High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization

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.

Overcoming the EQE × Li-Fi Frequency Constraint by Modulating the PbS CQDs Distribution in Perovskite Film

Advanced photodetectors are crucial for high-fidelity optical communication. However, the tradeoff between high external quantum efficiency (EQE) and high light fidelity (Li-Fi) frequency often limits data transmission accuracy and timeliness. Here, we report a photodetector consisting of lead sulfide (PbS) colloidal quantum dots (CQDs) with near-infrared responsiveness and perovskite frameworks responsible for the charge transport to overcome the EQE × Li-Fi constraint. Optimizing the PbS CQDs distribution and trap depth in the perovskite layer enhances charge injection, achieving a device gain of 11892% for 1200 nm photons and a response frequency of 24 kHz at -2 V. The device exhibits a record EQE × Li-Fi frequency product of 106 Hz. We have applied the detector to near-infrared optical communications at a data transfer rate of 2000 bits per second (2 kbps) to demonstrate the advances in high fidelity, the device retains over 98% of the original waveform information in its output.

Cathodoluminescence of MAPbCl3 Halide Perovskite Single Crystal

Chloride perovskites are semiconductors with a near-ultraviolet bandgap that are promising for applications in optoelectronics and photonics. One of the most studied representatives of this family is the methylammonium lead chloride MAPbCl3 (MA+ = CH3NH3+). Low-temperature luminescence spectroscopy of this material demonstrates a complex emission structure. In this work, we have studied the cathodoluminescecne of the MAPbCl3 halide perovskite single crystal at 70 K. Excitation by an electron beam was used to localize different emitters: excitons, defect-related states, and inclusions, previously assigned to the material itself. Exciton luminescence is observed from an undamaged sample, while the defect band is emitted from regions with dislocations, growth defects, and crystal damage. Defect formation under electron beam irradiation was studied. It was found that MAPbCl3 is resistant to irradiation, which supports the defect tolerance of halide perovskites and paves the way for their electron-beam modification for applications.

Realizing Color Transitions for Three Copper (I) Cluster Organic-Inorganic Hybrid Materials by Adjusting Reaction Conditions

Copper iodide organic-inorganic hybrid materials have been favored by many researchers in the field of solid-state lighting (SSL) due to their structural diversity and optical adjustability. In this paper, three isomeric copper iodide cluster hybrid materials, Cu4I6(L)2(1), Cu5I4.5Cl2.5(L)2(2) and Cu5I7(L)2) (3) (L=1-(4-methylpyrimidin-2-yl)-1,4-diazabicyclo[2.2.2]octan-1-ium), were achieved by adjusting the reaction conditions. The crystal color transit from green, yellow to orange and the internal quantum yield (IQY) increase from 57 %-88 %. All three complexes have good thermal stability, good solution processability, and high quantum yield. And origin and mechanism of luminescence of complexes were further studied. This study can provide ideas and theoretical basis for the regulation of cuprous iodide cluster luminescent materials.

Physical Properties of an Efficient MAPbBr3/GaAs Hybrid Heterostructure for Visible/Near-Infrared Detectors

Semiconductor photodetectors can work only in specific material-dependent light wavelength ranges, connected with the bandgaps and absorption capabilities of the utilized semiconductors. This limitation has driven the development of hybrid devices that exceed the capabilities of individual materials. In this study, for the first time, a hybrid heterojunction photodetector based on methylammonium lead bromide (MAPbBr3) polycrystalline film deposited on gallium arsenide (GaAs) was presented, along with comprehensive morphological, structural, optical, and photoelectrical investigations. The MAPbBr3/GaAs heterojunction photodetector exhibited wide spectral responsivity, from 540 to 900 nm. The fabrication steps of the prototype device, including a new preparation recipe for the MAPbBr3 solution and spinning, will be disclosed and discussed. It will be shown that extending the soaking time and refining the precursor solution's stoichiometry may enhance surface coverage, adhesion to the GaAs, and film uniformity, as well as provide a new way to integrate MAPbBr3 on GaAs. Compared to the pristine MAPbBr3, the enhanced structural purity of the perovskite on GaAs was confirmed by X-ray Diffraction (XRD) upon optimization compared to the conventional glass substrate. Scanning Electron Microscopy (SEM) revealed the formation of microcube-like structures on the top of an otherwise continuous MAPbBr3 polycrystalline film, with increased grain size and reduced grain boundary effects pointed by Energy-Dispersive Spectroscopy (EDS) and cathodoluminescence (CL). Enhanced absorption was demonstrated in the visible range and broadened photoluminescence (PL) emission at room temperature, with traces of reduction in the orthorhombic tilting revealed by temperature-dependent PL. A reduced average carrier lifetime was reduced to 13.8 ns, revealed by time-resolved PL (TRPL). The dark current was typically around 8.8 × 10-8 A. Broad photoresponsivity between 540 and 875 nm reached a maximum of 3 mA/W and 16 mA/W, corresponding to a detectivity of 6 × 1010 and 1 × 1011 Jones at -1 V and 50 V, respectively. In case of on/off measurements, the rise and fall times were 0.40 s and 0.61 s or 0.62 s and 0.89 s for illumination, with 500 nm or 875 nm photons, respectively. A long-term stability test at room temperature in air confirmed the optical and structural stability of the proposed hybrid structure. This work provides insights into the physical mechanisms of new hybrid junctions for high-performance photodetectors.

Single Crystal Sn-Based Halide Perovskites

Sn-based halide perovskites are expected to be the best replacement for toxic lead-based counterparts, owing to their similar ionic radii and the optimal band gap for use in solar cells, as well as their versatile use in light-emitting diodes and photodetection applications. Concerns, however, exist about their stability under ambient conditions, an issue that is exacerbated in polycrystalline films because grain boundaries present large concentrations of defects and act as entrance points for oxygen and water, causing Sn oxidation. A current thriving research area in perovskite materials is the fabrication of perovskite single crystals, promising improved optoelectronic properties due to excellent uniformity, reduced defects, and the absence of grain boundaries. This review summarizes the most recent advances in the fabrication of single crystal Sn-based halide perovskites, with emphasis on synthesis methods, compositional engineering, and formation mechanisms, followed by a discussion of various challenges and appropriate strategies for improving their performance in optoelectronic applications.

Unprecedented Richness of Temperature- and Pressure-Induced Polymorphism in 1D Lead Iodide Perovskite

Inherent features of metal halide perovskites are their softness, complex lattice dynamics, and phase transitions spectacularly tuning their structures and properties. While the structural transformations are well described and classified in 3D perovskites, their 1D analogs are much less understood. Herein, both temperature- and pressure-dependent structural evolutions of a 1D AcaPbI3 perovskitoid incorporating acetamidinium (Aca) cation are examined. The study reveals the existence of nine phases of δ-AcaPbI3, which present the most diverse polymorphic collection among known perovskite materials. Interestingly, temperature- and pressure-triggered phase transitions in the 1D perovskotoid exhibit fundamentally different natures: the thermal transformations are mainly associated with the collective translations of rigid polyanionic units and ordering/disordering dynamics of Aca cations, while the compression primarily affects inorganic polymer chains. Moreover, in the 1-D chains featuring the face-sharing connection mode of the PbI6 octahedra the Pb···Pb distances are significantly shortened compared to the corner-sharing 3D perovskite frameworks, hence operating in the van der Waals territory. Strikingly, a good correlation is found between the Pb···Pb distances and the pressure evolution of the bandgap values in the δ-AcaPbI3, indicating that in 1D perovskitoid structures, the contacts between Pb2+ ions are one of the critical parameters determining their properties.

