Multi-Axial Self-Driven X-Ray Detection by a Two-Dimensional Biaxial Hybrid Organic-Inorganic Perovskite Ferroelectric

Metal halide perovskite ferroelectrics combining spontaneous polarization and excellent semiconducting properties is an ideal platform for enabling self-driven X-ray detection. However, achievements to date have been only based on uniaxiality, which increases the complexity of device fabrication. Multi-axial ferroelectric materials have multiple equivalent polarization directions, making them potentially amenable to multi-axial self-driven X-ray detection, but the report on these types of materials is still a huge blank. Herein, a high-quality (BA)2(EA)2Pb3I10 (1) biaxial ferroelectric single crystal was successfully grown, which exhibited significant spontaneous polarization along the c-axis and b-axis. Under X-ray irradiation, bulk photovoltaic effect (BPVE) was exhibited along both the c-axis and b-axis, with open circuit voltages (Voc) of 0.23 V and 0.22 V, respectively. Then, the BPVE revealed along the inversion of polarized direction with the polarized electric fields. Intriguingly, due to the BPVE of 1, 1 achieved multi-axial self-driven X-ray detection for the first time (c-axis and b-axis) with relatively high sensitivities and ultralow detection limits (17.2 nGyair s-1 and 19.4 nGyair s-1, respectively). This work provides a reference for the subsequent use of multi-axial ferroelectricity for multi-axial self-driven optoelectronic detection.

Crystalline engineering of FAPbI3 via pyrrolidinium ionic liquid for stable perovskite solar cells with 21.72% efficiency

Improving the crystallinity of formamidinium triiodide (FAPbI3) perovskite layer is one of the most effective approaches to increase the photovoltaic performance and stability of FAPbI3-based solar cells (FSCs). In the current study, FAPbI3 layers were fabricated through a sequential deposition method. The morphology and crystalline properties of the FAPbI3 layers were modified by controlling the lead iodide (PbI2) precursor by adding pyrrolidinium (Pyr) material into the PbI2 layer and modulating the FAPbI3 crystallization. The Pyr contributed to obtain (001)-preferred FAPbI3 orientation with no yellow photo-inactive phase. Subsequently, it reduced the unreacted PbI2 phase in the perovskite layer and suppressed the defect density, resulting in extended carrier lifetimes and improved ambient air and illumination stabilities. The Pyr-mediated FSCs recorded a champion efficiency of 21.72%, which is higher than that of control FSCs with a maximum efficiency of 19.08%. The developed Pyr-mediated method offers a practical and effective approach to fabricate stable and efficient FSCs.

Recent Progress on Perovskite Materials for VOC Gas Sensing

Volatile organic compound (VOC) gases are highly hazardous to human health, and their presence in the human breath plays an indispensable role for the early diagnosis of various diseases (cancer, renal failure, etc.). In recent times, perovskite materials have shown notable performance in the detection of VOC gases with high accuracy, fast response, recovery time, selectivity, and sensitivity, owing to their unique crystallographic structures and excellent optoelectronic properties. In this Review, we look at recent reports on perovskite-based sensors and their sensing performance toward VOC gases. Here, we focus on the sensing mechanisms of two types of perovskite materials, metal halide and metal oxide perovskites, and explain the differences in their crystal structures. We also discuss the common preparation methods used by researchers for the synthesis of these perovskite materials. Further, we elucidate various important factors influencing the sensing performance of perovskite-based sensors, such as doping, defects, morphology, temperature, humidity, and light. We conclude with the future prospects and challenges related to these perovskite-based sensors toward the detection of VOC gases.

White Light Emission in Zero-Dimensional Indium Hybrid with Hydrogen Bond

Low-dimensional organic-inorganic metal halides (OIMHs) have been explored as single-component white light emitters for applications in solid-state lighting. Herein, we report a zero-dimensional (0D) In-based OIMH (TMPDA)[InCl5(H2O)] (TMPDA = N,N,N',N'-tetramethyl-1,4-phenylenediamine), which crystallizes in the noncentrosymmetric P212121 space group and contains hydrogen bonds between the adjacent [InCl5(H2O)]2- octahedra in structure. It exhibits a large optical band gap (4.10 eV) and dual-band emission under UV light. Spectroscopic analysis and theoretical calculation indicate that the high (404 nm)- and low (513 nm)-energy emissions are attributed to the bound excitons in organic ligands and self-trapped excitons in [InCl5(H2O)]2- units, respectively. It is found that Sb doping in this 0D hybrid provides additional orange (590 nm) emission assigned to the 3P1 → 1S0 triplet radiative recombination. By adjusting the doping level, the emission color can be turned from turquoise to orange, and interestingly, a single-component white-light emission is realized by balancing the high-energy emission from organic ligand, the turquoise emission from [InCl5(H2O)]2-, and the orange one from [SbCl5(H2O)]2-. This work not only provides a new OIMH showing the single-component white light emission but also demonstrates the potential of In-based hybrids with hydrogen bonds for solid-state luminescence.

A three-dimensional lead iodide perovskite analog featuring hydrogen-bonded dual monovalent cations

Three-dimensional (3D) halide perovskites have attracted considerable research interest, yet the selection of A-site cations is restricted by the Goldschmidt tolerance factor. To accommodate cations beyond this acceptable range, novel 3D perovskite analog structures with edge- and face-sharing motifs have been developed. Until now, these structures have been limited to divalent cations due to significant electrostatic repulsion when incorporating two monovalent cations. Herein, we employ a supramolecular synthon mechanism to address the issue and an effective hydrogen-bonding pattern is achieved in a novel 3D lead iodide hybrid perovskite, (ammonium)(morpholinium)Pb2I6 (1). The inorganic framework of 1 consists of two edge-shared [PbI6] octahedra connected via corner-sharing, thus forming a continuous 3D network. Structural analysis indicates that the spatial separation of N atoms and the existence of N-H⋯O hydrogen bonds effectively eliminate electrostatic repulsion. This work has demonstrated the potential to mitigate constraints of cation selection on 3D frameworks and could spur the development of novel 3D perovskite materials and related fields.

