk water leads to uncontrolled chemical transformation. Here, we report a controlled chemical transformation of CsPbBr3 to CsPb2Br5 triggered by nanoconfined water by placing CsPbBr3 in the nonpolar phase within a reverse micelle. The chemical transformation reaction is probed by using steady-state and time-resolved optical spectroscopy. We observe absorption and photoluminescence in the UV region stemming clearly from the CsPb2Br5 phase upon interaction with the reverse micellar aqueous solution. Transmission electron microscopy and X-ray diffraction measurements further provided the structure and morphology. Our results direct the formation of CsPbBr3-CsPb2Br5 nanocomposite under dry conditions while the chemically transformed CsPb2Br5 phase exists only in moist conditions, which we explain via the CsBr-stripping mechanism.

Band Structure Optimized by Electron-Acceptor Cations for Sensitive Perovskite Single Crystal Self-Powered Photodetectors

Low-dimensional perovskites afford improved stability against moisture, heat, and ionic migration. However, the low dimensionality typically results in a wide bandgap and strong electron-phonon coupling, which is undesirable for optoelectronic applications. Herein, semiconducting A-site organic cation engineering by electron-acceptor bipyridine (bpy) cations (2,2'-bpy2+ and 4,4'-bpy2+) is employed to optimize band structure in low-dimensional perovskites. Benefiting from the merits of lower lowest unoccupied molecular orbital (LUMO) energy for 4,4'-bpy2+ cation, the corresponding (4,4'-bpy)PbI4 is endowed with a smaller bandgap (1.44 eV) than the (CH3NH3)PbI3 (1.57 eV) benchmark. Encouragingly, an intramolecular type II band alignment formation between inorganic Pb-I octahedron anions and bpy2+ cations favors photogenerated electron-hole pairs separation. In addition, a shortening distance between inorganic Pb-I octahedral chains in (4,4'-bpy)PbI4 single crystal (SC) can effectively promote carrier transfer. As a result, a self-powered photodetector based on (4,4'-bpy)PbI4 SC exhibits 131 folds higher on/off ratio (3807) than the counterpart of (2,2'-bpy)2Pb3I10 SC (29). The presented result provides an effective strategy for exporting novel organic cation-based low-dimensional perovskite SC for high-performance optoelectronic devices.

Harnessing strong aromatic conjugation in low-dimensional perovskite heterojunctions for high-performance photovoltaic devices

Low-dimensional/three-dimensional perovskite heterojunctions have shown great potential for improving the performance of perovskite photovoltaics, but large organic cations in low-dimensional perovskites hinder charge transport and cause carrier mobility anisotropy at the heterojunction interface. Here, we report a low-dimensional/three-dimensional perovskite heterojunction that introduces strong aromatic conjugated low-dimensional perovskites in p-i-n devices to reduce the electron transport resistance crossing the perovskite/electron extraction interface. The strong aromatic conjugated π-conjugated network results in continuous energy orbits among [Pb2I6]2- frameworks, thereby effectively suppressing interfacial non-radiative recombination and boosting carrier extraction. Consequently, the devices achieved an improved efficiency to 25.66% (certified 25.20%), and maintained over 95% of the initial efficiency after 1200 hours and 1000 hours under ISOS-L-1I and ISOS-D-1 protocols, respectively. The chemical design of strong aromatic conjugated molecules in perovskite heterojunctions provides a promising avenue for developing efficient and stable perovskite photovoltaics.

Chlorophyl-Passivated Ytterbium-Doped Perovskite Quantum-Cutting Film for High-Performance Solar Energy Conversion and Near-Infrared Light-Emitting Diode Applications

The quantum cutting ytterbium (Yb3+)-doped CsPbX3 (X = Cl, Cl, or Br) nanocrystals, exhibiting photoluminescence quantum yields (PLQYs) exceeding 100%, hold significant promise for applications in solar energy conversion technologies and near-infrared (NIR) light-emitting diodes (LEDs). This work investigates the usage of chlorophyll (CHL), a naturally existing organic pigment, as an efficient molecular passivator to improve the performance of quantum cutting films. With the assistance of CHL, the resultant perovskite film displays an increased PLQY of 176%. The commercial silicon solar cells (SSCs) with CHL-treated perovskite films demonstrate a remarkable photon-to-current conversion efficiency improvement of 1.83% for a 330.15 cm2 area SSC device. Additionally, a CHL-modified Yb3+:CsPbCl3 film was used to create 988 nm NIR LEDs with an external quantum efficiency of 3.2%. This work provides a new, eco-friendly approach for producing high-quality, large-area Yb3+-doped perovskite film for deployment in photoelectric and night vision applications.