Mapping Surface-Defect and Ions Migration in Mixed-Cation Perovskite Crystals

Single crystal perovskites have garnered significant attention as potential replacements for existing absorber layer materials. Despite the extensive investigations on their photoinduced charge-carriers dynamics, most of the time-resolved techniques focus on bulk properties, neglecting surface characteristic which plays a crucial role for their optoelectronic performance. Herein, 4D ultrafast scanning electron microscopy (4D-USEM) is utilized to probing the photogenerated carrier transport at the first few nanometers, alongside density functional theory (DFT) to track both defect centers and ions migration. Two compositions of mixed cation are investigated: FA0.6MA0.4PbI3 and FA0.4MA0.6PbI3, interestingly, the former displays a longer lifetime compared to the latter due the presence of a higher surface-defect centers. DFT calculations fully support that revealing samples with higher FA content have a lower energy barrier for iodide ions to migrate from the bulk to top layer, assisting in passivating surface vacancies, and a higher energy diffusion barrier to escape from surface to vacuum, resulting in fewer vacancies and longer-lived hole-electron pairs. These findings manifest the influence of cation selection on charge carrier transport and formation of defects, and emphasize the importance of understanding ion migrations role in controlling surface vacancies to assist engineering high-performance optoelectronic devices based on single crystal perovskites.

Self-Driving Laboratories for Chemistry and Materials Science

Self-driving laboratories (SDLs) promise an accelerated application of the scientific method. Through the automation of experimental workflows, along with autonomous experimental planning, SDLs hold the potential to greatly accelerate research in chemistry and materials discovery. This review provides an in-depth analysis of the state-of-the-art in SDL technology, its applications across various scientific disciplines, and the potential implications for research and industry. This review additionally provides an overview of the enabling technologies for SDLs, including their hardware, software, and integration with laboratory infrastructure. Most importantly, this review explores the diverse range of scientific domains where SDLs have made significant contributions, from drug discovery and materials science to genomics and chemistry. We provide a comprehensive review of existing real-world examples of SDLs, their different levels of automation, and the challenges and limitations associated with each domain.

Pattern-Matched Polymer Ligands Toward Near-Perfect Synergistic Passivation for High-Performance and Stable Br/Cl Mixed Perovskite Light-Emitting Diodes

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure-blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter-functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non-radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure-blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1 %) and record spectral and operational stabilities (~80 mins) in mixed-halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high-performance and stable pure-color PeLEDs towards display applications.

Single Crystal Ruddlesden-Popper and Dion-Jacobson Metal Halide Perovskites for Visible Light Photodetectors: Present Status and Future Perspectives

2D metal halide perovskites (MHPs), mainly the studied Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases, have gained enormous popularity as optoelectronic materials owing to their self-assembled multiple quantum well structures, tunable semiconducting properties, and improved structural stability compared to their bulk 3D counterparts. The performance of polycrystalline thin film devices is limited due to the formation of defects and trap states. However, as studied so far, single crystal-based devices can provide a better platform to improve device performance and investigate their fundamental properties more reliably. This Review provides the first comprehensive report on the emerging field of RP and DJ perovskite single crystals and their use in visible light photodetectors of varied device configurations. This Review structurally summarizes the 2D MHP single crystal growth methods and the parameters that control the crystal growth process. In addition, the characterization techniques used to investigate their crystal properties are discussed. The review further provides detailed insights into the working mechanisms as well as the operational performance of 2D MHP single crystal photodetector devices. In the end, to outline the present status and future directions, this Review provides a forward-looking perspective concerning the technical challenges and bottlenecks associated with the developing field of RP and DJ perovskite single crystals. Therefore, this timely review will provide a detailed overview of the fast-growing field of 2D MHP single crystal-based photodetectors as well as ignite new concepts for a wide range of applications including solar cells, photocatalysts, solar H2 production, neuromorphic bioelectronics, memory devices, etc.

Rapid Recovery of Degraded Perovskite Single-Crystal Radiation Detectors via Infrared Healing

Radiation detectors based on metal halide perovskite (MHP) single crystals (SCs) have exhibited exceptional sensitivity, low detection limit, and remarkable energy resolution. However, the operational stability issue still dramatically impedes their commercialization due to degradation induced by high-energy irradiation and large bias. Here, we propose an innovative infrared healing strategy to restore the devices that have undergone severe damage from both long-term biasing and X-ray irradiation. Compared to the slow and inefficient intrinsic self-healing process of MHPs, the infrared healing method demonstrates the capacity to achieve rapid recovery of the detection performance of the degraded devices within just 1 h. We reveal that the healing mechanism is mainly related to the reduction of the ion-migration activation energy in MHP SCs under infrared illumination, which promotes the back diffusion of the displaced ions to their original lattice positions and remedies defects. Finally, the healing effect is further confirmed through the gamma-ray spectroscopy acquisition with degraded MHP SCs, whose energy resolution at 59.5 keV of 241Am source is improved from 36% to 12% following infrared illumination. These results present infrared healing as a simple and economic method to extend the service life of MHP SC-based detectors.

What Matters for the Charge Transport of 2D Perovskites?

Compared to 3D perovskites, 2D perovskites exhibit excellent stability, structural diversity, and tunable bandgaps, making them highly promising for applications in solar cells, light-emitting diodes, and photodetectors. However, the trade-off for worse charge transport is a critical issue that needs to be addressed. This comprehensive review first discusses the structure of 3D and 2D metal halide perovskites, then summarizes the significant factors influencing charge transport in detail and provides a brief overview of the testing methods. Subsequently, various strategies to improve the charge transport are presented, including tuning A'-site organic spacer cations, A-site cations, B-site metal cations, and X-site halide ions. Finally, an outlook on the future development of improving the 2D perovskites' charge transport is discussed.

Printed On-Chip Perovskite Heterostructure Arrays for Optical Switchable Logic Gates

The use of optoelectronic devices for high-speed and low-power data transmission and computing is considered in the next-generation logic circuits. Heterostructures, which can generate and transmit photoresponse signals dealing with different input lights, are highly desirable for optoelectronic logic gates. Here, the printed on-chip perovskite heterostructures are demonstrated to achieve optical-controlled "AND" and "OR" optoelectronic logic gates. Perovskite heterostructures are printed with a high degree of control over composition, site, and crystallization. Different regions of the printed perovskite heterostructures exhibit distinguishable photoresponse to varied wavelengths of input lights, which can be utilized to achieve optical-controlled logic functions. Correspondingly, parallel operations of the two logic gates ("AND" and "OR") by way of choosing the output electrodes under the single perovskite heterostructure. Benefiting from the uniform crystallization and strict alignment of the printed perovskite heterostructures, the integrated 3 × 3 pixels all exhibit 100% logic operation accuracy. Finally, optical-controlled logic gates responding to multiwavelength light can be printed on the predesigned microelectrodes as the on-chip integrated circuits. This printing strategy allows for integrating heterostructure-based optical and electronic devices from a unit-scale device to a system-scale device.

