Direct Vapor Growth of Perovskite CsPbBr3 Nanoplate Electroluminescence Devices

Synthesis and Properties of Size-Adjustable CsPbBr3 Nanosheets for Potential Photocatalysis

Amidst the rapid advancements in the fields of photovoltaics and optoelectronic devices, CsPbBr3 nanosheets (NSs) have emerged as a focal point of research due to their exceptional optical and electronic properties. This work explores the application potential of CsPbBr3 NSs in photonic and catalytic domains. Utilizing an optimized hot-injection method and a ZnBr2-assisted in situ passivation strategy, we successfully synthesized CsPbBr3 NSs with controlled dimensions and optical characteristics. Comprehensive characterization revealed that the nucleation environment and thickness significantly influenced the structure and optical performance of the materials. The results indicate that the optimized synthesis method enables control over the lateral dimensions of the nanoparticles, ranging from 9.1 ± 0.06 nm to 334.5 ± 4.40 nm, facilitating the tuning of the excitation wavelength from 460 nm (blue) to 510 nm (green). Further analyses involving photoresponse and electrochemical impedance spectroscopy demonstrated the substantial potential of these NSs in applications such as photocatalysis and energy conversion.

A Digital-Analog Bimodal Memristor Based on CsPbBr3 for Tactile Sensory Neuromorphic Computing

Memristor with digital and analog bipolar bimodal resistive switching offers a promising opportunity for the information-processing component. However, it still remains a huge challenge that the memristor enables bimodal digital and analog types and fabrication of artificial sensory neural network system. Here, a proposed CsPbBr3 -based memristor demonstrates a high ON/OFF ratio (>103 ), long retention (>104 s), stable endurance (100 cycles), and multilevel resistance memory, which acts as an artificial synapse to realize fundamental biological synaptic functions and neuromorphic computing based on controllable resistance modulation. Moreover, a 5 × 5 spinosum-structured piezoresistive sensor array (sensitivity of 22.4 kPa-1 , durability of 1.5 × 104 cycles, and fast response time of 2.43 ms) is constructed as a tactile sensory receptor to transform mechanical stimuli into electrical signals, which can be further processed by the CsPbBr3 -based memristor with synaptic plasticity. More importantly, this artificial sensory neural network system combined the artificial synapse with 5 × 5 tactile sensing array based on piezoresistive sensors can recognize the handwritten patterns of different letters with high accuracy of 94.44% under assistance of supervised learning. Consequently, the digital-analog bimodal memristor would demonstrate potential application in human-machine interaction, prosthetics, and artificial intelligence.

Optoelectronic Devices of Large-Scale Transferred All-Inorganic Lead Halide Perovskite Thin Films

We report the large-scale transfer process for monocrystalline CsPbBr₃ thin films prepared by chemical vapor deposition (CVD) with excellent optical properties and stability. The transfer process is robust, simple, and effective, in which CsPbBr₃ thin films could be transferred to several substrates and effectively avoid chemical or physical fabrication processes to damage the perovskite surface. Moreover, the transfer process endows CsPbBr₃ and substrates with atomically clean and electronically flat interfaces. We utilize this transfer process to realize several optoelectronic devices, including a photonic laser with a threshold of 61 μJ/cm², a photodetector with a responsivity of 2.4 A/W, and a transistor with a hole mobility of 11.47 cm² V^-1 s^-1. High device performances mainly originate from low defects of high-quality single-crystal perovskite and seamless contact between CsPbBr₃ and target substrates. The large-scale nondestructive transfer process provides promising opportunities for optoelectronic applications based on monocrystalline perovskites.

Organic-Inorganic Lead Halide Perovskite Single Crystal: From Synthesis to Applications

Organic-inorganic lead halide perovskite is widely used in the photoelectric field due to its excellent photoelectric characteristics. Among them, perovskite single crystals have attracted much attention due to its lower trap density and better carrier transport capacity than their corresponding polycrystalline materials. Owing to these characteristics, perovskite single crystals have been widely used in solar cells, photodetectors, light-emitting diode (LED), and so on, which have greater potential than polycrystals in a series of optoelectronic applications. However, the fabrication of single-crystal devices is limited by size, thickness, and interface problems, which makes the development of single-crystal devices inferior to polycrystalline devices, which also limits their future development. Here, several representative optoelectronic applications of perovskite single crystals are introduced, and some existing problems and challenges are discussed. Finally, we outlook the growth mechanism of single crystals and further the prospects of perovskite single crystals in the further field of microelectronics.

Review on Perovskite Semiconductor Field‑Effect Transistors and Their Applications

Perovskite materials are considered as the most alluring successor to the conventional semiconductor materials to fabricate solar cells, light emitting diodes and electronic displays. However, the use of the perovskite semiconductors as a channel material in field effect transistors (FET) are much lower than expected due to the poor performance of the devices. Despite low attention, the perovskite FETs are used in widespread applications on account of their unique opto-electrical properties. This review focuses on the previous works on perovskite FETs which are summarized into tables based on their structures and electrical properties. Further, this review focuses on the applications of perovskite FETs in photodetectors, phototransistors, light emitting FETs and memory devices. Moreover, this review highlights the challenges faced by the perovskite FETs to meet the current standards along with the future directions of these FETs. Overall, the review summarizes all the available information on existing perovskite FET works and their applications reported so far.

