Carrier Diffusion Research Articles

Electrospun Nano-Porous Cellulose Acetate Membrane Casted with Chitosan for Solid-State Sodium-Ion Batteries

Emerging as a safe and economically viable alternative to lithium-ion batteries, the solid-state sodium ion battery (ss-SIB) has captured increasing attention as a transformative technology for realizing a decarbonized economy and ensuring a sustainable energy supply. Here we report a nanoarchitecture strategy of biodegradable, biocompatible, and naturally abundant cellulose derivative (cellulose acetate, CA) and chitosan (CH) biopolymer-based nano-porous electrospun composite electrolyte (ECE) for flexible and wearable ss-SIBs. A simple combination of electrospinning and solution casting was utilized to fabricate mechanically robust (13.76 MPa), thin-film (0.067 mm), highly flexible, and high room temperature Na-ion conductive (1.04 x 10-4 S.cm-2) ECE. Lower activation energy (Ea = 0.13 eV) indicates easy charge carrier diffusion ability of as prepared ECE. The electrochemical stability window (ESW = 3.45 V) of ECE is studied by the linear sweep voltammetry (LSV) with respect to stainless steel and sodium metal electrodes. Uniform galvanostatic Na plating and stripping at room temperature is observed over 900 hrs at 0.5 mA•cm-2 current density in symmetric (Na|ECE|Na) cell performance, this underscores impressive electrochemical stability and compatibility with sodium metal. Using Na3V2(PO4)3 (NVP) as cathode, ECE, and Na metal as anode in the full cell, specific discharge capacity of 83 mA×h×g-1 at room temperature was attained at 0.1 C rate, highlighting the practical applicability of the nanostructured electrospun composite electrolyte for flexible and wearable ss-SIBs. Keywords Cellulose acetate, chitosan, electrospun, solid-state sodium-ion battery, specific discharge capacity.

(Invited) Spatially–Resolved Luminescence Properties of Etched Quantum Well Microstructures

Fabrication processes for photonic devices, especially micro- or nano-photonic devices, call for some kind of control of the materials’ optical properties at the stage of the final device. Our study focusses on measuring the optical quality of quantum well (QW) containing materials after device processing, using steps such as etching which allows fabrication of optical waveguides for example. We first designed and realized specific material structures based on an InP substrate, with a series of InAsxP1-x quantum wells such as illustrated on the figure. The samples were grown by gas-phase molecular beam epitaxy. The samples were characterized by spatially-resolved photoluminescence (PL) at low temperature (10 K). The top right part shows a typical spectrum measured from the sample we have grown: sharp lines associated with each QW can be clearly identified thanks to a careful grading of the As/P composition in each QW, while keeping its thickness to a constant value (typically 7 to 8 nm). Then we etched the samples (in the form of rectangular ridges as shown) using different etching processes, based either on wet etching or reactive ion etching (RIE), and recorded the PL spectra with high spatial resolution across the obtained structures. In parallel, the samples after etching were also characterized by cross-sectional scanning electron microscopy. Data processing from the series of PL spectra was then performed in order the characterize the effects of etching on the QW materials.We show PL intensity profiles across a series of etched stripes of different widths resulting from a RIE process. These intensity profiles were obtained from the lines associated with the different QWs in the structure. One can observe, first of all, that the PL intensity gradually increases from the edges to the center of the stripes, over a range of up to 10 µm. One can also observe that for “wide” stripes, i.e. 30 or 50 µm, the PL intensity for each line saturates at the same level in the central part. However, for the narrower stripes (10 or 20 µm), the PL signal does not reach the same level. This is the signature of some PL-limitation phenomenon, which extends its effects far from the etched sidewalls. A “standard” phenomenon resulting solely from non-radiative recombination at the etched sidewalls is excluded. Non-radiative recombination can only affect regions which are less than one charge carrier diffusion length from the sidewalls. Diffusion length in our materials is less than 1 µm. Therefore, some kind of “long range” interaction seems to affect our samples. We propose that this long range interaction is due to some stray static electric field resulting from the presence of residual ions left by the etching process at the sidewalls. The electric field affects the PL intensity through dissociation of excitons. Moreover, we observed that different conditions for the etching process (wet etching versus RIE, crystallographic orientation of the stripes) impact the magnitude of this PL intensity quenching.[1] Pearton S 1997 Materials Science and Engineering: B 44 1–7[2] Landesman J P, Isik-Goktas N, LaPierre R R, Levallois C, Ghanad-Tavakoli S, Pargon E, Petit-Etienne C and Jiménez J 2021 Journal of Physics D: Applied Physics 54 445106[3] Fiore A, Rossetti M, Alloing B, Paranthoen C, Chen J X, Geelhaar L and Riechert H 2004 Physical Review B 70 205311[4] Bludau W and Wagner E 1976 Physical Review B 13 5410–5414 Figure 1

