Supramolecular Assembly Enhanced Linear and Nonlinear Chiroptical Properties of Chiral Manganese Halides

Chiral hybrid organic-inorganic metal halides (HOMHs) hold great promise in broad applications ranging from ferroelectrics, spintronics to nonlinear optics, owing to their broken inversion symmetry and tunable chiroptoelectronic properties. Typically, chiral HOMHs are constructed by chiral organic cations and metal anion polyhedra, with the latter regarded as optoelectronic active units. However, the primary design approaches are largely constrained to regulation of general components within structural formula. Herein, supramolecular approaches have been taken for the functionalization of chiral enantiomers by anchoring chiral cations with crown ether hosting molecules. Chiral HOMHs of R-/S-(18-crown-6@ClMBA)2MnBr4 have been thus obtained with boosted linear and nonlinear chiroptical properties. The self-assembled cations lead to enhanced structural rigidity, which promote near-unity green light emission and strong circularly polarized luminescence with a high asymmetry factor, along with high efficiency second-order nonlinear optical responses. In particular, these chiral HOMH single crystals demonstrate a sensitive discrimination for circularly polarized laser in the near-infrared region with the nonlinear optical asymmetry factor (gSHG-CD) as high as 1.8. This work highlights the contribution of supramolecular assembly in improving chiroptical performances, offering valuable insights for the design of new chiral HOMH materials with promising application potentials as linear and nonlinear CPL emitters and detectors.

Mapping the Energy Carrier Diffusion Tensor in Perovskite Semiconductors

Understanding energy transport in semiconductors is critical for the design of electronic and optoelectronic devices. Semiconductor material properties, such as charge carrier mobility or diffusion length, are commonly measured in bulk crystals and determined using models that describe transport behavior in homogeneous media, where structural boundary effects are minimal. However, most emerging semiconductors exhibit nano- and microscale heterogeneity. Therefore, experimental techniques with high spatial resolution paired with models that capture anisotropy and domain boundary behavior are needed. We develop a diffusion tensor-based framework to analyze experimental photoluminescence (PL) diffusion maps accounting for material nano- and microstructure. Specifically, we quantify both carrier transport and recombination in single crystal and polycrystalline lead halide perovskites by globally fitting diffusion maps with spatial, temporal, and PL intensity data. We reveal a 29% difference in principal diffusion coefficients and alignment between electronically coupled grains for CH3NH3PbI3 polycrystalline films. This framework allows for understanding and optimizing anisotropic energy transport in heterogeneous materials.

Low-Dimensional Lead-Free Metal Halides for Efficient Electrically Driven Light-Emitting Diodes

Electrically driven light-emitting diodes (ED LEDs) based on 3D metal halide perovskites have seen remarkable advancements during the past decade. However, the highest-performing devices are largely based on lead-containing 3D perovskites, presenting two key challenges - toxicity and stability - that must be addressed for commercialization. Reducing structural dimensionality and incorporating non-lead metals present promising pathways to address these issues. Although research on ED LEDs based on low-dimensional, lead-free metal halides (LD LFMHs) is growing, their performance still significantly lags behind that of 3D lead halide perovskites. This review seeks to deliver a comprehensive overview of ED LEDs based on LD LFMHs, covering a brief history of their development, methods for material synthesis, luminescence mechanisms, and applications in electroluminescent devices. It also examines current challenges and proposes practical strategies to enhance device performance, with the goal of inspiring further progress in the field.

Electrically Generated Exciton Polaritons with Spin On-Demand

Generation and manipulation of exciton polaritons with controllable spin could deeply impact spintronic applications, quantum simulations, and quantum information processing, but is inherently challenging due to the charge neutrality of the polariton and the device complexity it requires. Here, electrical generation of spin-polarized exciton polaritons in a monolithic dielectric perovskite metasurface embedded in a light-emitting transistor is demonstrated. A finely tailored interplay of in- and out-of-plane symmetry breaking of the metasurface allows to lift the spin degeneracy through the polaritonic Rashba effect, yielding high spin purity with normalized Stokes parameter of S3 ≈ 0.8. Leveraging on spin-momentum locking, the unique metatransistor device architecture enables electrical control of spin and directionality of the polaritonic emission. Here, the development of compact and tunable spintronic devices is advanced and an important step toward the realization of electrically pumped inversionless spin-lasers is represented.

High-Performing Direct X-Ray Detection Made of One-Dimensional Perovskite-Like (TMHD)SbBr5 Single Crystal With Anisotropic Response

3D and 2D organic hybrid perovskites, as well as double perovskites, have demonstrated their suitability for direct X-ray detection. However, the sensitivity and stability of 3D perovskite X-ray detectors are currently being hindered by the existing constraints on ion movement. Therefore, there is an immediate need to develop X-ray detectors that are both highly sensitive and stable while also being environmentally friendly. The novel low-dimensional perovskites demonstrate exceptional inherent stability and effectively mitigate ion migration, thereby showcasing their remarkable photoelectric performance. Inspired by this, a solution crystallization method is employed to synthesize novel single crystals (SCs) of one dimensional (1D) (TMHD)SbBr5. The dimensions of the chained (TMHD)SbBr5 SC are 13 × 1.3 × 1.2 mm3 in size. The device based on a perovskite chain (TMHD)SbBr5 exhibits unique anisotropic X-ray detection performance with a sensitivity of 62.8 and 30.5 µC Gyair -1cm-2 in the parallel and perpendicular orientations, respectively. It can lead to the directional movement of ions, resulting in large carrier mobility under the action of electric fields, and effectively increase the sensitivity to X-ray detection.

A Study of Halide Ion Exchange-Induced Phase Transition in CsPbBr3 Perovskite Quantum Dots for Detecting Chlorinated Volatile Compounds

The unique optical properties of perovskite quantum dots (PQDs), particularly the tunable photoluminescence (PL) across the visible spectrum, make them a promising tool for chlorinated detection. However, the correlation between the fluorescence emission shift behavior and the interface of phase transformation in PQDs has not been thoroughly explored. In this study, we synthesized CsPbBr3 PQDs via the hot-injection method and demonstrated their ability to detect chlorinated volatile compounds such as HCl and NaOCl through a halide exchange process between the PQDs' solid thin film and the chlorinated vapor phase. This exchange process, which occurs alongside chloride (Cl) and bromine (Br) ion exchange and halide atom rearrangement, leads to sequential structural changes: the initial CsPbBr3 cubic Pm3̅m phase transitions to the CsPb2BrxCl5-x tetragonal I4/mcm phase, which subsequently transforms into the CsPbBrxCl3-x orthorhombic Pnma phase. The detailed exploration of this proposed mechanism during chlorinated vapor detection with CsPbBr3 PQDs thin films, supported by X-ray diffraction (XRD) analysis and PL spectrum over time, revealed high sensitivity to HCl vapor. The limit of detection (LOD) for HCl vapor was determined to be 0.02 ppm in visual recognition and 0.005 ppm via PL spectra. Additionally, the LOD for NaOCl was established at 0.50 ppm, facilitated by the photolysis reaction accelerating the conversion of NaOCl to HCl vapor under UV light irradiation. These insights have enriched our understanding of the mechanisms involved and broadened the potential use of CsPbBr3 PQDs as PL detection probes for chloride ions.

