Lead Halide Research Articles

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

Color-Tunable Lead Halide Perovskite Single-Mode Chiral Microlasers with Exceptionally High glum.

Chiral microlasers hold great promise for optoelectronics from integrated photonic devices to high-density quantum information processing. Despite significant progress in lead-halide perovskite emitters, chiral lasing with high dissymmetry factors (glum) has not yet been realized. Here, we demonstrate chiral single-mode microlasers with exceptional stability and tunable emission across the visible range by combining CsPbClxBr3-x perovskite microrods (MRs) with a cholesteric liquid crystal (CLC) layer. The MRs lase via a whispering gallery mode (WGM) microcavity and confer chirality through the encapsulated CLC layer, thus exhibiting circularly polarized lasing with dissymmetry factors reaching 1.62. Importantly, we demonstrate wavelength-tunable high dissymmetry chiral lasers in a broad spectral range by tuning the halide composition and using CLC layers with the desired photonic bandgap (PBG). This facile approach to generate chiral lasing not only is applicable to semiconductor nano- and microcrystals but also paves the way for potential integration into nanoscale photonic devices.

Extreme Electron-Photon Interaction in Disordered Perovskites.

The interaction of light with solids can be dramatically enhanced owing to electron-photon momentum matching. This mechanism manifests when light scattering from nanometer-sized clusters including a specific case of self-assembled nanostructures that form a long-range translational order but local disorder (crystal-liquid duality). In this paper, a new strategy based on both cases for the light-matter-interaction enhancement in a direct bandgap semiconductor - lead halide perovskite CsPbBr3 - by using electric pulse-driven structural disorder, is addressed. The disordered state allows the generation of confined photons, and the formation of an electronic continuum of static/dynamic defect states across the forbidden gap (Urbach bridge). Both mechanisms underlie photon-momentum-enabled electronic Raman scattering (ERS) and single-photon anti-Stokes photoluminescence (PL) under sub-band pump. PL/ERS blinking is discussed to be associated with thermal fluctuations of cross-linked [PbBr6]4- octahedra. Time-delayed synchronization of PL/ERS blinking causes enhanced spontaneous emission at room temperature. These findings indicate the role of photon momentum in enhanced light-matter interactions in disordered and nanostructured solids.

Roles of defects in perovskite CsPbX3 (X=I, Br, Cl): a first- principles investigation

Inorganic lead halide perovskite CsPbX3 (X=I, Br, Cl) have a promising application in optoelectronic fields due to their excellent photovoltaic properties. The defects, which have a significant impact on the performance of materials, are often introduced during the synthesis process. However, there is still a lack of systematic theoretical investigation of the effects of these defects. In this study, the effects of vacancies and H-atom interstitial point defects on the structural, electronic and optical properties of CsPbX3 are systematically investigated by using first-principles approach based on density-functional theory. The calculated results show that the introduction of different defects have significantly effect on the band gap, effective mass, semiconductor properties, ion migration and optical absorption coefficient of the perovskite materials. It is also found that VCs and VPb defects introduce shallow transition levels that do not negatively impact the optoelectronic properties. However, VX and interstitial H defects generate deep transition levels within the bandgap, which acts as non-radiative recombination centers and reduce the optoelectronic performance of the perovskite material. This study contributes to the understanding of the nature of halide chalcogenides and optimally regulating the performance of optoelectronic devices.

Evidence and engineering of x-ray luminescence in lead free perovskite Cs2AgInCl6 with Bi substitutions

Cs2AgInCl6 belongs to the family of lead-free halide double perovskites. Lead-free halide double perovskite appears as a viable contender for scintillator applications due to its inexpensive production costs, low intrinsic trap density, and nanosecond quick reaction. Perovskite crystals have a substantially lower trap density than lead halide and traditional oxide scintillator materials, according to thermo-luminescence measurements. Cs2AgInCl6 structure and dimensionality were engineered by Bi doping. Bi substitution reduces the bandgap, making it suited for scintillation applications. Bi substitution allows for easy tuning of Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50) due to its wide versatility in scintillation properties. For Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50), x-ray power dependent luminescence increases with increasing power. Because of their nontoxicity, sensitivity, reaction time, and stability, Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50) double perovskite crystals are promising for x-ray scintillation.

Nanometer-Resolved Mapping of Organic Cation Migration Behavior in Methylammonium Lead Halide Perovskites.

