Low‐Noise and Large‐Linear‐Dynamic‐Range Photodetectors Based on Hybrid‐Perovskite Thin‐Single‐Crystals

Organic–inorganic halide perovskites are promising photodetector materials due to their strong absorption, large carrier mobility, and easily tunable bandgap. Up to now, perovskite photodetectors are mainly based on polycrystalline thin films, which have some undesired properties such as large defective grain boundaries hindering the further improvement of the detector performance. Here, perovskite thin‐single‐crystal (TSC) photodetectors are fabricated with a vertical p–i–n structure. Due to the absence of grain‐boundaries, the trap densities of TSCs are 10–100 folds lower than that of polycrystalline thin films. The photodetectors based on CH₃NH₃PbBr₃ and CH₃NH₃PbI₃ TSCs show low noise of 1–2 fA Hz^?1/2, yielding a high specific detectivity of 1.5 × 10¹³ cm Hz^1/2 W^?1. The absence of grain boundaries reduces charge recombination and enables a linear response under strong light, superior to polycrystalline photodetectors. The CH₃NH₃PbBr₃ photodetectors show a linear response to green light from 0.35 pW cm^?2 to 2.1 W cm^?2, corresponding to a linear dynamic range of 256 dB.     

A 1300 mm2 Ultrahigh‐Performance Digital Imaging Assembly using High‐Quality Perovskite Single Crystals

By fine‐tuning the crystal nucleation and growth process, a low‐temperature‐gradient crystallization method is developed to fabricate high‐quality perovskite CH₃NH₃PbBr₃ single crystals with high carrier mobility of 81 ± 5 cm² V^?1 s^?1 (>3 times larger than their thin film counterpart), long carrier lifetime of 899 ± 127 ns (>5 times larger than their thin film counterpart), and ultralow trap state density of 6.2 ± 2.7 × 10⁹ cm^?3 (even four orders of magnitude lower than that of single‐crystalline silicon wafers). In fact, they are better than perovskite single crystals reported in prior work: their application in photosensors gives superior detectivity as high as 6 × 10¹³ Jones, ≈10–100 times better than commercial sensors made of silicon and InGaAs. Meanwhile, the response speed is as fast as 40 µs, ≈3 orders of magnitude faster than their thin film devices. A large‐area (≈1300 mm²) imaging assembly composed of a 729‐pixel sensor array is further designed and constructed, showing excellent imaging capability thanks to its superior quality and uniformity. This opens a new possibility to use the high‐quality perovskite single‐crystal‐based devices for more advanced imaging sensors.     

Photostriction of CH3NH3PbBr3 Perovskite Crystals

Organic–inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light–matter interactions. The photoinduced strain of CH₃NH₃PbBr₃ is investigated using high‐resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH₃NH₃PbBr₃ is calculated as 2.08 × 10^?8 m² W^?1 at room temperature under visible light illumination. The significant photostriction of CH₃NH₃PbBr₃ is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation–rotation coupling. Unlike CH₃NH₃PbI₃, it is noted that the photostriction of CH₃NH₃PbBr₃ is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH₃NH₃PbBr₃ for applications in next‐generation optical micro‐electromechanical devices.     

A Self‐Powered and Flexible Organometallic Halide Perovskite Photodetector with Very High Detectivity

Flexible and self‐powered photodetectors (PDs) are highly desirable for applications in image sensing, smart building, and optical communications. In this paper, a self‐powered and flexible PD based on the methylammonium lead iodide (CH₃NH₃PBI₃) perovskite is demonstrated. Such a self‐powered PD can operate even with irregular motion such as human finger tapping, which enables it to work without a bulky external power source. In addition, with high‐quality CH₃NH₃PBI₃ perovskite thin film fabricated with solvent engineering, the PD exhibits an impressive detectivity of 1.22 × 10¹³ Jones. In the self‐powered voltage detection mode, it achieves a large responsivity of up to 79.4 V mW^?1 cm^?2 and a voltage response of up to ≈90%. Moreover, as the PD is made of flexible and transparent polymer films, it can operate under bending and functions at 360 ° of illumination. As a result, the self‐powered, flexible, 360 ° omnidirectional perovskite PD, featuring high detectivity and responsivity along with real‐world sensing capability, suggests a new direction for next‐generation optical communications, sensing, and imaging applications.     