Achieving Low-Dose Rate X-Ray Imaging Based on 2D/3D-Mixed Perovskite Films

X-ray detection and imaging are widely used in medical diagnosis, product inspection, security monitoring, etc. Large-scale polycrystalline perovskite thick films possess high potential for direct X-ray imaging. However, the notorious problems of baseline drift and high detection limit caused by ions migration are still remained. Here, ion migration is reduced by incorporating 2D perovskite into 3D perovskite, thereby increasing the ion activation energy. This approach hinders ion migration within the perovskite film, consequently suppressing baseline drift and reducing the lowest detection limit(LOD) of the device. As a result, the baseline drifting declines by 20 times and the LOD reduces to 21.1 nGy s-1, while the device maintains a satisfactory sensitivity of 5.6 × 103 µC Gy-1 cm-2. This work provides a new strategy to achieve low ion migration in large-scale X-ray detectors and may provide new thoughts for the application of mixed-dimension perovskite.

Large dynamic scissoring mode displacements coupled to band gap opening in the cubic phase of the methylammonium lead halide perovskites

Hybrid perovskites are a rapidly growing research area, having reached photovoltaic power conversion efficiencies of over 25%. There is a increasing consensus that the structures of these materials, and hence their electronic structures, cannot be understood purely from the time and space averaged crystal structures observable by conventional methods. We apply a symmetry-motivated analysis method to analyse x-ray pair distribution function data of the cubic phases of the hybrid perovskites MAPbX3(X= I, Br, Cl). We demonstrate that, even in the cubic phase, the local structure of the inorganic components of MAPbX3(X= I, Br, Cl), are dominated by scissoring type deformations of the PbX6octahedra. We find these modes to have a larger amplitude than equivalent distortions in theA-site deficient perovskite ScF3and demonstrate that they show a significant departure from the harmonic approximation. Calculations performed on an inorganic perovskite analogue, FrPbBr3, show that the large amplitudes of the scissoring modes are coupled to a dynamic opening of the electronic band gap. Finally, we use density functional theory calculations to show that the organic MA cations reorientate to accommodate the large amplitude scissoring modes.

Recent Advances in Fast-Decaying Metal Halide Perovskites Scintillators

Fast-decaying scintillators show subnanoseconds or nanoseconds lifetime and high time resolution, making them important in nuclear physics, medical diagnostics, scientific research, and other fields. Metal halide perovskites (MHPs) show great potential for scintillator applications owing to their easy synthesis procedure and attractive optical properties. However, MHPs scintillators still need further improvement in decay lifetime. To optimize the decay lifetime, great progress has been achieved recently. In this Perspective, we first summarize the structural characteristics of MHPs in various dimensions, which brings different exciton behaviors. Then, recent advances in designing fast-decaying MHPs according to different exciton behaviors have been concluded, focusing on the photophysical mechanisms to achieve fast-decaying lifetimes. These advancements in decay lifetimes could facilitate the MHPs scintillators in advanced applications, such as time-of-flight positron emission tomography (TOF-PET), photon-counting computed tomography (PCCT), etc. Finally, the challenges and future opportunities are discussed to provide a roadmap for designing novel fast-decaying MHPs scintillators.

Direct detection of minimum ionizing charged particles in a perovskite single crystal detector with single particle sensitivity

We report the detection of high energy electrons of some hundreds of MeV, crossing a methylammonium lead bromide single crystal device with sensitivity down to a single electron. In the device, the released energy is close to the energy released by minimum-ionizing particles. This is the first demonstration of a perovskite-based device that can be used for tracking and counting minimum-ionizing charged particles. The device reaches single particle sensitivity with a low bias voltage of 5 V. It also shows a good linearity of the response as a function of the number of electrons in a dynamic range of approximately 104.

Understanding of Defect Passivation Effect on Wide Band Gap p-i-n Perovskite Solar Cell

The wide band gap perovskite solar cells (PSCs) have attracted considerable attention for their great potential as top cells in high efficiency tandem cell application. However, the photovoltaic performance and stability of PSCs are constrained by nonradiative recombination, primarily stemming from defects within the bulk and at the interface of charge transport layer/perovskite and phase segregation. In this study, we systematically investigated the effects of 2-thiopheneethylammonium chloride (TEACl) on a wide band gap (∼1.67 eV) Cs0.15FA0.65MA0.20Pb(I0.8Br0.2)3 (CsFAMA) perovskite solar cell. TEACl was employed as a passivation layer between the perovskite and electron transport layer (ETL). With TEACl treatment, charged defects responsible for sub-band absorption and electrostatic potential fluctuation were effectively suppressed by the passivation of bulk defects. The incorporation of TEACl, which led to the formation of a TEA2PbX4/Perovskite (2D/3D) heterojunction, facilitated better band alignment and effective passivation of interface defects at the ETL/CsFAMA. Owing to these beneficial effects, the TEACl passivated PSC achieved a photo conversion efficiency (PCE) of 19.70% and retained ∼85% of initial PCE over ∼1900 h, surpassing the performance of the untreated PSC, which exhibited a PCE of 16.69% and retained only ∼37% of its initial PCE.

Recent advances in two-dimensional perovskite materials for light-emitting diodes

Light-emitting diodes (LEDs) are an indispensable part of our daily life. After being studied for a few decades, this field still has some room for improvement. In this regard, perovskite materials may take the leading role. In recent years, LEDs have become a most explored topic, owing to their various applications in photodetectors, solar cells, lasers, and so on. Noticeably, they exhibit significant characteristics in developing LEDs. The luminous efficiency of LEDs can be significantly enhanced by the combination of a poor illumination LED with low-dimensional perovskite. In 2014, the first perovskite-based LED was illuminated at room temperature. Furthermore, two-dimensional (2D) perovskites have enriched this field because of their optical and electronic properties and comparatively high stability in ambient conditions. Recent and relevant advancements in LEDs using low-dimensional perovskites including zero-dimensional to three-dimensional materials is reported. The major focus of this article is based on the 2D perovskites and their heterostructures (i.e., a combination of 2D perovskites with transition metal dichalcogenides, graphene, and hexagonal boron nitride). In comparison to 2D perovskites, heterostructures exhibit more potential for application in LEDs. State-of-the-art perovskite-based LEDs, current challenges, and prospects are also discussed.

Tuning Thermal Conductivity of Hybrid Perovskites through Halide Alloying

Tuning the thermal transport properties of hybrid halide perovskites is critical for their applications in optoelectronics, thermoelectrics, and photovoltaics. Here, an effective strategy is demonstrated to modulate the thermal transport property of hybrid perovskites by halide alloying. A highly tunable thermal conductivity of mixed-halide hybrid perovskites is achieved due to halide-alloying and structural distortion. The experimental measurements show that the room temperature thermal conductivity of MAPb(BrxI1- x)3 (x = 0─1) can be largely modulated from 0.27 ± 0.07 W m-1 K-1 (x = 0.5) to 0.47 ± 0.09 W m-1 K-1 (x = 1). Molecular dynamics simulations further demonstrate that the thermal conductivity reduction of hybrid halide perovskites results from the suppression of the mean free paths of the low-frequency acoustic and optical phonons. It is found that halide alloying and the induced structural distortion can largely increase the scatterings of optical and acoustic phonons, respectively. The confined diffusion of MA+ cations in the octahedra cage is found to act as an additional thermal transport channel in hybrid perovskites and can contribute around 10-20% of the total thermal conductivity. The findings provide a strategy for tailoring the thermal transport in hybrid halide perovskites, which may largely benefit their related applications.