Mid-Infrared Optoelectronic Devices Based on Two-Dimensional Materials beyond Graphene: Status and Trends

Since atomically thin two-dimensional (2D) graphene was successfully synthesized in 2004, it has garnered considerable interest due to its advanced properties. However, the weak optical absorption and zero bandgap strictly limit its further development in optoelectronic applications. In this regard, other 2D materials, including black phosphorus (BP), transition metal dichalcogenides (TMDCs), 2D Te nanoflakes, and so forth, possess advantage properties, such as tunable bandgap, high carrier mobility, ultra-broadband optical absorption, and response, enable 2D materials to hold great potential for next-generation optoelectronic devices, in particular, mid-infrared (MIR) band, which has attracted much attention due to its intensive applications, such as target acquisition, remote sensing, optical communication, and night vision. Motivated by this, this article will focus on the recent progress of semiconducting 2D materials in MIR optoelectronic devices that present a suitable category of 2D materials for light emission devices, modulators, and photodetectors in the MIR band. The challenges encountered and prospects are summarized at the end. We believe that milestone investigations of 2D materials beyond graphene-based MIR optoelectronic devices will emerge soon, and their positive contribution to the nano device commercialization is highly expected.

High-Luminance Microsized CH3NH3PbBr3 Single-Crystal-Based Light-Emitting Diodes via a Facile Liquid-Insulator Bridging Route

Micro-/nanosized organic-inorganic hybrid perovskite single crystals (SCs) with appropriate thickness and high crystallinity are promising candidates for high-performance electroluminescent (EL) devices. However, their small lateral size poses a great challenge for efficient device construction and performance optimization, causing perovskite SC-based light-emitting diodes (PSC-LEDs) to demonstrate poor EL performance. Here, we develop a facile liquid-insulator bridging (LIB) strategy to fabricate high-luminance PSC-LEDs based on single-crystalline CH₃NH₃PbBr₃ microflakes. By introducing a blade-coated poly(methyl methacrylate) (PMMA) insulating layer to effectively overcome the problems of leakage current and possible short circuits between electrodes, we achieve the reliable fabrication of PSC-LEDs. The LIB method also allows us to systematically boost the device performance through crystal growth regulation and device architecture optimization. Consequently, we realize the best CH₃NH₃PbBr₃ microflake-based PSC-LED with an ultrahigh luminance of 136100 cd m^-2 and a half-lifetime of 88.2 min at an initial luminance of ∼1100 cd m^-2, which is among the highest for organic-inorganic hybrid perovskite LEDs reported to date. Moreover, we observe the strong polarized edge emission of the microflake-based PSC-LEDs with a high degree of polarization up to 0.69. Our work offers a viable approach for the development of high-performance perovskite SC-based EL devices.

Photoelectric Logic and In Situ Memory Transistors with Stepped Floating Gates of Perovskite Quantum Dots

Electronic-Photonic integrated systems have attracted intensive attention in addressing the explosively increasing data-processing issue in the post-Moore era. However, the tremendous size difference between basic electronic and photonic units poses challenges for the further deep convergence of optoelectronic microprocessors. Here, we report a floating-gate transistor fabricated with complementary metal-oxide-semiconductor compatible technologies, which can realize multilevel photoelectric logic computing and in situ memory simultaneously. The transistor presents stepped floating gates of perovskite quantum dots with different bandgaps and exhibits nonvolatile multilevel memory states written/erased by electrical and high-bandwidth optical signals. Meanwhile, the device can also realize logic functions such as an optoelectronic AND gate by separably programming the states of the stepped floating gates with bias and optical wavelength. A convergence of multilevel logic computing and storage is further achieved on the transistor. By demonstrating such multifunctionality in a single device, the photoelectric transistors, even with a rather large size to match photonic cells, can provide the optoelectronic microprocessors with substantially improved performances.

Shedding light on the energy applications of emerging 2D hybrid organic-inorganic halide perovskites

Unique performance of the hybrid organic-inorganic halide perovskites (HOIPs) has attracted great attention because of their continuous exploration and breakthrough in a multitude of energy-related applications. However, the instability and lead-induced toxicity that arise in bulk perovskites are the two major challenges that impede their future commercialization process. To find a solution, a series of two-dimensional HOIPs (2D HOIPs) are investigated to prolong the device lifetime with highly efficient photoelectric conversion and energy storage. Herein, the recent advances of 2D HOIPs and their structural derivatives for the energy realms are summarized and discussed. The basic understanding of crystal structures, physicochemical properties, and growth mechanisms is presented. In addition, the current challenges and future directions to provide a roadmap for the development of next generation 2D HOIPs are prospected

A Review of Phototransistors Using Metal Oxide Semiconductors: Research Progress and Future Directions

Metal oxide thin-film transistors have been continuously researched and mass-produced in the display industry. However, their phototransistors are still in their infancy. In particular, utilizing metal oxide semiconductors as phototransistors is difficult because of the limited light absorption wavelength range and persistent photocurrent (PPC) phenomenon. Numerous studies have attempted to improve the detectable light wavelength range and the PPC phenomenon. Here, recent studies on metal oxide phototransistors are reviewed, which have improved the range of light wavelengths and the PPC phenomenon by introducing an absorption layer of oxide or non-oxide hybrid structure. The materials of the absorption layer applied to absorb long-wavelength light are classified into oxides, chalcogenides, organic materials, perovskites, and nanodots. Finally, next-generation convergence studies combined with other research fields are introduced and future research directions are detailed.

