Organometal Halide Perovskite Quantum Dot Light‐Emitting Diodes

Organometal halide perovskites quantum dots (OHP‐QDs) with bright, color‐tunable, and narrow‐band photoluminescence have significant advantages in display, lighting, and laser applications. Due to sparse concentrations and difficulties in the enrichment of OHP‐QDs, production of large‐area uniform films of OHP‐QDs is a challenging task, which largely impedes their use in electroluminescence devices. Here, a simple dip‐coating method has been reported to effectively fabricate large‐area uniform films of OHP‐QDs. Using this technique, multicolor OHP‐QDs light‐emitting diodes (OQ‐LEDs) emitting in blue, blue‐green, green, orange, and red color have been successfully produced by simply tuning the halide composition or size of QDs. The blue, green, and red OQ‐LEDs exhibited, respectively, a maximum luminance of 2673, 2398, and 986 cd m^?2 at a current efficiency of 4.01, 3.72, and 1.52 cd A^?1, and an external quantum efficiency of 1.38%, 1.06%, and 0.53%, which are much better than most LEDs based on OHP films. The packaged OQ‐LEDs show long‐term stability in air (humidity ≈50%) for at least 7 d. The results demonstrate the great potential of the dip‐coating method to fabricate large‐area uniform films for various QDs. The high‐efficiency OQ‐LEDs also demonstrate the promising potential of OHP‐QDs for low‐cost display, lighting, and optical communication applications.     

Two‐Step Sequential Deposition of Organometal Halide Perovskite for Photovoltaic Application

Organometal halide perovskite materials have become a superstar in the photovoltaic (PV) field because of their advantageous properties, which boost the power conversion efficiency (PCE) of perovskite solar cells (PSCs) from about 3.8% to above 22% in just seven years. Most importantly, such promising achievement is mainly based on its low‐cost and solution‐processed fabrication technique. One of the most promising and famous approaches to fabricating perovskite is a two‐step sequential deposition method because precursor (e.g., PbI₂) deposition is controllable, versatile, and flexible. Due to tremendous efforts, great progress has been achieved on the two‐step sequential deposition method, which helps to promote the development of PSCs. Herein, the progresses on the two‐step sequential deposition method of perovskite layers is reviewed thoroughly. At first, the reaction process and principle is introduced and discussed. Then, the research on the deposition techniques, structures, and compositions of precursors (the first step) is presented. Subsequently, the developments on the conversion techniques, conversion solutions, and growth of large crystals at the second step are introduced. Finally, four important issues on the two‐step sequential deposition method will be stated, accompanied with proposed solutions.     

Suppressing Ion Migration Enables Stable Perovskite Light‐Emitting Diodes with All‐Inorganic Strategy

Stability issue is one of the major concerns that limit emergent perovskite light‐emitting diodes (PeLEDs) techniques. Generally, ion migration is considered as the most important origin of PeLEDs degradation. In this work, an all‐inorganic device architecture, LiF/perovskite/LiF/ZnS/ZnSe, is proposed to address this imperative problem. The inorganic (Cs_1?xRb_x)_1?yK_yPbBr₃ perovskite is optimized with achieving a photoluminescence quantum yield of 67%. Depth profile analysis of X‐ray photoelectron spectroscopy indicates that the LiF/perovskite/LiF structure and the ZnS/ZnSe cascade electron transport layers significantly suppress the electric‐field‐induced ion migrations of the perovskite layers, and impede the diffusion of metallic atoms from cathode into perovskites. The as‐prepared PeLEDs display excellent shelf stability (maintaining 90% of the initial external quantum efficiency [EQE] after 264 h) and operational stability (half‐lifetime of about 255 h at an initial luminance of 120 cd m^?2). The devices also exhibit a maximum brightness of 15 6155 cd m^?2 and an EQE of 11.05%.     

Metal Halide Perovskite Light‐Emitting Devices: Promising Technology for Next‐Generation Displays

As the requirements and expectation for displays in society are growing, higher standards of the display technology are proposed, including wider color gamut, higher color purity, and higher resolution. The recent emergence of light‐emitting halide perovskites has come with numerous advantages, such as high charge‐carrier mobility, tunable emission wavelength, narrow emission linewidth, and intrinsically high photoluminescence quantum yield. Recent advancement of perovskite‐based light‐emitting diodes (PeLEDs) as a promising technology for next‐generation displays is reviewed. Here, how the attractive optical and electrical properties of perovskite materials can be translated into high PeLED performance are discussed, and working mechanisms and optimization approaches of both perovskite materials and the respective devices are analyzed. On the material side this includes the control of size and composition of perovskites grains and nanocrystals, surface and interface passivation, doping and alloying, while on the device side this includes the interfacial engineering and energy level adjustments, and photon emission enhancement. Several challenges such as performance of blue PeLEDs, the environmental and operational stability of PeLEDs, and the toxicity issues of lead halide perovskites are discussed, and perspectives on future developments of perovskite materials and PeLEDs for the display technology are offered.     