Cation-π interactions enabled water-stable perovskite X-ray flat mini-panel imager

Sensitive and stable perovskite X-ray detectors are attractive in low-dosage medical examinations. The high sensitivity, tunable chemical compositions, electronic dimensions, and low-cost raw materials make perovskites promising next-generation semiconductors. However, their ionic nature brings serious concerns about their chemical and water stability, limiting their applications in well-established technologies like crystal polishing, micro-processing, photolithography, etc. Herein we report a one-dimensional tryptamine lead iodide perovskite, which is stable in water for several months as the strong cation-π interactions between organic cations. The one-dimensional and two-dimensional tryptamine lead iodide perovskite tablets are switchable through thermal-annealing or water-soaking treatments to relax microstrains. The water-stable and microstrain-free one-dimensional perovskite tablets yield a large sensitivity of 2.5 × 106 μC Gyair-1 cm-2 with the lowest detectable dose rate of 5 nGyair s-1. Microelectrode arrays are realized by surface photolithography to construct high-performance X-ray flat mini-panels with good X-ray imaging capability, and a record spatial resolution of 17.2 lp mm-1 is demonstrated.

Intra- and Intermolecular Cation-π Interactions between Onium Salts and Alkynes/Acetylene: Experimental and Theoretical Insights

Cation-π interactions between various onium salts, alkynes, and acetylene were studied, taking into account the substituents of the triple bond, the nature of the anions, and the polarity of the solvent, through a combination of MP2 calculations and experiments. In an intramolecular setting, these data (including single-crystal X-ray crystallography) concurred with the stability of folded conformers of alkynyl onium salts, even substituted with electron-withdrawing groups. To examine the contribution of these interactions on the alkyne electronic population, a thorough in silico study was carried out using natural bonding orbital analysis of the conformers. Intramolecular interactions from sulfonium salt tethered to phenylalkyne were highlighted, as illustrated above by the computed folded conformation (MP2) along with noncovalent interaction (NCI) analysis. Furthermore, investigations of intermolecular interactions, involving acetylene or phenylacetylene with various onium ions, revealed the high energy interactions of their complexes with phenyldimethylsulfonium chloride, as illustrated above with the complex PhC≡CH/PhMe2SCl (MP2 calculations and NCI analysis).

Fabricating a type II heterojunction by growing lead-free perovskite Cs2AgBiBr6in situ on graphite-like g-C3N4 nanosheets for enhanced photocatalytic CO2 reduction

Perovskite-based photocatalysts have received significant attention for converting CO2 into fuels, such as CO, CH4 or long alkyl chains. However, the use of these catalysts is plagued by several limitations, such as poor stability, lead toxicity, and inadequate conversion efficiency due to the rapid recombination of carriers. Herein, a g-C3N4@Cs2AgBiBr6 (CABB) type II heterojunction photocatalyst has been prepared by growing lead-free CABB nanocrystals (10-14 nm) on the graphite-like carbon nitride (g-C3N4) nanosheet using the in situ crystallization method. The resulting nanocomposite, g-C3N4@CABB, demonstrated an efficient charge transfer pathway via a typical type II heterojunction. With formation rates of 10.30 μmol g-1 h-1 for CO and 0.88 μmol g-1 h-1 for CH4 under visible light irradiation, the nanocomposite exhibited enhanced photocatalytic efficiency in CO2 reduction compared to CABB and g-C3N4. The improved photocatalytic performance of the g-C3N4@CABB nanocomposite was attributed to the fabricated type II heterojunction, which boosted the interfacial charge transfer from g-C3N4 to CABB. This work will inspire the design of heterojunction-based photocatalysts and increase the fundamental understanding of perovskite-based catalysts in the CO2 photoreduction process.