Highly Efficient Blue Light-Emitting Diodes Enabled by Gradient Core/Shell-Structured Perovskite Quantum Dots

Room temperature (RT) synthesized mixed bromine and chlorine CsPbBrxCl3-x perovskite quantum dots (Pe-QDs) offer notable advantages for blue quantum dot light-emitting diodes (QLEDs), such as cost-effective processing and narrow luminescence peaks. However, the efficiency of blue QLEDs using these RT-synthesized QDs has been limited by inferior crystallinity and deep defect presence. In this study, we demonstrate a precise approach to constructing high-quality gradient core-shell (CS) structures of CsPbBrxCl3-x QD through anion exchange. Characterization shows that these CS-QDs exhibit a type-I band alignment with a high bromine concentration in the core and a high chlorine concentration in the shell. This unique configuration results in a larger exciton binding energy and reduced defect density, leading to enhanced exciton radiative recombination. Consequently, QLEDs using CS-QDs achieve an external quantum efficiency (EQE) of 16.28%, a maximum luminance of 8423.35 cd/m2, and improved operational stability, surpassing the 12.80% EQE of reference QLEDs made with homogeneous structured QDs (HS-QDs). These findings present a strategy for developing high-quality RT-synthesized blue CS-QDs, marking a significant advancement in the field of efficient pure-blue QLEDs.

Mitigating the Efficiency Deficit in Single-Crystal Perovskite Solar Cells by Precise Control of the Growth Processes

The power conversion efficiencies (PCEs) of polycrystalline perovskite solar cells (PC-PSCs) have now reached a plateau after a decade of rapid development, leaving a distinct gap from their Shockley-Queisser limit. To continuously mitigate the PCE deficit, nonradiative carrier losses resulting from defects should be further optimized. Single-crystal perovskites are considered an ideal platform to study the efficiency limit of perovskite solar cells due to their intrinsically low defect density, as demonstrated in bulk single crystals. However, current single-crystal perovskite solar cells (SC-PSCs) based on single-crystal thin film (SCTF) suffer from severe nonradiative carrier losses at the interface and in the bulk simultaneously due to the immature SCTF growth techniques. In this study, we show that the SC-PSCs can outperform state-of-the-art PC-PSCs, with MAPbI3 as an example, by suppressing carrier losses at the interface and in the bulk in device-compatible SCTFs through precisely controlling their growth.

Multifunctional Graphdiyne Enables Efficient Perovskite Solar Cells via Anti-Solvent Additive Engineering

Finding ways to produce dense and smooth perovskite films with negligible defects is vital for achieving high-efficiency perovskite solar cells (PSCs). Herein, we aim to enhance the quality of the perovskite films through the utilization of a multifunctional additive in the perovskite anti-solvent, a strategy referred to as anti-solvent additive engineering. Specifically, we introduce ortho-substituted-4'-(4,4″-di-tert-butyl-1,1':3',1″-terphenyl)-graphdiyne (o-TB-GDY) as an AAE additive, characterized by its sp/sp2-cohybridized and highly π-conjugated structure, into the anti-solvent. o-TB-GDY not only significantly passivates undercoordinated lead defects (through potent coordination originating from specific high π-electron conjugation), but also serves as nucleation seeds to effectively enhance the nucleation and growth of perovskite crystals. This markedly reduces defects and non-radiative recombination, thereby increasing the power conversion efficiency (PCE) to 25.62% (certified as 25.01%). Meanwhile, the PSCs exhibit largely enhanced stability, maintaining 92.6% of their initial PCEs after 500 h continuous 1-sun illumination at ~ 23 °C in a nitrogen-filled glove box.

Photoinduced Fröhlich Interaction-Driven Distinct Electron- and Hole-Polaron Behaviors in Hybrid Organic-Inorganic Perovskites by Ultrafast Terahertz Probes

The formation of large polarons resulting from the Fröhlich coupling of photogenerated carriers with the polarized crystal lattice is considered crucial in shaping the outstanding optoelectronic properties in hybrid organic-inorganic perovskite crystals. Until now, the initial polaron dynamics after photoexcitation have remained elusive in the hybrid perovskite system. Here, based on the terahertz time-domain spectroscopy and optical-pump terahertz probe, we access the nature of interplay between photoexcited unbound charge carriers and optical phonons in MAPbBr3 within the initial 5 ps after excitation and have demonstrated the simultaneous existence of both electron- and hole-polarons, together with the photogenerated carrier dynamic process. Two resonant peaks in the frequency-dependent photoconductivity are interpreted by the Drude-Smith-Lorentz model along with the ab initio excitation calculation, revealing that the electron-/hole-polaron is related to the vibration modes of the stretched/contracted Pb-Br bond. The red /blue shift of the corresponding peaks as the fingerprints of electron-/hole-polaron provides a channel for observing their dynamic behavior. Different from polarons with long lifetime (>300 ps) in single-crystalline grains, we observed in thin films the transient process from the formation to the dissociation of polarons occurring at timescales within ∼5 ps, resulting from the Mott phase transition for carriers at high concentrations. Moreover, the observation of the polaron dynamic process of the virtual state-assisted band gap transition (800 nm excitation) further reveals the competition of carriers cooling and polaron formation with photocarrier density. Our observations demonstrate a strategy for direct observation and manipulation of bipolar polaron transport in hybrid perovskites.

Point defects at grain boundaries can create structural instabilities and persistent deep traps in metal halide perovskites

Metal halide perovskites (MHPs) have attracted strong interest for a variety of applications due to their low cost and excellent performance, attributed largely to favorable defect properties. MHPs exhibit complex dynamics of charges and ions that are coupled in unusual ways. Focusing on a combination of two common MHP defects, i.e., a grain boundary (GB) and a Pb interstitial, we developed a machine learning model of the interaction potential, and studied the structural and electronic dynamics on a nanosecond timescale. We demonstrate that point defects at MHP GBs can create new chemical species, such as Pb-Pb-Pb trimers, that are less likely to occur with point defects in bulk. The formed species create structural instabilities in the GB and prevent it from healing towards the pristine structure. Pb-Pb-Pb trimers produce deep trap states that can persist for hundreds of picoseconds, having a strong negative influence on the charge carrier mobility and lifetime. Such stable chemical defects at MHP GBs can only be broken by chemical means, e.g., the introduction of excess halide, highlighting the importance of proper defect passivation strategies. Long-lived GB structures with both deep and shallow trap states are found, rationalizing the contradictory statements in the literature regarding the influence of MHP GBs on performance.

Role of A-Site Cation Hydrogen Bonds in Hybrid Organic-Inorganic Perovskites: A Theoretical Insight

Hybrid organic-inorganic halide perovskites (HOIPs) have garnered a significant amount of attention due to their exceptional photoelectric conversion efficiency. However, they still face considerable challenges in large-scale applications, primarily due to their instability. One key factor influencing this instability is the lattice softness attributed to the A-site cations. In this study, we investigated the effects of four different A-site cations (MA, FA, EA, and GA) on the lattice softness of perovskites by using a combination of ab initio molecular dynamics and first-principles calculations. Our results demonstrate that an increase in the number of hydrogen bonds for A-site cations correlates with enhanced lattice and atomic fluctuations, resulting in a reduction in the bulk modulus and an increase in the lattice softness. The strength of hydrogen bonding of the A-site cation increases the rotational energy barrier of the cation, along with the formation energy and kinetic coupling between the A-site cation and the [PbI6]4- octahedron. Consequently, this increases the lifetime of hydrogen bonding and enhances the rigidity of the perovskite lattice. Notably, we found that EA cations, which exhibit stronger hydrogen bonding with fewer total hydrogen bonds, can limit the rotation of the A-site cation, inhibit the rocking motion of the [PbI6]4- octahedron, and thereby increase the rigidity of the inherently soft perovskite lattice, ultimately enhancing the stability of the material. Our findings elucidate the effect of hydrogen bonding in A-site cations on the lattice softness of perovskites, providing valuable theoretical insights for the design of more stable HOIPs.