The Role of Chlorine in the Formation Process of “CH3NH3PbI3‐xClx” Perovskite

CH₃NH₃PbI_3‐xCl_x is a commonly used chemical formula to represent the methylammonium lead halide perovskite fabricated from mixed chlorine‐ and iodine‐containing salt precursors. Despite the rapid progress in improving its photovoltaic efficiency, fundamental questions remain regarding the atomic ratio of Cl in the perovskite as well as the reaction mechanism that leads to its formation and crystallization. In this work we investigated these questions through a combination of chemical, morphological, structural and thermal characterizations. The elemental analyses reveal unambiguously the negligible amount of Cl atoms in the CH₃NH₃PbI_3‐xCl_x perovskite. By studying the thermal characteristics of methylammonium halides as well as the annealing process in a polymer/perovskite/FTO glass structure, we show that the formation of the CH₃NH₃PbI_3‐xCl_x perovskite is likely driven by release of gaseous CH₃NH₃Cl (or other organic chlorides) through an intermediate organometal mixed halide phase. Furthermore, the comparative study on CH₃NH₃I/PbCl₂ and CH₃NH₃I/PbI₂ precursor combinations with different molar ratios suggest that the initial introduction of a CH₃NH₃⁺ rich environment is critical to slow down the perovskite formation process and thus improve the growth of the crystal domains during annealing; accordingly, the function of Cl^? is to facilitate the release of excess CH₃NH₃⁺ at a relatively low annealing temperatures.     

Enhanced Hole-Carrier Selectivity in Wide Bandgap Halide Perovskite Photovoltaic Devices for Indoor Internet of Things Applications

Halide perovskite-based photovoltaic (PV) devices have recently emerged for low energy consumption electronic devices such as Internet of Things (IoT). In this work, an effective strategy to form a hole-selective layer using phenethylammonium iodide (PEAI) salt is presented that demonstrates unprecedently high open-circuit voltage of 0.9 V with 18 µW cm⁻² under 200 lux (cool white light-emitting diodes). An appropriate post-deposited amount of PEAI (2 mg) strongly interacts with the perovskite surface forming a conformal coating of PEAI on the perovskite film surface, which improves the crystallinity and absorption of the film. Here, Kelvin probe force microscopy results indicate the diminished potential difference across the grain boundaries and grain interiors after the PEAI deposition, constructing an electrically and chemically homogeneous surface. Also, the surface becomes more p-type with a downshift of a valence band maximum, confirmed by ultraviolet photoelectron spectroscopy measurement, facilitating the transport of holes to the hole transport layer (HTL). The hole-selective layer-deposited devices exhibit reduced hysteresis in light current density–voltage curves and maintain steadily high fill factor across the different light intensities (200–1000 lux). This work highlights the importance of the HTL/perovskite interface that prepares the indoor halide perovskite PV devices for powering IoT device.     

Influence of Bulky Organo‐Ammonium Halide Additive Choice on the Flexibility and Efficiency of Perovskite Light‐Emitting Devices

Perovskite light‐emitting diodes (LEDs) require small grain sizes to spatially confine charge carriers for efficient radiative recombination. As grain size decreases, passivation of surface defects becomes increasingly important. Additionally, polycrystalline perovskite films are highly brittle and mechanically fragile, limiting their practical applications in flexible electronics. In this work, the introduction of properly chosen bulky organo‐ammonium halide additives is shown to be able to improve both optoelectronic and mechanical properties of perovskites, yielding highly efficient, robust, and flexible perovskite LEDs with external quantum efficiency of up to 13% and no degradation after bending for 10 000 cycles at a radius of 2 mm. Furthermore, insight of the improvements regarding molecular structure, size, and polarity at the atomic level is obtained with first‐principles calculations, and design principles are provided to overcome trade‐offs between optoelectronic and mechanical properties, thus increasing the scope for future highly efficient, robust, and flexible perovskite electronic device development.     