Dion-Jacobson Type Lead-Free Double Perovskite with Ultra-Narrow Aromatic Interlayer Spacing for Highly Sensitive and Stable X-ray Detection

The low-toxic and environmentally friendly 2D lead-free perovskite has made significant progress in the exploration of "green" X-ray detectors. However, the gap in detection performance between them and their lead-based analogues remains a matter of concern that cannot be ignored. To reduce this gap, shortening the interlayer spacing to accelerate the migration and collection of X-ray carriers is a promising strategy. Herein, a Dion-Jacobson (DJ) lead-free double perovskite (4-AP)2AgBiBr8 (1, 4-AP = 4-amidinopyridine) with an ultra-narrow interlayer spacing of 3.0 Å, is constructed by utilizing π-conjugated aromatic spacers. Strikingly, the subsequent enhanced carrier transport and increased crystal density lead to X-ray detectors based on bulk single crystals of 1 with a high sensitivity of 1117.3 µC Gy-1 cm-2, superior to the vast majority of similar double perovskites. In particular, the tight connection of the inorganic layers by the divalent cations enhances structural rigidity and stability, further endowing 1 detector with ultralow dark current drift (3.06 × 10-8 nA cm-1 s-1 V-1, 80 V), excellent multiple cycles switching X-ray irradiation stability, as well as long-term environmental stability (maintains over 94% photoresponse after 90 days). This work brings lead-free double perovskites one step closer to realizing efficient practical green applications.

Cost-Effective Synthesis Method: Toxic Solvent-Free Approach for Stable Mixed Cation Perovskite Powders in Photovoltaic Applications

Organometallic lead halide perovskite powders have gained widespread attention for their intriguing properties, showcasing remarkable performance in the optoelectronic applications. In this study, formamidinium lead iodide (α-FAPbI3) microcrystals (MCs) is synthesized using retrograde solubility-driven crystallization. Additionally, methylammonium lead bromide (MAPbBr3) and cesium lead iodide (δ-CsPbI3) MCs are prepared through a sonochemical process, employing low-grade PbX2 (X = I & Br) precursors and an eco-friendly green solvent (γ-Valerolactone). The study encompasses an analysis of the structural, optical, thermal, elemental, and morphological characteristics of FAPbI3, MAPbBr3, and CsPbI3 MCs. Upon analysing phase stability, a phase transition in FAPbI3 MCs is observed after 2 weeks. To address this issue, a powder-based mechanochemical method is employed to synthesize stable mixed cation perovskite powders (MCPs) by subjecting FAPbI3 and MAPbBr3 MCs with varying concentrations of CsPbI3. Furthermore, the performance of mixed cation perovskites are examined using the Solar Cell Capacitance Simulator (SCAPS-1D) software. The impact of cesium incorporation in the photovoltaic characteristics is elucidated. All mixed cation absorbers exhibited optimal device performance with a thickness ranging between 0.6-1.5 µm. It's worth noting that the MCPs exhibit impressive ambient stability, remaining structurally intact and retaining their properties without significant degradation for 70 days of ambient exposure.

Ethanol purification enables high-quality α-phase FAPbI3 perovskite microcrystals for commercial photovoltaic applications

Reliable quality and sustainable processes must be developed for commodities to enter the commercial stage. For next-generation photovoltaic applications such as perovskite solar cells, it is essential to manufacture high-quality photoactive perovskites via eco-friendly processes. We demonstrate that ethanol, an ideal green solvent, can be applied to yield efficient alpha-phase FAPbI3 perovskite microcrystals.

Enhancement of Photodetector Characteristics by Zn-Porphyrin-Passivated MAPbBr3 Single Crystals

Perovskite single crystals have garnered significant interest in photodetector applications due to their exceptional optoelectronic properties. The outstanding crystalline quality of these materials further enhances their potential for efficient charge transport, making them promising candidates for next-generation photodetector devices. This article reports the synthesis of methyl ammonium lead bromide (MAPbBr3) perovskite single crystal (SC) via the inverse-temperature crystallization method. To further improve the performance of the photodetector, Zn-porphyrin (Zn-PP) was used as a passivating agent during the growth of SC. The optical characterization confirmed the enhancement of optical properties with Zn-PP passivation. On single-crystal surfaces, integrated photodetectors are fabricated, and their photodetection performances are evaluated. The results show that the single-crystalline photodetector passivated with 0.05% Zn-PP enhanced photodetection properties and rapid response speed. The photoelectric performance of the device, including its responsivity (R), external quantum efficiency (EQE), detective nature (D), and noise-equivalent power (NEP), showed an enhancement of the un-passivated devices. This development introduces a new potential to employ high-quality perovskite single-crystal-based devices for more advanced optoelectronics.

Reproducible high-quality perovskite single crystals by flux-regulated crystallization with a feedback loop

Controlling the linear growth rate, a critical factor that determines crystal quality, has been a challenge in solution-grown single crystals due to complex crystallization kinetics influenced by multiple parameters. Here we introduce a flux-regulated crystallization (FRC) method to directly monitor and feedback-control the linear growth rate, circumventing the need to control individual growth conditions. When applied to metal halide perovskites, the FRC maintains a stable linear growth rate for over 40 h in synthesizing CH3NH3PbBr3 and CsPbBr3 single crystals, achieving outstanding crystallinity (quantified by a full width at half-maximum of 15.3 arcsec in the X-ray rocking curve) in a centimetre-scale single crystal. The FRC is a reliable platform for synthesizing high-quality crystals essential for commercialization and systematically exploring crystallization conditions, maintaining a key parameter-the linear growth rate-constant, which enables a comprehensive understanding of the impact of other influencing factors.

Perovskite Single Crystals by Vacuum Evaporation Crystallization

Perovskite single crystals have attracted tremendous attention owing to their excellent optoelectronic properties and stability compared to typical multicrystal structures. However, the growth of high-quality perovskite single crystals (PSCs) generally relies on temperature gradients or the introduction of additives to promote crystal growth. In this study, a vacuum evaporation crystallization technique is developed that allows PSCs to be grown under extremely stable conditions at constant temperature and without requiring additives to promote crystal growth. The new method enables the growth of PSCs of unprecedented quality, that is, MAPbBr3 single crystals that exhibit an ultranarrow full width at half maximum of 0.00701°, which surpasses that of all previously reported values. In addition, the MAPbBr3 single crystals deliver exceptional optoelectronic performance, including a long carrier lifetime of 1006 ns, an ultralow trap-state density of 3.67 × 109 cm-3, and an ultrahigh carrier mobility of 185.86 cm2 V-1 s-1. This method is applicable to various types of PSCs, including organic-inorganic hybrids, fully inorganic structures, and low-dimensional structures.