Efficient light-emitting diodes based on oriented perovskite nanoplatelets

Solution-processed planar perovskite light-emitting diodes (LEDs) promise high-performance and cost-effective electroluminescent devices ideal for large-area display and lighting applications. Exploiting emission layers with high ratios of horizontal transition dipole moments (TDMs) is expected to boost the photon outcoupling of planar LEDs. However, LEDs based on anisotropic perovskite nanoemitters remain to be inefficient (external quantum efficiency, EQE <5%) due to the difficulties of simultaneously controlling the orientations of TDMs, achieving high photoluminescence quantum yields (PLQYs) and realizing charge balance in the films of assembled nanostructures. Here, we demonstrate efficient electroluminescence from an in situ grown perovskite film composed of a monolayer of face-on oriented nanoplatelets. The ratio of horizontal TDMs of the perovskite nanoplatelet film is ~84%, which leads to a light-outcoupling efficiency of ~31%, substantially higher than that of isotropic emitters (~23%). In consequence, LEDs with a peak EQE of 23.6% are achieved, representing highly efficient planar perovskite LEDs.

Unusual Temperature Dependence of Bandgap in 2D Inorganic Lead-Halide Perovskite Nanoplatelets

Understanding the origin of temperature-dependent bandgap in inorganic lead-halide perovskites is essential and important for their applications in photovoltaics and optoelectronics. Herein, it is found that the temperature dependence of bandgap in CsPbBr3 perovskites is variable with material dimensionality. In contrast to the monotonous redshift ordinarily observed in bulk-like CsPbBr3 nanocrystals (NCs), the bandgap of 2D CsPbBr3 nanoplatelets (NPLs) exhibits an initial blueshift then redshift trend with decreasing temperature (290-10 K). The Bose-Einstein two-oscillator modeling manifests that the blueshift-redshift crossover of bandgap in the NPLs is attributed to the significantly larger weight of contribution from electron-optical phonon interaction to the bandgap renormalization in the NPLs than in the NCs. These new findings may gain deep insights into the origin of bandgap shift with temperature for both fundamentals and applications of perovskite semiconductor materials.

Solution Epitaxy of Halide Perovskite Thin Single Crystals for Stable Transistors

Halide perovskites hold promise for energy and optoelectronic applications due to their fascinating photophysical properties and facile processing. Among various forms, epitaxial thin single crystals (TSCs) are highly desirable due to their high crystallinity, reduced defects, and easy epitaxial integration with other materials. However, a cost-effective method for obtaining TSCs with perfect epitaxial features remains elusive. Here, we demonstrate a direct epitaxial growth of high-quality all-inorganic perovskite CsPbBr₃ TSCs on various substrates through a facile solution process under near-ambient conditions. Structural characterizations reveal a high-quality epitaxy between the obtained perovskite TSCs and substrates, thus leading to efficiently reduced defects. The resultant TSCs display a low trap density (∼10¹¹ cm^-3) and a long carrier lifetime (∼10.16 ns). Top-gate/top-contact transistors based on these TSCs exhibit high on/off ratios of over 10⁵, an optimal hole mobility of 3.9 cm² V^-1 s^-1, almost hysteresis-free operation, and high stability at room temperature. Such a facile approach for the high-yield production of perovskite epitaxial TSCs will enable a broad range of high-performance electronic applications.

All-inorganic perovskite quantum dot light-emitting memories

Field-induced ionic motions in all-inorganic CsPbBr₃ perovskite quantum dots (QDs) strongly dictate not only their electro-optical characteristics but also the ultimate optoelectronic device performance. Here, we show that the functionality of a single Ag/CsPbBr₃/ITO device can be actively switched on a sub-millisecond scale from a resistive random-access memory (RRAM) to a light-emitting electrochemical cell (LEC), or vice versa, by simply modulating its bias polarity. We then realize for the first time a fast, all-perovskite light-emitting memory (LEM) operating at 5 kHz by pairing such two identical devices in series, in which one functions as an RRAM to electrically read the encoded data while the other simultaneously as an LEC for a parallel, non-contact optical reading. We further show that the digital status of the LEM can be perceived in real time from its emission color. Our work opens up a completely new horizon for more advanced all-inorganic perovskite optoelectronic technologies.