Zipper-Like Dynamic Switching of Coordination Bonds Gives a Polar Bimetallic Halide Toward Self-Driven X-Ray Detection

Polar molecular crystals hold a promise for controlling bulk physical properties originated in their unique switchable polarity via structural transformation. However, the mechanisms for switching polarization are mainly limited to displacive and disorder-order phase transitions, which rarely involve the reconstruction of chemical bonds. Here, we have switched and tuned electric polarization in a bimetallic halide, (Neopentylammonium)4AgBiBr8 (1), as verified by light-excited pyroelectric effect. Most notably, its Ag-Br coordination bonds show a zipper-like dynamic switching behavior from the 'locked' to 'unlocked' state, namely, reconstruction of chemical bonds. Coupling with the dynamic ordering of organic cations, this bond-switching transition makes a contribution to switchable polarization of 1. As expected, its polarity creates pyroelectric effect for self-driven X-ray detection with high sensitivity (3.8×103 μC Gy-1 cm-2) and low limit of detection (4.8 nGy s-1). This work on the bond-switching mechanism provides an avenue to design polar molecular candidate for smart optoelectronic devices.

An Intermediate-Aided Perovskite Phase Purification for High-Performance Solar Cells

In recent years, perovskite solar cells (PSCs) have garnered considerable attention as a prime candidate for next-generation photovoltaic technology. Ensuring the structural stability of perovskites is crucial to the operational reliability of these devices. However, the nonphotoactive yellow phase (δ-FAPbI3) of formamidine (FA)-based perovskites is more favorable in thermodynamics, making it challenging to achieve pure α phase in crystallization. Herein, we introduce a language machine learning approach to analyze suitable additives to achieve the desired phase purification. By fast analyzing ∼106 abstracts in chemistry and materials science, our approach identifies aminoguanidine (AG) hydrochloride as a promising candidate for intermediate phase formation during nucleation. The experiments confirm that AG forms a novel one-dimensional intermediate phase (AGPbI3), which suppresses the solvent intermediate phase and δ-phase formation and promotes development of the α-phase. Consequently, the efficiency of the solar cells increased from 23.99 to 25.46%. The long-term thermal stability and photostability were significantly enhanced owing to the purified α-phase, maintaining 82% of the initial efficiency after 1056 h aging at 85 °C and 94.6% of the initial efficiency after 835 h of illumination in an N2 atmosphere, respectively. This strategy also enhanced the performance of flexible solar cells, increasing their efficiency from 21.24 to 22.86%. This work is designed to fast explore new intermediate phases in improving the efficiency and operation stability of thin-film solar cells.

Single-crystal CsPbBr3-based vertical cavity surface emitting laser

All-inorganic perovskite materials have been widely used in various devices, including lasers, light-emitting diodes (LEDs), and solar cells, due to their exceptional optoelectronic properties. Devices utilizing high-quality single crystals are anticipated to achieve significantly enhanced performance. In this work, we present a high-performance vertical cavity surface emitting laser (VCSEL) based on a single-crystal CsPbBr3 microplatelet, fabricated through a simple solution process and sandwiched between two distributed Bragg reflector (DBRs). The VCSEL demonstrated single-mode lasing at 542 nm, a low threshold of 5 µJ/cm2, and a high Q-factor of 2893. Additionally, time-resolved photoluminescence (TRPL) measurements using a streak camera revealed picosecond-scale lasing dynamics. This study offers a novel, to the best of our knowledge, approach for realizing laser devices using perovskite single-crystal microplatelets.

Evolution of Two-Dimensional Perovskite Films Under Atmospheric Exposure and Its Impact on Photovoltaic Performance

Two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) have garnered significant attention due to their enhanced stability compared with their three-dimensional counterparts. However, the power conversion efficiency (PCE) of 2D perovskite solar cells (2D-PSCs) remains lower than that of 3D-PSCs. Understanding the microstructural evolution of 2D perovskite films during fabrication is essential for improving their performance. This study demonstrates that exposing bare 2D perovskite films to the atmosphere during device fabrication can significantly enhance the PCE of 2D-PSCs. The performance improvement is primarily attributed to the gradual evaporation of organic butylammonium (BA+) spacer cations from the film as butylamine (BA) gas. This evaporation refines the film's composition and structure, leading to the spontaneous formation of larger-n phase RPPs, which exhibit superior carrier mobility. Consequently, the PCE of 2D-PSCs is enhanced. This work offers new insights into the structural evolution of 2D RPP films under ambient conditions and provides a feasible strategy for optimizing the performance of 2D-PSCs and other optoelectronic devices.

Schottky Defects Suppress Nonradiative Recombination in CH3NH3PbI3 through Charge Localization

Hybrid lead halide perovskites are promising materials for photovoltaic applications due to their exceptional optoelectronic properties. Here, we investigate the impact of Schottky defects─specifically PbI2(VPbI2) and CH3NH3I (VMAI) vacancies─on nonradiative recombination in CH3NH3PbI3 using time-dependent density functional theory and nonadiabatic (NA) molecular dynamics. Our results reveal that Schottky defects do not alter the fundamental bandgap or introduce trap states but instead distort the surrounding lattice, localizing the hole distribution. This reduces the spatial overlap of electron and hole wave functions, weakening NA coupling and increasing intensitieis of high-intensity phonon modes that accelerate dephasing. Consequently, nonradiative recombination lifetimes extend to 2.1 and 2.6 ns for VPbI2 and VMAI, respectively─over double that of pristine CH3NH3PbI3. This work demonstrates the potential of Schottky defects to enhance perovskite solar cell performance by suppressing nonradiative recombination.

Fast, Highly Stable, and Low-Bandgap 2D Halide Perovskite Photodetectors Based on Short-Chained Fluorinated Piperidinium as a Spacer

Ruddlesden-Popper (RP) two-dimensional (2D) halide perovskite (HP), with attractive structural and optoelectronic properties, has shown great potential in optoelectrical devices. However, the relatively wide bandgap (Eg) and stability, which cause inferior efficiency, prevent its feasibility from further applications. To tackle these issues, for the first time, a novel fluorine-containing piperidinium spacer, (3-HCF2CF2CH2OCH2-PPH+), abbreviated as (4FH-PPH+), has been designed for the stable and efficient n = 1 2D HPs. Its fluorophobicity can significantly enhance the noncovalent interactions between cations and [PbI6]4- octahedra. The observed Eg of the fluorinated (4FH-PPH)2PbI4 perovskite is found to be 2.22 eV, which is the lowest value among all fluorinated perovskites reported so far. Interestingly, this fluorinated film-based 2D perovskite photodetector (PD) exhibits the outstanding responsivity of 502 mA W-1, photodetectivity of 5.73 × 1010 cm Hz1/2 W-1, and impressive response/recovery time of 42/46 ms under 450 nm at 20 V. To the best of our knowledge, it is found for the first time that the 2D HP, with the fluorinated short-chained segment included into the organic spacer, shows remarkable stability for up to 49 days. These results strongly demonstrate the potential of the 2D fluorinated short-chained (4FH-PPH)2PbI4 HP with a low Eg as a promising candidate for next-generation optoelectronic devices.

