Lead Halide Research Articles

Precise Single-Atom Modification of Hybrid Lead Chlorides for Electron Donor-Acceptor Effect and Enhanced Photocatalytic Aerobic Oxidation.

Hybrid lead halides show significant potential in photocatalysis due to their excellent photophysical properties, but the atomically precise modification of their organic component to achieve synergistic interactions with the lead halide units remains a great challenge. Herein, for the first time, we have employed the crystal engineering strategy to construct a class of single-atom-substituted hybrid lead halides with electron donor-acceptor (D-A) effect. The lead halide frameworks consist of 1D linear [PbCl]+ chains as inorganic building units and benzoxadiazole/benzothiadiazole/ benzoselenadiazole-funtionalized dicarboxylates as linkers. The covalent bonding between the organic ligands with electron-withdrawing groups and the electron-rich lead halide units not only facilitate the charge separation, but also enhance structural robustness that is critical for photocatalysis. The D-A structured lead halides serve as highly efficient heterogeneous photooxidation catalysts, including aerobic oxidation of C(sp3)-H bonds, oxidative coupling of primary amines, oxidation of phenylboronic acids and selective oxidation of sulfides that are demonstrated in 30 examples. Importantly, these photooxidation reactions are able to be driven by natural sunlight and ambient air to afford quantitative yields. Moreover, our lead halide photocatalysts are successful to fix into a photocatalytic flow system, which enables the flow-type synthesis of high value-added photooxidation products on a gram scale.

Multi-Noncentrosymmetric Polar Order in 2D Hybrid Lead Chloride with Broadband Emission and High-Temperature Second-Harmonic Generation Switching.

Two-dimensional lead halide perovskites represent a fascinating class of hybrid semiconductors for solar cell, light-emitting, nonlinear optical (NLO), and ferroelectric applications. A notable subset within this category is luminescent ferroelectrics, which have garnered considerable attention for their potential in integrated photoelectronic devices. In this study, we employed an organic amine halogenation strategy (also referred to as halogen engineering), which is renowned for its efficacy in inducing polar order through crystal engineering. Consequently, we synthesized a layered Ruddlesden-Popper (RP) lead chloride comprising 3-chloropropylammonium cations (CPA+), with the chemical formula CPA2PbCl4. This compound features as many as four temperature-dependent crystal phases, with phase transitions observed at T1 = 353.1 K (343.9 K), T2 = 211.7 K (208.6 K), and T3 = 182.0 K (178.2 K) in the heating (cooling) cycles. Employing a multitechnique approach─including thermal analysis, X-ray diffraction, dielectric and pyroelectric current measurements, Raman spectroscopy, and second-harmonic generation (SHG) studies─we determined the mechanisms of the structural phase transitions. Our findings demonstrate polar order of phase II (space group Cmc21), phase III (space group Pna21), and phase IV (space group Pca21), while also confirming the centrosymmetric nature of phase I (space group Cmce). X-ray diffraction data revealed that the I to II PT is of a ferroelectric nature, devoid of ferroelastic strain, a conclusion further supported by pyroelectric measurements. CPA2PbCl4 features negative linear thermal expansion and broadband emission, which transitions to white light above 180 K. Remarkably, CPA2PbCl4 also demonstrates high-temperature SHG on-off switching with a high contrast ratio of 300:1 along with good switching stability, as evidenced by SHG cycling studies at heating/cooling rates ranging from 5 to 50 K/min. This SHG study also sets new standards for the field of SHG switching by providing a method to quantify the thermal responsiveness of SHG-switchable materials using the treq (time requirement) parameter. Overall, our findings show that the halogenation strategy has led to the discovery of a rare example of an RP perovskite exhibiting coexistence of white-light emission, SHG on-off thermal bistability, ferroelectricity, and negative linear thermal expansion.

Synthetic Control of Water-Stable Hybrid Perovskitoid Semiconductors.