Electric field induced ion migration is a well-known phenomenon in perovskite, but the consequences are notorious, and thus needs to be prevented. Here, on the other hand, the authors cleverly manipulate this event for realising resistive random-access memory and light-emitting electrochemical cell in one device based on CsPbBr₃ quantum dots.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Three-Dimensional Perovskite Nanopixels for Ultrahigh-Resolution Color Displays and Multilevel Anticounterfeiting

Hybrid perovskites are emerging as a promising, high-performance luminescent material; however, the technological challenges associated with generating high-resolution, free-form perovskite structures remain unresolved, limiting innovation in optoelectronic devices. Here, we report nanoscale three-dimensional (3D) printing of colored perovskite pixels with programmed dimensions, placements, and emission characteristics. Notably, a meniscus comprising femtoliters of ink is used to guide a highly confined, out-of-plane crystallization process, which generates 3D red, green, and blue (RGB) perovskite nanopixels with ultrahigh integration density. We show that the 3D form of these nanopixels enhances their emission brightness without sacrificing their lateral resolution, thereby enabling the fabrication of high-resolution displays with improved brightness. Furthermore, 3D pixels can store and encode additional information into their vertical heights, providing multilevel security against counterfeiting. The proof-of-concept experiments demonstrate the potential of 3D printing to become a platform for the manufacture of smart, high-performance photonic devices without design restrictions.

High-Quality All-Inorganic Perovskite CsPbBr3 Microsheet Crystals as Low-Loss Subwavelength Exciton-Polariton Waveguides

Nanostructured all-inorganic metal halide perovskites have attracted considerable attention due to their outstanding photonic and optoelectronic properties. Particularly, they can exhibit room-temperature exciton-polaritons (EPs) capable of confining electromagnetic fields down to the subwavelength scale, enabling efficient light harvesting and guiding. However, a real-space nanoimaging study of the EPs in perovskite crystals is still absent. Additionally, few studies focused on the ambient-pressure and reliable fabrication of large-area CsPbBr₃ microsheets. Here, CsPbBr₃ orthorhombic microsheet single crystals were successfully synthesized under ambient pressure. Their EPs were examined using a real-space nanoimaging technique, which reveal EP waveguide modes spanning the visible to near-infrared spectral region. The EPs exhibit a sufficient long propagation length of over 16 μm and a very low propagation loss of less than 0.072 dB·μm^-1. These results demonstrate the potential applications of CsPbBr₃ microsheets as subwavelength waveguides in integrated optics.

Low-Dimensional Metal Halide Perovskite Photodetectors

Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record-breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high-performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low-dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low-dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low-dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low-dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low-dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low-dimensional MHP-based PDs in the future.

Realizing CsPbBr3 Light-Emitting Diode Arrays Based on PDMS Template Confined Solution Growth of Single-Crystalline Perovskite

Metal-halide perovskites have shown excellent optoelectronic properties, among which the array-type architecture is highly desirable. However, both the susceptibility of perovskites to polar solvents and the complex 3D geometry of array structure have led to great challenges for device fabrication and performance, which hinders their further applications. Here, we report a simple but efficient approach highly compatible with the state-of-the-art microelectronics processes to construct single-crystalline array light-emitting diodes (LEDs) of perovskite. The well-aligned single-crystalline array was sandwiched as the emission layer, among the carefully designed multilayer ITO/NiO/CsPbBr₃/PMMA/ZnO/Ag structure. Through systematically altering the size of CsPbBr₃ single crystal and the thickness of insulation layer, the device performance has been optimized and eventually achieved a 99% working ratio in a 62 × 47 array. Moreover, a prototype device of LED display was also fabricated. These results clearly demonstrate that our strategy is efficient, reliable, and versatile, which can be easily extended to other perovskites.

Trap-Mediated Energy Transfer in Er-Doped Cesium Lead Halide Perovskite

Substitutional doping lanthanide ions (Ln³⁺) in CsPbX₃ has been proven to be an efficient strategy for expanding the properties of the perovskite (PVK). Here, erbium (Er³⁺) uniformly doped CsPbX₃ perovskite microplates are grown through a chemical vapor deposition method. Two fluorescence peaks at 430 and 520 nm which respectively correspond to the PVK and Er³⁺ emissions are observed. The time-resolved photoluminescence of both PVK host and Er dopants demonstrates that trap states play a critical role in facilitating the energy transfer between the PVK host and the Er dopants, which is vital to sensitizing the Er³⁺. A photophysical model was put forward to comprehensively describe this trap-mediated energy-transfer process, and the dynamics processes are modeled using correlated rate equations. The rates of the carrier's relaxation and energy transfer are respectively obtained as 6.6 and 49 ns^-1, and a total energy transfer efficiency was obtained as ∼32.6%.