Intercalation Electrode and Grain Reconstruction Induce Significant Sensitivity Enhancement for Perovskite X-ray Detectors

Organic-inorganic hybrid perovskites have been recognized as potential candidates in direct X-ray detectors and have triggered tremendous interest in the past years. The blade coating method meets the requirements of large area and low cost for perovskite X-ray detectors, while the low compactness resulting from solvent evaporation limits the charge collection efficiency (CCE) and device sensitivity. Most of the reports are focused on the melioration of perovskite films to increase device sensitivity; there are still problems of low CCE. Herein, we introduce an intercalation-electrode device structure and achieve a ∼20-fold sensitivity enhancement. Carrier distribution throughout the thick films is simulated, and the electrode intercalating site can be optimized according to the mobility-lifetime factor to achieve the highest CCE. A methylamine thiocyanate (MASCN) additive-assisted coating strategy is developed, and pinhole free thick films with regrown particles are obtained without frequently used hot/soft pressing. A sensitivity level of ∼105 μC Gyair-1 cm-2 as well as a detection limit of 77 nGyair s-1 is achieved under low bias, which is among the best performance for polycrystalline perovskite direct X-ray detectors. This work provides a universal device structure design to overcome carrier loss through a long transport distance and enhances the CCE for ultrahigh sensitivity.

Space-Charge-Limited Current Measurements: A Problematic Technique for Metal Halide Perovskites

Space-charge-limited current (SCLC) measurements play a crucial role in the electrical characterization of semiconductors, particularly for metal halide perovskites. Accurate reporting and analysis of SCLC are essential for gaining meaningful insights into charge transport and defect density in these systems. Unfortunately, performing SCLC measurements on perovskites is complicated by their mixed electronic-ionic conductivity. This complexity led to SCLC data often being incorrectly analyzed using simplified models unsuitable for these materials and reported without essential information about how the measurements were performed. In light of recently published SCLC data, common challenges in using SCLC measurements on perovskite materials are addressed, and solutions are discussed in this paper. The applicability of the often-used analytical models, the overlooked issues related to the mixed ionic-electronic conductivity of perovskites, and the complexity of creating single-carrier devices are investigated using drift-diffusion simulations. Finally, guidelines for more accurate reporting and improved analysis are provided.

Recent Progress of Thin Crystal Engineering for Perovskite Solar Cells

Metal halide perovskite single crystals hold promise for photovoltaics with high efficiency and stability due to their superior optoelectronic properties and weak bulk ion migration. The past several years have witnessed rapid development of single-crystal perovskite solar cells (PSCs) with efficiency rocketed from 6.5 % to 24.3 %, however, which still lags behind their polycrystalline counterparts. Moreover, the poor device stability under light illumination is contrary to the high ion migration barrier of perovskite single crystals. The key limiting factors should be the low crystalline quality and high surface defect density of solution-grown thin single crystals. Under this circumstance, a review paper summarizing the recent progress and challenges will be instructive for future development of this emerging field. In this manuscript, the crystal engineering used to enhance carrier transport and suppress carrier recombination in vertical single-crystal PSCs will be summarized initially, including crystal growth, component control, surface and interface modification. Subsequently, the application of perovskite single crystals in lateral single-crystal PSCs will be discussed and compared with the conventionally vertical structure. Finally, the challenges and proposed strategies for the development of single-crystal PSCs are provided.

Defect Passivation and Crystallization Regulation for Efficient and Stable Formamidinium Lead Iodide Solar Cells with Multifunctional Amidino Additive

Amidino-based additives show great potential in high-performance perovskite solar cells (PSCs). However, the role of different functional groups in amidino-based additives have not been well elucidated. Herein, two multifunctional amidino additives 4-amidinobenzoic acid hydrochloride (ABAc) and 4-amidinobenzamide hydrochloride (ABAm) are employed to improve the film quality of formamidinium lead iodide (FAPbI3) perovskites. Compared with ABAc, the amide group imparts ABAm with larger dipole moment and thus stronger interactions with the perovskite components, i.e., the hydrogen bonds between N…H and I- anion and coordination bonds between C = O and Pb2+ cation. It strengthens the passivation effect of iodine vacancy defect and slows down the crystallization process of α-FAPbI3, resulting in the significantly reduced non-radiative recombination, long carrier lifetime of 1.7 µs, uniformly large crystalline grains, and enhances hydrophobicity. Profiting from the improved film quality, the ABAm-treated PSC achieves a high efficiency of 24.60%, and maintains 93% of the initial efficiency after storage in ambient environment for 1200 hours. This work provides new insights for rational design of multifunctional additives regarding of defect passivation and crystallization control toward highly efficient and stable PSCs.

Se-Elemental Concentration Gradient Regulation for Efficient Sb2(S,Se)3 Solar Cells With High Open-Circuit Voltages

Antimony selenosulfide (Sb2(S,Se)3), featuring large absorption coefficient, excellent crystal structure stability, benign non-toxic characteristic, outstanding humidity and ultraviolet tolerability, has recently attracted enormous attention and research interest regarding its photoelectric conversion properties. However, the open-circuit voltage (Voc) for Sb2(S,Se)3-based photovoltaic devices is relatively low, especially for the device with a high power conversion efficiency (η). Herein, an innovative Se-elemental concentration gradient regulation strategy has been exploited to produce high-quality Sb2(S,Se)3 films on TiO2/CdS substrates through a thioacetamide(TA)-synergistic dual-sulfur source hydrothermal-processed method. The Se-elemental gradient distribution produces a favorable energy band structure, which suppresses the energy level barriers for hole transport and enhances the driving force for electron transport in Sb2(S,Se)3 film. This facilitates efficient charge transport/separation of photogenerated carriers and boosts significantly the Voc of Sb2(S,Se)3 photovoltaic devices. The champion TA-Sb2(S,Se)3 planar heterojunction (PHJ) solar cell displays an considerable η of 9.28 % accompanied by an exciting Voc rising to 0.70 V that is currently the highest among Sb2(S,Se)3-based solar cells with efficiencies exceeding 9.0 %. This research is anticipated to contribute to the preparation of high-quality Sb2(S,Se)3 thin film and the achievement of efficient inorganic Sb2(S,Se)3 PHJ photovoltaic device.

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.

Bottom Contact Engineering for Ambient Fabrication of >25% Durable Perovskite Solar Cells

The bottom contact in perovskite solar cells (PSCs) is easy to cause deep trap states and severe instability issues, especially under maximum power point tracking (MPPT). In this study, sodium gluconate (SG) is employed to disperse tin oxide (SnO2) nanoparticles (NPs) and regulate the interface contact at the buried interface. The SG-SnO2 electron transfer layer (ETL) enabled the deposition of pinhole-free perovskite films in ambient air and improved interface contact by bridging effect. SG-SnO2 PSCs achieved an impressive power conversion efficiency (PCE) of 25.34% (certified as 25.17%) with a high open-circuit voltage (VOC) exceeding 1.19 V. The VOC loss is less than 0.34 V relative to the 1.53 eV bandgap, and the fill factor (FF) loss is only 2.02% due to the improved contact. The SG-SnO2 PSCs retained around 90% of their initial PCEs after 1000 h operation (T90 = 1000 h), higher than T80 = 1000 h for the control SnO2 PSC. Microstructure analysis revealed that light-induced degradation primarily occurred at the buried holes and grain boundaries and highlighted the importance of bottom-contact engineering.