Hybrid metal-halide perovskites and their derived materials have emerged as the next-generation semiconductors with a wide range of applications, including photovoltaics, light-emitting devices, and other optoelectronics. Over the past decade, numerous single-crystalline perovskite derivatives have been synthesized and developed. However, the synthetic methods for these derivatives mainly rely on acidic crystallization conditions. This approach leads to crystals comprising metal halide building blocks, which show problematic stability when directly exposed to water. In this study, a methodology is developed for synthesizing hybrid metal-halide compounds using lead iodide and the zwitterionic bifunctional molecule cysteamine (CYS), to form various perovskitoid structures under a broad pH range. Interestingly, the different pH conditions alter the coordination environment of lead halides, leading to lead-sulfide and lead-nitride covalent bond formation. This modification significantly enhances their stability when in direct contact with water, lasting for months. Photoluminescence measurements and first principal density functional theory (DFT) calculations reveal that the perovskitoids synthesized under basic and acidic pH conditions exhibit a direct bandgap nature, while those synthesized under neutral conditions display an indirect bandgap. This approach opens new avenues for manipulating synthetic methods to develop water-stable hybrid semiconductors suitable for a wide range of applications, such as solid-state light emitters.

Consequences of the Pb-S Bond Formation for Lead Halide Perovskites.

Lead halide perovskites are structurally not stable due to their ionic bonds. Using sulfur agents in the crystal growth improves the stability and performance of the photovoltaic and light-emitting devices. In this theoretical work, we use a small toy S-radical in place of A cation in the bulk of lead iodide perovskite, and highlight the significance of the Pb-S covalent-double-bond formation for: the charge redistribution on the neighboring bonds that also turn to be covalent, phase transformation to a stable non-perovskite structure, and superior optoelectronic properties. The chemical analysis was performed with the Quantum Theory of Atoms In Molecules (QTAIM) and Non-Covalent Interactions (NCI) index. Excitonic properties were obtained from the solution of ab initio Bethe-Salpeter equation. Presence of the spin-orbit coupling triggers an interplay between the Frenkel and charge-transfer multiexcitons, switching between the photovoltaic and laser applications. Multiexcitons obey the exciton-fission preconditions.

Stable Halide Perovskite CsPbBr3 Nanocrystals Assisted by Covalent-Organic Frameworks for Electrochemiluminescence Analysis in an Aqueous Medium.

Lead halide perovskites have garnered attention as promising electrochemiluminescence (ECL) emitters owing to their superior photophysical characteristics. However, their poor water stability severely restricts their application in aqueous media for ECL. In this study, inorganic perovskite CsPbBr3 was assembled in situ in the imine-linked covalent-organic framework (COF-LZU1) as a novel ECL emitter. The expansive surface area and robust hydrophobic architecture of COF-LZU1 not only improved the water stability of CsPbBr3 but also guaranteed its exceptional ECL performance. The novel composite nanoluminescent material was coated onto an indium tin oxide (ITO) electrode via spin-coating and calcination processes to serve as an electrochemiluminescence (ECL) platform. A sensor was developed by combining a DNA hydrogel target-induced release system with a platform using ascorbic acid (AA) as a coreactant and T-2 toxin as the target analyte model. This method achieved a detection limit as low as 3.56 fg·mL-1 and was successfully applied to the analysis of the T-2 toxin content in corn samples. This study offers a novel path for the advancement of perovskite-based ECL emitters and their utilization in aqueous environments within the ECL field.

Strong Grain Boundary Passivation Effect of Coevaporated Dopants Enhances the Photoemission of Lead Halide Perovskites.

Herein, we demonstrate that coevaporated dopants provide a means to passivate buried interfacial defects occurring at perovskite grain boundaries in evaporated perovskite thin films, thus giving rise to an enhanced photoluminescence. By means of an extensive photophysical characterization, we provide experimental evidence that indicate that the codopant acts mainly at the grain boundaries. They passivate interfacial traps and prevent the formation of photoinduced deep traps. On the other hand, the presence of an excessive amount of organic dopant can lead to a barrier for carrier diffusion. Hence, the passivation process demands a proper balance between the two effects. Our analysis on the role of the dopant, performed under different excitation regimes, permits evaluation of the performance of the material under conditions more adapted to photovoltaic or light emitting applications. In this context, the approach taken herein provides a screening method to evaluate the suitability of a passivating strategy prior to its incorporation into a device.