The performance and stability of organic metal halide perovskite (OMHP) optoelectronic devices have been associated with ion migration. Understanding of nanoscale resolved organic cation migration mechanism would facilitate structure engineering and commercialization of OMHP. Here, we report a three-dimensional approach for in situ nanoscale infrared imaging of organic ion migration behavior in OMHPs, enabling to distinguish migrations along grain boundary and in crystal lattice. Our results reveal that organic cation migration along OMHP film surface and grain boundaries (GBs) occurs at lower biases than in crystal lattice. We visualize the transition of organic cation migration channels from GBs to volume upon increasing electric field. The temporal resolved results demonstrate the fast MA+ migration kinetics at GBs, which is comparable to diffusivity of halide ions. Our findings help understand the role of organic cations in the performance of OMHP devices, and the proposed approach holds broad applicability for revealing migration mechanisms of organic ions in OMHPs based optoelectronic devices.

Synthesis of a perovskite surface-coated polymer brush by photo-induced atom transfer radical polymerization

Lead halide perovskite nanocrystals (PNCs) are expected to be applied in the field of optoelectronics due to their color tunability, high color purity, and near-unity photoluminescence quantum yields. Moreover, the construction of nanocomposite structures with functional polymers has been reported to improve the material stability as well as the ordered structure with high orientation and periodicity. In this study, we demonstrated the synthesis of polymethyl methacrylate (PMMA) on the PNCs by surface-initiated polymerization. We synthesized PMMA polymer brushes by photo-induced atom transfer radical polymerization (p-ATRP) after coordinating the initiator on the PNC surface. We succeeded in obtaining PMMA-PNCs with a degree of polymerization of 21. Moreover, thermal stability tests showed that PMMA-PNCs achieved improved thermal stability compared to pristine-PNCs. This work can provide guidance for developing polymer brush-PNCs via surface-initiated polymerization.

Structural reconstruction synthesis of highly luminous water-stable CsPbBr3@CsPb2Br5@DSPE core-shell perovskite nanocrystals for bioimaging, pattering, and LEDs

Lead halide perovskite (LHP) nanocrystals (NCs) suffer from poor stability against environmental factors (heat, moisture, oxygen, etc.), which seriously hinders their practical application. Constructing a core-shell structure could be an effective approach to improve the stability and optical properties of the LHP NCs. Herein, a novel strategy of water-triggered phase transformation and phospholipid (DSPE) micelle encapsulation is proposed, generating highly luminescent water-dispersed CsPbBr3@CsPb2Br5@DSPE core-shell-shell nanocrystals. The epitaxial growth of the CsPb2Br5 shell is induced by the in-situ reconstruction of the CsPbBr3 surface by water erosion, and the lattice mismatch with the CsPbBr3 core is small (3.8%). The further amphipathic phospholipid encapsulation guarantees their excellent water dispersity and stability. Revealed by the femtosecond transient absorption spectroscopy, the dense CsPb2Br5@DSPE shell effectively passivates the surface of the CsPbBr3 core, thus improving its stability and luminescence performance. The resulting CsPbBr3@CsPb2Br5@DSPE nanoparticles exhibit excellent performance as fluorescent probes for bioimaging, aqueous inks for high-resolution pattering, and light conversion layers for LEDs, demonstrating their promising potential in multiple applications.

Functionalized sp2 Carbon-Conjugated Covalent Organic Frameworks for Interfacial Modulation of Inverted Perovskite Solar Cells.

Interfacial modulation utilizing functional materials is proven to be crucial for obtaining high photovoltaic performance in lead halide perovskite solar cells (PSCs). This study investigates, for the first time, the utilization of a pyrene-based sp2 carbon-conjugated covalent organic framework (sp2c-COF) as an interfacial layer in inverted PSCs. Functionalized with cyano (-CN) Lewis base groups, the sp2c-COF exhibits a dual effect, simultaneously passivating both the NiOx and the perovskite layers. Detailed characterization results highlight the role of sp2c-COF in reducing the Ni3+ defect density in NiOx films and forming Lewis acid-base adducts with undercoordinated Pb2+ on the perovskite surfaces, thereby inhibiting interfacial redox reactions and suppressing non-radiative recombination. Moreover, sp2c-COF leads to improved crystallinity of perovskite films. Benefiting from the synergistic effects, sp2c-COF-modified devices delivered a champion efficiency of 17.64%. These findings underscore the potential of sp2c-COF as a functional interface material for PSCs, offering enhanced efficiency and stability. The study contributes to advancing the understanding and application of covalent organic frameworks in photovoltaic technologies.