Real-Time Structural Dynamics at the 3D/2D Perovskite Interface in CsPbBr3/PEA2PbBr4 Nano-heterostructures

Three-dimensional (3D) and two-dimensional (2D) perovskite hybrid systems, known for their exceptional optoelectronic properties and stability, are revolutionizing optoelectronic materials research. However, fundamental physics of the 3D/2D interfaces and their dynamics remain poorly understood. We use fluorescence microspectroscopy to study the photoluminescence (PL) properties of 3D/2D nano-heterostructures of CsPbBr3/PEA2PbBr4 formed by postgrowth self-assembly. The in situ PL spectra uncover the presence of new structural phases, quasi-2D PEA2Csn-1PbnBr3n+1 layers of varying n, at the 3D/2D interface and demonstrate their reversible restructuring under light excitation at room temperature. The restructuring is a result of layer-by-layer cation diffusion at the epitaxial interfaces, manifested as reversible spectral shifts occurring on a time scale of seconds. Such dynamics ultimately leads to optimized distribution of the quasi-2D phases in the system for efficient energy transfer from the 2D to the 3D phases. Our findings provide new insights into controlling energy flow in 3D/2D perovskites for next-generation optoelectronic devices.

Ultra-Sensitive Abscisic Acid Detection Using Gold and 4-Mercaptopyridine Perovskite-Engineered Robust Nanofibers (GLAMPER-NFs) under Surface-Enhanced Raman Spectroscopy

This study explores the development and application of gold and 4-mercaptopyridine (MPY) perovskite-engineered robust nanofibers (GLAMPER-NFs) for the ultrasensitive detection of Abscisic acid (ABA) under Raman spectroscopy, a crucial plant hormone. The GLAMPER-NFs composite material, consisting of MAPbCl3 nanofibers integrated with MPY-coated gold nanostructures, demonstrates exceptional performance in surface-enhanced Raman scattering (SERS)-based sensing. The study elucidates the material structure and properties through comprehensive characterization using scanning electron microscopy (SEM), UV-vis spectroscopy, fluorescence spectroscopy, Fourier transform infrared, and Raman spectroscopy. The SEM analysis reveals uniform nanofibers with diameter of 107.8 ± 3.06 nm, while spectroscopic studies confirm the successful synthesis and integration of the composite components. The SERS-based detection of ABA showcases remarkable sensitivity, with a linear detection range (R2 = 0.9957) spanning 7 orders of magnitude (10-14-10-7 M) and presented a limit of detection of 10-11 and enhancement factor of 1.08 × 107. This surpasses the performance of existing sensing platforms, demonstrating clear spectral responses even at femtomolar concentrations. The synergistic effects of the perovskite structure, plasmonic gold nanoparticles, and MPY linking molecules contributed exceptional sensing capabilities to the GLAMPER-NFs material. Fluorescence studies further corroborate the sensitivity and provide insights into the photophysical interactions between ABA and the composite material. This research advances the understanding of perovskite-based hybrid materials and presents a promising GLAMPER-NFs as SERS substrate for ultrasensitive plant hormone detection, with potential applications in agricultural monitoring and plant science research.

Advances in Metal Halide Perovskite Memristors: A Review from a Co-Design Perspective

The memristor has recently demonstrated considerable potential in the field of large-scale data information processing. Metal halide perovskites (MHPs) have emerged as the leading contenders for memristors due to their sensitive optoelectronic response, low power consumption, and ability to be prepared at low temperatures. This work presents a comprehensive enumeration and analysis of the predominant research advancements in mechanisms of resistance switch (RS) behaviors in MHPs-based memristors, along with a summary of useful characterization techniques. The impact of diverse optimization techniques on the functionality of perovskite memristors is examined and synthesized. Additionally, the potential of MHPs memristors in data processing, physical encryption devices, artificial synapses, and brain-like computing advancement of MHPs memristors is evaluated. This review can prove a valuable reference point for the future development of perovskite memristors applications. In conclusion, the current challenges and prospects of MHPs-based memristors are discussed in order to provide insights into potential avenues for the development of next-generation information storage technologies and biomimetic applications.

Mesoporous structured MoS2 as an electron transport layer for efficient and stable perovskite solar cells

Mesoporous structured electron transport layers (ETLs) in perovskite solar cells (PSCs) have an increased surface contact with the perovskite layer, enabling effective charge separation and extraction, and high-efficiency devices. However, the most widely used ETL material in PSCs, TiO2, requires a sintering temperature of more than 500 °C and undergoes photocatalytic reaction under incident illumination that limits operational stability. Recent efforts have focused on finding alternative ETL materials, such as SnO2. Here we propose mesoporous MoS2 as an efficient and stable ETL material. The MoS2 interlayer increases the surface contact area with the adjacent perovskite layer, improving charge transfer dynamics between the two layers. In addition, the matching between the MoS2 and the perovskite lattices facilitates preferential growth of perovskite crystals with low residual strain, compared with TiO2. Using mesoporous structured MoS2 as ETL, we obtain PSCs with 25.7% (0.08 cm2, certified 25.4%) and 22.4% (1.00 cm2) efficiencies. Under continuous illumination, our cell remains stable for more than 2,000 h, demonstrating improved photostability with respect to TiO2.

Steady-State Inverse-Temperature Crystallization Enabling Low Defect Perovskite Single Crystal and Efficient X-Ray Detectors

Organic-inorganic halide perovskite single crystals (SCs) have shown great potential in radiation detection applications due to their large radiation stopping power and excellent carrier transport properties. The spatial-confined inverse-temperature crystallization (ITC) method has been widely adopted to obtain large-sized SCs. However, they usually face the problems of uneven stress distribution and high defect density due to the limited crystal growth space and varied growth rate with the increase in temperature, making it difficult to fabricate highly sensitive and stable radiation detectors. In this study, the steady-state inverse-temperature crystallization method (SS-ITC) is developed to regulate the growth process of SCs by controlling the growth speed precisely to achieve a constant rate of growth as the temperature increases. Compared with the conventional ITC-grown samples, the lattice spacing of SCs prepared by the SS-ITC method is reduced by 1.2% due to tensile stress relaxation, resulting in a lower defect density of 7.93 × 109 cm-3 and a remarkable uniformity over a large area. As a result, the co-planar X-ray detectors based on these high-quality SCs exhibit a high sensitivity of 1.67 × 105 µC Gyair -1 cm-2, representing the best performing MAPbBr3-based X-ray detectors reported to date.

Wide-Bandgap Lead Halide Perovskites for Next-Generation Optoelectronics: Current Status and Future Prospects

Over the past decade, lead halide perovskites (LHPs), an emerging class of organic-inorganic ionic-type semiconductors, have drawn worldwide attention, which injects vitality into next-generation optoelectronics. Facilely tunable bandgap is one of the fascinating features of LHPs, enabling them to be widely used in various nano/microscale applications. Notably, wide-bandgap (WBG) LHPs have been considered as promising alternatives to traditional WBG semiconductors owing to the merits of low-cost, solution processability, superior optoelectronic characteristics, and flexibility, which could improve the cost-effectiveness and expand the application scenarios of traditional WBG devices. Herein, we provide a comprehensive review on the up-to-date research progress of WBG LHPs and their optoelectronics in terms of material fundamentals, optoelectronic devices, and their practical applications. First, the features and shortcomings of WBG LHPs are introduced to objectively display their natural features. Then we separately depict three typical optoelectronic devices based on WBG LHPs, including solar cells, light emitting diodes, and photodetectors. Sequentially, the inspiring applications of these optoelectronic devices in integrated functional systems are elaborately demonstrated. At last, the remaining challenges and future promise of WBG LHPs in optoelectronic applications are discussed. This review highlights the significance of WGB LHPs for promoting the development of the next-generation optoelectronics industry.