Photoluminescent Spectral Broadening of Lead Halide Perovskite Nanocrystals Investigated by Emission Wavelength Dependent Lifetime

Despite intensive efforts, the fluorescence of perovskite nanocrystals (NCs) still suffers from a poor color purity, which limits the applications in light emitting and multicolor display. A deep understanding on the fundamental of the photoluminescent (PL) spectral broadening is thus of great significance. Herein, the PL decay curves of the CsPbCl_xBr_3-x NCs are monitored at different wavelengths covering the entire PL band. Moreover, energy relaxation time τ and radiative recombination time β are obtained by numerical fittings. The dependences of τ and 1/β on the detection wavelength agree well with the steady-state PL spectrum, indicating the observed PL broadening is an intrinsic effect due to the resonance and off-resonance exciton radiative recombination processes. This work not only provides a new analysis method for time-resolved PL spectra of perovskites, but also gains a deep insight into the spectral broadening of the lead halide perovskite NCs.

The influence of electrode for electroluminescence devices based on all-inorganic halide perovskite CsPbBr3

Electroluminescence devices based on all-inorganic halide perovskite material with excellent luminescence performance have been studied extensively in recent years. However, the important role for the electrodes of electroluminescence devices is payed few attention by theoretical and experimental studies. Appropriate electrodes can reduce the Schottky barrier height to decrease the energy loss, and prevent the metal impurities from diffusing into the perovskite material to generate deep traps levels, which improves the luminous efficiency and lifetime of devices. In this paper, not only the interface effects between CsPbBr₃ and common metal electrode (Ag, Au, Ni, Cu and Pt) are studied by first-principle calculations, but also the diffusion effects of metal electrode atom into the CsPbBr₃ layer are also explored by nudged elastic band calculations. The calculated results show the metal Ag is more suitable for the cathode for CsPbBr₃ electroluminescence devices, while the metal Pt is more applicable for the anode. Based on the overall consideration about the interface effects and diffusion effects of the CsPbBr₃-metal electrode junctions, the essential principle is analyzed. The work provides theoretical guidance for how to select the right electrode for the electroluminescence performance of all-inorganic halide perovskite. The critical factor of Schottky barrier height between the electrode and the light-emitting semiconductor, and transition level generated by metal impurities also provide a valuable reference how to select the suitable electrodes for other electroluminescence devices.

Synthesis, Structure and Photoluminescence Properties of 2D Organic–Inorganic Hybrid Perovskites

Two-dimensional (2D) layered hybrid organic–inorganic perovskites have potential applications in solar cells, electroluminescent devices and radiation detection because of their unique optoelectronic properties. In this paper, four 2D layered hybrid organic–inorganic halide perovskites of (C6H5CH2NH3)2PbCl4, (C6H5CH2NH3)2PbBr4, (C6H5CH2NH3)2PbI4 and (C4H9NH3)2PbBr4 were synthesized by solvent evaporation. Their crystal structure and surface morphology were studied. The effects of different halogens and organic amines on perovskites’ absorption spectra were investigated, and the photoluminescence (PL) properties were studied by femtosecond ultrafast spectroscopy. The experimental results show that the four perovskites are well crystallized and oriented. With the increase of halogen atom number (Cl, Br, I) in turn, the UV-Vis absorption spectra peaks of perovskites redshift due to the increasing of the layer spacing, but organic amines have little effect on the spectra of perovskites. The PL intensity increases with increasing laser power, but the lifetime decreases with increasing laser power, which is mainly due to the non-geminate recombination. This research is of great significance for realizing the spectral regulation of organic–inorganic hybrid perovskites and promoting their application in nano-photonics and optoelectronic devices.

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

Metal halide perovskites (MHPs) have recently attracted great attention from the scientific community due to their excellent photovoltaic performance as well as their tremendous potential for other optoelectronic applications such as light-emitting diodes, lasers, and photodetectors. Despite the rapid progress in device applications, a solid understanding of the photophysical properties behind the device performance is highly desirable for MHPs. Here, the properties of excitons and photogenerated charge carriers in MHPs are explored. The unique dielectric constant properties, crystal-liquid duality, and fundamental optical processes of MHPs are first discussed. The properties of excitons and related phenomena in MHPs are then detailed, including the exciton binding energy determined by various methods and their influence factors, exciton dynamics, exciton-photon coupling and related applications, and exciton-phonon coupling in MHPs. The properties of photogenerated free charge carriers in MHPs such as the carrier diffusion length, mobility, and recombination are described. Recent progress in various applications is also demonstrated. Finally, a conclusion and perspectives of future studies for MHPs are presented.

Strategies to Improve Luminescence Efficiency of Metal-Halide Perovskites and Light-Emitting Diodes

Metal-halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light-emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted efforts to increase the LE of MHP emitters and PeLEDs. Within three and half years, PeLEDs have shown rapidly increased LE from external quantum efficiency ≈0.1% to ≈14.36%. Herein, the factors that limit the LE of PeLEDs are reviewed; the factors are characterized into the following groups: i) photophysical properties of MHP crystals, ii) morphological factors of MHP layers, and iii) problems caused by device architectures. Then, the strategies to overcome those luminescence-limiting factors in MHP emitters and PeLEDs are critically evaluated. Finally, research directions to further increase the LE of MHP emitters and the potential of MHPs as a core component in next-generation displays and solid-state lightings are suggested.