Unveiling the role of Cs ion in perovskite phase formation during solid–vapor reactions

The preparation of perovskite solar cells (PSCs) using a solid–vapor reaction has shown great potential due to its scalability and lack of organic solvent. The phase formation process in the solid–vapor reaction is crucial for the crystallization of perovskite films. Previous studies mainly introduced Cs into the solid–vapor reaction, but insufficient attention was paid to the role of Cs in purifying the phase formation path during the crystallization process. In this study, we investigated the effect of Cs on the phase formation process in the solid–vapor reaction and found that Cs can decrease the crystallinity of lead halide films, induce a purified phase formation process to prevent the formation of δ-phase and other impurity phases, regulate the crystallization rate of perovskite, and produce high-quality, low-defect perovskite films. The result was achieving a champion power conversion efficiency (PCE) of 21.54 % for a small area (0.148 cm2) and 18.65 % for larger mini-modules (5 × 5 cm2). Furthermore, the devices maintained over 80 % of their initial efficiencies after 450 h of continuous operation under AM 1.5 G irradiation. This work underscores the importance of purified phase formation paths in solid–vapor reactions for outstanding crystal quality in high-performance perovskite solar cells.

In-Situ comparative study of photo-induced charge behavior in single-perovskite Cs3Bi2Br9 and double-perovskite Cs2AgBiBr6

While organic-inorganic lead halide perovskites excel in optoelectronic applications, their use is limited by toxicity and degradation. Consequently, lead-free alternatives like Cs2AgBiBr6, offering greater stability and diverse applications, have been investigated. However, the fundamental structural, optical, and electronic properties of Cs2AgBiBr6 remain insufficiently understood. In this study, we compared the exciton dynamics and photo-induced charge separation in Cs3Bi2Br9 and Cs2AgBiBr6 films using in-situ surface techniques. Both materials display similar surface photovoltage (SPV) peaks in the 450–500 nm range, supporting the hypothesis of Bi 6s-6p orbital transitions in distorted [BiBr6]3− structures. Although many theories propose the presence of self-trapped excitons (STE) in bismuth-based perovskites, sufficient evidence has been lacking. Our observation of a significant redshift in the SPV peak compared to the band edge absorption peak supports STE hypothesis, with Cs2AgBiBr6 showing a more pronounced redshift due to its more complex electronic structure and stronger electron-phonon coupling. Additionally, we observed that Cs2AgBiBr6 exhibits superior charge separation efficiency compared to Cs3Bi2Br9. Notably, Cs2AgBiBr6 shows significantly shorter rise times, indicating more rapid photogenerated charge separation. However, both materials exhibit similar fall times, suggesting comparable charge recombination rates. Light-chopping-frequency dependent SPV measurements further reveal that Cs2AgBiBr6 has a higher charge separation rate than Cs3Bi2Br9. These findings underscore the potential of bismuth-based perovskites for optoelectronic applications and highlight the importance of a comprehensive understanding of their structure-property relationships.

Instability of colloidal lead halide perovskite nanocrystals: Causes, improvement, and evaluation

Instability of colloidal lead halide perovskite nanocrystals: Causes, improvement, and evaluation

Chirality-Mediated 1D-to-2D Phase Transition in Hybrid Lead Halide Perovskites.

Dimensionality engineering plays a pivotal role in optimizing the performance, ensuring long-term stability, and expanding the versatile applications of lead halide perovskites (LHPs). Currently, the manipulation of LHP dimensions primarily occurs during the synthesis stage, a procedure hampered by constraints, including synthetic complexity and irreversibility. This investigation successfully achieved a transition from one-dimensional (1D) to two-dimensional (2D) structures in chiral LHPs by applying hydrostatic pressure. Remarkably, this pressure-induced transition in dimensionality is absent in the racemic analogue due to the staggered arrangement of inorganic chains and the elevated steric hindrance posed by the organic cations. Notably, the hydrogen bonding between organic cations and the inorganic framework adopts a symmetrical arrangement in the racemic system but a helical configuration along the 1D chain direction in the chiral counterparts. This distinct helical arrangement induces a consequential distortion in the inorganic moiety, resulting in the emergence of a spin-polarized Rashba-Dresselhaus texture that explains the chirality's electronic spin origin. Furthermore, both experimental and density functional theory calculation results demonstrate that the 1D-to-2D phase transition in chiral halide perovskites can induce significant modifications in the electronic structures and associated optical emissions. In summary, the findings unveil novel avenues for manipulating optoelectronic properties in chiral perovskites through dimensionality engineering.

Strategies To Achieve Long-Term Stability in Lead Halide Perovskite Nanocrystals and Its Optoelectronic Applications.

The lead halide perovskite (LHP) nanocrystals (NCs) research area is flourishing due to their exceptional properties and great potential for a wide range of applications in optoelectronics and photovoltaics. Yet, despite the momentum in the field, perovskite devices are not yet ready for commercialization due to degradation caused by intrinsic phase transitions and external factors such as moisture, temperature, and ultraviolet (UV) light. To attain long-term stability, we analyze the origin of instabilities and describe different strategies such as surface modification, encapsulation, and doping for long-term viability. We also assess how these stabilizing strategies have been utilized to obtain optoelectronic devices with long-term stability. This Mini-Review also outlines the future direction of each strategy for producing highly efficient and ultrastable LHP NCs for sustainable applications.