Fabry–Pérot Oscillation and Room Temperature Lasing in Perovskite Cube‐Corner Pyramid Cavities

Recently, organometal halide perovskite‐based optoelectronics, particularly lasers, have attracted intensive attentions because of its outstanding spectral coherence, low threshold, and wideband tunability. In this work, high‐quality CH₃NH₃PbBr₃ single crystals with a unique shape of cube‐corner pyramids are synthesized on mica substrates using chemical vapor deposition method. These micropyramids naturally form cube‐corner cavities, which are eminent candidates for small‐sized resonators and retroreflectors. The as‐grown perovskites show strong emission ≈530 nm in the vertical direction at room temperature. A special Fabry–Pérot (F–P) mode is employed to interpret the light confinement in the cavity. Lasing from the perovskite pyramids is observed from 80 to 200 K, with threshold ranging from ≈92 µJ cm^?2 to 2.2 mJ cm^?2, yielding a characteristic temperature of T₀ = 35 K. By coating a thin layer of Ag film, the threshold is reduced from ≈92 to 26 µJ cm^?2, which is accompanied by room temperature lasing with a threshold of ≈75 µJ cm^?2. This work advocates the prospect of shape‐engineered perovskite crystals toward developing micro‐sized optoelectronic devices and potentially investigating light–matter coupling in quantum optics.     

Highly Reproducible Large‐Area Perovskite Solar Cell Fabrication via Continuous Megasonic Spray Coating of CH3NH3PbI3

A simple, low‐cost, large area, and continuous scalable coating method is proposed for the fabrication of hybrid organic–inorganic perovskite solar cells. A megasonic spray‐coating method utilizing a 1.7 MHz megasonic nebulizer that could fabricate reproducible large‐area planar efficient perovskite films is developed. The coating method fabricates uniform large‐area perovskite film with large‐sized grain since smaller and narrower sized mist droplets than those generated by existing ultrasonic spray methods could be generated by megasonic spraying. The volume flow rate of the CH₃NH₃PbI₃ precursor solution and the reaction temperature are controlled, to obtain a high quality perovskite active layer. The devices reach a maximum efficiency of 16.9%, with an average efficiency of 16.4% from 21 samples. The applicability of megasonic spray coating to the fabrication of large‐area solar cells (1 cm²), with a power conversion efficiency of 14.2%, is also demonstrated. This is a record high efficiency for large‐area perovskite solar cells fabricated by continuous spray coating.     

Direct Observation of Halide Migration and its Effect on the Photoluminescence of Methylammonium Lead Bromide Perovskite Single Crystals

Optoelectronic devices based on hybrid perovskites have demonstrated outstanding performance within a few years of intense study. However, commercialization of these devices requires barriers to their development to be overcome, such as their chemical instability under operating conditions. To investigate this instability and its consequences, the electric field applied to single crystals of methylammonium lead bromide (CH₃NH₃PbBr₃) is varied, and changes are mapped in both their elemental composition and photoluminescence. Synchrotron‐based nanoprobe X‐ray fluorescence (nano‐XRF) with 250 nm resolution reveals quasi‐reversible field‐assisted halide migration, with corresponding changes in photoluminescence. It is observed that higher local bromide concentration is correlated to superior optoelectronic performance in CH₃NH₃PbBr₃. A lower limit on the electromigration rate is calculated from these experiments and the motion is interpreted as vacancy‐mediated migration based on nudged elastic band density functional theory (DFT) simulations. The XRF mapping data provide direct evidence of field‐assisted ionic migration in a model hybrid‐perovskite thin single crystal, while the link with photoluminescence proves that the halide stoichiometry plays a key role in the optoelectronic properties of the perovskite.     

High Performance and Stable All‐Inorganic Metal Halide Perovskite‐Based Photodetectors for Optical Communication Applications

Photodetectors are critical parts of an optical communication system for achieving efficient photoelectronic conversion of signals, and the response speed directly determines the bandwidth of the whole system. Metal halide perovskites, an emerging class of low‐cost solution‐processed semiconductors, exhibiting strong optical absorption, low trap states, and high carrier mobility, are widely investigated in photodetection applications. Herein, through optimizing the device engineering and film quality, high‐performance photodetectors based on all‐inorganic cesium lead halide perovskite (CsPbI_xBr_3–x), which simultaneously possess high sensitivity and fast response, are demonstrated. The optimized devices processed from CsPbIBr₂ perovskite show a practically measured detectable limit of about 21.5 pW cm^?2 and a fast response time of 20 ns, which are both among the highest reported device performance of perovskite‐based photodetectors. Moreover, the photodetectors exhibit outstanding long‐term environmental stability, with negligible degradation of the photoresponse property after 2000 h under ambient conditions. In addition, the resulting perovskite photodetector is successfully integrated into an optical communication system and its applications as an optical signal receiver on transmitting text and audio signals is demonstrated. The results suggest that all‐inorganic metal halide perovskite‐based photodetectors have great application potential for optical communication.     