Mapping and Characterization of Local Structures of CsPbBr3.

Inorganic perovskite CsPbBr3 is a promising material for optoelectronic applications and high-energy radiation detection due to its excellent photophysical properties, high carrier mobility, large carrier diffusion length, and higher stability than organic perovskite materials. Understanding phase transitions at the atomic level is crucial for optimizing its applications. Here, we employ experimental characterizations and molecular dynamics simulations to study the phase transitions in CsPbBr3 as a function of temperature. The simulation results are compared with the experimental results, which include X-ray diffraction (XRD). Our simulations provide new insights into the electronic structure and dynamic behavior of the Cs, Pb, and Br atoms as a function of temperature. We observe distinct phase transitions from monoclinic to cubic and analyze the associated changes in the local environment through atomic density contour maps. Our analysis of the atomic density distributions of the Pb, Br, and Cs atoms provides information about the crystal symmetry as a function of temperature. The tilt and rotation angles of [PbBr6] octahedra are increasing with the temperature increase and are found nonzero above 410 K when the structure is cubic, exhibiting the presence of dynamic tilting. Overall, our findings shed light on the thermal stability and structural dynamics of CsPbBr3, contribute to the fundamental understanding of its phase behavior, and provide a crucial pivot for guiding the design of next-generation optoelectronic and radiation detection devices.

Porous Bismuth Vanadate Photoelectrodes for Solar Water Oxidation Reaction

Bismuth vanadate (BiVO4), a material known for its high visible light activity and good stability, is a promising candidate as a photoanode for overall water splitting [1]. Its performance is limited by its relatively short charge carrier diffusion length, which has recently been estimated to be ~15 nm [2]. For these kinds of photo-absorbers, commercial flat transparent conducting oxide (TCO) substrates are unsuitable since the thickness needed to absorb a sufficient amount of light far exceeds the carrier diffusion length. With this in mind, deposition of very thin semiconductor film onto the internal structure of (micro)porous, conducting substrates can ensure sufficient light absorption [3], whilst ensuring the individual film thickness is uniformly lower than the carrier diffusion length. Nanostructured TCO substrates can be fabricated using a convenient template-free technique called glancing angle deposition (GLAD). The glancing angle deposition method can be used to synthesize different variations of highly oriented submicron-sized pillars, ranging from vertical and tilted columns to zig-zag and helical structures with the help of shadowing effects and substrate rotation [4]. The optical and electrical properties of nanostructured TCO’s were found to depend on the type of material and the substrate temperature during deposition. We find that pillars made from tin-doped indium oxide show good conductivity (79 Ohm/sq) and are promising for the fabrication of nanostructured substrates for bismuth vanadate. A recently developed alternative approach is the use of transparent, porous, conducting substrates (TPCS) made from quartz felt, in which the quartz fibers are coated with F-doped SnO2 [5]. We found that a BiVO4 film thickness of 50 nm within these porous substrates is enough to absorb the same amount of light as a compact 400 nm bismuth vanadate film. We will discuss the deposition of BiVO4 into the TPCS substrates and the photoelectrochemical performance of these porous photoanodes.[1] K. Sivula and R. van de Krol, Nat. Rev. Mater. 1, 15010 (2016)[2] M. Schleuning, M. Kölbach, F. F. Abdi, K. Schwarzburg, M. Stolterfoht, R. Eichberger, R. van de Krol, D. Friedrich, H. Hempel, PRX Energy 1, 023008 (2022)[3] U. Björksten, J. Moser and M. Grätzel, Chem. Mater. 6, 858 (1994)[4] M. M. Hawkeye, M. T. Taschuk and M. J. Brett, “Glancing Angle Deposition of Thin Films”, John Wiley & Sons, Ltd., Chichester, UK (2014).[5] M. Caretti, E. Mensi, R.-A. Kessler, L. Lazouni, B. Goldman, L. Carbone, S. Nussbaum, R. A. Wells, H. Johnson, E. Rideau, J.-h. Yum, K. Sivula, Adv. Mater. 35, 2208740 (2023)