Deploying a Dipole Electric Field at the CsPbI3 Perovskite/Carbon Interface for Enhancing Hole Extraction and Photovoltaic Performance

Carbon-based CsPbI3 perovskite solar cells without hole transporter (C-PSCs) have achieved intense attention due to its simple device structure and high chemical stability. However, the severe interface energy loss at the CsPbI3/carbon interface, attributed to the lower hole selectivity for inefficient charge separation, greatly limits device performance. Hence, dipole electric field (DEF) is deployed at the above interface to address the above issue by using a pole molecule, 4-trifluoromethyl-Phenylammonium iodide (CF3-PAI), in which the ─NH3 group anchors on the perovskite surface and the ─CF3 group extends away from it and connects with carbon electrode. The DEF is proven to align with the built-in electric field, that is pointing toward carbon electrode, which well enhances hole selectivity and charge separation at the interface. Besides, CF3-PAI molecules also serve as defect passivator for reducing trap state density, which further suppresses defect-induced non-radiative recombination. Consequently, the CsPbI3 C-PSCs achieve an excellent efficiency of 18.33% with a high VOC of 1.144 V for inorganic C-PSCs without hole transporter.

High-Efficiency Inverted Perovskite Solar Cells via In Situ Passivation Directed Crystallization

Lead halide perovskite solar cells (PSCs) have emerged as one of the influential photovoltaic technologies with promising cost-effectiveness. Though with mild processabilities to massive production, inverted PSCs have long suffered from inferior photovoltaic performances due to intractable defective states at boundaries and interfaces. Herein, an in situ passivation (ISP) method is presented to effectively adjust crystal growth kinetics and obtain the well-orientated perovskite films with the passivated boundaries and interfaces, successfully enabled the new access of high-performance inverted PSCs. The study unravels that the strong yet anisotropic ISP additive adsorption between different facets and the accompanied additive engineering yield the high-quality (111)-orientated perovskite crystallites with superior photovoltaic properties. The ISP-derived inverted perovskite solar cells (PSCs) have achieved remarkable power conversion efficiencies (PCEs) of 26.7% (certified as 26.09% at a 5.97 mm2 active area) and 24.5% (certified as 23.53% at a 1.28 cm2 active area), along with decent operational stabilities.

Energy Level Tuning in CsPbBr3 Perovskite Solar Cells through In Situ-Polymerized PEDOT Hole Transport Layer

The all-inorganic CsPbBr3 perovskite solar cells exhibit excellent stability against humidity and thermal conditions as well as relatively low production cost, rendering them a gradually emerging research hot spot in the field of photovoltaics. However, the absence of a hole transport layer (HTL) in its common structure and the substantial energy level difference of up to 0.6 eV between the highest occupied molecular orbital (HOMO) level of CsPbBr3 and the work function of the carbon electrode have emerged as the primary factor limiting the improvement of its power conversion efficiency (PCE). In this work, the monomer 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) is spin-coated onto the surface of the CsPbBr3 film directly and then subjected to annealing; DBEDOT undergoes in situ polymerization to form poly(3,4-ethylenedioxythiophene) (PEDOT), which aims to ameliorate the issue of excessive energy level difference between CsPbBr3 and the carbon electrode, and to facilitate the extraction and transport efficiency of holes between the CsPbBr3 perovskite and the carbon electrode. Compared to the pristine device, the PCE of the device based on in situ polymerization is enhanced and achieves a maximum efficiency of 9.81%. Furthermore, the unencapsulated devices based on in situ polymerization maintain 95.9% of their original efficiency after 40 days of stability testing.

Polymers for Perovskite Solar Cells

Perovskite solar cells (PSCs) are recognized as one of the most promising next-generation photovoltaics, primarily due to their exceptional power conversion efficiency, ease of processing, and cost-effectiveness. Despite these advantages, challenges remain in achieving high-quality films and ensuring the long-term stability of PSCs, which hinder their widespread commercialization. Polymers, characterized by multifunctional groups, superior thermal stability, flexible long chains, and cross-linking capabilities, offer significant potential to enhance the performance and reliability of PSCs. This review comprehensively presents the multifaceted roles that polymers play in PSCs. Through carefully controlling interactions between polymers and perovskites, crucial aspects such as film crystallization kinetics, carrier transport process, ion migration issues, and mechanical properties under bending can be effectively regulated to maximize the device performance. Furthermore, the hydrophobic properties and strong chelated cross-linking networks of polymers significantly enhance the stability of PSCs under various environmental conditions while effectively mitigating lead leakage, thereby addressing environmental concerns and long-term durability. Moreover, this Perspective identifies potential pathways for further advancing polymer-based strategies in PSC applications.

Flexible Single-Crystal Perovskite Photodetectors via Polymer-Controlled Transfer

The large-sized perovskite single-crystal sheet (SCS) serves as the ideal research platform for perovskite photodetectors due to its outstanding carrier photophysics, pronounced geometric aspect ratio, and ultrahigh material utilization rate. However, its performance in flexible device applications is relatively lackluster due to the rigid and brittle nature of the three-dimensional cubic lattices. In this work, the indium tin oxide (ITO)-based multimillimeter-sized MAPbBr3 SCS is transformed into MAPbI3 SCS via ion exchange strategy. Significantly, we proposed and implemented a polymer-controlled transfer strategy─utilizing the dichloromethane (DCM) solution of poly(methyl methacrylate) (PMMA)─to nondestructively transfer the whole perovskite SCS off the ITO substrates and subsequently adhere it onto a flexible polyethylene terephthalate (PET) substrate of interdigital electrode, thereby fabricating a lateral-structured photodetector with a PMMA-SCS-Au-PET multilayer configuration. The tight self-encapsulation between the top PMMA membrane and the bottom PET substrate imparts excellent waterproof stability and concurrently excellent mechanical flexibility to these devices; additionally, the MAPbI3 device exhibits comprehensively superior performance to the MAPbBr3 one. This work represents a proactive attempt and exploration of the high-performance advancement of large-sized SCS photodetectors, undoubtedly introducing novel momentum and solutions to this domain.