Perovskite-Based Artificial Multiple Quantum Wells

Semiconductor quantum well structures have been critical to the development of modern photonics and solid-state optoelectronics. Quantum level tunable structures have introduced new transformative device applications and afforded a myriad of groundbreaking studies of fundamental quantum phenomena. However, noncolloidal, III-V compound quantum well structures are limited to traditional semiconductor materials fabricated by stringent epitaxial growth processes. This report introduces artificial multiple quantum wells (MQWs) built from CsPbBr₃ perovskite materials using commonly available thermal evaporator systems. These perovskite-based MQWs are spatially aligned on a large-area substrate with multiple stacking and systematic control over well/barrier thicknesses, resulting in tunable optical properties and a carrier confinement effect. The fabricated CsPbBr₃ artificial MQWs can be designed to display a variety of photoluminescence (PL) characteristics, such as a PL peak shift commensurate with the well/barrier thickness, multiwavelength emissions from asymmetric quantum wells, the quantum tunneling effect, and long-lived hot-carrier states. These new artificial MQWs pave the way toward widely available semiconductor heterostructures for light-conversion applications that are not restricted by periodicity or a narrow set of dimensions.

Direct Vapor-Liquid-Solid Synthesis of All-Inorganic Perovskite Nanowires for High-Performance Electronics and Optoelectronics

Controlled synthesis of lead halide perovskite (LHP) nanostructures not only benefits fundamental research but also offers promise for applications. Among many synthesis techniques, although catalytic vapor-liquid-solid (VLS) growth is recognized as an effective route to achieve high-quality nanostructures, until now, there is no detailed report on VLS grown LHP nanomaterials due to the emerging challenges in perovskite synthesis. Here, we develop a direct VLS growth for single-crystalline all-inorganic lead halide perovskite ( i.e., CsPbX₃; X = Cl, Br, or I) nanowires (NWs). These NWs exhibit high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 10¹² Jones toward the visible light regime. Field-effect transistors (FET) based on individual CsPbX₃ NWs are also fabricated, where they show the superior hole mobility of up to 3.05 cm²/(V s), higher than other all-inorganic LHP devices. This work provides important guidelines for the further improvement of these perovskite nanostructures for utilizations.

Photoinduced photoluminescence enhancement in self-assembled clusters of formamidinium lead bromide perovskite nanocrystals

Nanocrystals of formamidinium lead bromide perovskite (FAPbBr3) self-assemble into clusters in powder and film samples and provide a prolonged photoluminescence lifetime, which is attributed to the diffusion of charge carriers through interparticle states formed among nanocrystals. Interestingly, the photoluminescence lifetime decreases and the emission intensity increases for the clusters, which is with the increase in the intensity of excitation light. By doping the nanocrystal clusters with C60, we successfully harvested the photogenerated charge carriers. Nonetheless, at high intensities of excitation, the rate of radiative recombination becomes comparable to that of the electron transfer to C60. Thus, the optimum rate of electron transfer to C60 is accomplished by minimally exciting the self-assembled nanocrystals.

Low-reflection, (110)-orientation-preferred CsPbBr3 nanonet films for application in high-performance perovskite photodetectors

All-inorganic metal halide perovskites have attracted great interest in recent years due to their good device performance with higher thermal stability than that of their organic-inorganic perovskite counterparts. However, the all-inorganic perovskite polycrystalline films prepared by the conventional spin-coating method possess many pinholes, nonuniform surface with many small crystals, and irregular agglomerates, limiting their device performance. Herein, we introduced a monolayer nano-polystyrene (PS) sphere confined growth method for obtaining CsPbBr3 nanonet films (NFs) with ordered nanostructures grown in the preferred (110) orientation, which is beneficial for the charge carrier transport and the light-harvesting efficiency. The (110) peak intensity of CsPbBr3 NFs increased with the increase of the diameter of the monolayer sphere, while the (001) peak intensity was suppressed greatly, indicating the more preferred (110) oriented growth. The PDs based on (110)-orientation-preferred CsPbBr3 NFs prepared by using 850 nm PS spheres showed the best performance. The best performing device displayed the biggest linear dynamic range of up to 120 dB. In addition, a responsivity of 2.84 A W-1 and a detectivity of 5.47 × 1012 Jones were also achieved.

Room temperature synthesis of blue and green emitting CsPbBr3 perovskite nanocrystals confined in mesoporous alumina film

A synthetic protocol has been described which demonstrates the room temperature synthesis of stable CsPbBr₃ nanocrystals inside mesoporous alumina film showing tunable emission.

Large and Ultrastable All-Inorganic CsPbBr3 Monocrystalline Films: Low-Temperature Growth and Application for High-Performance Photodetectors

Stability is a key problem that hinders the practical application of lead halide perovskite. Therefore, all-inorganic perovskite CsPbX₃ monocrystalline films are urgently needed to fabricate photoelectric devices. Herein, a low-temperature and substrate-independent growth method is demonstrated to grow millimeter-level inorganic perovskite monocrystalline thin films. These films present good optical and electrical properties comparable to bulk ones. What is more, they exhibit excellent long-term stability toward humidity and thermal treatment. The as-grown CsPbBr₃ monocrystalline films are then fabricated into photodetectors with high photodetection performance. These results demonstrate that the CsPbBr₃ monocrystalline films have potential in fabricating high-performance optoelectronic devices.