Low-dimensional halide perovskites for advanced electronics

Halide perovskites are gaining prominence as promising materials for future electronic applications, primarily due to their unique properties including long carrier diffusion lengths, tunable bandgap, facile synthesis, and cost efficiency. However, polycrystalline halide perovskite thin films, which have been widely studied to date, have significant drawbacks including uncontrollable grain boundaries and instability issues. Recently, low-dimensional halide perovskites (LD HPs) offer enhanced stability and adaptable morphologies, making them attractive candidates for next-generation electronics beyond optoelectronics. This review comprehensively explores recent advancements in LD HP-based electronics, covering structural characteristics, synthesis methods tailored to different dimensions, and diverse applications. Furthermore, the impressive performance demonstrated by LD HPs in electronic applications including resistive random-access memory, advanced transistors, and neuromorphic computing hardware is discussed. Finally, the review outlines the challenges and perspectives required to scale up LD HP-based advanced electronics for commercial production, offering valuable insights for researchers venturing into the realm of new materials for advanced electronics.

Analytical Model for Current-Voltage Characteristics in Perovskite Solar Cells Incorporating Bulk and Surface Recombination.

The effects of surface recombination on the steady-state carrier profiles and photocurrent in perovskite solar cells are investigated in this paper. The continuity equations for both holes and electrons are solved considering carrier drift and diffusion under the exponential carrier generation profile in the perovskite layer and considering both bulk and interface carrier recombination. An analytical expression for the solar-induced photocurrent is derived. The rate of carrier recombination at the interfaces has a very significant effect on the carrier profile, photocurrent, and, hence, on the charge collection efficiency. The external current density is calculated considering the dark current and nominal solar spectrum-induced photocurrent. The proposed model is fitted and verified with published experimental results from various publications. The fittings of the model with experimental results provide information about the interface and bulk charge carrier transport parameters.

Carrier diffusion in long wavelength InGaN quantum well LEDs after injection through V-defects

The efficiency of operation of GaN-based light emitting diodes (LEDs) to a large degree relies on realization of a uniform hole distribution between multiple quantum wells (QWs) of the active region. Since the direct thermionic transport between the QWs is inefficient, the hole injection through semipolar 101¯1 QWs that form on the facets of V-defects has been suggested as an alternative approach. However, for an efficient LED operation, the carrier distribution should be uniform not only vertically, between the QWs but also laterally, within individual QWs. In this work, the lateral carrier distribution in long wavelength InGaN/GaN QW LEDs is studied by the scanning near-field optical microscopy. The measurements have shown that emission is concentrated around the V-defect injectors. At high currents, the diffusion length of holes in polar QWs was found to be ∼0.6–1 μm and the hole diffusion coefficient ∼0.6 cm2/s. The obtained data should aid design of the V-defect injectors for a laterally uniform carrier distribution in the active region QWs.

Review about Organic-Inorganic Perovskite Single Crystal : Synthesis Methods, Properties and Applications

Due to their easy synthesis and exceptional optoelectronic characteristics, such as their long carrier diffusion length, high carrier mobility, low trap density, and tuneable absorption edge ranging from ultraviolet (UV) to near-infrared (NIR), perovskite single crystals have attracted a lot of attention in recent years. These properties have the potential to be used in solar cells, photo-detectors (PDs), lasers, and other devices. In this review provides detailed information about the synthesis methods and applications of perovskite single crystals.