Controlled Homoepitaxial Growth of Hybrid Perovskites

Organic–inorganic hybrid perovskites have demonstrated tremendous potential for the next‐generation electronic and optoelectronic devices due to their remarkable carrier dynamics. Current studies are focusing on polycrystals, since controlled growth of device compatible single crystals is extremely challenging. Here, the first chemical epitaxial growth of single crystal CH₃NH₃PbBr₃ with controlled locations, morphologies, and orientations, using combined strategies of advanced microfabrication, homoepitaxy, and low temperature solution method is reported. The growth is found to follow a layer‐by‐layer model. A light emitting diode array, with each CH₃NH₃PbBr₃ crystal as a single pixel, with enhanced quantum efficiencies than its polycrystalline counterparts is demonstrated.     

Atomic‐Layer Deposition‐Assisted Double‐Side Interfacial Engineering for High‐Performance Flexible and Stable CsPbBr3 Perovskite Photodetectors toward Visible Light Communication Applications

Self‐powered photodetectors (PDs) based on inorganic metal halide perovskites are regarded as promising alternatives for the next generation of photodetectors. However, uncontrollable film growth and sluggish charge extraction at interfaces directly limit the sensitivity and response speed of perovskite‐based photodetectors. Herein, by assistance of an atomic layer deposition (ALD) technique, CsPbBr₃ perovskite thin films with preferred orientation and enlarged grain size are obtained on predeposited interfacial modification layers. Thanks to improved film quality and double side interfacial engineering, the optimized CsPbBr₃ (Al₂O₃/CsPbBr₃/TiO₂, ACT) perovskite PDs exhibit outstanding performance with ultralow dark current of 10^?11 A, high detectivity of 1.88 × 10¹³ Jones and broad linear dynamic range (LDR) of 172.7 dB. Significantly, excellent long‐term environmental stability (ambient conditions >100 d) and flexibility stability (>3000 cycles) are also achieved. The remarkable performance is credited to the synergistic effects of high carrier conductivity and collection efficiency, which is assisted by ALD modification layers. Finally, the ACT PDs are successfully integrated into a visible light communication system as a light receiver on transmitting texts, showing a bit rate as high as 100 kbps. These results open the window of high performance all‐inorganic halide perovskite photodetectors and extends to rational applications for optical communication.     

Real‐Time Observation of Order‐Disorder Transformation of Organic Cations Induced Phase Transition and Anomalous Photoluminescence in Hybrid Perovskites

A fundamental understanding of the interplay between the microscopic structure and macroscopic optoelectronic properties of organic‐inorganic hybrid perovskite materials is essential to design new materials and improve device performance. However, how exactly the organic cations affect the structural phase transition and optoelectronic properties of the materials is not well understood. Here, real‐time, in situ temperature‐dependent neutron/X‐ray diffraction and photoluminescence (PL) measurements reveal a transformation of the organic cation CH₃NH₃ ⁺ from order to disorder with increasing temperature in CH₃NH₃PbBr₃ perovskites. The molecular‐level order‐to‐disorder transformation of CH₃NH₃ ⁺ not only leads to an anomalous increase in PL intensity, but also results in a multidomain to single‐domain structural transition. This discovery establishes the important role that organic cation ordering has in dictating structural order and anomalous optoelectronic phenomenon in hybrid perovskites.     

Large‐Scale Synthesis of Freestanding Layer‐Structured PbI2 and MAPbI3 Nanosheets for High‐Performance Photodetection

Recently, due to the possibility of thinning down to the atomic thickness to achieve exotic properties, layered materials have attracted extensive research attention. In particular, PbI₂, a kind of layered material, and its perovskite derivatives, CH₃NH₃PbI₃ (i.e., MAPbI₃), have demonstrated impressive photoresponsivities for efficient photodetection. Herein, the synthesis of large‐scale, high‐density, and freestanding PbI₂ nanosheets is demonstrated by manipulating the microenvironment during physical vapor deposition. In contrast to conventional two‐dimensional (2D) growth along the substrate surface, the essence here is the effective nucleation of microplanes with different angles relative to the in‐plane direction of underlying rough‐surfaced substrates. When configured into photodetectors, the fabricated device exhibits a photoresponsivity of 410 mA W^?1, a detectivity of 3.1 × 10¹¹ Jones, and a fast response with the rise and decay time constants of 86 and 150 ms, respectively, under a wavelength of 405 nm. These PbI₂ nanosheets can also be completely converted into MAPbI₃ materials via chemical vapor deposition with an improved photoresponsivity up to 40 A W^?1. All these performance parameters are comparable to those of state‐of‐the‐art layered‐material‐based photodetectors, revealing the technological potency of these freestanding nanosheets for next‐generation high‐performance optoelectronics.     