All-Inorganic Lead-Free Doped-Metal Halides for Bright Solid-State Emission from Primary Colors to White Light

Metal halides have been explored with the aid of strong photoluminescence for optical and optoelectronic applications. However, the preparation of lead (Pb)-free solid-state emitters with high photoluminescence quantum yields (PLQYs) and tunable emission remains exceptionally challenging. Herein, we report metal ion (Cu(I), Mn(II), and Sn(II))-doped Cs₃ZnI₅ single crystals that are primary color (violet, green, and orange/red) emitters with extremely high PLQYs. Whereas the Mn-doping leads to bright green emissions with 100% PLQY, the Cu- and Sn-doping give rise to blue and red emissions with PLQYs of 57 and 64%, respectively. Interestingly, higher Mn doping results in white light emissive crystals as a side product, which are found to be Mn-doped CsI single crystals. The bright white light emissive crystals can be synthesized in a pure form in large quantities and exhibit a high color rendering index (CRI) of 78 and CIE coordinates of (0.30, 0.38), which are close to daylight conditions. To the best of our knowledge, this is the first demonstration of white light emission from a complete inorganic system. Importantly, the single crystals of all colors exhibit high long-term stability as their PLQY remains unchanged even after 2 months of preparation, and are thermally stable up to 600 °C.

2D nanosheets of layered double perovskites: synthesis, photostable bright orange emission and photoluminescence blinking

Lead (Pb)-free layered double perovskites (LDPs) with exciting optical properties and environmental stability have sparked attention in optoelectronics, but their high photoluminescence (PL) quantum yield and understanding of the PL blinking phenomenon at the single particle level are still elusive. Herein, we not only demonstrate a hot-injection route for the synthesis of two-dimensional (2D) ∼2-3 layer thick nanosheets (NSs) of LDP, Cs₄CdBi₂Cl₁₂ (pristine), and its partially Mn-substituted analogue [i.e., Cs₄Cd_0.6Mn_0.4Bi₂Cl₁₂ (Mn-substituted)], but also present a solvent-free mechanochemical synthesis of these samples as bulk powders. Bright and intense orange emission has been perceived for partially Mn-substituted 2D NSs with a relatively high PL quantum yield (PLQY) of ∼21%. The PL and lifetime measurements both at cryogenic (77 K) and room temperatures were employed to understand the de-excitation pathways of charge carriers. With the implementation of super-resolved fluorescence microscopy and time-resolved single particle tracking, we identified the occurrence of metastable non-radiative recombination channels in a single NS. In contrast to the rapid photo-bleaching that resulted in a PL blinking-like nature of the controlled pristine NS, the 2D NS of the Mn-substituted sample displayed negligible photo-bleaching with suppression of PL fluctuation under continuous illumination. The blinking-like nature in pristine NSs appeared due to a dynamic equilibrium flanked by the active and in-active states of metastable non-radiative channels. However, the partial substitution of Mn²⁺ stabilized the in-active state of the non-radiative channels, which increased the PLQY and suppressed PL fluctuation and photo-bleaching events in Mn-substituted NSs.

Modulating Resonance Energy Transfer with Supramolecular Control in a Layered Hybrid Perovskite and Chromium Photosensitizer Assembly

Recently, the low-dimensional organic-inorganic halide perovskites (OIHP) have been exploited heavily for their favorable exciton dynamics, broad-band emission, remarkable stability, and tunable band-edge excited-state energy compared to their 3D counterparts for potential optoelectronic applications. Low-dimensional perovskites are generally good candidates for utilization as room-temperature photoluminescence (PL) materials. Further, doping divalent transition metals like Mn²⁺ into OIHP is expected to introduce a ⁴T₁-⁶A₁-based low-energy luminescence emission around 600 nm; an optical property that is favorable for biomedical optoelectronics. Doping Mn²⁺ in the perovskite lattice is also expected to induce the generation of cytotoxic singlet oxygen species (¹O₂), a ROS that is being exploited for various therapeutic applications. To integrate these optical and therapeutic properties of a 2D (PEA)₂PbBr₄ (Pb PeV; PEA = phenylethylammonium cation) perovskite alloyed with Mn²⁺ ions (Mn:PbPeV) and the option for a photoinduced energy transfer process involving a Cr(III)-based ¹O₂ generating photosensitizer (CrPS), we designed a unique purpose-built nanoassembly (Mn:PbPeV@PCD) using the encapsulation properties of a water-soluble polymer derived from β-cyclodextrin (PCD). Here the PCD is observed to modulate the classical internal energy transfer of Pb²⁺ exciton to alloyed Mn²⁺ orange emission, resulting in the emergence of a new blue emission. The addition of CrPS into the Mn:PbPeV@PCD to generate the CrPS@Mn:PbPeV@PCD assembly results in restoring perovskite luminescence followed by the external energy transfer to CrPS. We have elucidated the mechanism of these cascade energy transfer processes between multiple components using steady-state and time-resolved luminescence techniques. Efficient ROS generation and its potential to induce an oxidation reaction of a biomolecule are realized using guanine as the target molecule. Further photoinduced cleavage studies with biomolecules confirmed the efficacy of the nanoassembly in inducing the cleavage of guanine-rich DNA. The study opens up a new direction in the field of perovskite for biomedical applications.