High-Entropy Design for 2D Halide Perovskite.

Hybrid halide perovskites are good candidates for a range of functional materials such as optical electronic and photovoltaic devices due to their tunable band gaps, long carrier diffusion lengths, and solution processability. However, the instability in moisture/air, the toxicity of lead, and rigorous reaction setup or complex postprocessing have long been the bottlenecks for practical application. Herein, we present a simultaneous configurational entropy design at A-sites, B-sites, and X-sites in the typical (CHA)2PbBr4 two-dimensional (2D) hybrid perovskite. Our results demonstrate that the high-entropy effect favors the stabilization of the hybrid perovskite phase and facilitates a simple crystallization process without precise control of the cooling rate to prepare regular crystals. Moreover, high-entropy 2D perovskite crystals exhibit tunable energy band gaps, broadband emission, and a long carrier lifetime. Meanwhile, the high-entropy composition almost maintains the initial crystal structure in deionized water for 18 h while the original (CHA)2PbBr4 crystal mostly decomposes, suggesting obviously improved humidity stability. This work offers a facile approach to synthesize humidity-stable hybrid perovskites under mild conditions, accelerating relevant preparation of optoelectronics and light-emitting devices and facilitating the ultimate commercialization of halide perovskite.

Electronic Properties and Mechanical Stability of Multi-Ion-Co-Intercalated Bilayered V2O5.

Incorporating metal cations into V2O5 has been proven to be an effective method for solving the poor long-term cycling performance of vanadium-based oxides as electrodes for mono- or multivalent aqueous rechargeable batteries. This is due to the existence of a bilayer structure with a large interlayer space in the V2O5 electrode and to the fact that the intercalated ions act as pillars to support the layered structure and facilitate the diffusion of charged carriers. However, a fundamental understanding of the mechanical stability of multi-ion-co-intercalated bilayered V2O5 is still lacking. In this paper, a variety of pillared vanadium pentoxides with two types of co-intercalated ions were studied. The root-mean-square deviation of the V-O bonds and the elastic constants calculated by density functional theory were used as references to evaluate the stability of the intercalated compounds. The d-band center and electronic band structures are also discussed. Our theoretical results show that the structural characteristics and stability of the system are quite strongly influenced by the intercalating strategy.

Composite scaffold of electrospun nano-porous cellulose acetate membrane casted with chitosan for flexible solid-state sodium-ion batteries

Emerging as a safe and economically viable alternative to lithium-ion batteries, the solid-state sodium ion battery (ss-SIB) has captured increasing attention as a transformative technology for realizing a decarbonized economy and ensuring a sustainable energy supply. Here we report a nanoarchitecture strategy of biodegradable, biocompatible, and naturally abundant cellulose derivative (cellulose acetate, CA) and chitosan (CH) biopolymer-based nano-porous electrospun composite electrolyte (ECE) for flexible and wearable ss-SIBs. A simple combination of electrospinning and solution casting was utilized to fabricate mechanically robust (13.76 MPa), thin-film (0.067 mm), and highly flexible ECE. The ionic conductivity of ECE was enhanced through optimization, taking into account the amount of sodium salt (NaPF6). The resulting ECE exhibited a sodium-ion conductivity of 1.04 ×10−4 S·cm−1 and a sodium ion transference number of 0.48 at room temperature (RT=23 °C). The obtained Na+ transference number of 0.48 and a low activation energy (Ea = 0.13 eV) indicate the easy charge carrier diffusion ability of as-prepared ECE. The electrochemical stability window (ESW = 4.04 V) of ECE is studied by the linear sweep voltammetry (LSV) with the assembly of stainless steel and sodium metal electrodes. Without any interfacial modification, a uniform, stable, and long-time room temperature (RT) galvanostatic Na plating-stripping was observed for 1000 hrs at 0.5 mA·cm−2 current density in a symmetric (Na|ECE|Na) cell, this underscores impressive electrochemical stability and compatibility of ECE with sodium metal. Utilizing Na3V2(PO4)3 (NVP) as cathode, fabricated ECE, and Na metal as anode in a hybrid full cell, a notable RT specific discharge capacity of 98.1 mA·h·g−1 was attained at a rate of 0.1 C with a capacity retention of 93.4 % over 120 charge-discharge cycles. This highlights the practical applicability of the nanostructured electrospun composite electrolyte for flexible and wearable ss-SIBs.