Efficient and selective photocatalytic oxidation of benzylic alcohols with built-in electric field CsPbBr3/SiO2 nanocomposites through Fe3+ gradient doping

Lead halide perovskite nanocrystals (PNCs) have emerged as promising materials for photocatalysis due to their exceptional optoelectronic properties, yet achieving efficient charge separation and selective oxidation reactions remains a significant challenge. In this study, we report the synthesis of Fe3+-doped CsPbBr3/SiO2 nanocomposites (Fe-PNCs/SNPs) with gradient energy levels, designed to enhance photocatalytic performance. Our results demonstrate that Fe3+ doping introduces mid-gap states, promotes photoinduced charge separation, and generates reactive oxygen species (ROS) such as O2− and OH radicals under sunlight-simulating light irradiation from a 300 W Xe arc lamp. The Fe20-PNCs/SNPs catalyst achieved over 99 % conversion of benzyl alcohol to benzaldehyde with high selectivity and stability in the ethanol under ambient conditions. Additionally, the catalyst exhibited excellent recyclability and broad substrate tolerance. These findings highlight the innovative design of gradient energy levels in perovskite nanocomposites, offering a new strategy for enhancing photocatalytic efficiency in selective organic transformations.

Photodiodes Made of Cascade Perovskite Single Crystals with Passivation Layers for High-Energy-Resolution γ-ray Spectroscopy.

Lead halide perovskite single crystals (LHPSC) are promising for room-temperature γ-ray spectroscopy in radiation detection. While MA(CH3NH3)-based LHPSCs are the most straightforward and cost-effective to synthesize from solution, their performance in γ-ray spectroscopy is hindered by significant noise and ion migration at high bias, which degrades their energy resolution (ER). The work introduced an n-type/intrinsic/n-type photodiode incorporating passivation layers of MA-based LHPSCs, grown through solution-process epitaxial growth. This single-polarity device demonstrated an outstanding ER of 3.6% for 662 keV γ-ray photons. Overall, this work provides useful information for developing room-temperature γ-ray detectors based on solution-processed lead halide perovskites.

Switchable Photovoltaic Effect and Robust Nonlinear Optical Response in a High-Temperature Molecular Ferroelectric [C8N2H22][PbI4

Hybrid organic-inorganic molecular ferroelectrics (HOIMFs) have garnered significant attention for their potential applications in nonvolatile memory and spintronic devices. However, few efforts have been devoted to the photoelectric properties of lead halide molecular ferroelectrics, despite the fact that robust ferroelectricity and flexibility are desirable for thin-film photoelectric devices. Herein, we present a novel lead halide molecular ferroelectric [C8N2H22][PbI4] (1) synthesized hydrothermally. A polar monoclinic structure of 1 was solved by single-crystal X-ray diffraction and second-harmonic generation (SHG) tests. A direct band gap of 2.36 eV was confirmed by UV-vis spectrum and theoretical calculation. Hysteresis measurements demonstrated inherent room-temperature (RT) ferroelectricity in 1 with a spontaneous polarization (Ps) of 3.2 μC/cm2. The 1-based photoelectric device shows a notable photovoltaic (PV) effect with Voc ∼ 0.27 V, Jsc ∼ 38 nA/cm2 under AM 1.5 G illumination, and a rapid response time of ∼1.5 ms. A considerable enhancement in PV performance has been achieved by adjusting the ferroelectric polarization, resulting in a maximum Voc ∼ 0.75 V, Jsc ∼ 2.28 μA/cm2. Notably, 1 exhibits a rather large SHG signal, which is approximately 2.61-fold higher than that of KH2PO4 (KDP) upon a 1064 nm laser radiation. This study offers a bright avenue for lead halide molecular ferroelectrics as promising optoelectronic devices and SHG materials.

Layered and Low-Dimensional Lead, Silver, and Bismuth Halide Perovskites Directed by Halogen-Substituted Spacer Cations

Layered and Low-Dimensional Lead, Silver, and Bismuth Halide Perovskites Directed by Halogen-Substituted Spacer Cations

Enhancing Extraction and Suppressing Cooling of Hot Electrons in Lead Halide Perovskites by Dipolar Surface Passivation.