Shining Light on the Photoluminescence Properties of Metal Halide Perovskites

Lead halide perovskites are a remarkable class of materials that have emerged over the past decade as being suitable for application in a broad range of devices, such as solar cells, light‐emitting diodes, lasers, transistors, and memory devices. While they are often solution‐processed semiconductors deposited at low temperatures, perovskites exhibit properties one would only expect from highly pure inorganic crystals that are grown at high temperatures. This unique phenomenon has resulted in fast‐paced progress toward record device performance. Unfortunately, the basic science behind the remarkable nature of these materials is still not well understood. This review assesses the current understanding of the photoluminescence properties of metal halide perovskite materials and highlights key areas that require further research. Furthermore, the need to standardize the methods for characterization of PL in order to improve comparability, reliability, and reproducibility of results is emphasized.     

2D Ruddlesden–Popper Perovskite Nanoplate Based Deep‐Blue Light‐Emitting Diodes for Light Communication

Ruddlesden–Popper perovskite, (PEA)₂PbBr₄ (PEA = C₈H₉NH₃), is a steady and inexpensive material with a broad bandgap and a narrow‐band emission. These features make it a potential candidate for deep‐blue light‐emitting diodes (LEDs). However, due to the weak exciton binding energy, LEDs based on the perovskite thin films usually possess a very low external quantum efficiency (EQE) of <0.03%. Here, for the first time, the construction of high‐performance deep‐blue LEDs based on 2D (PEA)₂PbBr₄ nanoplates (NPs) is demonstrated. The as‐fabricated (PEA)₂PbBr₄ NPs film shows a deep‐blue emission at 410 nm with excellent stability under ambient conditions. Impressively, LEDs based on the (PEA)₂PbBr₄ NPs film deliver a bright deep‐blue emission with a maximum luminance of 147.6 cd m^?2 and a high EQE up to 0.31%, which represents the most efficient and brightest perovskite LEDs operating at deep‐blue wavelengths. Furthermore, the LEDs retain over 80% of their efficiencies for over 1350 min under ≈60% relative humidity. The steady and bright deep‐blue LEDs can be used as an excitation light source to realize white light emission, which shows the potential for light communication. The work provides scope for developing perovskite into efficient and deep‐blue LEDs for low‐cost light source and light communication.     

Halide Perovskite Materials for Energy Storage Applications

Halide perovskites, traditionally a solar‐cell material that exhibits superior energy conversion properties, have recently been deployed in energy storage systems such as lithium‐ion batteries and photorechargeable batteries. Here, recent progress in halide perovskite‐based energy storage systems is presented, focusing on halide perovskite lithium‐ion batteries and halide perovskite photorechargeable batteries. Halide‐perovskite‐based supercapacitors and photosupercapacitors are also discussed. The photorechargeable batteries and photorechargeable supercapacitors employ solar energy to photocharge the battery; this saves energy and improves device portability. These lightweight, integrated halide perovskite‐based systems, which are pertinent to electric vehicles and portable electronic devices, are reviewed in detail. Suggestions on future research into the design of halide‐perovskite‐based energy storage materials are also given. This review provides a foundation for the development of integrated lightweight energy conversion and storage materials.     

Materials Discovery of Stable and Nontoxic Halide Perovskite Materials for High‐Efficiency Solar Cells

Two critical limitations of organic–inorganic lead halide perovskite materials for solar cells are their poor stability in humid environments and inclusion of toxic lead. In this study, high‐throughput density functional theory (DFT) methods are used to computationally model and screen 1845 halide perovskites in search of new materials without these limitations that are promising for solar cell applications. This study focuses on finding materials that are comprised of nontoxic elements, stable in a humid operating environment, and have an optimal bandgap for one of single junction, tandem Si‐perovskite, or quantum dot–based solar cells. Single junction materials are also screened on predicted single junction photovoltaic (PV) efficiencies exceeding 22.7%, which is the current highest reported PV efficiency for halide perovskites. Generally, these methods qualitatively reproduce the properties of known promising nontoxic halide perovskites that are either experimentally evaluated or predicted from theory. From a set of 1845 materials, 15 materials pass all screening criteria for single junction cell applications, 13 of which are not previously investigated, such as (CH₃NH₃)_0.75Cs_0.25SnI₃, ((NH₂)₂CH)Ag_0.5Sb_0.5Br₃, CsMn_0.875Fe_0.125I₃, ((CH₃)₂NH₂)Ag_0.5Bi_0.5I₃, and ((NH₂)₂CH)_0.5Rb_0.5SnI₃. These materials, together with others predicted in this study, may be promising candidate materials for stable, highly efficient, and nontoxic perovskite‐based solar cells.     