Surface Engineering of Perovskite Single Crystals by Atomic Layer Deposited Tin Oxide for Optical Communication

Perovskite single crystals with excellent physical properties have broad prospects in the field of optoelectronics. However, the presence of dangling bonds, surface dislocations, and chemical impurities results in high surface defect density and sensitivity to humidity. Unfortunately, there are relatively few surface engineering strategies for single perovskite single crystals. We present a strategy utilizing atomic layer deposited SnOx to passivate surface defects in perovskite single crystals. The photodetector prepared based on the modified FAPbBr3 single crystals exhibits a low dark current of 1.89 × 10-9 A at a 5 V bias, close to 4 times lower with respect to the pristine device, a high detectivity of 2.3 × 1010 jones, and a fast response time of 27 μs. Moreover, the photodetectors feature long-term operational stability because the presence of a dense SnOx capping layer hinders the ingress of moisture and diffusion of ions. We further demonstrate the promise of our perovskite single crystal detectors for real-time subaqueous optical communication.

Improvement of Light Output of MAPbBr3 Single Crystal for Ultrafast and Bright Cryogenic Scintillator

The remarkable brightness and rapid scintillation observed in perovskite single crystals (SCs) become even more striking when they are operated at cryogenic temperatures. In this study, we present advancements in enhancing the scintillation properties of methylammonium lead bromide (MAPbBr3) SCs by optimizing the synthesis process. We successfully synthesized millimeter-sized MAPbBr3 SCs with bright green luminescence under UV light. However, both MAPbBr3 (Control-1M and THF-0.4M) SCs display notable radioluminescence exclusively at low temperatures due to their phase transitions. Notably, the THF-0.4M SCs exhibit a remarkable improvement in radioluminescence light yield, surpassing Control-1M SCs more than 2-fold. Further, THF-0.4M SCs demonstrate an ultrafast decay component of 0.52 ns (82.2%) and a slower component of 1.80 ns (17.8%), contributing to a rapid scintillation response at low temperatures. Therefore, the amalgamation of ultrafast decay components and improved radioluminescence light yield equips THF-0.4M SCs to emerge as a top choice for perovskite scintillators for X-ray timing applications.

Dimensionality Engineering of Organic-Inorganic Halide Perovskites for Next-Generation X-Ray Detector

The next-generation X-ray detectors require novel semiconductors with low material/fabrication cost, excellent X-ray response characteristics, and robust operational stability. The family of organic-inorganic hybrid perovskites (OIHPs) materials comprises a range of crystal configuration (i.e., films, wafers, and single crystals) with tunable chemical composition, structures, and electronic properties, which can perfectly meet the multiple-stringent requirements of high-energy radiation detection, making them emerging as the cutting-edge candidate for next-generation X-ray detectors. From the perspective of molecular dimensionality, the physicochemical and optoelectronic characteristics of OIHPs exhibit dimensionality-dependent behavior, and thus the structural dimensionality is recognized as the key factor that determines the device performance of OIHPs-based X-ray detectors. Nevertheless, the correlation between dimensionality of OIHPs and performance of their X-ray detectors is still short of theoretical guidance, which become a bottleneck that impedes the development of efficient X-ray detectors. In the review, the advanced studies on the dimensionality engineering of OIHPs are critically assessed in X-ray detection application, discussing the current understanding on the "dimensionality-property" relationship of OIHPs and the state-of-the-art progresses on the dimensionality-engineered OIHPs-based X-ray detector, and highlight the open challenges and future outlook of this field.

Perovskite Smart Windows: The Light Manipulator in Energy-Efficient Buildings

Uncontrolled sunlight entering through windows contributes to substantial heating and cooling demands in buildings, which leads to high energy consumption from the buildings. Recently, perovskite smart windows have emerged as innovative energy-saving technologies, offering the potential to adaptively control indoor solar heat gain through their impressive sunlight modulation capabilities. Moreover, harnessing the high-efficiency photovoltaic properties of perovskite materials, these windows have the potential to generate power, thereby realizing more advanced windows with combined light modulation and energy harvesting capabilities. This review summarizes the recent advancements in various chromic perovskite materials for achieving light modulation, focusing on both perovskite structures and underlying switching mechanisms. The discussion also encompasses device engineering strategies for smart windows, including the improvement of their optical and transition performance, durability, combination with electricity generation, and the evaluation of their energy-saving performance in building applications. Furthermore, the challenges and opportunities associated with perovskite smart windows are explicated, aimed at stimulating more academic research and advancing their pragmatic implementation for building energy efficiency and sustainability.

Can thick metal-halide perovskite single crystals have narrower optical bandgaps with near-infrared absorption?

Metal-halide perovskite (MHP) single crystals are emerging as potential competitors to their polycrystalline thin-film counterparts. These materials have shown the specific feature of extended absorbance towards the near-infrared (NIR) region, which promises further extension of their applications in the field of photovoltaics and photodetectors. This notable expansion of absorbance has been explained by the narrower effective optical bandgap of MHP single crystals promoted by their large thickness over several micrometres to millimetres. Herein, the attributes of the material's thickness and the measurement technique used to estimate these characteristics are discussed to elucidate the actual origins of the extended absorbance of MHP single crystals. Contrary to the general belief of the narrower bandgap of the MHP single crystals, we demonstrate that the extended NIR absorption in the MHP single crystals mainly originates from the combination of unique below-bandgap absorption of MHPs, the thickness of single crystals, and the technical limitation of the spectrophotometer, with the key attributes of (i) significantly large thickness of the MHP single crystals by suppressing the transmitted light and (ii) the detector's limited dynamic range. Combining the theoretical and experimental characterizations, we clarify the significant role of the large thickness together with the limited sensitivity of the detector in promoting the well-known red shift of the absorption onset of the MHP single crystals. The observations evidently show that in some special circumstances, the acquired absorption spectrum cannot reliably represent the optical bandgap of MHP materials. This highlights some misinterpretations in the estimation of the narrower optical bandgap of the MHP single crystals from conventional optical methods, while the optical bandgap is an inherent property independent of the thickness. The proposed broad applications of the MHP single crystals are dictated by their fascinating properties, and therefore, a deep insight into these features should be considered besides device applications, because much of their property-function relationships are still ambiguous and a subject of debate.

Optically Transparent Lead Halide Perovskite Polycrystalline Ceramics

We utilize room-temperature uniaxial pressing at applied loads achievable with low-cost, laboratory-scale presses to fabricate freestanding CH3NH3PbX3 (X- = Br-, Cl-) polycrystalline ceramics with millimeter thicknesses and optical transparency up to ∼70% in the infrared. As-fabricated perovskite ceramics can be produced with desirable form factors (i.e., size, shape, and thickness) and high-quality surfaces without any postprocessing (e.g., cutting or polishing). This method should be broadly applicable to a large swath of metal halide perovskites, not just the compositions shown here. In addition to fabrication, we analyze microstructure-optical property relationships through detailed experiments (e.g., transmission measurements, electron microscopy, X-ray tomography, optical profilometry, etc.) as well as modeling based on Mie theory. The optical, electrical, and mechanical properties of perovskite polycrystalline ceramics are benchmarked against those of single-crystalline analogues through spectroscopic ellipsometry, Hall measurements, and nanoindentation. Finally, γ-ray scintillation from a transparent MAPbBr3 ceramic is demonstrated under irradiation from a 137Cs source. From a broader perspective, scalable methods to produce freestanding polycrystalline lead halide perovskites with comparable properties to their single-crystal counterparts could enable key advancements in the commercial production of perovskite-based technologies (e.g., direct X-ray/γ-ray detectors, scintillators, and nonlinear optics).