Sufficient energy band utilization profited from spatially discrete heterogeneous interfaces to induce efficient photoelectrochemical water splitting for ZnIn2S4 photoanode

The applied possibility of ZnIn2S4 is improved in the photoelectrochemical (PEC) energy transfer filed through elevated light absorption, accelerating charges transfer and suppressed carrier recombination. Consequently, Sb2S3/ZnIn2S4/Cu2S ternary composite photoanode is obtained through the induction of Sb2S3/ZnIn2S4 and ZnIn2S4/Cu2S heterogeneous interfaces at different spatial locations in ZnIn2S4, which enhances photocurrent density of ZnIn2S4-based photoanode to 2.81 mA/cm2 from 0.15 mA/cm2 with the nearly full visible spectrum absorption range of ∼ 776 nm. The deposition of Sb2S3 leads to enhanced quantum efficiencies, carrier diffusion time, and number of surface states. The loading of Cu2S top layer predominantly results in optimized surface states style and holes injection efficiency of SS/ZIS/CS. The comprehensive measurements and density functional theory (DFT) calculation demonstrate Sb2S3 and Cu2S are together employed to enhance the hybridization efficiencies of energy bands, accelerate charge transfer, revise the reaction sites, reduce free energy barrier of rate-determining steps and reaction over potential of ZnIn2S4 to enhance PEC water spitting. This work pioneers the construction of ZnIn2S4-based multijunction photoanodes with sufficient energy band utilization and confirms the conspicuous prospect for remaining photoanodes.

Enhance Carrier Diffusion of Monolayer MoSe2 by Interface Engineering.

Two-dimensional materials hold great potentials for beyond-CMOS (complementary metal-oxide-semiconductor) electronical and optoelectrical applications, and the development of field effect transistors (FET) with excellent performance using such materials is of particular interest. How to improve the performance of devices thus becomes an urgent issue. The performance of FETs depends greatly on the intrinsic electrical properties of the channel materials, meanwhile the device interface quality, such as extrinsic scattering of charged impurities, charge traps, and substrate surface roughness have a great influence on the performance. In this paper, the impact of the interface quality on the carrier diffusion behaviors of monolayer (ML) MoSe2 has been investigated by using an in situ ultrafast laser technique to avoid the surface contamination during device fabrication process. Two types of self-assembled monolayers (SAMs) are introduced to modify the gate dielectric surface through an interface engineering approach to obtain chemical-stable interfaces. The results showed that the transport properties of ML MoSe2 were enhanced after interface engineering, for example, the carrier mobility of ML MoSe2 was improved from ∼59.4 to ∼166.5 cm2 V-1 s-1 after the SAM modification. Meanwhile, the photocarrier dynamics of ML MoSe2 before and after interfacial engineering were also carefully studied. Our studies provide a feasible method for improving the carrier diffusion behaviors of such materials, and making them suited for application in future integrated circuit.

Forward bias annealing of proton radiation damage in NiO/Ga2O3 rectifiers

17 MeV proton irradiation at fluences from 3–7 × 1013 cm−2 of vertical geometry NiO/β-Ga2O3 heterojunction rectifiers produced carrier removal rates in the range 120–150 cm−1 in the drift region. The forward current density decreased by up to 2 orders of magnitude for the highest fluence, while the reverse leakage current increased by a factor of ∼20. Low-temperature annealing methods are of interest for mitigating radiation damage in such devices where thermal annealing is not feasible at the temperatures needed to remove defects. While thermal annealing has previously been shown to produce a limited recovery of the damage under these conditions, athermal annealing by minority carrier injection from NiO into the Ga2O3 has not previously been attempted. Forward bias annealing produced an increase in forward current and a partial recovery of the proton-induced damage. Since the minority carrier diffusion length is 150–200 nm in proton irradiated Ga2O3, recombination-enhanced annealing of point defects cannot be the mechanism for this recovery, and we suggest that electron wind force annealing occurs.