All‐Day Operating Quaternary Blend Organic Photovoltaics

The unique properties of organic photovoltaics (OPVs) offer great promise in emerging applications such as wearable electronics or the Internet of Things. For their successful utilization, OPV operation should be designed for versatile irradiation circumstances in addition to solar light since they should be capable of providing electric power when there is no sunlight or when they operate indoors. Here, a quaternary OPV (Q‐OPV) as a semitransparent, colorful energy platform that operates efficiently under both solar and artificial light irradiation is demonstrated. The experimentally optimized Q‐OPV shows a broadened spectral response and improved charge transport process with suppressed recombination, thereby providing high output powers that are sufficient to autonomously operate low‐power electronic devices. In addition, the Q‐OPV benefits from improved morphological stability with a reduced driving force for grain growth by the increased entropy in the quaternary blend system. The important features of the Q‐OPV platform such as semitransparency, high tolerance to film thickness, and color codability, while pursuing the improved performance and thermal durability, further open new opportunities as an all‐day (24/7/365) power generator in broad practical applications.     

Perovskite Origami for Programmable Microtube Lasing

Metal halide perovskites are promising materials for optoelectronic and photonic applications ranging from photovoltaics to laser devices. However, current perovskite devices are constrained to simple low-dimensional structures suffering from limited design freedom and holding up performance improvement and functionality upgrades. Here, a micro-origami technique is developed to program 3D perovskite microarchitectures toward a new type of microcavity laser. The design flexibility in 3D supports not only outstanding laser performance such as low threshold, tunable output, and high stability but also yields new functionalities like 3D confined mode lasing and directional emission in, for example, laser “array-in-array” systems. The results represent a significant step forward toward programmable microarchitectures that take perovskite optoelectronics and photonics into the 3D era.     

Efficient Perovskite Hybrid Photovoltaics via Alcohol‐Vapor Annealing Treatment

In this work, alcohol‐vapor solvent annealing treatment on CH₃NH₃PbI₃ thin films is reported, aiming to improve the crystal growth and increase the grain size of the CH₃NH₃PbI₃ crystal, thus boosting the performance of perovskite photovoltaics. By selectively controlling the CH₃NH₃I precursor, larger‐grain size, higher crystallinity, and pinhole‐free CH₃NH₃PbI₃ thin films are realized, which result in enhanced charge carrier diffusion length, decreased charge carrier recombination, and suppressed dark currents. As a result, over 43% enhanced efficiency along with high reproducibility and eliminated photocurrent hysteresis behavior are observed from perovskite hybrid solar cells (pero‐HSCs) where the CH₃NH₃PbI₃ thin films are treated by methanol vapor as compared with that of pristine pero‐HSCs where the CH₃NH₃PbI₃ thin films are without any alcohol vapor treatment. In addition, the dramatically restrained dark currents and raised photocurrents give rise to over ten times enhanced detectivities for perovskite hybrid photodetectors, reaching over 10¹³ cm Hz^1/2 W^?1 (Jones) from 375 to 800 nm. These results demonstrate that the method provides a simple and facile way to boost the device performance of perovskite photovoltaics.     

Efficient Perovskite Light‐Emitting Diodes Using Polycrystalline Core–Shell‐Mimicked Nanograins

Making small nanograins in polycrystalline organic–inorganic halide perovskite (OIHP) films is critical to improving the luminescent efficiency in perovskite light‐emitting diodes (PeLEDs). 3D polycrystalline OIHPs have fundamental limitations related to exciton binding energy and exciton diffusion length. At the same time, passivating the defects at the grain boundaries is also critical when the grain size becomes smaller. Molecular additives can be incorporated to shield the nanograins to suppress defects at grain boundaries; however, unevenly distributed molecular additives can cause imbalanced charge distribution and inefficient local defect passivation in polycrystalline OIHP films. Here, a kinetically controlled polycrystalline organic‐shielded nanograin (OSN) film with a uniformly distributed organic semiconducting additive (2,2′,2′′‐(1,3,5‐benzinetriyl)‐tris(1‐phenyl‐1‐H‐benzimidazole), TPBI) is developed mimicking core–shell nanoparticles. The OSN film causes improved photophysical and electroluminescent properties with improved light out‐coupling by possessing a low refractive index. Finally, highly improved electroluminescent efficiencies of 21.81% ph el^?1 and 87.35 cd A^?1 are achieved with a half‐sphere lens and four‐time increased half‐lifetime in polycrystalline PeLEDs. This strategy to make homogeneous, defect‐healed polycrystalline core–shell‐mimicked nanograin film with better optical out‐coupling will provide a simple and efficient way to make highly efficient perovskite polycrystal films and their optoelectronics devices.     