Visualizing the Low-Energy Electronic Structure of Prototypical Hybrid Halide Perovskite through Clear Band Measurements

Organic-inorganic hybrid perovskites (OIHPs) are a promising class of materials that rival conventional semiconductors in various optoelectronic applications. However, unraveling the precise nature of their low-energy electronic structures continues to pose a significant challenge, primarily due to the absence of clear band measurements. Here, we investigate the low-energy electronic structure of CH3NH3PbI3 (MAPI3) using angle-resolved photoelectron spectroscopy combined with ab initio density functional theory. We successfully visualize the electronic structure of MAPI3 near the bulk valence band maximum by using a laboratory photon source (He Iα, 21.2 eV) at low temperature and explore its fundamental properties. The observed valence band exhibits a highly isotropic and parabolic band characterized by small effective masses of 0.20-0.21 me, without notable spectral signatures associated with a large polaron or the Rashba effect, subjects that are intensely debated in the literature. Concurrently, our spin-resolved measurements directly disprove the giant Rashba scenario previously suggested in a similar perovskite compound by establishing an upper limit for the Rashba parameter (αR) of 0.28 eV Å. Our results unveil the unusually complex nature of the low-energy electronic structure of OIHPs, thereby advancing our fundamental understanding of this important class of materials.

Using N-I-N Photodiodes Made of Perovskite Single Crystals for Low Noise Gamma-Ray Spectroscopy

Solution-processed lead halide perovskite single crystals (LHPSCs) are believed to have great potential in gamma-ray spectroscopy. However, obtaining low-defect LHPSCs from a solution at low temperatures is difficult compared to obtaining Bridgman single crystals such as CdTe and Si. Herein, noise from the intrinsic defects of LHPSCs is considered as the main problem hindering their gamma-ray detection performance. By isolating the defect-induced holes in LHPSCs via energy barriers, we show that NIN photodiodes based on three types of LHPSCs, i.e., MAPbBr3 (MA = CH3NH3), MAPbBr2.5Cl0.5, and cascade LHPSCs, have demonstrated good energy resolution in the range of 6.7-10.3% for 662 keV 137Cs gamma-ray photons. The noise for >10 mm3 devices is low, in the order of 340-860 electrons, and the electron collection efficiency reaches 23-43%. These results pave the way for obtaining low-cost, large, high energy-resolution gamma-ray detectors at room temperature (300 K).

Hole Mobility Enhancement in Benzo[1,2-b:4,5-b']Dithiophene-Based Conjugated Polymer Transistors through Directional Alignment, Perovskite Functionalization and Solid-State Electrolyte Gating

Tunability in electronic and optical properties has been intensively explored for developing conjugated polymers and their applications in organic and perovskite-based electronics. Particularly, the charge carrier mobility of conjugated polymer semiconductors has been deemed to be a vital figure-of-merit for achieving high-performance organic field-effect transistors (OFETs). In this study, the systematic hole carrier mobility improvement of benzo[1,2-b:4,5-b']dithiophene-based conjugated polymer in perovskite-functionalized organic transistors is demonstrated. In conventional OFETs with a poly(methyl methacrylate) (PMMA) gate dielectric, improvements in hole mobility of 0.019 cm2 V-1 s-1 are measured using an off-center spin-coating technique, which exceeds those of on-center counterparts (0.22 ± 0.07 × 10-2 cm2 V-1 s-1). Furthermore, the mobility drastically increases by adopting solid-state electrolyte gating, corresponding to 2.99 ± 1.03 cm2 V-1 s-1 for the control, and the best hole mobility is 8.03 cm2 V-1 s-1 (average ≈ 6.94 ± 0.59 cm2 V-1 s-1) for perovskite-functionalized OFETs with a high current on/off ratio of >106. The achieved device performance would be attributed to the enhanced film crystallinity and charge carrier density in the hybrid perovskite-functionalized organic transistor channel, resulting from the high-capacitance electrolyte dielectric.

Experimental and theoretical study of improved mesoporous titanium dioxide perovskite solar cell: The impact of modification with graphene oxide

The present study serves experimental and theoretical analyses in developing a hybrid advanced structure as a photolysis, which is based on electrospun Graphene Oxide-titanium dioxide (GO-TiO2) nanofibers as an electron transfer material (ETMs) functionalized for perovskite solar cell (PVSCs) with GO. The prepared ETMs were utilized for the synthesis of mixed-cation (FAPbI3)0.8(MAPbBr3)0.2. The effect of GO on TiO2 and their chemical structure, electronic and morphological characteristic were investigated and discussed. The elaborated device, namely ITO/Bl-TiO2/3 wt% GO-TiO2/(FAPbI3)0.8(MAPbBr3)0.2/spiro-MeTAD/Pt, displayed 20.14% disposition and conversion solar energy with fill factor (FF) of 1.176%, short circuit current density (Jsc) of 20.56 mA/cm2 and open circuit voltage (VOC) 0.912 V. The obtained efficiency is higher than titanium oxide (18.42%) and other prepared GO-TiO2 composite nanofibers based ETMs. The developed materials and device would facilitate elaboration of advanced functional materials and devices for energy storage applications.

High-Performance and Stable Perovskite X-ray Detection and Imaging Based on a Ti Cathode

High-energy radiation detectors with a good imaging resolution, fast response, and high sensitivity are desired to operate at a high electric field. However, strong ion migration triggered by electrochemical reactions at the interface between a high-potential electrode and an organic-inorganic hybrid perovskite limits the stability of radiation detectors under a high electric field. Herein, we demonstrate that such ion migration could be effectively suppressed in devices with a Ti cathode, even at a high electric field of 50 V mm-1, through time-of-flight secondary-ion mass spectrometry. X-ray photoelectron spectroscopy illustrates that Ti-N bonds formed at the interface of MAPbBr3 perovskite single crystals/Ti electrode effectively inhibit the electrochemical reaction in organic-inorganic hybrid perovskite devices and ultimately improve the operating stability under a high electric field. The device with a Ti electrode reaches a high sensitivity of 96 ± 1 mC Gyair-1 cm-2 and a low detection limit of 2.8 ± 0.3 nGy s-1 under hard X-ray energy.

Perovskite Single Crystals with Self-Cleaning Surface for Efficient Photovoltaics

Metal halide perovskite single crystals are promising for diverse optoelectronic applications. As a universal issue of solution-grown perovskite single crystals, surface contamination causes adverse effect on material properties and device performance. Herein, learning from the self-cleaning effect of lotus leaf, we address the surface contamination issue by introducing an amphiphilic long-chain organic amine into the perovskite crystal growth solution. Self-assembly of CTAC provides a hydrophobic crystal surface, inducing spontaneous removal of residual growth solution, which results in clean surface and better optoelectronic properties of perovskite single crystals. An impressive efficiency of 23.4 % is obtained, setting a new record for FAx MA1-x PbI3 single-crystal perovskite solar cells (PSCs). Moreover, our strategy also applies to perovskite single crystals with different morphology and composition, which may contribute to improvement of other single-crystal perovskite optoelectronic devices.