Efficient Circularly Polarized Electroluminescence Enabled by Low-Dimensional Bichiral Perovskite Nanocrystals

Chiral organic-inorganic hybrid perovskite nanocrystals have gained attention as promising materials for circularly polarized luminescence emission, owing to their high photoluminescence efficiency and superior charge-carrier mobility. However, achieving circularly polarized electroluminescence (CPEL) from mixed-phase perovskite nanocrystals remains a significant challenge. We present bichiral formamidinium lead bromide (FAPbBr3) nanocrystals that achieve room-temperature circularly polarized light-emitting diodes (LEDs) via a synergistic effect between a chiral interior spacer (methylbenzylamine cation, MBA+) and a chiral surface ligand (camphorsulfonic acid, CSA). The incorporation of MBA+ induces chiral crystal lattices, while CSA ligands, featuring sulfonate groups, effectively passivate defects, suppress exciton spin-flip, and enhance conductivity. The resulting circularly polarized LEDs exhibit an enhanced electroluminescence asymmetry factor (gEL) of ∼2 × 10-3, along with an external quantum efficiency (EQE) of 3.1%. These bichiral nanocrystals represent a significant advancement in luminescence efficiency and enantioselectivity, indicating their potential for next-generation chiroptoelectronic applications.

In-Situ Growth of One-Dimensional Blocking Layer to Mitigate Deficient Surface of Single-Crystal Perovskites

Organic-inorganic halide perovskite (OIHP) single crystals are promising for optoelectronic application, but their high surface trap density and associated ion migration hinders device performance and stability. Herein, a one-dimensional (1D) perovskites are designed and proposed as blocking layer at the crystal/electrode interface to mitigate the surface issues. As a model system, the interface ion migration in Cs0.05FA0.95PbI3 (FA=formamidinium) single-crystal perovskite solar cells (PSCs) is obviously suppressed, leading to increase of T90 lifetime from 260 to 1000 hours, five times better than previously reported results. Besides, the reduction of surface iodide ion vacancies inhibits nonradiative recombination, thus increasing the efficiency from 22.1 % to 23.8 %, which is one of the highest values for single-crystal PSCs. Since the deficient crystal surface is a universal and open issue, our strategy is instructive for optimizing diverse single-crystal perovskite devices.

Highly Durable Inverted Inorganic Perovskite/Organic Tandem Solar Cells Enabled by Multifunctional Additives

Inverted perovskite/organic tandem solar cells (P/O TSCs) suffer from poor long-term device stability due to halide segregation in organic-inorganic hybrid wide-band gap (WBG) perovskites, which hinders their practical deployment. Therefore, developing all-inorganic WBG perovskites for incorporation into P/O TSCs is a promising strategy because of their superior stability under continuous illumination. However, these inorganic WBG perovskites also face some critical issues, including rapid crystallization, phase instability, and large energy loss, etc. To tackle these issues, two multifunctional additives based on 9,10-anthraquinone-2-sulfonic acid (AQS) are developed to regulate the perovskite crystallization by mediating the intermediate phases and suppress the halide segregation through the redox-shuttle effect. By coupling with organic cations having the desirable functional groups and dipole moments, these additives can effectively passivate the defects and adjust the alignment of interface energy levels. Consequently, a record Voc approaching 1.3 V with high power conversion efficiency (PCE) of 18.59 % could be achieved in a 1.78 eV band gap single-junction inverted all-inorganic PSC. More importantly, the P/O TSC derived from this cell demonstrates a T90 lifetime of 1000 h under continuous operation, presenting the most stable P/O TSCs reported so far.

Ultrafast Carrier Diffusion in Perovskite Monocrystalline Films

Monocrystalline perovskite materials exhibit superior properties compared with polycrystalline perovskites, including lower defect density, minimal grain boundaries, and enhanced carrier mobility. Nevertheless, the preparation of large-area, high-quality single-crystal films, which could prove invaluable for photoelectronic applications, remains a significant challenge. The study of how their unique properties go beyond polycrystalline thin films is still missing. In our experiment, using polarization-selective transient absorption microscopy, we directly observed the spatial carrier transportation in methylammonium lead iodide (CH3NH3PbI3, MAPbI3) strip-shaped monocrystalline ultrathin films. Ultrafast carrier diffusion transportation was observed. The monocrystalline carrier diffusion coefficient D (∼22 cm2 s-1) is an order of magnitude higher than that in polycrystalline films. Anisotropic carrier diffusion of the MAPbI3 single crystal has been discovered. It is also discovered that the electrons and holes are of different anisotropy and diffusion speed. This ultralong carrier transport inside the monocrystalline film provides solid support for the development of perovskite based photoelectronic devices.

Structural Reconfiguration via Alternating Cation Intercalation of Chiral Hybrid Perovskites for Efficient Self-Driven X-ray Detection

2D hybrid perovskites (HPs) have great potential for high-performance X-ray detection due to their strong radiation absorption and flexible structure. However, there remains a need to explore avenues for enhancing their detection capabilities. Optimizing the detection performance through modification of their structural properties presents a promising strategy. Herein, we explore the impact of modifying the organic spacer layer in two distinct 2D layered HPs, namely, Ruddlesden-Popper (R-MPA)2PbBr4 (R-1, R-MPA = methylphenethylammonium) and (R-MPA)EAPbBr4 (EA = ethylammonium) (R-2) with alternating cation intercalation (ACI), on their X-ray detection performance. The insertion of EA into R-2 results in a flatter inorganic skeleton, narrower spacing, and higher density compared to R-1. This structural modification effectively optimizes carrier transport and X-ray absorption in R-2, enhancing the X-ray detection performance. Notably, R-2 exhibits a polar structure with intrinsic spontaneous polarization, contributing to a bulk photovoltaic of 0.4 V. This feature enables R-2 single-crystal detectors to achieve self-driven X-ray detection with a low detection limit of 82.5 nGy s-1 under a 0 V bias. This work highlights the efficacy of the ACI strategy in structural modification and its significant effect on X-ray detection properties, providing insights for the design and optimization of new materials.

Preparation Techniques for Perovskite Single Crystal Films: From Nucleation to Growth

Thickness-controllable perovskite single crystal films exhibit tremendous potential for various optoelectronic applications due to their capacity to leverage the relationship between diffusion length and absorption depth. However, the fabrication processes have suffered from difficulties in large-area production and poor quality with abundant surface defects. While post-treatments, such as passivation and polishing, can provide partial improvement in surface quality, the fundamental solution lies in the direct growth of high-quality single crystal films. In this work, we firstly summarize the basic principles of nucleation and growth phenomenon of crystalline materials. Advanced growth methods of perovskite single crystal films, including solution-based, vapor phase epitaxial growth, and top-down method, are discussed, highlighting their respective advantages and limitations. Finally, we also present future directions and the challenges that lie ahead in perovskite single crystal films.

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.

High-Sensitivity and Fast-Response Photomultiplication Type Photodetectors Based on Quasi-2D Perovskite Films for Weak-Light Detection

Photovoltaic photodiodes often face challenges in effectively harvesting electrical signals, especially when detecting faint light. In contrast, photomultiplication type photodetectors (PM-PDs) are renowned for their exceptional sensitivity to weak signals. Here, an advanced PM-PD is introduced based on quasi 2D Ruddlesden-Popper (Q-2D RP) perovskites, optimized for weak light detection at minimal operating voltages. The abundant traps at the Q-2D RP surface capture charge carriers, inducing a trap-assisted tunneling mechanism that leads to the photomultiplication (PM) effect. Deep-lying trap states within the Q-2D RP bulk accelerate charge carrier recombination, resulting in an outstanding rise/fall time of 1.14/1.72 µs for the PM-PDs. The PM-PD achieves a remarkable response level of up to 45.89 A W-1 and an extraordinary external quantum efficiency of 14400% at -1 V under an illumination of 1 µW cm- 2. The intrinsic high resistance of the Q-2D perovskite results in a low dark current, enabling an impressive detectivity of 4.23 × 1012 Jones based on noise current at -1 V. Furthermore, the practical application of PM-PDs has been demonstrated in weak-light, high-rate communication systems. These findings confirm the significant potential of PM-PDs based on Q-2D perovskites for weak light detection and suggest new directions for developing low-power, high-performance PM-PDs for future applications.