Unravelling the mechanism of temperature modulated exciton binding energy for MAPbBr3 perovskites

The excitonic effect significantly influences the optoelectronic characteristics of halide perovskites. However, consensus on the temperature modulated exciton binding energy remains elusive, even for extensively studied materials like MAPbBr3 perovskites. In this study, we utilized UV-vis absorption spectra and the Elliott model to extract the exciton binding energies of MAPbBr3 in the range of 170-290 K. Elliott model fitted results reveal a linear increasing trend in bandgap and exciton binding energy for both cubic and tetragonal phases with temperature, with the tetragonal phase exhibiting a higher increasing rate. Additionally, we found that regardless of the temperature, the strongest absorption peaks are always dominated by the exciton absorption, and our fitted exciton absorption peak blue-shifts with the increase of temperature, accounting for the observed blue-shift of the strongest absorption peak for our fabricated MAPbBr3 sample. However, with the increase of temperature, the weight of continuum state absorption increases significantly, which widens the absorption tails to the longer wavelength, leading to the red-shift of Tauc-plotted optical bandgaps. This is the first work considering the temperature-modulated excitonic properties of halide perovskites, which offers valuable insights into the behavior of MAPbBr3 under varying temperature conditions. After a series of theoretical simulations on the temperature modulated electronic properties, including band structures, carrier effective masses, optical dielectric properties and Born effective charges, we provide rational interpretations for the experimentally observed temperature induced variation of the optical properties. These works are helpful to deepen our understanding of the temperature modulated optical properties of MAPbBr3 perovskites.

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.

Synergetic Electrostatic and Steric Effects in α-FAPbI3 Single Crystals For X-Ray Detection and Imaging

It is still challenging to stabilize α-FAPbI3 perovskite for high performance optoelectrical devices. Herein, a novel strategy is proposed utilizing the synergetic electrostatic and steric effect to stabilize the α-FAPbI3 phase and suppress the ion migration. Dimethylamine (DMA+) cations are chosen as the dopant to fabricate FA0.96DMA0.04PbI3 single crystals (SCs). DFT calculations reveal that DMA+ cations can improve the stability of α-FAPbI3 phase in both thermodynamics (lower Gibbs free energy) and kinetics (higher defect formation and migration energy). The resulting SCs exhibit an environmental stability over 100 days and an extraordinary low dark current drift of 3.7 × 10-7 nA cm-1 s-1 V-1, comparable to 2D perovskite SCs. The X-ray detectors have also achieved the-state-of-the-art performance in X-ray detection and imaging. This work demonstrates the significance of electrostatic and steric effects in improving the phase and operational stability of perovskites.

High-n Phase Suppression for Efficient and Stable Blue Perovskite Light-Emitting Diodes

Quasi-2D perovskites light-emitting diodes (PeLEDs) have achieved significant progress due to their superior optical and electronic properties. However, the blue PeLEDs still exist inefficient energy transfer and electroluminescence performance caused by mixed multidimensional phase distribution. In this work, transition metal salt (zinc bromide, ZnBr2) is introduced to modulate phase distributions by suppressing the nucleation of high n phase perovskites, which effectively shortens the energy transfer path for blue emission. Moreover, ZnBr2 also facilitates energy level matching and reduces non-radiative recombination, thus improving electroluminescence (EL) efficiency. Benefiting from these combined improvements, an efficient blue PeLEDs is obtained with a maximum external quantum efficiency (EQE) of 16.2% peaking located at 486 nm. This work provides a promising approach to tune phase distribution of quasi-2D perovskites and achieving highly efficient blue PeLEDs.

Day-Night imaging without Infrared Cutfilter removal based on metal-gradient perovskite single crystal photodetector

Day-Night imaging technology that obtains full-color and infrared images has great market demands for security monitoring and autonomous driving. The current mainstream solution relies on wide-spectrum silicon photodetectors combined with Infrared Cutfilter Removal, which increases complexity and failure rate. Here, we address these challenges by employing a perovskite photodetector based on Pb-Sn alloyed single crystal with a vertical bandgap-graded structure that presents variable-spectrum responses at different biases and extends the infrared detection range close to 1100 nm. Taking advantage of the Pb-Sn gradients in mobility and built-in field, the perovskite photodetector shows a large linear dynamic range of 177 dB. In addition, the optoelectronic characteristics feature long-term operational stability over a year. We further develop an imaging module prototype without Infrared Cutfilter Removal that exhibits excellent color fidelity with RGB color differences ranging from 0.48 to 2.46 under infrared interference and provides over 26-bit grayscale resolution in infrared imaging.

Highly stable two-dimensional Ruddlesden-Popper perovskite-based resistive switching memory devices

Resistive switching random-access memory (ReRAM) devices based on organic-inorganic halide perovskites (OIHPs) have emerged as a new class of data storage devices. Recently, two-dimensional (2D) OIHPs have attracted much attention for ReRAM applications because of their structural diversity and superior stability. Here, the RS characteristics of ReRAM devices fabricated utilizing pure 2D Ruddlesden-Popper (RP) perovskite crystals, namely (TEA)2PbBr4 and (TEA)2PbI4, are reported. The RS memory devices exhibit reliable and reproducible bipolar switching properties with high ON/OFF ratio (∼104), excellent data retention of over 104 s, and good endurance characteristics of 200 cycles. This study investigates temperature-dependent RS behaviors, elucidating the creation and annihilation of a conducting pathway in the presence of an external electric field. Additionally, the RS property of 2D RP perovskite-based memory devices is found to be retained over 45 days at ambient conditions under a relative humidity of 47% ± 4%. Our findings may accelerate the technological deployment of stable 2D perovskite-based RS memory devices for successful logic application.

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.

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.

Highly Diffusive Nonluminescent Carriers in Hybrid Phase Lead Triiodide Perovskite Nanowires

Crystal structural rearrangements unavoidably introduce defects into materials, where even these small changes in local lattice structure could arouse a prominent impact on the overall nature of crystals. Contrary to the traditional notion that defects obstruct carrier transport, herein, we report a promoted transport mechanism of nonluminescent carriers in single-crystalline CH3NH3PbI3 nanowires (1345.2 cm2 V-1 s-1, about a 14-fold improvement), enabled by the phase transition induced defects (PTIDs). Carriers captured by PTIDs evade both the radiative and non-radiative recombinations during the incomplete tetragonal-to-orthorhombic phase transition at low temperatures, forming a specific nonluminescent state that exhibits an efficient long-distance transport and thereby realize a prominent enhancement of photocurrent responsivity for photodetector applications. The findings provide broader insights into the carrier transport mechanism in perovskite semiconductors and have significant implications for their rational design for photoelectronic applications at varied operating temperatures.