Flexophotovoltaic Effect and Above-Band-Gap Photovoltage Induced by Strain Gradients in Halide Perovskites

We have measured the flexophotovoltaic effect of single crystals of halide perovskites MAPbBr_{3} and MAPbI_{3}, as well as the benchmark oxide perovskite SrTiO_{3}. For halide perovskites, the flexophotovoltaic effect is found to be orders of magnitude larger than for SrTiO_{3}, and indeed large enough to induce photovoltages bigger than the band gap. Moreover, we find that in MAPbI_{3} the flexophotovoltaic effect is additional to a native bulk photovoltaic response that is switchable and ferroelectric-like. The results suggest that strain gradient engineering can be a powerful tool to modify the photovoltaic output even in already well-established photovoltaic materials.

Perovskite materials in X-ray detection and imaging: recent progress, challenges, and future prospects

Perovskite materials have attracted significant attention as innovative and efficient X-ray detectors owing to their unique properties compared to traditional X-ray detectors. Herein, chronologically, we present an in-depth analysis of X-ray detection technologies employing organic-inorganic hybrids (OIHs), all-inorganic and lead-free perovskite material-based single crystals (SCs), thin/thick films and wafers. Particularly, this review systematically scrutinizes the advancement of the diverse synthesis methods, structural modifications, and device architectures exploited to enhance the radiation sensing performance. In addition, a critical analysis of the crucial factors affecting the performance of the devices is also provided. Our findings revealed that the improvement from single crystallization techniques dominated the film and wafer growth techniques. The probable reason for this is that SC-based devices display a lower trap density, higher resistivity, large carrier mobility and lifetime compared to film- and wafer-based devices. Ultimately, devices with SCs showed outstanding sensitivity and the lowest detectable dose rate (LDDR). These results are superior to some traditional X-ray detectors such as amorphous selenium and CZT. In addition, the limited performance of film-based devices is attributed to the defect formation in the bulk film, surfaces, and grain boundaries. However, wafer-based devices showed the worst performance because of the formation of voids, which impede the movement of charge carriers. We also observed that by performing structural modification, various research groups achieved high-performance devices together with stability. Finally, by fusing the findings from diverse research works, we provide a valuable resource for researchers in the field of X-ray detection, imaging and materials science. Ultimately, this review will serve as a roadmap for directing the difficulties associated with perovskite materials in X-ray detection and imaging, proposing insights into the recent status, challenges, and promising directions for future research.

Large-n quasi-phase-pure two-dimensional halide perovskite: A toolbox from materials to devices

Despite their excellent environmental stability, low defect density, and high carrier mobility, large-n quasi-two-dimensional halide perovskites (quasi-2DHPs) feature a limited application scope because of the formation of self-assembled multiple quantum wells (QWs) due to the similar thermal stabilities of large-n phases. However, large-n quasi-phase-pure 2DHPs (quasi-PP-2DHPs) can solve this problem perfectly. This review discusses the structures, formation mechanisms, and photoelectronic and physical properties of quasi-PP-2DHPs, summarises the corresponding single crystals, thin films, and heterojunction preparation methods, and presents the related advances. Moreover, we focus on applications of large-n quasi-PP-2DHPs in solar cells, photodetectors, lasers, light-emitting diodes, and field-effect transistors, discuss the challenges and prospects of these emerging photoelectronic materials, and review the potential technological developments in this area.

Bicyclopentadithiophene-Based Organic Semiconductor for Stable and High-Performance Perovskite Solar Cells Exceeding 22

Well-performing organic-inorganic halide perovskites are susceptible to poor efficiency and instability due to their various defects at the interphases, grain boundaries (GBs), and surfaces. In this study, an in situ method is utilized for effectively passivating the under-coordinated Pb2+ defects of perovskite with new non-fullerene acceptors (NFAs) (INXBCDT; X = H, Cl, and Br) through their carbonyl and cyano functional groups during the antisolvent dripping process. It reveals that the bicyclopentadithiophene (BCDT) core with highly electron-withdrawing end-capping groups passivates GBs and boosts perovskite grain growth. This effective defect passivation decreases the trap density to increase the carrier recombination lifetime of the perovskite film. As a result, bromo-substituted dicyanomethylene indanone (INBr)-end-capped BCDT (INBrBCDT-b8; 3a)-passivated devices exhibit the highest power conversion efficiency (PCE) of 22.20% (vs those of 18.09% obtained for perovskite films without passivation) upon an optimized film preparation process. Note that devices treated with more soluble 2-ethylhexyl-substituted compounds (1a, 2a, and 3a) exhibit higher PCE than those treated with less soluble octyl-substituted compounds (1b, 2b, and 3b). It is also worth noting that BCDT is a cost-effective six-ring core that is easier to synthesize with a higher yield and therefore much cheaper than those with highly fused-ring cores. In addition, a long-term stability test in a glovebox for 1500 h reveals that the perovskite solar cells (PSCs) based on a perovskite absorber treated with compound 3a maintain ∼90% of their initial PCE. This is the first example of the simplest high-conjugation additive for perovskite film to achieve a PCE greater than 22% of the corresponding lead-based PSCs.

Highly Crystalized MAPbX3 Perovskite Triangular Nanowire Arrays for Optoelectronic Applications

Here, a facile fabrication approach for the high-quality 1D perovskite triangular nanowire (TNW) array synthesis through space-confined effect is reported. A soft stamp containing 1D triangular linear array pattern is used to confine the MAPbX3 solution and to guide the growth of the nanowires along the prescribed direction with good crystallinity. The further constructed photodetectors based on the obtained MAPbI3 TNWs exhibit superior photoresponse properties with a responsivity of (125.2 ± 2.5) A W-1 and detectivity of (2.8 ± 0.8) × 1013 Jones at the wavelength of 650 nm. This excellent performance is attributed to the highly crystalline TNW with optical anisotropy and a small asymptotic height, which reduces the probability of the photon reflection and promotes the carrier transport. More interestingly, the increased surface area of the triangular device can present superior flexibility after a couple of thousands of bending cycles. Furthermore, by fabricating 7 × 7 photodetector arrays, the potential image sensor application is demonstrated. The perovskite nanowire fabrication approach is scalable and compatible with current semiconductor manufacturing, which indicates their great potential in broad applications.

Defect passivation in methylammonium/bromine free inverted perovskite solar cells using charge-modulated molecular bonding

Molecular passivation is a prominent approach for improving the performance and operation stability of halide perovskite solar cells (HPSCs). Herein, we reveal discernible effects of diammonium molecules with either an aryl or alkyl core onto Methylammonium-free perovskites. Piperazine dihydriodide (PZDI), characterized by an alkyl core-electron cloud-rich-NH terminal, proves effective in mitigating surface and bulk defects and modifying surface chemistry or interfacial energy band, ultimately leading to improved carrier extraction. Benefiting from superior PZDI passivation, the device achieves an impressive efficiency of 23.17% (area ~1 cm2) (low open circuit voltage deficit ~0.327 V) along with superior operational stability. We achieve a certified efficiency of ~21.47% (area ~1.024 cm2) for inverted HPSC. PZDI strengthens adhesion to the perovskite via -NH2I and Mulliken charge distribution. Device analysis corroborates that stronger bonding interaction attenuates the defect densities and suppresses ion migration. This work underscores the crucial role of bifunctional molecules with stronger surface adsorption in defect mitigation, setting the stage for the design of charge-regulated molecular passivation to enhance the performance and stability of HPSC.