Nonstoichiometry Promoted Solventless Recrystallization of a Thick and Compact CsPbBr3 Film for Real-Time Dynamic X-Ray Imaging

Inorganic CsPbBr3 perovskite emerges as a promising material for the development of next-generation X-ray detectors. However, the formation of a high-quality thick film of CsPbBr3 has been challenging due to the low solubility of its precursor and its high melting point. To address this limitation, a nonstoichiometry approach is taken that allows lower-temperature crystallization of the target perovskite under the solventless condition. This approach capitalizes on the presence of excess volatile PbBr2 within the CsPbBr3 film, which induces melting point depression and promotes recrystallization of CsPbBr3 at a temperature much lower than its melting point concomitant with the escape of PbBr2. Consequently, thick and compact films of CsPbBr3 are formed with grains ten times larger than those in the pristine films. The resulting X-ray detector exhibits a remarkable sensitivity of 4.2 × 104 µC Gyair -1 cm-2 and a low detection limit of 136 nGyair s-1, along with exceptional operational stability. Notably, the CsPbBr3-based flat-panel detector achieves a high resolution of 0.65 lp pix-1 and the first demonstration of real-time dynamic X-ray imaging for perovskite-based devices.

Effect of Sb-Bi alloying on electron-hole recombination time of Cs2AgBiBr6 double perovskite

The double perovskite material Cs2AgBiBr6, characterized by high stability, low toxicity, and excellent optoelectronic properties, has emerged as a promising alternative to lead-based halide perovskites in photovoltaic applications. However, its photovoltaic conversion efficiency after integration into solar cell devices is less than 3%, significantly lower than that of traditional perovskite solar cells. While alloying methods have been widely applied in the design of photovoltaic materials, their specific role in modulating the lifetime of photo-generated charge carriers in double-perovskite solar cells remains inadequately explored. In this study, through nonadiabatic molecular dynamics (NAMD) simulations, the excited-state dynamics properties of Cs2AgBiBr6 and alloyed Cs2AgSb0.375Bi0.625Br6 samples were compared. The results revealed that the introduction of Sb ions into the double perovskite structure induces lattice deformation upon heating to 300 K, leading to distortion of Bi-Br bonds and enhanced valence band delocalization. Using the decoherence-induced surface hopping method, the capture and recombination processes of charge carriers between different states were simulated. It was suggested that hole lifetime serves as the primary limiting factor for carrier lifetime in Cs2AgBiBr6, and replacing 0.375 proportion of Bi with Sb can decelerate the hole capture rate, extending carrier lifetime by 3-4 times. This study demonstrates that alloying offers a viable approach to optimizing the optoelectronic performance of the Cs2AgBiBr6 perovskite, thereby advancing the application of double perovskite materials in the field of photovoltaics.

Two-Step Chemical Vapor Deposition for Fabrication of FAPbI3 Single-Crystal Microsheets with High Exciton Binding Energy

Hybrid perovskites exhibit highly efficient optoelectronic properties and find widespread applications in areas such as solar cells, light-emitting diodes, photodetectors, and lasers. Here, we report the innovative synthesis of formamidinium lead iodide (FAPbI3) single-crystal microsheets via a two-step chemical vapor deposition (CVD) method. The microsheets exhibit hexagonal and trapezoidal shapes, with hexagonal FAPbI3 growing parallel to the substrate and trapezoidal FAPbI3 growing perpendicular to the substrate. The dominant role of single-exciton recombination in the photoluminescence (PL) of these microsheets is observed, especially pronounced at low temperatures, attributed to the relatively large exciton binding energies of the samples. Calculations reveal exciton binding energies as high as 110.8 meV for hexagonal and 133.3 meV for trapezoidal FAPbI3 single-crystal microsheets, attributed to reduced rotational freedom of the formamidinium (FA) ions. Further investigation into low-temperature phase transitions indicates lower transition temperatures (around 100 K) for these microsheets, suggesting reduced FA ion rotational freedom and consequently higher exciton binding energies.

Outstanding Stability and Resistive Switching Performance through Octa-Amino-Polyhedral Oligomeric Silsesquioxane Modification in Flexible Perovskite Resistive Random-Access Memories

Resistive random access memory (RRAM) has emerged as a promising candidate for next-generation storage technologies due to its simple structure, high running speed, excellent durability, high integration density, and low power consumption. This paper focuses on the application of organic-inorganic hybrid perovskite (OIHP) materials in RRAM by introducing an innovative three-dimensional POPA modification strategy, which is realized by binding octa-amine-polyhedral oligomeric silsesquioxanes (8NH2-POSS) onto the side chains of poly(acrylic acid) (PAA), thereby enhancing the material's resilience under elevated temperatures and humidity conditions. POPA cross-links with perovskite grains at crystalline boundaries through multiple -NH3+ and -C═O chemical anchoring sites on its branch chain, enhancing the grain adhesion, optimizing the film quality, and improving the cage structure distribution at the perovskite grain boundaries. The experimental results demonstrate that the POPA-modified OIHP RRAM exhibits an excellent resistance switching performance, with an optimal ON/OFF ratio of 5.0 × 105 and a data retention time of 104 s. After 150 days of environmental exposure, the ON/OFF ratio remains at 1.0 × 105, indicating good stability. Furthermore, the POPA modification endows the perovskite film with considerable flexibility, maintaining stable resistance switching performance under various bending radii. This study provides a vital reference for flexible, high-performance, and long-lifespan perovskite memory devices.

Luminescence Patterns on Multimillimeter Single-Crystal MAPbBr3 Microplatelets via Thermal Ablation Effects

The single crystal distinguishes itself as the most outstanding representative of excellent optoelectronic performance among perovskite semiconductors due to its exceptional charge carrier properties, extraordinary optophysics, precise structural geometries, and superior material stabilities. However, it exhibits mediocre performance in light emission, which can be attributed to its excessive carrier diffusion lengths and extremely low recombination rates. To address this challenge, this study puts forward a controllable high-temperature annealing treatment strategy concentrating on multimillimeter-scale MAPbBr3 micrometer-thick platelet single crystals (MPSCs). Through the utilization of thermal ablation effects to convert the surface monocrystalline lattices into polycrystalline perovskite nanocrystals (PNCs) with a remarkably increased specific surface area, the fluorescence intensity arising from the rapid recombination of free carriers on the PNC surface is enhanced by 320 times compared to the pristine MPSC surface. These PNCs produced through surface annealing, with the characteristic of loose adhesion to surfaces, can be mechanically wiped away and regenerated in situ via reannealing the residual MAPbBr3 MPSCs, guaranteeing high intensity, durability, and standard geometric fluorescence. Moreover, by regulating the surface distributions of thermal ablation effects and carrying out embossing annealing treatment or laser direct writing, we can design and fabricate relatively complex, high-contrast (255×), and clearly resolved fluorescence patterns on MPSC surfaces.