Heterostructures via a Solution-Based Anion Exchange in Microcrystalline 2D Layered Metal-Halide Perovskites.

Layered perovskites consist of stacks of inorganic semiconducting metal-halide octahedra lattices sandwiched between organic layers with typically dielectric behavior. The in-plane confinement of electrical carriers in such two-dimensional metal halide perovskites drives a large range of appealing electronic properties, such as strong exciton binding, anisotropic charge diffusion, and polarization-directionality. Heterostructures provide additional control on carrier diffusion and localization, and in-plane heterojunctions are interesting because of the associated high charge mobility. Here, this work demonstrates a versatile solution-based approach to fabricate in-plane heterostructures with different halide composition in two-dimensional lead-halide perovskite microcrystals. This leads to spatially separated halide phases with different band gap and light emission. Interestingly, the composition of the exchanged phase and the morphology of the phase boundary depends on the exchange route, which can be related to the preferred localization of the halides at the equatorial or axial octahedra positions that either leads to dissolution and recrystallization of the octahedra lattice (for bromide to iodide), or allows for ion diffusion within the lattice (for iodide to bromide). These detailed insights on the ion exchange processes in layered perovskites will stimulate the development of heterostructures that can be tailored for different applications such as photocatalysis, energy storage, and light emission.

High‐performance 110 kVp hard x‐ray detector based on all‐crystalline‐surface passivated perovskite single crystals

AbstractHalide perovskite single crystals (SCs) have attracted much attention for their application in high‐performance x‐ray detectors owing to their desirable properties, including low defect density, high mobility–lifetime product (μτ), and long carrier diffusion length. However, suppressing the inherent defects in perovskites and overcoming the ion migration primarily caused by these defects remains a challenge. This study proposes a facile process for dipping Cs0.05FA0.9MA0.05PbI3 SCs synthesized by a solution‐based inverse temperature crystallization method into a 2‐phenylethylammonium iodide (PEAI) solution to reduce the number of defects, inhibit ion migration, and increase x‐ray sensitivity. Compared to conventional spin coating, this simple dipping process forms a two‐dimensional PEA2PbI4 layer on all SC surfaces without further treatment, effectively passivating all surfaces of the inherently defective SCs and minimizing ion migration. As a result, the PEAI‐treated perovskite SC‐based x‐ray detector achieves a record x‐ray sensitivity of 1.3 × 105 μC Gyair−1 cm−2 with a bias voltage of 30 V at realistic clinical dose rates of 1–5 mGy s−1 (peak potential of 110 kVp), which is 6 times more sensitive than an untreated SC‐based detector and 3 orders of magnitude more sensitive than a commercial α‐Se‐based detector. Furthermore, the PEAI‐treated‐perovskite SC‐based x‐ray detector exhibits a low detection limit (73 nGy s−1), improved x‐ray response, and clear x‐ray images by a scanning method, highlighting the effectiveness of the PEAI dipping approach for fabricating next‐generation x‐ray detectors.image

Fast and broadband spatial-photoresistance modulation in graphene–silicon heterojunctions

Abstract Different types of devices with modulable resistance are attractive for the significant potential applications such as sensors, information storage, computation, etc. Although extensive research has been reported on resistance effects, there is still a need for exploring new mechanisms that offer advantages of low power consumption, high sensitivity, and long-term stability. Here, we report a graphene–Si based spatial-dependence photo-rheostat (SDPR), which enables bipolar resistance modulation in the range of 5 mm with a resistance sensitivity exceeding 1,000 Ω/mm at operating wavelengths from visible to near infrared band (1,550 nm). Especially, at ultra-low energy consumption, the device can achieve modulation of even 5 orders of magnitude of resistance and response speed up to 10 kHz. A theoretical model based on carrier dynamics is established to reveal the diffusion and drift of carriers as a mechanism explaining such experimental phenomenon. This work provides a new avenue to modulate resistance at low power consumption as novel opto-potentiometers in various photoelectric applications.