All‐Inorganic Perovskite Nanocrystals for High‐Efficiency Light Emitting Diodes: Dual‐Phase CsPbBr3‐CsPb2Br5 Composites

A dual‐phase all‐inorganic composite CsPbBr₃‐CsPb₂Br₅ is developed and applied as the emitting layer in LEDs, which exhibited a maximum luminance of 3853 cd m^–2, with current density (CE) of ≈8.98 cd A^–1 and external quantum efficiency (EQE) of ≈2.21%, respectively. The parasite of secondary phase CsPb₂Br₅ nanoparticles on the cubic CsPbBr₃ nanocrystals could enhance the current efficiency by reducing diffusion length of excitons on one side, and decrease the trap density in the band gap on the other side. In addition, the introduction of CsPb₂Br₅ nanoparticles could increase the ionic conductivity by reducing the barrier against the electronic and ionic transport, and improve emission lifetime by decreasing nonradiative energy transfer to the trap states via controlling the trap density. The dual‐phase all‐inorganic CsPbBr₃‐CsPb₂Br₅ composite nanocrystals present a new route of perovskite material for advanced light emission applications.     

Nickel Silicide Nanowire Arrays for Anti‐Reflective Electrodes in Photovoltaics

Conductive nanowires (NWs) provide several advantages as a template and electrode material for solar cells due to their favorable light scattering properties. While the majority of NW solar cell architectures studied are based on semiconductor materials, metallic NWs could provide equivalent anti‐reflection properties, while acting as a low‐resistance back contact for charge transport, and facilitate light scattering in thin layers of semiconductors coated on the surface. However, fabrication of single‐crystalline highly anti‐reflective NWs on low‐cost, flexible substrates remains a challenge to drive down the cost of NW solar cells. In this study, metallic Ni_xSi NW arrays are fabricated by a simple, bottom‐up, and low‐cost method based on the thermal decomposition of silane on the surface of flexible Ni foil substrates without the need for lithography, etching or catalysts. The optical properties of these NW arrays demonstrate broadband suppression of reflection to levels below 1% from 350 nm to 1100 nm, which is among the highest values reported for NWs. A simple route to control the diameter and density of the NWs is introduced based on variations in a carrier gas flow rate. A high‐resolution TEM, XRD and TEM‐EDS study of the NWs reveals that they are single crystalline, with the phase and composition varying between Ni₂Si and NiSi. The nanowire resistivity is measured to be 10^?4 Ω‐cm, suggesting their use as an efficient back electrode material for nanostructured solar cells with favorable light scattering properties.     

High‐Performance Flexible Broadband Photodetector Based on Organolead Halide Perovskite

Organolead halide perovskites have attracted extensive attentions as light harvesting materials for solar cells recently, because of its high charge‐carrier mobilities, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Herein, with CH₃NH₃PbI₃ film deposited on flexible ITO coated substrate, the first organolead halide perovskite based broadband photodetector is demonstrated. The organolead halide perovskite photodetector is sensitive to a broadband wavelength from the ultraviolet light to entire visible light, showing a photo‐responsivity of 3.49 A W^?1, 0.0367 A W^?1, an external quantum efficiency of 1.19×10³%, 5.84% at 365 nm and 780 nm with a voltage bias of 3 V, respectively. Additionally, the as‐fabricated photodetector exhibit excellent flexibility and robustness with no obvious variation of photocurrent after bending for several times. The organolead halide perovskite photodetector with high sensitivity, high speed and broad spectrum photoresponse is promising for further practical applications. And this platform creates new opportunities for the development of low‐cost, solution‐processed and high‐efficiency photodetectors.     

Lycopene-Based Bionic Membrane for Stable Perovskite Photovoltaics

Perovskite (PVSK) photovoltaics have been a promising field in the exploitation of renewable energy due to the fascinating performances of PVSK materials and devices. Although the efficiency is gradually approaching that of traditional solar cells, the stability is still a challenge. Hence, tomato lycopene, a botanic antioxidant, is introduced as a modification layer on the PVSK absorber layer to prevent moisture and oxygen erosion, for enhanced both intrinsic and environmental stabilities. This inserted protection layer can also interact with the PVSK material through carbon-halogen bonds and influence its crystallinity. Therefore, PVSK films are obtained with less defects and better intrinsic stability. The device achieved a champion outdoor efficiency at AM 1.5G more than 21% and its indoor efficiency at 1000 lux can reach 40.24%. In addition, the efficiency can keep almost 90% of the original value after exposure to wet oxygen ambience for 1000 h. The antioxidant gives a unique perspective towards enhancing the stability of solar cells