Combining π-Conjugation and Cation-π Interaction for Water-Stable and Photoconductive One-Dimensional Hybrid Lead Bromide

Hybrid lead halide perovskites and their derivatives are important optoelectronic materials but suffer from water instability. Combining both the optoelectronics and the water stability of such systems is a major challenge in material design today. To address this issue, we employ the well-known π-conjugation and cation-π interaction concepts in designing a hybrid lead halide perovskite derivative system. (4,4'-VDP)Pb₂Br₆ (VDP = vinylenedipyridinium) single crystals are prepared. They have a one-dimensional (1D) arrangement of inorganic Pb-Br sublattices connected via the 4,4'-VDP organic sublattice. The π-conjugation in the 4,4'-VDP sublattice allows electronic communication between the 1D Pb-Br units, reducing the band gap and improving the photoconductivity. Importantly, N⁺ of one 4,4'-VDP molecular ion interacts with the π-electron cloud of the adjacent one. This intermolecular cation-π interaction extends throughout the organic sublattice, making the hybrid crystal stable when stored under water for more than a year without requiring any encapsulations.

Organic-inorganic Hybrid Perovskite-Based Light-Assisted Li-oxygen Battery with Low Overpotential

Organic-inorganic hybrid perovskites have emerged in the last decade as promising semiconductors due to the excellent optoelectronic properties. This kind of perovskites exhibited respectable photocatalytic activities toward potential application in battery; however, the instability issue still hindered their practical use. Herein, a hybrid perovskite material, 4,4'-ethylenedipyridinium lead bromide [(4,4'-EDP)Pb₂ Br₆ ], was assembled onto the carbon materials to function as photoelectrode of the Li-oxygen battery. The strong cation-π interactions between the A-site cations enabled this hybrid perovskite to endure the cycling process as well as the exposure to battery electrolyte and oxygen. Benefitting from the photo-generated carriers of the photoelectrode under illumination, the formation/decomposition of the discharge product was accelerated, thus leading to a reduced overpotential from 1.3 V to an optimized 0.5 V compared to the Li-oxygen battery without illumination. The overpotential could be maintained lower than 0.9 V after cycling for 170 h. Furthermore, when exposed to the sunlight, the charging voltage was reduced by over 0.2 V. The intrinsic stability and strong light absorption of perovskites together with the optimized perovskite/carbon cathode interfaces contributed to the improved performance under different light sources without complex material design, which shed light on the exploration of organic-inorganic hybrid perovskites in Li-oxygen battery applications.

Releasable Water Charge-Trapping and Water-Resistant Photodetection using 1D Perovskitoid Hydrate Single Crystal

Hydrates of hybrid organic-inorganic perovskites have been discovered with MAPbI₃ and are proved to be unstable in atmosphere. However, the influence of water molecules on the performance of optoelectronic devices is still not fully understood. Here, using a dication, 2-(dimethylamino) ethylamine (DMEN²⁺ ), a stable quasi-1D perovskitoid hydrate single crystal is designed and successfully synthesized, which is formulated as DMENPb₂ I₆ ·H₂ O. In this design, both corner-sharing and edge-sharing connectivity are adopted, and water molecules are connected with the crystal through hydrogen bonding. It is discovered that such water sites distributed along the inorganic chains function both as charge traps and as releasable charge stocks. Optical excitation that overcomes the potential wells formed on these water sites may release these stocked charges and facilitate enhanced transportable charge density. Meanwhile, exciton diffusion and charge transport are strongly confined in the 1D transport channels. Above mechanisms are verified both by the transient absorption spectroscopy and by the photodetection performance. This introduces a new design strategy with a trapping-stock-releasing-transport roadmap for perovskitoid materials. Excellent water resistance endows this material with more advantages in the development of a new generation of optoelectronic devices.