Intrinsic ultralow lattice thermal conductivity in lead-free halide perovskites Cs3Bi2X9 (X = Br, I)

Lead-free halide perovskites have recently garnered significant attention due to their rich structural diversity and exceptionally ultralow lattice thermal conductivity (κL). Here, we employ first-principles calculations in conjunction with self-consistent phonon theory and Boltzmann transport equations to investigate the crystal structure, electronic structure, mechanical properties, and κLs of two typical vacancy-ordered halide perovskites, denoted with the general formula Cs3Bi2X9 (X = Br, I). Ultralow κLs of 0.401 and 0.262 W mK-1 at 300 K are predicted for Cs3Bi2Br9 and Cs3Bi2I9, respectively. Our findings reveal that the ultralow κLs are mainly associated with the Cs rattling-like motion, vibrations of halide polyhedral frameworks, and strong scattering in the acoustic and low-frequency optical phonon branches. The structural analysis indicates that these phonon dynamic properties are closely relevant to the bonding hierarchy. The presence of the extended Bi-X antibonding states at the valence band maximum contributes to the soft elastic lattice and low phonon group velocities. Compared to Cs3Bi2Br9, the face-sharing feature and weaker bond strength in Cs3Bi2I9 lead to a softer elasticity modulus and stronger anharmonicity. Additionally, we demonstrate the presence of wave-like κC in Cs3Bi2X9 by evaluating the coherent contribution. Our work provides the physical microscopic mechanisms of the wave-like κC in two typical lead-free halide perovskites, which are beneficial to designing intrinsic materials with the feature of ultralow κL.

Interfacial Layer Materials with a Truxene Core for Dopant-Free NiOx-Based Inverted Perovskite Solar Cells

Nickel oxide (NiOx) is commonly used as a holetransporting material (HTM) in p-i-n perovskite solar cells. However, the weak chemical interaction between the NiOx and CH3NH3PbI3 (MAPbI3) interface results in poor crystallinity, ineffective hole extraction, and enhanced carrier recombination, which are the leading causes for the limited stability and power conversion efficiency (PCE). Herein, two HTMs, TRUX-D1 (N2,N7,N12-tris(9,9-dimethyl-9H-fluoren-2-yl)-5,5,10,10,15,15-hexaheptyl-N2,N7,N12-tris(4-methoxyphenyl)-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene-2,7,12-triamine) and TRUX-D2 (5,5,10,10,15,15-hexaheptyl-N2,N7,N12-tris(4-methoxyphenyl)-N2,N7,N12-tris(10-methyl-10H-phenothiazin-3-yl)-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene-2,7,12-triamine), are designed with a rigid planar C3 symmetry truxene core integrated with electron-donating amino groups at peripheral positions. The TRUX-D molecules are employed as effective interfacial layer (IFL) materials between the NiOx and MAPbI3 interface. The incorporation of truxene-based IFLs improves the quality of perovskite crystallinity, minimizes nonradiative recombination, and accelerates charge extraction which has been confirmed by various characterization techniques. As a result, the TRUX-D1 exhibits a maximum PCE of up to 20.8% with an impressive long-term stability. The unencapsulated device retains 98% of their initial performance following 210 days of aging in a glove box and 75.5% for the device after 80 days under ambient air condition with humidity over 40% at 25 °C.

Enhancing Carrier Transport in 2D/3D Perovskite Heterostructures through Organic Cation Fluorination

The interfacial 2D/3D perovskite heterostructures have attracted extensive attention due to their unique ability to combine the high stability of 2D perovskites with the remarkable efficiency of 3D perovskites. However, the carrier transport mechanism within the 2D/3D perovskite heterostructures remains unclear. In this study, the carrier transport dynamics in 2D/3D perovskite heterostructures through a variety of time-resolved spectroscopic measurements is systematically investigated. Time-resolved photoluminescence results reveal nanosecond hole transfer from the 3D to 2D perovskites, with enhanced efficiency through the introduction of fluorine atoms on the phenethylammonium (PEA) cation. Transient absorption measurements unveil the ultrafast picosecond electron and energy transfer from 2D to 3D perovskites. Furthermore, it is demonstrated that the positioning of fluorination on the PEA cations effectively regulates the efficiency of charge and energy transfer within the heterostructures. These insightful findings shed light on the underlying carrier transport mechanism and underscore the critical role of cation fluorination in optimizing carrier transport within 2D/3D perovskite heterostructure-based devices.

Elimination of Intragrain Defect to Enhance the Performance of FAPbI3 Perovskite Solar Cells by Ionic Liquid

Ionic liquids have been widely used to improve the efficiency and stability of perovskite solar cells (PSCs), and are generally believed to passivate defects on the grain boundaries of perovskites. However, few studies have focused on the relevant effects of ionic liquids on intragrain defects in perovskites which have been shown to be critical for the performance of PSCs. In this work, the effect of ionic liquid 1-hexyl-3-methylimidazolium iodide (HMII) on intragrain defects of formamidinium lead iodide (FAPbI3) perovskite is investigated. Abundant {111}c intragrain planar defects in pure FAPbI3 grains are found to be significantly reduced by the addition of the ionic liquid HMII, shown by using ultra-low-dose selected area electron diffraction. As a result, longer charge carrier lifetimes, higher photoluminescence quantum yield, better charge carrier transport properties, lower Urbach energy, and current-voltage hysteresis are achieved, and the champion power conversion efficiency of 24.09% is demonstrated. These observations suggest that ionic liquids significantly improve device performance resulting from the elimination of {111}c intragrain planar defects.

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.

Research progress of green antisolvent for perovskite solar cells

Conventional antisolvents such as chlorobenzene and benzotrifluoride are highly toxic and volatile, and therefore not preferred for large-scale fabrication. As such, green antisolvents are favored for the eco-friendly fabrication of perovskite films. This review primarily discusses the impact of various green antisolvents on the fabrication of thin perovskite films and analyzes the main chemical characteristics of these green antisolvents. It also interprets the impact of green antisolvent treatment on crystal growth and nucleation crystallization mechanisms. It introduces the effective fabrication of large-area devices using green antisolvents and analyzes the mechanisms by which green antisolvents enhance device stability. Subsequently, several green antisolvents capable of preparing highly stable and efficient devices are listed. Finally, we outline the key challenges and future prospects of antisolvent treatment. This review paves the way for green fabrication of industrial perovskite solar cells.

