High-performance yellow emitter is the key to achieve high-quality complementary white organic electroluminescence. Herein, a novel yellow iridium(Ⅲ) complex (Ir1) is synthesized by using chlorine-bearing cyclometalated ligand under the mild condition. The complex is confirmed by nuclear magnetic resonance and X-ray diffraction analysis. In degassed CH2Cl2, the complex shows bright yellow phosphorescent emission with high luminescent quantum yield of 51% and lifetime of 129 μs at room temperature. Notably, the full width at half maximum (FWHM) of emission spectrum is up to 101 nm. Moreover, complex Ir1 is served as triplet emitter in organic light-emitting device. The device exhibits broad yellow emission at 568 nm with FWHM of 88 nm, maximum brightness of 18 310 cd/m2, external quantum efficiency of 20.8%, current efficiency of 58.2 cd/A and power efficiency of 48.3 lm/W.

Organic light-emitting devices (OLEDs) have been developed and applied rapidly in the past three decades as both display and lighting panels due to their advantages. However, inherent low light extraction efficiency always makes them require to integrating the light extraction micro/nano structures. On the other hand, organic semiconductor laser (OSL) also has attracted much attention due to the advantages of wide emission spectrum, simple fabrication, low cost and easy integration. Also, micro/nano structures should be fabricated in the OSL as resonator geometries for optical feedback to achieve lasing action. Among the different fabrication techniques, nanoimprint lithography (NIL) as a patterning process with high-resolution, high-throughput and cost effective, is considered to be one of the most promising technologies. NIL not only can break the limitation from diffraction limit and beam scattering, but also guarantee the inherent optical and electronic properties of organic optoelectronic materials. Here, we summarize and evaluate the fabrication of nanostructured electrode, functional layers and encapsulation films in the OLEDs and nanostructured dye-doped polymer and luminescent materials in the OSLs.

With the rapid development of the optoelectronic information industry, light-emitting diodes (LEDs) as the core unit of solid-state lighting and display equipment, have been widely concerned by researchers. According to the different driving modes, LEDs can be generally divided into constant voltage or direct current driven LEDs (DC-LEDs) and alternating current driven LEDs (AC-LEDs). Compared to DC-LEDs, AC-LEDs can effectively avoid the charge accumulation for the improved device efficiency and operational lifetime. In addition, AC-LEDs can be readily connected to AC power systems without voltage transformation and rectification systems, which greatly simplifies the device integration process with better practical application prospects. This review firstly introduces the light-emitting mechanism of AC-LEDs and summarizes several AC-LED device structures including double-insulation, single-insulation, double-injection, tandem and parallel structures. Then, the recent advances of various AC-LEDs are presented and the influences of various factors on device performance are discussed. It is found that the balanced carrier transport and the high dielectric properties of insulator are two key factors in achieving high-performance AC-LEDs. Finally, the opportunities and challenges for the future development of AC-LEDs are discussed.

The design of device structure and the development of functional materials are the keys to achieve high efficiency organic light emitting diodes (OLEDs) over the past 30 years. Inverted structure device is considered to be a feasible solution for OLEDs to realize high efficiency and long lifetime. However, the electron injection barrier from the ITO cathode to organic layer is large, which limits the further development of the inverted device. In this paper, we introduce the related research work of n-type doping, dipole layer modification and tunneling injection, which bases on the different mechanisms of electron injection for inverted devices. Finally, three different strategies to improve the electron injection performance of inverted devices are summarized and prospected.