Harnessing Cu2O-Doped 4-tert-Butylpyridine in Spiro-OMeTAD: Study on Improved Performance and Longevity of Perovskite Solar Cells

Recently, spiro-OMeTAD has gained prominence as a hole-transporting material (HTM) in high-performance perovskite solar cells (PSCs) due to its superior properties, cutting-edge HOMO state of energy, and solution processability. To promote hole mobility and conductivity, hygroscopic dopants and additives such as lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (TBP) are typically incorporated. However, these components can lead to aggregation and hydrolysis in ambient conditions, forming pinholes and voids in the films. In this study, we introduce Cu2O as a spiro-OMeTAD additive to reduce voids and improve the quality of films. Incorporating Cu2O alleviates TBP evaporation and provides a more consistent dispersion of Li-TFSI, decreasing the formation of pinholes and bubbles. As a result, additional anions are added to spiro-OMeTAD+ during the oxidation process, promoting the conductivity and hole mobility of the hole-transporting layer and thus boosting PSC performance. Thus, the power conversion efficiency (PCE) percentage of the Cu2O-modified HTM reaches 14.17%, surpassing that of the control HTM at 12.25%. Furthermore, the introduction of Cu2O protects the perovskite layer from water-induced deterioration, ensuring the stability of the PSCs. Our findings offer a promising approach to enhancing both the performance and stability of HTMs and PSCs.

Enabling Fast Photoresponse in Hybrid Perovskite/MoS2 Photodetectors by Separating Local Photocharge Generation and Recombination

Interfacing CH3NH3PbI3 (MAPbI3) with 2D van der Waals materials in lateral photodetectors can suppress the dark current and driving voltage, while the interlayer charge separation also renders slower charge dynamics. In this work, we show that more than one order of magnitude faster photoresponse time can be achieved in MAPbI3/MoS2 lateral photodetectors by locally separating the photocharge generation and recombination through a parallel channel of single-layer MAPbI3. Photocurrent (Iph) mapping reveals electron diffusion lengths of about 20 μm in single-layer MAPbI3 and 4 μm in the MAPbI3/MoS2 heterostructure. The illumination-power scaling of Iph and time-resolved photoluminescence studies point to the dominant roles of the heterostructure region in photogeneration and single-layer MAPbI3 in charge recombination. Our results shed new light on the material design that can concurrently enhance photoresponsivity, reduce driving voltage, and sustain high operation speed, paving the path for developing high-performance lateral photodetectors based on hybrid perovskites.

Ultralong Compositional Gradient Perovskite Nanowires Fabricated by Source-Limiting Anion Exchange

Anion exchange in halide perovskites offers prospective approaches to band gap engineering for miniaturized and integrated optoelectronic devices. However, the band engineering at the nanoscale is uncontrollable due to the rapid and random exchange nature in the liquid or gas phase. Here, we report a source-limiting mechanism in solid-state anion exchange between low-dimensional perovskites, which readily gives access to ultralong compositional gradient nanowires (NWs) with lengths of up to 100 μm. The exchanged NWs remain single-crystalline with intact morphology, while the halogen content exhibits an apparent gradient distribution, leading to a tapered energy band profile along a NW. In the dynamic study of anion behavior, it is shown that the spatial stoichiometric composition can be precisely tuned following Fick's law of diffusion. In addition, self-powered, spectrally resolved photodetectors incorporating multiple detection units within a single gradient NW are demonstrated. This work provides a feasible strategy for the realization of perovskite-based ultracompact optoelectronics, imaging sensors, and other miniaturized semiconductor devices.

Flexible Narrow Bandgap Sn-Pb Perovskite Solar Cells with 21% Efficiency Using N,N'-Carbonyldiimidazole Treatments

Flexible tin-lead (Sn-Pb) mixed perovskite solar cells (PSCs) are among the promising flexible photovoltaics, owing to the narrow bandgap (NBG) of Sn-Pb perovskites, flexible and wearable features, and their role as a critical component in all-perovskite tandem photovoltaics. However, the flexible Sn-Pb PSCs suffer from a low power conversion efficiency, no higher than 18.5%, along with limited stability. Herein, we reported an efficient and stable flexible NBG Sn-Pb PSC via an N,N'-carbonyldiimidazole (CDI) passivation strategy. CDI, with strong adsorption energy, preferentially binds to Sn2+ compared with oxygen (O2), thus effectively inhibiting the adsorption of O2 on perovskite surfaces. The transfer of electron density around Sn2+ dramatically decreased, thus suppressing Sn2+ oxidation. The CDI treatments endowed the Sn-Pb mixed films with fewer defects, improved crystallinity, better morphology, and matched energy-level alignment. The flexible Sn-Pb devices exhibited a high PCE of 21.02%. Besides, the devices showed enhanced stability and promoted flexibility. This work provides a pathway to visibly increase the efficiency and stability of the flexible Sn-Pb mixed photovoltaic cells.

Transient Exciton-Charge Interconversion in Single-Crystal Hybrid Perovskites

Ultrafast oscillatory transient absorption (TA) dynamics are observed in single crystals of hybrid organic-inorganic perovskite (CH3NH3)PbX3 with X = I, Br, Cl. High-density photoinduced charges, low binding energy of the excitons, efficient generation and high mobility of charges, and long diffusion length of both excitons and charges led to transient interconversion between excitons and charges with high efficiency, which is responsible for the oscillatory TA dynamics at re-excitation by the probe pulses. The pump pulses initiated a quasi-equilibrium scheme of coexisting excitons and charges with high densities, the probe pulse triggered a perturbation through interconversion between these two kinds of excited "particles," which was overlapped on the intrinsic exciton relaxation dynamics, producing an oscillatory modulation with time delay. This not only reveals important photoelectronic processes with determined time scales, but also supplies physics for applications of this group of materials.

Template-Assisted Growth of High-Quality α-Phase FAPbI3 Crystals in Perovskite Solar Cells Using Thiol-Functionalized MoS2 Nanosheets

Formamidinium lead iodide (FAPI) has gained attention for hybrid perovskite solar cell (PSC) applications due to its enhanced stability and narrow bandgap. However, a significant challenge remains in inducing and stabilizing the elusive perovskite "black phase"─photoactive cubic α-FAPI─as the relatively bulky FA+ cations tend to favor the thermodynamically stable nonphotoactive "yellow phase". In this study, we present a templated growth strategy employing thiol-functionalized MoS2 nanosheets as templates. By introduction of 3-mercaptopropionic acid (MPA)-functionalized MoS2 as a growth template, precise control over crystal formation was achieved, favoring the growth of high-quality α-FAPI films. These advanced templated films exhibited substantial improvements in charge transport properties, efficient light absorption, and enhanced charge extraction. As a result, the PSCs achieved a significantly enhanced power conversion efficiency (PCE) compared to the nontemplated control device, increasing from 20.6 to 22.5%. The MoS2-incorporated device also demonstrated excellent shelf stability, maintaining 91% of the initial PCE even after 1600 h of storage without device encapsulation.

Single-Crystal Perovskite for Solar Cell Applications

The advent of organic-inorganic hybrid metal halide perovskites has revolutionized photovoltaics, with polycrystalline thin films reaching over 26% efficiency and single-crystal perovskite solar cells (IC-PSCs) demonstrating ≈24%. However, research on single-crystal perovskites remains limited, leaving a crucial gap in optimizing solar energy conversion. Unlike polycrystalline films, which suffer from high defect densities and instability, single-crystal perovskites offer minimal defects, extended carrier lifetimes, and longer diffusion lengths, making them ideal for high-performance optoelectronics and essential for understanding perovskite material behavior. This review explores the advancements and potential of IC-PSCs, focusing on their superior efficiency, stability, and role in overcoming the limitations of polycrystalline counterparts. It covers device architecture, material composition, preparation methodologies, and recent breakthroughs, emphasizing the importance of further research to propel IC-PSCs toward commercial viability and future dominance in photovoltaic technology.