Chiral three-dimensional organic-inorganic lead iodide hybrid semiconductors

Chiral hybrid metal halides (CHMHs) have received a considerable amount of attention in chiroptoelectronics, spintronics, and ferroelectrics due to their superior optoelectrical properties and structural flexibility. Owing to limitations in synthesis, the theoretical prediction of room-temperature stable chiral three-dimensional (3D) CHFClNH3PbI3 has not been successfully prepared, and the optoelectronic properties of such structures cannot be studied. Herein, we have successfully constructed two pairs of chiral 3D lead iodide hybrids (R/S/Rac-3AEP)Pb2I6 (3R/S/Rac, 3AEP = 3-(1-aminoethyl)pyridin-1-ium) and (R/S/Rac-2AEP)Pb2I6 (2R/S/Rac, 2AEP = 2-(1-aminoethyl)pyridin-1-ium) through chiral introduction and ortho substitution strategies, and obtained bulk single crystals of 3R/S/Rac. The 3R/S exhibits optical activity and bulk photovoltaic effect induced by chirality. The 3R crystal device exhibits stable circularly polarized light performance at 565 nm with a maximum anisotropy factor of 0.07, responsivity of 0.25 A W-1, and detectivity of 3.4 × 1012 jones. This study provides new insights into the synthesis of chiral 3D lead halide hybrids and the development of chiral electronic devices.

Flexible Multimodal Sensors Enhanced by Electrospun Lead-Free Perovskite and PVDF-HFP Composite Form-Stable Mesh Membranes for In Situ Plant Monitoring

The pH and humidity of the crop environment are essential indicators for monitoring crop growth status. This study reports a lead-free perovskite/polyvinylidene fluoride-hexafluoropropylene composite (LPPC) to enhance the stability and reliability of in situ plant pH and humidity monitoring. The mesh composite membrane of LPPC illustrates a hydrophobic contact angle of 101.982°, a tensile strain of 800%, and an opposing surface potential of less than -184.9 mV, which ensures fast response, high sensitivity, and stability of the sensor during long-term plant monitoring. The LPPC-coated pH electrode possesses a sensitivity of -63.90 mV/pH, which provides a fast response within 5 s and is inert to environmental temperature interference. The LPPC-coated humidity sensor obtains a sensitivity of -145.7 Ω/% RH, responds in 28 s, and works well under varying light conditions. The flexible multimodal sensor coated with an LPPC membrane completed real-time in situ monitoring of soilless strawberries for 17 consecutive days. Satisfactory consistency and accuracy performance are observed. The study provides a simple solution for developing reliable, flexible wearable multiparameter sensors for in situ monitoring of multiple parameters of crop environments.

Precise Control Light Emission of PVDF-CH3NH3PbBr3-xClx Nanocrystalline Films Using a Cl-(CH3OH)n System

Methylammonium lead halide perovskites with highly efficient pure-color or white-light generation have gained increasing scientific interest and promote the development of a great commercial opportunity in displays, lighting, and other applications. However, the poor stabilities, lead toxicity, and unfriendly solvents and ligands in the growth process severely restrict their commercial application. Here, we proposed a green method for preparing uniform and stable polymer-encapsulated photoluminescence (PL) tunable CH3NH3PbBr3-xClx NC thin films at room temperature. Utilizing the swelling effect between alcohol compounds and organic polymers and the ionization of NaCl in methanol solution, the anion exchange process can be achieved rapidly within 7 min. Moreover, the PL wavelengths of the CH3NH3PbBr3-xClx NCs films were precisely tuned with steps as fine as 2 nm. Experimental results showed that NaCl dissolved in methanol solution can form Cl-(CH3OH)n, which brings ionized Cl into the polymer-encapsulated CH3NH3PbBr3 NCs film for CH3NH3PbBr3-xClx NCs film growth. Based on the swelling and anion exchange dynamics, a modified NaCl-CH3OH-MABr solution system was developed to trigger CH3NH3PbBr3-xClx NCs film PL emission tuning from 528 to 463 nm with several-fold intensity enhancement. The realization of precisely controlled photoluminescence from the perovskite nanocrystal film would have wide applications in the optical and imaging fields.

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.

Conformal zinc sulfide coating of vertically aligned ZnO nanorods by two-step hydrothermal synthesis on wide bandgap seed layers for lead-free perovskite solar cells

Vertically aligned ZnO nanorods (NRs) were grown hydrothermally on the wide bandgap (∼3.86 - 4.04 eV) seed layers (SLs) of grain size ∼162 ± 35 nm, prepared using ball-milled derived ZnO powder. The synthesized ZnO NRs were further decorated with ZnS nanocrystals to achieve a ZnO NR-ZnS core-shell (CS)-like nano-scaffolds by a subsequent hydrothermal synthesis at 70 °C for 1 h. UV-Vis-NIR spectroscopy, x-ray diffractometry (XRD), Raman spectroscopy and Field emission scanning electron microscopy (FESEM) coupled with Energy dispersive x-ray spectroscopy (EDX) analyses confirmed the formation of ZnS atop the vertically aligned ZnO NR arrays of ∼1.79 ± 0.17µm length and ∼165 ± 27 nm diameter. Transmission electron microscopy (TEM)/EDX analyses revealed that vertically aligned ZnO NRs (core dia. ∼181 ± 12 nm) arrays are conformally coated by an ultrathin ZnS (∼25 ± 7 nm) shell layer with a preferential ZnS{111}/ZnO{10-10}-like partial epitaxy. The ZnO NRs exhibited a sharp band edge near ∼384 nm having optical bandgap energy (Eg) of ∼3.23 eV. However, the ZnO NR-ZnS CS exhibited double absorption bands atEg∼ 3.20 eV (ZnO-core) andEg∼ 3.78 eV (ZnS-shell). The ZnS{111}/ZnO{10-10}-nano-scaffolds could be utilized to facilitate the enhanced absorption of UV photons as well as the radial junction formation between the Pb-free perovskite absorber and ZnS/ZnO NRs layers.