Real-Time Tracking of Hot Carrier Injection at the Interface of FAPbBr3 Perovskite Using Femtosecond Mid-IR Spectroscopy

One of the most effective approaches to optimizing the performance of perovskite solar cells is to fully understand the ultrafast carrier dynamics at the interfaces between absorber and transporting layers at both the molecular and atomic levels. Here, the injection dynamics of hot and relaxed charge carriers at the interface between the hybrid perovskite, formamidinium lead bromide (FAPbBr3), and the organic electron acceptor, IEICO-4F, are investigated and deciphered by using femtosecond (fs) mid-infrared (IR), transient absorption (TA), and fluorescence spectroscopies. The visible femtosecond-TA measurements reveal the generation of hot carriers and their transition to free carriers in the pure FAPbBr3 film. Meanwhile, the efficient extraction of hot carriers in the mixed FAPbBr3/IEICO-4F film is clearly evidenced by the complete disappearance of their spectral signature. More specifically, the time-resolved results reveal that hot carriers are injected from FAPbBr3 to IEICO-4F within 150 fs, while the transfer time for the relaxed carriers is about 205 fs. The time-resolved mid-IR experiments also demonstrate the ultrafast formation of two peaks at 2115 and 2233 cm-1, which can be attributed to the C≡N symmetrical and asymmetrical vibrational modes of anionic IEICO-4F, thus providing crystal clear evidence for the electron transfer process between the donor and acceptor units. Moreover, photoluminescence (PL) lifetime measurements reveal an approximately 10-fold decrease in the donor lifetime in the presence of IEICO-4F, thereby confirming the efficient electron injection from the perovskite to the acceptor unit. In addition, the efficient electron injection at the FAPbBr3/IEICO-4F interface and its impact on the C≡N bond character are experimentally evidenced and align with density functional theory (DFT) calculations. This work offers new insights into the electron injection process at the FAPbBr3/IEICO-4F interface, which is crucial for developing efficient optoelectronic devices.

Growth methods' effect on the physical characteristics of CsPbBr3 single crystal

This study offers an extensive exploration into approaches for cultivating CsPbBr3 SCs using inverse temperature crystallization (ITC), with a specific focus on seed-induced (method (1)) and nucleation-mediated (method (2)) growth techniques. Our findings reveal that leveraging seed-assisted growth at lower temperatures yields noteworthy enhancements in the material's optical and electrical behaviors, outperforming the outcomes achieved through nucleation-driven growth. Concretely, through the employment of the space charge limited current (SCLC) technique, an evident contrast emerges in the trap-populated threshold voltage between the seed-facilitated crystal (SC1) (measuring 0.309 V) and its nucleation-facilitated counterpart (SC2) (measuring 1.513 V), consequently giving rise to discernable dissimilarities in trap density assessments. Evidence from temperature-dependent analysis of space charge limited currents substantiates these findings, revealing trap density values of 8.81 × 109 cm-3 for SC1, juxtaposed with 2.08 × 1010 cm-3 for SC2. Additionally, the SC1 displays a notably diminished trap energy level. Furthermore, the investigation underscores the affirmative influence of method (1) at lower temperatures on the optical and crystalline characteristics of the substance. This effect is evidenced by enhanced photoluminescence (PL) reactions and reduced lattice strain (Ls), as determined through X-ray diffraction (XRD) techniques. Moreover, the research establishes the substantial impact of this enhanced crystallization technique on the photodetector (PD) attributes of the crystal. This effect induces elevated levels of detectivity and responsivity for method (1).

Surface Microstructure Engineering in MAPbBr3 Microsheets for Performance-Enhanced Photodetectors

Metal halide-perovskite-based photodetectors have recently emerged as a class of promising optoelectronic devices in various fields. Meanwhile, nano/microstructuring perovskite-based photodetectors are a facile integration with complementary metal-oxide semiconductors for miniaturized imaging systems. However, there are still challenges to be overcome in reducing the losses caused by light reflection on the surface of microstructural perovskites. In this work, surface microstructure engineering is employed in MAPbBr3 microsheets for reducing light reflection and improving light absorption, resulting in high-performance perovskite photodetectors. MAPbBr3 microsheets, which possess different surface morphologies of flat, upright hemisphere arrays and inverted hemisphere arrays (IHAs), are fabricated by a simple microstructure template-assisted space confinement process. The light absorption capacity of IHA MAPbBr3 is significantly higher than that of the other two structures. Hence, IHA photodetectors with excellent figures of merit, including low dark current, decent responsivity, and fast speed, are achieved. Furthermore, the noise of the IHA photodetectors is only ∼10-13 A/H z , which results in the superior sensitivity for weak light detection with a specific detectivity up to 1011 Jones. Our results demonstrate that surface engineering is a simple, low-cost, yet effective approach to improve the performance of nano-/micro-optoelectronic devices.

Zero-Dimensional Tellurium-Based Organic-Inorganic Hybrid Halide Single Crystal with Yellow-Orange Emission from Self-Trapped Excitons

Organic-inorganic hybrid halides and their analogs that exhibit efficient broadband emission from self-trapped excitons (STEs) offers an unique pathway towards realization of highly efficient white light sources for lighting applications. An appropriate dilution of ns2 ions into a halide host is essential to produce auxiliary emissions. However, the realization of ns2 cation-based halides phosphor that can be excited by blue light-emitting diode (LED) is still rarely reported. In this study, a zero-dimensional Te-based single crystal (C8H20N)2TeCl6 was synthesized, which exhibits a yellow-orange emission centered at 600 nm with a full width at half maximum of 130 nm upon excitation under 437 nm. Intense electron-phonon coupling was confirmed in the (C8H20N)2TeCl6 single crystal and the light emitting mechanism is comprehensively discussed. The results of this study are pertinent to the emissive mechanism of Te-based hybrid halides and can facilitate discovery of unidentified metal halides with broadband excitation features.

Deciphering Reaction Products in Formamidine-Based Perovskites with Methylammonium Chloride Additive

The fabrication of formamidinium lead iodide (FAPbI3) perovskite solar cells (PSCs) involves the addition of methylammonium chloride (MACl) to promote low-temperature α-phase formation and grain growth. However, as the added MACl deprotonates and volatilizes into methylamine (MA0) and HCl for removal, MA0 can chemically interact with formamidinium (FA+), forming methyl formamidinium (MFA+) as a byproduct. Despite its significance, the chemical interactions among FAPbI3 perovskites, MACl additives, and their byproducts remain poorly understood. Our findings reveal that the FA+ and MA0 reaction primarily yields a mixture of cis/trans-N-methyl formamidinium iodide (MFAI) isomers, with cis-MFAI prevailing as the dominant species. Moreover, MFAI subsequently reacts with PbI2 to yield fully formed cis-MFAPbI3 2H-phase perovskite. We elucidated the effects of MFAI on the crystal growth, phase stability, and band gap of formamidine-based perovskites through the growth of single crystals. This research offers valuable insights into the role of these byproducts in influencing the efficiency and long-term stability of future PSCs.