Zero-Dimensional Zn-Based Halides with Ultra-Long Room-Temperature Phosphorescence for Time-Resolved Anti-Counterfeiting

Though fluorescence-tag-based anti-counterfeiting technology has distinguished itself with cost-effective features and huge information loading capacity, the clonable decryption process of spatial-resolved anti-counterfeiting cannot meet the requirements for high-security-level anti-counterfeiting. Herein, we demonstrate a spatial-time-dual-resolved anti-counterfeiting system based on new organic-inorganic hybrid halides BAPPZn₂ (Cl_y Br_1-y )₈ (BAPP=1,4-bis(3-ammoniopropyl)piperazinium, y=0-1) with ultra-long room-temperature phosphorescence (RTP). Remarkably, the afterglow lifetime can be facilely tuned by regulating the halide-induced heavy-atom effect and can be identified by the naked eyes or with the help of a simple machine vision system. Therefore, the short-lived unicolor fluorescence and lasting-time-tunable RTP provide the prerequisites for unicolor-time-resolved anti-counterfeiting, which lowers the decryption-device requirements and further provides the design strategy of advanced portable anti-counterfeiting technology.

Enhancing the Intrinsic and Extrinsic Stability of Halide Perovskite Nanocrystals for Efficient and Durable Optoelectronics

Over the past few years, metal halide perovskite nanocrystals have been at the forefront of colloidal semiconductor nanomaterial research because of their fascinating properties and potential applications. However, their intrinsic phase instability and chemical degradation under external exposures (high temperature, water, oxygen, and light) are currently limiting the real-world applications of perovskite optoelectronics. To overcome these stability issues, researchers have reported various strategies such as doping and encapsulation. The doping improves the optical and photoactive phase stability, whereas the encapsulation protects the perovskite NCs from external exposures. This perspective discusses the rationale of various strategies to enhance the stability of perovskite NCs and suggests possible future directions for the fabrication of optoelectronic devices with long-term stability while maintaining high efficiency.

Highly Stable and Moisture-Immune Monocomponent White Perovskite Phosphor by Trifluoromethyl (-CF3) Regulation

Halide perovskites are emerging as promising candidates for white light solid state lighting. Nevertheless, there are still challenges of a high water stability, a tunable color temperature, and a high photoluminescence quantum yield (PLQY). Herein, we report hydrophobic, electron-withdrawing trifluoromethyl (-CF₃)-modified phenethylamine lead bromide (PEA₂PbBr₄) with ultrahigh stability in water for >2 months, and the broadband white light emission is illustrated by self-trapped excitons attributed to exciton-phonon coupling that coordinate molecular vibration, lattice distortion, and electrostatic interaction. In particular, by Mn²⁺ doping, the emission color can be tuned from cold (10237 K) to warm (2406 K), and a greatly enhanced PLQY of ≤87.93% can be achieved. Furthermore, the perovskites also possess an excellent color rendering index (the highest is 94). A monocomponent white light-emitting diode with amazing CIE 1931 coordinates of (0.33, 0.32) is further assembled, demonstrating a luminance of 471.5 cd m^-2 at 50 mA and good long-term operation stability after >2 months. This study of highly efficient and stable perovskites with high-quality white light emission will open up new opportunities in solid state lighting.

Exciton Dynamics in Colloidal CdS Quantum Dots with Intense and Stokes Shifted Photoluminescence in a Single Decay Channel

CdS quantum dots (QDs), synthesized by a sol-gel method, exhibit significantly Stokes shifted bright photoluminescence (PL), predominantly from the trap states. Surprisingly, the PL decay at the emission maximum is single-exponential. This is an unusual observation for as-prepared QDs and indicates a narrow distribution in the nature of trap states. A closer look reveals an additional fast component for the decays at shorter emission wavelengths, presumably due to the band edge emission, which remains elusive in the steady-state spectra. Indeed, a significantly narrower and blue-shifted emission band is observed in the decay-associated spectra. The contribution of this component to the steady-state PL intensity is shown to be overwhelmed by that of the significantly stronger trap emission. Exciton dynamics in the quantum dots is elucidated using transient absorption spectra, in which the stimulated emission is observed even at low pump power.