Solar-Driven Conversion of CO2 to C2 Products by the 3d Transition Metal Intercalates of Layered Lead Iodides

Photocatalytic CO2 reduction to high-value-added C2+ products presents significant challenges, which is attributed to the slow kinetics of multi-e- CO2 photoreduction and the high thermodynamic barrier for C-C coupling. Incorporating redox-active Co2+/Ni2+ cations into lead halide photocatalysts has high potentials to improve carrier transport and introduce charge polarized bimetallic sites, addressing the kinetic and thermodynamic issues, respectively. In this study, a coordination-driven synthetic strategy is developed to introduce 3d transition metals into the interlamellar region of layered organolead iodides with atomic precision. The resultant bimetallic halide hybrids exhibit selective photoreduction of CO2 to C2H5OH using H2O vapor at the evolution rates of 24.9-31.4 µmol g-1 h-1 and high selectivity of 89.5-93.6%, while pristine layered lead iodide yields only C1 products. Band structure calculations and photoluminescence studies indicate that the interlayer Co2+/Ni2+ species greatly contribute to the frontier orbitals and enhance exciton dissociation into free carriers, facilitating carrier transport between adjacent lead iodide layers. In addition, Bader charge distribution calculations and in situ experimental spectroscopic studies reveal that the asymmetric Ni-O-Pb bimetallic catalytic sites exhibit intrinsic charge polarization, promoting C-C coupling and leading to the formation of the key *OC-CHO intermediate.

Halide Anions Tuning of Lead-Free Perovskite-Type Ferroelectric Semiconductors with Inverse High-Temperature Symmetry Breaking

There is a noticeable gap in the literature regarding research on halogen-substitution-regulated ferroelectric semiconductors featuring multiple phase transitions. Here, a new category of 1D perovskite ferroelectrics (DFP)2SbX5 (DFP+ = 3,3-difluoropyrrolidium, X- = I-, Br-, abbreviated as I-1 and Br-2) with twophase transitions (PTs) is reported. The first low-temperature PT is a mmmFmm2 ferroelectric PT, while the high-temperature PT is a counterintuitive inverse temperature symmetry-breaking PT. By the substitution of iodine with bromine, the Curie temperature (Tc) significantly increases from 348 K of I-1 to 374 K of Br-2. Their ferroelectricity and pyroelectricity are improved (Ps value from 1.3 to 4.0 µC cm-2, pe value from 0.2 to 0.48 µC cm-2 K-1 for I-1 and Br-2), while their optical bandgaps increased from 2.1 to 2.7 eV. A critical slowing down phenomenon is observed in the dielectric measurement of I-1 while Br-2 exhibits the ferroelastic domain. Structural and computational analyses elucidate that the order-disorder movement of cations and the distortion of the chain perovskite [SbX5]2- anions skeleton lead to PT. The semiconductor properties are determined by [SbX5]2- anions. The findings contribute to the development of ferroelectric semiconductors and materials with multiple PTs and provide materials for potential applications in the optoelectronic field.

Durable Perovskite Solar Cells with 24.5% Average Efficiency: The Role of Rigid Conjugated Core in Molecular Semiconductors

Efficient and robust n-i-p perovskite solar cells necessitate superior organic hole-transport materials with both mechanical and electronic prowess. Deciphering the structure-property relationship of these materials is crucial for practical perovskite solar cell applications. Through direct arylation, two high glass transition temperature molecular semiconductors, DBC-ETPA (202 °C) and TPE-ETPA (180 °C) are synthesized, using dibenzo[g,p]chrysene (DBC) and 1,1,2,2-tetraphenylethene (TPE) tetrabromides with triphenylene-ethylenedioxythiophene-dimethoxytriphenylamine (ETPA). In comparison to spiro-OMeTAD, both semiconductors exhibit shallower HOMO energy levels, resulting in increased hole densities (generated by air oxidation doping) and accelerated hole extraction from photoexcited perovskite. Experimental and theoretical studies highlight the more rigid DBC core, enhancing hole mobility due to reduced reorganization energy and lower energy disorder. Importantly, DBC-ETPA possesses a higher cohesive energy density, leading to lower ion diffusion coefficients and higher Young's moduli. Leveraging these attributes, DBC-ETPA is employed as the primary hole-transport layer component, yielding perovskite solar cells with an average efficiency of 24.5%, surpassing spiro-OMeTAD reference cells (24.0%). Furthermore, DBC-ETPA-based cells exhibit superior operational stability and 85 °C thermal storage stability.

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.

All-Round Passivation Strategy Yield Flexible Perovskite/CuInGaSe2 Tandem Solar Cells with Efficiency Exceeding 26.5

The perovskite/Cu(InGa)Se2 (CIGS) tandem solar cells (TSCs) presents a compelling technological combination poised for the next generation of flexible and lightweight photovoltaic (PV) tandem devices, featuring a tunable bandgap, high power conversion efficiency (PCE), lightweight flexibility, and enhanced stability and durability. Over the years, the imperative to enhance the performance of wide bandgap (WBG) perovskite solar cells (PSCs) has grown significantly, particularly in the context of a flexible tandem device. In this study, an all-round passivation strategy known as Dual Passivation at Grains and Interfaces (DPGI) is introduced for WBG PSCs in perovskite/CIGS tandem structures. The implementation of DPGI is tailored to improve film crystallinity and passivate defects across the solar cell structure, leading to a substantial performance enhancement for WBG PSCs. Subsequently, both rigid and flexible tandem devices are assembled. Impressively, a fully flexible 4T perovskite/CIGS TSCs is successfully fabricated with a PCE of 26.57%, making it the highest value in this field and highlighting its potential applications in the next generation of flexible lightweight PV tandem devices.

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.

Stability Enhancement in All-Inorganic Perovskite Light Emitting Diodes via Dual Encapsulation

Addressing the challenge of lighting stability in perovskite white light emitting diodes (WLEDs) is crucial for their commercial viability. CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are promising for next-generation lighting due to their superior optical and electronic properties. However, the inherent soft material structure of CsPbX3 NCs is particularly susceptible to the elevated temperatures associated with prolonged WLED operation. Additionally, these NCs face stability challenges in high humidity environments, leading to reduced lighting performance. This study introduces a two-step dual encapsulation method, resulting in CsPbBr3@SiO2/Al2SiO5 composite fibers (CFs) with enhanced optical stability under extreme conditions. In testing, WLEDs incorporating these CFs, even under prolonged operation at high power (100 mA for 9 h), maintain consistent electroluminescence (EL) intensity and optoelectronic parameters, with surface temperatures reaching 84.2 °C. Crucially, when subjected to 85 °C and 85% relative humidity for 200 h, the WLEDs preserve 97% of their initial fluorescence efficiency. These findings underscore the efficacy of the dual encapsulation strategy in significantly improving perovskite material stability, marking a significant step toward their commercial application in optoelectronic lighting.