Slowing hot carrier (HC) cooling and improving HC extraction are considered two pivotal factors for enhancing power conversion efficiency in emerging HC photovoltaic applications of perovskites and other materials. Employing ab initio quantum dynamics simulations, we demonstrate the simultaneous slow cooling and efficient extraction of hot electrons at the C60/CsPbI3 interface through dipolar surface passivation with phenethylammonium and 4-fluorophenethylammonium ligands. The passivation effectively suppresses I-Pb lattice vibrations, weakens the hot electron-phonon interaction in CsPbI3, and thus slows down the HC cooling. At the same time, the dipolar surface passivation elevates the LUMO + 1 state in C60 and reduces the energy gap for HC extraction. Concurrently, higher-frequency vibrations of the dipolar layer enhance the coupling between C60 and CsPbI3, promoting efficient HC extraction further. These phenomena are intensified with increased polarity of the dipolar layer. Furthermore, we find that dipolar passivation has the opposite influence on cold electron collection at the band edge, underscoring the fact that the observed improvement in photovoltaic performance stems preferentially from the effective utilization of HCs rather than cold electrons. The work provides a new strategy for achieving high-performance HC perovskite solar cells.

Antisolvent controls the shape and size of anisotropic lead halide perovskite nanocrystals

Colloidal lead halide perovskite nanocrystals have potential for lighting applications due to their optical properties. Precise control of the nanocrystal dimensions and composition is a prerequisite for establishing practical applications. However, the rapid nature of their synthesis precludes a detailed understanding of the synthetic pathways, thereby limiting the optimisation. Here, we deduce the formation mechanisms of anisotropic lead halide perovskite nanocrystals, 1D nanorods and 2D nanoplatelets, by combining in situ X-ray scattering and photoluminescence spectroscopy. In both cases, emissive prolate nanoclusters form when the two precursor solutions are mixed. The ensuing antisolvent addition induces the divergent anisotropy: The intermediate nanoclusters are driven into a dense hexagonal mesophase, fusing to form nanorods. Contrastingly, nanoplatelets grow freely dispersed from dissolving nanoclusters, stacking subsequently in lamellar superstructures. Shape and size control of the nanocrystals are determined primarily by the antisolvent’s dipole moment and Hansen hydrogen bonding parameter. Exploiting the interplay of antisolvent and organic ligands could enable more complex nanocrystal geometries in the future.

Pt and Pt‐group transition metal 0D vacancy ordered halide perovskites: A review

AbstractLead halide perovskites (LHPs), have attracted considerable attention across various applications owing to their exceptional optoelectronic properties. However, the main challenge hindering the broad adoption of lead halide perovskites lies in their stability and toxicity. In this review, we summarize the outstanding properties of platinum (Pt) halide perovskites, with a particular focus on the stability and applications of Cs2PtI6 and its derivatives. Cs2PtI6 has shown promising efficiency for photovoltaic devices, as well as photoelectrochemical water splitting with stable behavior in acid or basic conditions. Cs2PtI6 also shows promise in gas sensing and thermoelectric devices. The emergence of 2D Pt (II) halide perovskites opens up new avenues for environmentally friendly materials for photonic and optoelectronic devices like room temperature phosphoresce and triplet‐triplet annihilation (TTA) based up‐conversion.image

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The in‐situ post‐synthetic treatment of CsPbBr₃ nanocrystals confined within nanoporous silica microspheres enhances their optical properties, addressing key challenges in lead halide perovskites. Surface passivation with Br⁻ ions boosts photoluminescence quantum yield, while Mn²⁺ doping introduces a new emission band, enabling precise control of optical properties. Coating with a SiO₂ shell further enhances the stability of the nanocrystals in polar solvents, expanding their potential for diverse applications. More details are discussed in the article by Huang et al. on pages 2779—2787. image

Tailoring Perovskite/C60 Interface by Reactive Passivators for Stable Tandem Solar Cells

AbstractIntegrating perovskite solar cells with crystalline silicon bottom cells in a monolithic two‐terminal tandem configuration enables power conversion efficiency (PCE) surpassing the theoretical limits of single‐junction cells. However, wide bandgap (WBG) perovskite films face challenges related to phase stability and open circuit voltage (VOC) deficit, particularly due to severe non‐radiative recombination at the perovskite/C60 interface. Here, the interfacial defects are passivated by incorporating a reactive passivator that reacts with lead halides to form low‐dimensional phases. The target product obtained by optimizing the reaction temperature not only suppresses recombination across the interface, but also facilitates the transfer of charge carriers. More importantly, this product can suppress phase segregation of WBG perovskite films under exposure to light illumination and moisture. This strategy enables a high VOC of 1.25 V for WBG perovskite device based on polymer hole transport layer and a certified stabilized PCE of 30.52% for a monolithic perovskite/silicon tandem solar cell. The unencapsulated tandem device retains 94% of its initial PCE over 200 h under continuous 1‐sun full spectrum illumination in air, demonstrating the improved phase stability.