Hybrid Perovskite Light‐Emitting Diodes Based on Perovskite Nanocrystals with Organic–Inorganic Mixed Cations

Organic–inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed‐cation perovskite nanocrystals based on FA_{(1?x )}Cs_x PbBr₃ (FA = CH(NH₂)₂). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA_{(1?x )}Cs_x PbBr₃, is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed‐cation perovskites are employed as light emitters in light‐emitting diodes (LEDs). With an optimized composition of FA_0.8Cs_0.2PbBr₃, the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m^?2 and a current efficiency of 10.09 cd A^?1. This work provides important instructions on the future compositional optimization of mixed‐cation perovskite for obtaining high‐performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs.     

A Highly Sensitive Single Crystal Perovskite–Graphene Hybrid Vertical Photodetector

Organolead trihalide perovskites have attracted significant attention for optoelectronic applications due to their excellent physical properties in the past decade. Generally, both grain boundaries in perovskite films and the device structure play key roles in determining the device performance, especially for horizontal‐structured device. Here, the first optimized vertical‐structured photodetector with the perovskite single crystal MAPbBr₃ as the light absorber and graphene as the transport layer is shown. The hybrid device combines strong photoabsorption characteristics of perovskite and high carrier mobility of flexible graphene, exhibits excellent photoresponse performance with high photoresponsivity (≈1017.1 A W^?1) and high photodetectivity (≈2.02 × 10¹³ Jones) in a low light intensity (0.66 mW cm^?2) under the actuations of 3 V bias and laser irradiation at 532 nm. In particular, an ultrahigh photoconductive gain of ≈2.37 × 10³ is attained because of fast charge transfer in the graphene and large recombination lifetime in the perovskite single crystal. The vertical architecture combining perovskite crystal with highly conductive graphene offers opportunities to fulfill the synergistic effect of perovskite and 2D materials, is thus promising for developing high‐performance electronic and optoelectronic devices.     

In Situ Growth of MAPbBr3 Nanocrystals on Few‐Layer MXene Nanosheets with Efficient Energy Transfer

The performance of perovskite nanocrystals (NCs) in optoelectronics and photocatalysis is severely limited by the presence of large amounts of crystal boundaries in NCs film that greatly restricts energy transfer. Creating heterostructures based on perovskite NCs and 2D materials is a common approach to improve the energy transport at the perovskite/2D materials interface. Herein, methylamine lead bromide (MAPbBr₃, MA: CH₃NH₃⁺) perovskite NCs are homogeneously deposited on highly conductive few‐layer MXene (Ti₃C₂T_x) nanosheets to form heterostructures through an in situ solution growth method. An optimal mixed solvent ratio is essential to realize the growth of perovskite NCs on Ti₃C₂T_x nanosheets. Time‐resolved photoluminescence spectroscopy, transient absorption spectroscopy, and the photoresponse of electron‐ and hole‐only photoelectric conversion devices reveal the interfacial energy transfer behavior within MAPbBr₃/Ti₃C₂T_x heterostructures. The present investigation may provide a useful guide toward use of halide perovskite/2D material heterostructures in applications such as photocatalysis as well as optoelectronics.     

Organometallic hybrid perovskites: structural,optical characteristic and application in Schottky diode

CH₃NH₃PbI₃ thin film was deposited by a dual-source evaporation system under high vacuum (~10^?4 Pa). The crystallographic phase of the thin film was determined by X-ray diffraction and its perovskite structure was confirmed. The crystal of annealed perovskite film was extremely smooth and significantly larger than that of as-deposited. The optical property of the thin film was investigated in the spectral range 300–1800 nm. By analyzing the absorption coefficient (α), the optical band gap (1.58 eV) and Urbach energy (0.082 eV) were revealed. The Al/CH₃NH₃PbI₃/ITO Schottky diode was fabricated in order to explore the potential applications of CH₃NH₃PbI₃. The basic device parameters, barrier height and ideality factor were determined by the current–voltage (I–V) measurement. It can be found that the charge transport was governed by space-charge-limited current mechanism by studying the forward bias characteristic.     