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.

Hole transport layer engineering in high performance quasi-2D perovskite blue light emitting diodes

Quasi-2D perovskites have emerged as highly promising materials for application in perovskite light-emitting diodes (PeLEDs), garnering significant attention due to their outstanding semiconductor properties. These materials boast an inherent multi-quantum well structure that imparts a robust confinement effect, particularly advantageous for blue emission. However, the development of blue emitters utilizing quasi-2D perovskites encounters challenges, notably colour instability, multipeak emission, and suboptimal fluorescence yield. The hole transfer layer (HTL) on which the perovskite layer is deposited in PeLEDs further affects the performance and efficiency. In this review, we delve into the evolution of blue PeLEDs and elucidate the optical properties of quasi-2D perovskites with the primary focus on HTL materials. We explore different HTL materials like PEDOT:PSS, metal oxides, and conjugated polyelectrolytes as well as ionic liquids, and their role in enhancing the colour stability, minimizing interfacial defects and increasing the fluorescence yield. This review endeavours to provide a holistic perspective of the different HTLs and serve as a valuable reference for researchers navigating the realm of HTL engineering towards the realization of high-performance blue quasi-2D PeLEDs.

Passivation of 1D@3D perovskite ferroelectric film with hydrophobic molecules for ferro-pyro-phototronic effect-based self-driven photodetector

High-performance, self-driven photodetectors in commercial and public applications show promising prospects. The pyro-phototronic effect is a promising method for building these detectors, but limitations in interfacial contact conditions hinder the use of the ferro-pyro-phototronic effect. By modifying the surface of 1D@3D perovskite ferroelectric film with tetra-ethyl ammonium (TEAI) molecules, the interfacial defect density is reduced, resulting in a high-performance, stable photodetector. Moreover, the passivation can greatly enhance the ferro-pyro-phototronic effect, which can be explained by the increased band bending and decreased trap states at the SnS/perovskite interface resulting in less re-distribution of charge carriers directly across the interface. Our work offers a feasible and effective method for producing pyro-phototronic responses in perovskite films-based devices, and thus presents a feasible solution for high-performance, self-driven and flexible photodetection.

Composite of formamidinium lead bromide perovskite FAPbBr3 with reduced graphene oxide (rGO) for efficient H2 evolution from HBr splitting

Solar hydrobromic acid (HBr) splitting using perovskite photocatalysts provides an attractive avenue to store solar energy into hydrogen (H2) and bromine (Br2), while an efficient photocatalytic system is still demanded. As for the semiconductor photocatalyst, formamidinium perovskites show some superiorities in structural stability, light adsorption and charge dynamics compared to their methylammonium counterparts, which are fitter for the photocatalysis process. Herein, the composite of formamidinium lead bromide perovskite (FAPbBr3) with reduced graphene oxide (rGO) is prepared using a facile photoreduction method. Under simulated sunlight irradiation (AM1.5G, 100 mW cm-2), this FAPbBr3/rGO composite (100 mg) demonstrates a noteworthy enhancement in photocatalytic H2 evolution activity of 386.7 μmol h-1, and it exhibits a notable stability with no significant decrease after 50 h of repeated tests. The single particle PL (photoluminescence) microscope is employed to study the charge dynamics, revealing that rGO in the composite effectively promotes the carrier separation. This work provides a highly efficient and stable photocatalyst for HBr splitting, and offers an effective modification strategy on lead bromide perovskites.

The Effect of Cesium Incorporation on the Vibrational and Elastic Properties of Methylammonium Lead Chloride Perovskite Single Crystals

Hybrid organic-inorganic lead halide perovskites (LHPs) have emerged as a highly significant class of materials due to their tunable and adaptable properties, which make them suitable for a wide range of applications. One of the strategies for tuning and optimizing LHP-based devices is the substitution of cations and/or anions in LHPs. The impact of Cs substitution at the A site on the structural, vibrational, and elastic properties of MAxCs1-xPbCl3-mixed single crystals was investigated using X-ray diffraction (XRD) and Raman and Brillouin light scattering techniques. The XRD results confirmed the successful synthesis of impurity-free single crystals, which exhibited a phase coexistence of dominant cubic and minor orthorhombic symmetries. Raman spectroscopy was used to analyze the vibrational modes associated with the PbCl6 octahedra and the A-site cation movements, thereby revealing the influence of cesium incorporation on the lattice dynamics. Brillouin spectroscopy was employed to investigate the changes in elastic properties resulting from the Cs substitution. The incorporation of Cs cations induced lattice distortions within the inorganic framework, disrupting the hydrogen bonding between the MA cations and PbCl6 octahedra, which in turn affected the elastic constants and the sound velocities. The substitution of the MA cations with smaller Cs cations resulted in a stiffer lattice structure, with the two elastic constants increasing up to a Cs content of 30%. The current findings facilitate a fundamental understanding of mixed lead chloride perovskite materials, providing valuable insights into their structural and vibrational properties.

Efficient, Color-Stable, Pure-Blue Light-Emitting Diodes Based on Aromatic Ligand-Engineered Perovskite Nanoplatelets

Perovskite nanoplatelets (NPLs) show great potential for high-color-purity light-emitting diodes (LEDs) due to their narrow line width and high exciton binding energy. However, the performance of perovskite NPL LEDs lags far behind perovskite quantum dot-/film-based LEDs, owing to their material instability and poor carrier transport. Here, we achieved efficient and stable pure blue-emitting CsPbBr3 NPLs with outstanding optical and electrical properties by using an aromatic ligand, 4-bromothiophene-2-carboxaldehyde (BTC). The BTC ligands with thiophene groups can guide two-dimensional growth and inhibit out-of-plane ripening of CsPbBr3 NPLs, which, meanwhile, increases their structural stability via strongly interacting with PbBr64- octahedra. Moreover, aromatic structures with delocalized π-bonds facilitate charge transport, diminish band tail states, and suppress Auger processes in CsPbBr3 NPLs. Consequently, the LEDs demonstrate efficient and color-stable blue emissions at 465 nm with a narrow emission line width of 17 nm and a maximum external quantum efficiency (EQE) of 5.4%, representing the state-of-the-art CsPbBr3 NPL LEDs.