Cs4PbX6 (X = Cl, Br, I) Nanocrystals: Preparation, Water-Triggered Transformation Behavior, and Anti-Counterfeiting Application

As a promising material, Cs₄PbX₆ (X = Cl, Br, I) nanocrystals (NCs) have attracted much attention. However, their luminescent property is still under debate. In this work, we first systematically studied the colloidal preparation of Cs₄PbX₆ NCs. It is found that the critical parameter for the formation of Cs₄PbX₆ NCs is the ratio between Cs and Pb. Pure Cs₄PbX₆ NCs are nonluminescent. The luminescence property of previous reported Cs₄PbX₆ NCs may come from the impurity of luminescent CsPbX₃ NCs. No coexistence of both Cs₄PbX₆ and CsPbX₃ phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent Cs₄PbX₆ NCs to luminescent CsPbX₃ NCs has been quantitatively studied. The potential application of Cs₄PbX₆ NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of Cs₄PbX₆ NCs but also demonstrated the potential application of such NCs.

Metal Halide Perovskites: Synthesis, Ion Migration, and Application in Field-Effect Transistors

The past several years have witnessed tremendous developments of metal halide perovskite (MHP)-based optoelectronics. Particularly, the intensive research of MHP-based light-emitting diodes, photodetectors, and solar cells could probably reform the optoelectronic semiconductor industry. In comparison, in spite of the large intrinsic charge carrier mobility of MHPs, the development of MHP-based field-effect transistors (MHP-FETs) is relatively slow, which is essentially due to the gate-field screening effect induced by the ion migration and accumulation in MHP-FETs. This work mainly aims to summarize the recent important work on MHP-FETs and propose solutions in terms of the development bottleneck of perovskite-based transistors, in an attempt to boost the research of MHP transistors further. First, the advantages and potential applications of MHP-FETs are briefly introduced, which is followed by a detailed description of the MHP crystalline structure and various material fabrication techniques. Afterward, MHP-FETs are discussed, including transistors based on hybrid organic-inorganic perovskites, all-inorganic perovskites, and lead-free perovskites.

Dark-Field Sensors based on Organometallic Halide Perovskite Microlasers

The detection of nanoscale objects is essential for homeland security, environmental monitoring, and early-stage diagnostics. In the past few years, optical sensors have mostly been developed with passive devices such as microcavity and plasmonic nanostructures, which require external laser sources to operate and significantly increase the costs and bulks of sensing systems. To date, the potential of their active counterparts in optical sensors has not been well explored. Herein, a novel and robust mechanism to detect nanoscale objects with lead halide perovskite microlasers is demonstrated. Nanoparticles can be simply detected and sized by measuring the intensity of scattered laser light. In principle, the proposed concept is also applicable to electrically driven microlasers and it could find applications in portable point-of-care devices.

Fast Charge Extraction in Perovskite-Based Core-Shell Nanowires

Realizing nanostructured interfaces with precise architectural control enables one to access properties unattainable using bulk materials. In particular, a nanostructured interface ( e. g., a core-shell nanowire) between two semiconductors leads to a short charge separation distance, such that photoexcited charge carriers can be more quickly and efficiently collected. While vapor-phase growth methods are used to synthesize uniform core-shell nanowire arrays of semiconductors such as Si and InP, more general strategies are required to produce related structures composed of a broader range of materials. Herein, we employ anodic aluminum oxide templates to synthesize CH₃NH₃PbI₃ perovskite core-copper thiocyanate shell nanowire arrays employing a combination of electrodeposition and solution casting methods. Using scanning electron microscopy, powder X-ray diffraction, and time-resolved photoluminescence spectroscopy, we confirm the target structure and show that adopting a core-shell nanowire architecture accelerates the rate of charge quenching by nearly 3 orders of magnitude compared to samples with only an axial junction. Subsequently, we fit decay curves to a triexponential function to attribute fast quenching in core-shell nanowires to charge extraction by the copper thiocyanate nanotubes, as opposed to recombination within the perovskite nanowires. Dramatic improvements to charge extraction speed and efficiency result from the substantially reduced charge separation distance and increased interfacial area achieved via the core-shell nanowire array architecture.

Robust Subwavelength Single-Mode Perovskite Nanocuboid Laser

On-chip photonic information processing systems require great research efforts toward miniaturization of the optical components. However, when approaching the classical diffraction limit, conventional dielectric lasers with all dimensions in nanoscale are difficult to realize due to the ultimate miniaturization limit of the cavity length and the extremely high requirement of optical gain to overcome the cavity loss. Herein, we have succeeded in reducing the laser size to subwavelength scale in three dimensions using an individual CsPbBr₃ perovskite nanocuboid. Even though the side length of the nanocuboid laser is only ∼400 nm, single-mode Fabry-Pérot lasing at room temperature with laser thresholds of 40.2 and 374 μJ/cm² for one- and two-photon excitation has been achieved, respectively, with the corresponding quality factors of 2075 and 1859. In addition, temperature-insensitive properties from 180 to 380 K have been demonstrated. The physical volume of a CsPbBr₃ nanocuboid laser is only ∼0.49λ³ (where λ is the lasing wavelength in air). Its three-dimensional subwavelength size, excellent stable lasing performance at room temperature, frequency up-conversion ability, and temperature-insensitive properties may lead to a miniaturized platform for nanolasers and integrated on-chip photonic devices in nanoscale.