Observation of Hot Carrier Localization Affected by A Cations in Hybrid Perovskites.

Organic-inorganic lead halide perovskites (OLHPs) have demonstrated exceptional properties in high-performance photoelectric devices. However, the impact of A-site cations, specifically formamidinium and methylammonium (MA), on the optoelectronic properties of OLHPs, particularly in the context of hot carrier utilization, remains a topic of debate. In this study, we propose a method for characterizing hot carrier transportation by measuring the hot carrier mobility and momentum-dependent transient photocurrent influenced by A-site cations in OLHPs. Our findings reveal that the direction of photon drag current is reversed upon substitution of the MA cation, suggesting the strong localization of hot carriers by the MA cation dipole. Furthermore, the correlation between the hot carrier photoconductivity and the electronic structure in different A-site cation samples indicates that hot carrier mobility in OLHPs can be reduced by >50% due to the influence of A-site cations.

Progress of Hole-Transport Layers in Mixed Sn-Pb Perovskite Solar Cells.

Hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have rapidly emerged as a promising photovoltaic technology, with record efficiencies surpassing 26%, approaching the theoretical Shockley-Queisser limit. The advent of all-perovskite tandem solar cells (APTSCs), integrating Pb-based wide-bandgap (WBG) with mixed Sn-Pb narrow-bandgap (NBG) perovskites, presents a compelling pathway to surpass this limit. Despite recent innovations in hole transport layers (HTLs) that have significantly improved the efficiency and stability of lead-based PSCs, an effective HTL tailored for Sn-Pb NBG PSCs remains an unmet need. This review highlights the essential role of HTLs in enhancing the performance of Sn-Pb PSCs, focusing on their ability to mitigate non-radiative recombination and optimize the buried interface, thereby improving film quality. The distinct attributes of Sn-Pb perovskites, such as their lower energy levels and accelerated crystallization rates, necessitate HTLs with specialized properties. In this study, the latest advancements in HTLs are systematically examined for Sn-Pb PSCs, encompassing organic, self-assembled monolayer (SAM), inorganic materials, and HTL-free designs. The review critically assesses the inherent limitations of each HTL category, and finally proposes strategies to surmount these obstacles to reach higher device performance.

Hexadecylpyridinium bromides as a new capping agent for improving stability and luminescence of cesium lead bromide perovskites

Because of exception properties, inorganic halide perovskites are promising materials for numerous applications. The efficiency of these materials are evaluated based on their photoluminescence quantum yield, which is the key indicator and proportional to the stability of the perovskite. Hence, to limit the instability of the perovskites, addition of surfactant as ligand has been applied during synthesis of nanoparticle based inorganic perovskite CsPbBr3. As far as we know, only a few researchers have studied the impact of hexadecylpyridinium bromide (CPB) on the stability of the crystal structure of CsPbBr3. In this work, we present a novel approach for lead halide perovskites by incorporating CPB to primarily maintain the perovskite's crystal structure, and later on to enhance the stability of CsPbBr3 NPs while boosting its photoluminescence quantum yield (PLQY). Results showed that CPB enhanced the thermal stability and boosted the PLQY to 90 %. Moreover, CPB had proven its efficiency as a capping agent preventing the exchange of anion between bromide and iodide ions in presence of lead iodide.

Structural Stability of Mixed‐Halide Perovskite Nanocrystals in Energy Storage: The Role of Iodine Expulsion

AbstractIn the pursuit of efficient optoelectronics devices, hybrid lead halide perovskite quantum dots (PQDs) have emerged as highly promising semiconductor materials due to their intriguing properties. While these materials have been used in many applications, the fundamental understanding of their behavior remains relatively unexplored, especially for the mixed halide perovskite samples. To facilitate the advancement of PQD technologies for commercial applications, it is essential to gain insights into the role of ion migration. This study delves into the fundamental aspects of ion migration in halide perovskite nanocrystals. Porous electrodes for supercapacitor application were fabricated using CsPbBr3–xIx (x=0,1,2) nanocrystals prepared via the ligand‐assisted re‐precipitation (LARP) method. Three‐electrode electrochemical measurements and several other characterizations were conducted under dark conditions to evaluate device performance and elucidate the impact of mixed halides on device kinetics and stability. X‐ray photoelectron spectroscopy before and after the electrochemical measurement reveals intriguing findings. Notably, the analysis uncovered the phase segregation in the metal halide perovskite nanocrystals with particular emphasis on CsPbBr2I due to its distinctive mixed‐halide behavior. The specific capacitance increases with the increasing cycles. Interestingly, as the iodide content increases, there is no selective halide expulsion as the structure collapses rapidly.