Conformal SnO2 and NiOx charge transport layers for pragmatic air-processed perovskite solar cells

The industrialization of perovskite (PVK) solar cells (PSCs) necessitates simple manufacturing, cheapness, nontoxicity, high efficiency, and stability. We report an air-processed lead halide PSCs with cheap, nontoxic, stable NiOx and SnO2 as the hole and electron transport layers separately, to meet all the above commercial requests. By preparing the NiOx (water-dispersible) and SnO2 (oil-dispersible) quantum dots (QDs) with good conductivity and energy band matched well with that of PVK, we fabricate inverted PSCs (ITO/NiOx/PVK/SnO2/Ag) with efficiency up to 20.1/14.6% for active areas of 0.0707/1 cm2, under 1 sun simulated illumination with enhanced UV light ratio. The UV-light resistant PSCs reported here will impel their application in the high altitude areas with strong UV light. Importantly, the monodisperse size and dominant (110) plane of SnO2 QDs achieved by controlling the solvothermal parameters, realize the conformal deposition and defect prevention of SnO2, respectively, thus improving the PSC efficiency and stability.

Achieving vertical orientation films with superior environmental stability in quasi-2D lead iodide perovskites

The incorporation of a spacer cation to improve the stability of lead halide perovskites entails a trade-off, notably compromising film quality and device performance, particularly in quais-2D variants employing a higher proportion of hydrophobic, larger spacer cations. Addressing this challenge in quasi-2D perovskite-based devices requires enhancement in film morphology, crystallinity, and vertical orientation to optimize charge transport. Herein, we present a simple one step spin coating synthesis approach for producing PEA2MAn-1PbnI3n+1 (n = 5–2) thin films from a single precursor solution. Notably, our method operates at room temperature without the need of usually toxic anti-solvent or specialized additives, resulting in high quality crystalline films that are vertically oriented and smooth. We systematically investigate the impact of annealing processes on crystal structure, including gradient annealing (GA) as well as thermal annealing at 100℃ for durations of 10 and 15 minutes. Our findings indicate that the films with n = 4 exhibits superior crystallinity and vertical crystallographic orientation, alongside reduced roughness, and minimal contamination of the lower n mixtures. Gradient annealing notably enhances the crystallinity of n = 3 films. While the surface of all the films appears smooth with flake-like structure, the n = 2 sample notably exhibits pitting.

Structural Modifications due to Bi-Doping in MAPbBr3 Single Crystals and Their Impact on Electronic Transport and Stability.

Doping strategy in lead halide perovskites is essential to enhance its optoelectrical properties and expand the potential applications. In this work, the mechanisms, for how dopants affect the overall structural, optical, electrical, and chemical properties and stability of lead halide perovskite materials, are investigated. This is done by specifically considering various bismuth (Bi)doping concentrations in MAPbBr3 single crystals grown using the inverse temperature crystallization method. The resultant doped single crystals exhibit a saturation point when Bi concentration exceeds 0.063% which is considered an optimum doping point. The highest thermal stability is also achieved at this doping concentration among the doped single crystals. This study clearly identifies how Bi doping affects the properties of MAPbBr3 and extends to consider stability, which has not been fully considered for MA-based perovskites previously. This will provide a clear understanding of evaluating doped perovskite materials for enhanced material properties, device performance, and stability.

Electronic Structure of Trions in Layered Hybrid Lead Halide Perovskites

Electronic Structure of Trions in Layered Hybrid Lead Halide Perovskites

How to Apply Raman Spectroscopy for Single Crystals and Thin Films of Organic–Inorganic Lead Halide Perovskite

How to Apply Raman Spectroscopy for Single Crystals and Thin Films of Organic–Inorganic Lead Halide Perovskite