Surface Photovoltage Spectroscopy as a Valuable Tool for Evaluating Oxidation Processes in the Microelectronics Industry

In the present study, the minority carrier diffusion length (MCDL), determined by surface photovoltage spectroscopy measurements, is compared in n‐ and p‐type Si wafers after their oxidation under different conditions using various tools (horizontal and vertical furnaces, atomic layer deposition (ALD), low‐pressure chemical vapor deposition, and plasma‐enhanced chemical vapor deposition). It is shown that MCDL varies significantly depending on the design of furnaces, oxidation temperatures, the type of gases used before and during oxidation, and their flow ratios. The type and crystal growth method of Si wafers used for the oxidation also play a significant role and influence MCDL. Additionally, MCDL after the deposition of alumina layers using ALD techniques is found to be significantly larger compared to that observed after the thermal oxidation of Si. The larger values of MCDL after the ALD of Al2O3 are detected independent of temperature and precursors used for the deposition. The origin of different MCDL values after various oxidation processes, with an emphasis on the formation of electrically active defects in Czochralski (CZ)‐ and float‐zone (FZ)‐grown Si wafers is discussed.

Halide perovskite x-ray detectors: Fundamentals, progress, and outlook

Halide perovskites have demonstrated great potential in x-ray detectors, due to their high x-ray attenuation coefficient, large bulk resistance, ultralong carrier diffusion length, and adjustable bandgap. Moreover, their abundant raw materials and simple processing combined with excellent compatibility with integrated circuits make them ideal for cost-efficient and high-efficiency real-world imaging applications. Herein, we comprehensively reviewed advances and progress in x-ray detection devices based on halide perovskites. We expound on the fundamental mechanisms of interactions between x rays and matter as background and indicate different parameters for different types of x-ray detectors, which guides the basic requirements on how to select and design suitable materials for active layers. After emphasizing the superb properties of halide perovskites through the shortcomings of commercial materials, we evaluate the latest advancements and ongoing progress in halide perovskites with different dimensions and structures for both direct and indirect x-ray detectors, and discuss the effect of dimensional varieties on the device performance. We also highlight current challenges in the area of perovskite x-ray detectors and propose corresponding solutions to optimize halide perovskites and optimize x-ray detectors for next-generation imaging applications.

Visualizing Carrier Diffusion in Cs‐Doping FAPbI3 Perovskite Thin Films Using Transient Absorption Microscopy

AbstractThe determination of the semiconducting materials performance heavily relies on the diffusion coefficient and length of the carrier. Recently, significant progress is made in enhancing solar cell efficiency through improved carrier diffusion in perovskite thin films. However, the spatial‐temporal mechanisms underlying carrier transport remain unclear. Recent advancements in utilizing transient absorption microscopy (TAM) offer promising opportunities to directly visualize the carrier transport dynamics within perovskite films. Here, the wide‐field imaging TAM combined with X‐ray diffraction and scanning electron microscopy is employed to investigate the spatial‐temporal carrier transport dynamics in FA1−xCsxPbI3 perovskites with varying Cs doping ratios. The experimental results indicate that the diffusion constant remains consistent regardless of the excitation power. Moreover, a decrease in the Cs doping ratio leads to an increase in the diffusion length within FA1−xCsxPbI3 perovskites. The measurements reveal a highest diffusion coefficient of up to 0.085 cm2 s−1 and a maximum diffusion length of ≈1.4 µm in FA0.97Cs0.03PbI3. Comparative analysis of short‐circuit current density, open‐circuit voltage, fill factor, and power conversion efficiency demonstrates that FA0.97Cs0.03PbI3 exhibits superior device efficiency. The TAM visualizes spatial/ temporal carrier diffusion dynamics, showing a significant correlation with device efficiency and thus providing valuable insights for further enhancing device performance.