Solution-Processed Micro-Nanostructured Electron Transport Layer via Bubble-Assisted Assembly for Efficient Perovskite Photovoltaics

Organic-inorganic halide perovskite solar cells (PSCs) have attracted significant attention in photovoltaic research, owing to their superior optoelectronic properties and cost-effective manufacturing techniques. However, the unbalanced charge carrier diffusion length in perovskite materials leads to the recombination of photogenerated electrons and holes. The inefficient charge carrier collecting process severely affects the power conversion efficiency (PCE) of the PSCs. Herein, a solution-processed SnO2 array electron transport layer with precisely tunable micro-nanostructures is fabricated via a bubble-template-assisted approach, serving as both electron transport layers and scaffolds for the perovskite layer. Due to the optimized electron transporting pathway and enlarged perovskite grain size, the PSCs achieve a PCE of 25.35% (25.07% certificated PCE).

Interfacial Engineering for Controlled Crystal Mosaicity in Single-Crystalline Perovskite Films

Organic-inorganic hybrid perovskites have attracted significant attention for optoelectronic applications due to their efficient photoconversion properties. However, grain boundaries and irregular crystal orientations in polycrystalline films remain issues. This study presents a method for producing crystalline-orientation-controlled perovskite single-crystal films using retarded solvent evaporation. It is shown that single-crystal films, grown via inverse temperature crystallization within a confined space, exhibit enhanced optoelectronic property. Using interfacial polymer layer, this method produces high-quality perovskite single-crystalline films with varying crystal orientations. Density functional theory calculations confirm favorable adsorption energies for (110) surfaces with methylammonium iodide and PbI2 terminations on poly(3-hexylthiophene), and stronger adsorption for (224) surfaces with I and methylammonium terminations on polystyrene, influenced by repulsive forces between the thiophene group and the perovskite surface. The correlation between charge transport characteristics and perovskite single-crystalline properties highlights potential advancements in perovskite optoelectronics, improving device performance and reliability.

Hetero-Nucleation Induced [111]-Oriented Mixed Halide Perovskite for Stable Pure Red Light-Emitting Diodes

Mixed halide 3D perovskites are promising for bright, efficient, and wide-color gamut light-emitting diodes (LEDs) due to their excellent carrier transport, high luminescence, and easily tunable bandgaps. However, serious halide ion migration inside mixed halide 3D perovskite results in poor operational and spectral stability of the as-fabricated LEDs. Here, a hetero-nucleation crystallization strategy is reported to grow [111]-orientation preferred mixed halide 3D perovskite CsPbI3-xBrx thin films for stable pure red LEDs. This hetero-nucleation crystallization is enabled by the addition of phosphoric acid (H3PO4) complexation, which promotes the growth of small perovskite grains into large grains with uniform [111]-orientation. The obtained [111]-orientation preferred film exhibits excellent stability under light or electric field stimulus as revealed by model analysis and experimental results compared to that of [001]-orientation preferred film. Thus, based on the [111]-orientation preferred film, the fabricated LED exhibits an external quantum efficiency of 22.8%, a maximum brightness of 12 000 cd m-2, and a half-life time of 4080 min under 1.5 mA cm-2. More importantly, the electroluminescence spectrum of the device remains stable during the continuous operation of 4080 min, showcasing the significant spectral stability improvement enabled by the hetero-nucleation induced [111]-orientation strategy.

Monoammonium Modified Dion-Jacobson Quasi-2D Perovskite for High Efficiency Pure-Blue Light Emitting Diodes

Quasi-2D perovskites exhibit impressive optoelectronic properties and hold significant promise for future light-emitting devices. However, the efficiency of perovskite light-emitting diodes (PeLEDs) is seriously limited by defect-induced nonradiative recombination and imbalanced charge injection. Here, the defect states are passivated and charge injection balance is effectively improved by introducing the additive cyclohexanemethylammonium (CHMA) to bromide-based Dion-Jacobson (D-J) structure quasi-2D perovskite emission layer. CHMA participates in the crystallization of perovskite, leading to high quality film composed of compact and well-contacted grains with enhanced hole transportation and less defects. As a result, the corresponding PeLEDs exhibit stable pure blue emission at 466 nm with a maximum external quantum efficiency (EQE) of 9.22%. According to current knowledge, this represents the highest EQE reported for pure-blue PeLEDs based on quasi-2D bromide perovskite thin films. These findings underscore the potential of quasi-2D perovskites for advanced light-emitting devices and pave the way for further advancements in PeLEDs.

Bidirectional Inhibiting Interfacial Ion Migration in the Inorganic Hole Transport Layer for Perovskite Light-Emitting Diodes

Cu2ZnSnS4 (CZTS) is strong candidate for hole transport in perovskite light emitting diodes (PeLEDs) due to their cost-effectiveness, deep highest occupied molecular orbital (HOMO), and high hole mobility. However, its inherent polymetallic ions usually deteriorate the quality of the perovskite emission layer (EML) affecting device performance. In this study, a bidirectional anchoring strategy is proposed by adding 15-crown-5 ether (15C5) into CZTS hole transport layer (HTL) to suppress the reaction between HTL and EML. The 15C5 molecule interacts with Cu+, Zn2+ and Sn2+ cations forming host-guest complexes to impede their migration, which is elucidated by density functional theory calculations. Additionally, 15C5 can neutralize lead (Pb) defects by the abundant oxygen (O) and high electronegative cavities to reduce the nonradiative recombination of FAPbBr3 film. This bidirectional anchoring strategy effectively improves hole charge transport efficiency and suppresses nonradiative recombination at the HTL/EML interface. As a result, the optimized PeLEDs present a 3.5 times peak external quantum efficiency (EQE) from 3.12% to 11.08% and the maximum luminance (Lmax) increased from 24495 to 50584 cd m-2. These findings offer innovative insights into addressing the metal ion migration issue commonly observed in inorganic HTLs.

In Situ Crystal Growth and Fusing-Confined Engineering of Quasi-Monocrystalline Perovskite Thick Junctions for X-ray Detection and Imaging

Metal halide perovskites exhibit great promise for utilization in X-ray detection owing to their excellent optoelectronic properties and high X-ray attenuation capabilities. However, fabricating large-area thick films for high-performance perovskite X-ray detection remains challenging. This study develops an in situ crystal growth and fusing-confined approach to prepare high-quality, large-scale perovskite quasi-monocrystalline thick junctions. The perovskite crystals are grown in situ using a highly concentrated perovskite colloidal solution in 2-methoxyethanol. Introducing methylammonium chloride enhances grain reorganization during in situ growth and fusing-confined processes, effectively reducing grain boundaries and surface defects. This allows for the preparation of quasi-monocrystalline thick junctions of large grains (>100 μm) with high crystallinity, uniform orientation, and vertical penetration across the film thickness. Additionally, the carrier mobility and lifetime of the thick junctions are significantly enhanced. The optimized MAPbI3 detectors demonstrate an X-ray sensitivity of 2.6 × 104 μC Gyair-1 cm-2 and an exceptionally low detection limit of 1 nGyair s-1. Furthermore, inspired by a honeycomb structure, these detectors realize X-ray imaging in 64 × 64 pixels through a pixelated separation design, effectively reducing the charge-sharing effect. This study offers valuable insights into the preparation of large-scale perovskite quasi-monocrystalline thick junctions for highly sensitive X-ray detection and imaging applications.