Distinguishable Detection of Ultraviolet,Visible, and Infrared Spectrum with High‐Responsivity Perovskite‐Based Flexible Photosensors

Distinguishable detection of the ultraviolet, visible, and infrared spectrum is promising and significant for the super visual system of artificial intelligences. However, it is challenging to provide a photosensor with such broad spectral response ability. In this work, the ultraviolet, visible, and infrared spectrum is distinguished by developing serial photosensors based on perovskite/carbon nanotube hybrids. Oraganolead halide perovskites (CH₃NH₃PbX₃) possess remarkable optoelectronic properties and tunable optical band gaps by changing the halogens, and integration with single‐walled carbon nanotubes can further improve their photoresponsivities. The CH₃NH₃PbCl₃‐based photosensor shows a responsivity up to 10⁵ A W^?1 to ultraviolet and no obvious response to visible light, which is superior to that of most ultraviolet sensors. The CH₃NH₃PbBr₃‐based photosensor exhibits a high responsivity to visible light. Serial devices of the two hybrid photosensors with comparable electric and sensory performances can distinguish the spectrum of ultraviolet, visible, and infrared even with varying light intensities. The photosensors also demonstrate excellent mechanical flexibility and bending stability. By taking full advantages of the oraganolead halide perovskites, this work provides flexible high‐responsivity photosensors specialized for ultraviolet, and gives a simple strategy for distinguishable detection of ultraviolet, visible, and infrared spectrum based on the serial flexible photosensors.     

Dopant‐Free Hole‐Transporting Materials for Stable and Efficient Perovskite Solar Cells

Molecularly engineered novel dopant‐free hole‐transporting materials for perovskite solar cells (PSCs) combined with mixed‐perovskite (FAPbI₃)_0.85(MAPbBr₃)_0.15 (MA: CH₃NH₃⁺, FA: NH=CHNH₃⁺) that exhibit an excellent power conversion efficiency of 18.9% under AM 1.5 conditions are investigated. The mobilities of FA‐CN, and TPA‐CN are determined to be 1.2 × 10^?4 cm² V^?1 s^?1 and 1.1 × 10^?4 cm² V^?1 s^?1, respectively. Exceptional stability up to 500 h is measured with the PSC based on FA‐CN. Additionally, it is found that the maximum power output collected after 1300 h remained 65% of its initial value. This opens up new avenue for efficient and stable PSCs exploring new materials as alternatives to Spiro‐OMeTAD.     

Superficial‐Layer‐Enhanced Raman Scattering (SLERS) for Depth Detection of Noncontact Molecules

Although the strength of Raman signals can be increased by many orders of magnitude on noble metal nanoparticles, this enhancement is confined to an extremely short distance from the Raman‐active surface. The key to the development of Raman spectroscopy for applications in diagnosis and detection of cancer and inflammatory diseases, and in pharmacology, relies on the capability of detecting analytes that are noninteractive with Raman‐active surfaces. Here, a new Raman enhancement system is constructed, superficial‐layer‐enhanced Raman scattering (SLERS), by covering elongated tetrahexahedral gold nanoparticle arrays with a superficial perovskite (CH₃NH₃PbBr₃) film. Plasmonic decay is depressed along the vertical direction away from the noble metal surface and the penetration depth is increased in the perovskite media. The vertical penetration of SLERS is verified by the spatial distribution of the analytes via Raman imaging in layer‐scanning mode.     

Divalent Anionic Doping in Perovskite Solar Cells for Enhanced Chemical Stability

The chemical stabilities of hybrid perovskite materials demand further improvement toward long‐term and large‐scale photovoltaic applications. Herein, the enhanced chemical stability of CH₃NH₃PbI₃ is reported by doping the divalent anion Se^2? in the form of PbSe in precursor solutions to enhance the hydrogen‐bonding‐like interactions between the organic cations and the inorganic framework. As a result, in 100% humidity at 40 °C, the 10% w/w PbSe‐doped CH₃NH₃PbI₃ films exhibited >140‐fold stability improvement over pristine CH₃NH₃PbI₃ films. As the PbSe‐doped CH₃NH₃PbI₃ films maintained the perovskite structure, a top efficiency of 10.4% with 70% retention after 700 h aging in ambient air is achieved with an unencapsulated 10% w/w PbSe:MAPbI₃‐based cell. As a bonus, the incorporated Se^2? also effectively suppresses iodine diffusion, leading to enhanced chemical stability of the silver electrodes.