Visualizing Carrier Transport in Metal Halide Perovskite Nanoplates via Electric Field Modulated Photoluminescence Imaging

Metal halide perovskite nanostructures have recently been the focus of intense research due to their exceptional optoelectronic properties and potential applications in integrated photonics devices. Charge transport in perovskite nanostructure is a crucial process that defines efficiency of optoelectronic devices but still requires a deep understanding. Herein, we report the study of the charge transport, particularly the drift of minority carrier in both all-inorganic CsPbBr₃ and organic-inorganic hybrid CH₃NH₃PbBr₃ perovskite nanoplates by electric field modulated photoluminescence (PL) imaging. Bias voltage dependent elongated PL emission patterns were observed due to the carrier drift at external electric fields. By fitting the drift length as a function of electric field, we obtained the carrier mobility of about 28 cm² V^-1 S^-1 in the CsPbBr₃ perovskite nanoplate. The result is consistent with the spatially resolved PL dynamics measurement, confirming the feasibility of the method. Furthermore, the electric field modulated PL imaging is successfully applied to the study of temperature-dependent carrier mobility in CsPbBr₃ nanoplates. This work not only offers insights for the mobile carrier in metal halide perovskite nanostructures, which is essential for optimizing device design and performance prediction, but also provides a novel and simple method to investigate charge transport in many other optoelectronic materials.

Self-Powered All-Inorganic Perovskite Microcrystal Photodetectors with High Detectivity

Organic-inorganic lead halide perovskite microcrystal (MC) films are attractive candidates for fabricating high-performance large-area self-powered photodetectors (PDs) because of their lower trap state density and higher carrier mobility than their polycrystalline counterparts and more suitability of synthesizing large lateral area films than their single-crystal counterparts. Here, we report on the fabrication of self-powered all-inorganic CsPbBr₃ perovskite MC PDs with high detectivity, using a modified solution synthesis method. The MCs are up to about 10 μm in size, and the MC layer is also about 11 μm in thickness. Under 473 nm laser (100 mW) illumination, the CsPbBr₃ MC PDs show responsivity values of up to 0.172 A W^-1, detectivity values of up to 4.8 × 10¹² Jones, on/off ratios of up to 1.3 × 10⁵, and linear dynamic ranges of up to 113 dB. These performances are significantly better than those of PDs based on polycrystalline perovskite thin films and comparable with those of PDs based on perovskite single crystals.

High binding ability ligand controlled formation of CsPbX3 (X = Cl/Br, Br, I) perovskite nanocrystals with high quantum yields and enhanced stability

CsPbX₃ NCs with both high photoluminescence quantum yields (PLQYs) and enhanced stability have been obtained by using high binding ability ligands. As a result, the CsPbI₃ NCs prepared using palmitic acid and oleylamine as ligands have high PLQY (up to 92%), and the PLQYs of CsPbX₃ perovskite NCs can be sustained for one month with a slight decrease. Impressively, the presence of palmitic acid and stearic acid can dramatically improve the chemical stability of CsPbX₃ NCs. Importantly, ¹H NMR measurements indicate that much more palmitic acid remained on the surface of CsPbX₃ NCs than oleic acid after purification using solvent, suggesting the higher binding ability of palmitic acid than oleic acid. Finally, the fabricated perovskite NCs were used as luminescent inks and phosphors of white light emitting diodes.

CsPbX₃ NCs with both high photoluminescence quantum yields (PLQYs) and enhanced stability have been obtained by using high binding ability ligands.

Directional Growth of Ultralong CsPbBr3 Perovskite Nanowires for High-Performance Photodetectors

Directional growth of ultralong nanowires (NWs) is significant for practical application of large-scale optoelectronic integration. Here, we demonstrate the controlled growth of in-plane directional perovskite CsPbBr₃ NWs, induced by graphoepitaxial effect on annealed M-plane sapphire substrates. The wires have a diameter of several hundred nanometers, with lengths up to several millimeters. Microstructure characterization shows that CsPbBr₃ NWs are high-quality single crystals, with smooth surfaces and well-defined cross section. The NWs have very strong band-edge photoluminescence (PL) with a long PL lifetime of ∼25 ns and can realize high-quality optical waveguides. Photodetectors constructed on these individual NWs exhibit excellent photoresponse with an ultrahigh responsivity of 4400 A/W and a very fast response speed of 252 μs. This work presents an important step toward scalable growth of high-quality perovskite NWs, which will provide promising opportunities in constructing integrated nanophotonic and optoelectronic systems.