Potential lead toxicity and leakage issues on lead halide perovskite photovoltaics

Recently, lead halide perovskite solar cells have become a promising next-generation photovoltaics candidate for large-scale application to realize low-cost renewable electricity generation. Although perovskite solar cells have tremendous advantages such as high photovoltaic performance, low cost and facile solution-based fabrication, the issues involving lead could be one of the main obstacles for its commercialization and large-scale applications. Lead has been widely used in photovoltaics industry, yielding its environmental and health issues of vital importance because of the widespread application of photovoltaics. When the solar cell panels especially perovskite solar cells are damaged, lead would possibly leak into the surrounding environment, causing air, soil and groundwater contamination. Therefore, lots of research efforts have been put into evaluating the lead toxicity and potential leakage issues, as well as studying the encapsulation of lead to deal with leakage issue during fire hazard and precipitation in photovoltaics. In this review, we summarize the latest progress on investigating the lead safety issue on photovoltaics, especially lead halide perovskite solar cells, and the corresponding solutions. We also outlook the future development towards solving the lead safety issues from different aspects.

Chiral 2D organic–inorganic hybrid perovskites based on l-histidine

The composition of new 2D chiral perovskites based on chiral l-histidine and lead halides was systematically adjusted to achieve tunable photoluminescence properties.

Water-Molecule-Induced Emission Transformation of Zero-Dimension Antimony-Based Metal Halide

Low-dimensional organic-inorganic metal halides have recently emerged as a class of promising luminescent materials. However, the intrinsic toxicity of lead would strongly hamper future application. Herein, we synthesized a new type of lead-free zero-dimensional (0D) antimony-based organic-inorganic metal halide single crystals, (PPZ)₂SbCl₇·5H₂O (PPZ = 1-phenylpiperazine), which features a broadband emission at 720 nm. Ultrafast transient absorption and temperature-dependent photoluminescence (PL) spectra are combined to investigate the PL mechanism, revealing that self-trapped exciton recombination was involved. Furthermore, it is interesting that (PPZ)₂SbCl₇·5H₂O material shows reversible PL emission transformation between red light (720 nm) and yellow light (590 nm) as water molecules are inserted or removed from the lattice. Such reversible emission transformation phenomenon renders the (PPZ)₂SbCl₇·5H₂O as a potential low-cost water sensing material.

Selective Luminescence Response of a Zero-Dimensional Hybrid Antimony(III) Halide to Solvent Molecules: Size-Effect and Supramolecular Interactions

Zero-dimensional (0D) metal halides with solid-state luminescence switching (SSLS) have attracted attention as sensors and luminescent anticounterfeiting. Herein, selective solvent molecule response and accordingly luminescence switching were discovered in 0D [EtPPh₃]₂[SbCl₅] (1, EtPPh₃ = ethyltriphenylphosphonium). More than a dozen kinds of solvent molecules have been tested to find out the selection rule for molecule absorption in 1, which is demonstrated to be the size effect of guest molecules. Confirmed by crystal structural analysis, only the solvents with molecular volume less than 22.3 ų could be accommodated in 1 leading to the solvatochromic photoluminescence (PL). The mechanism of solvatochromic PL was also deeply studied, which was found to be closely related to the supramolecular interactions between solvent molecules and the host material. Different functional groups of the solvent molecule can affect its strength of hydrogen bonding with [SbCl₅]^2-, which is crucial for the distortion level of [SbCl₅]^2- unit and thus results in not only distinct solvatochromic PL but also distinct thermochromic PL. In addition, they all show typical self-trapped exciton triplet emissions. The additional supramolecular interactions from guest molecules can enhance the photoluminescence quantum yield to be as high as 95%.

Chemically Spiraling CsPbBr3 Perovskite Nanorods

Light emitting lead halide perovskite nanocrystals are currently emerging as the workhorse in quantum dot research. Most of these reported nanocrystals are isotropic cubes or polyhedral; but anisotropic nanostructures with controlled anisotropic directions still remain a major challenge. For orthorhombic CsPbBr₃, the 1D shaped nanostructures reported are linear and along either of the axial directions ⟨100⟩. In contrast, herein, spiral CsPbBr₃ perovskite nanorods in the orthorhombic phase are reported with unusual anisotropy having (101) planes remaining perpendicular to the major axis [201]. While these nanorods are synthesized using the prelattice of orthorhombic Cs₂CdBr₄ with Pb(II) diffusion, the spirality is controlled by manipulation of the compositions of alkylammonium ions in the reaction system which selectively dissolve some spiral facets of the nanorods. Further, as spirality varied with facet creation and elimination, these nanorods were explored as photocatalysts for CO₂ reduction, and the evolution of methane was also found to be dependent on the depth of the spiral nanorods. The entire study demonstrates facet manipulation of complex nanorods, and these results suggest that even if perovskites are ionic in nature, their shape could be constructed by design with proper reaction manipulation.