An organic electron-transport compound for phosphorescent OLEDs is reported, which possesses the advantages of low molecular weight, enhanced glass transition temperature and electron mobility upon doping with 8-hydroxyquinolatolithium (Liq) as well as facile synthesis and purification. The analytically pure NaAN-m-TRZ (m/z = 611.73) is obtained through coupling the 4,6-diphenyl-1,3,5-triazin-2-yl unit via a 1,3-phenylene linker with 10-(naphth-2-yl)-anthracen-9-yl moiety. The residual bromo intermediate could be easily removed by column chromatography and/or recrystallization from CH2Cl2, hence eliminating a high-risk factor for OLED stability. Thermal analyses show that it exhibits a Tg of 157 ℃ and decomposition temperature of 353 ℃ at 1% weight loss. NaAN-m-TRZ has a HOMO level of -5.76 eV determined by the ultraviolet photoelectron spectroscopy measurement and an estimated LUMO level of -2.84 eV. Doping NaAN-m-TRZ with 50% (mass fraction) Liq yields impressive electron mobility of 6.23×10-5~7.19×10-4 cm2·V-1·s-1 @ E = (2~5)×105 V·cm-1 using space-charge-limited current model, which contributes to suppressing triplet-polaron annihilation in the phosphorescent OLEDs. Consequently, based on the single NaAN-m-TRZ∶Liq electron-transport layer, the top-emission green phosphorescent OLED involving Ir(ppy)2(m-mbppy) produces extraordinary durability with projected lifetime t97 of 2 567 h @ 1 000 cd·m-2 as well as a luminous efficiency of 72.2 cd·A-1 and power efficiency of 81 lm·W-1@ 1 000 cd·m-2.

Near-infrared (NIR) emitting materials and devices have broad application prospects in fields of information security, optical fiber communication, bioimaging and medical diagnosis. In recent years, new mechanisms based on thermally activated delayed fluorescence (TADF), hybridized local and charge-transfer excited state (HLCT) and radical-based doublet emission, make the NIR devices full exciton utilization and high electroluminescent performance. In this paper, the progress of NIR organic small-molecule electroluminescent materials is reviewed. These materials are classified with different luminescent mechanism, and their electroluminescent performances and further development prospects are summarized.

Development of high performance near-infrared (NIR) visualization devices offers an exciting opportunity for a plethora of applications in bio imaging, food, wellness, surveillance, and environmental monitoring. NIR visualization devices include an NIR photodetector (PD) unit monolithically integrated with a visible light-emitting diode (LED) unit, enabling the direct visualization of the incident invisible NIR light. In a NIR visualization device, the NIR PD unit serves as one of the charge-injection layers in the LED unit. The hole-electron current balance in the NIR visualization device is controlled by the photocurrent generated in the NIR PD in the presence of the NIR light. The visible light emission in the LED unit is observed in area where the effective charge injection occurs, adjusted by the NIR PD unit in the presence of the NIR light, such that the objects reflecting or illuminating NIR light can be visualized. Likewise, the charge injection in the LED unit can be suppressed in the absent of NIR light or it is reduced due to the decrease in photocurrent in the NIR PD unit, e.g., the presence of the NIR absorbing materials that partially block the NIR light. This review provides a comprehensive overview discussing the operation principle of the NIR visualization devices and the recent progresses made in different types of NIR visualization devices prepared using different inorganic, organic functional semiconductor materials and their combinations. The photon-to-photon conversion efficiency is highly dependent on the quantum efficiency of the NIR PD unit and the LED unit in the NIR visualization device. The efforts and progresses in the development of a series of NIR visualization devices and the applications in 3D image analysis, NIR detection card, bio images, health and environmental monitoring and detection are presented.

Metal halide perovskite materials are a new class of semiconductor materials with unlimited potential. They have the advantages of low cost, high color saturation, narrow half-width (FWHM = 20 nm), adjustable band gap (380~1 000 nm). The study in advantages of high photoluminescence quantum yield (PLQY) and excellent charge transport performance have been extensively researched in various optoelectronic fields and have achieved rapid development, such as perovskite solar cells, perovskite Perovskite light emitting diodes (PeLEDs), perovskite memory, perovskite photodetectors, etc. Since 2014, researchers have firstly observed the electroluminescence of perovskite materials at room temperature, the external quantum efficiency (EQE) of green light, red light and near-infrared perovskite electroluminescent diodes has developed rapidly, and has exceeded 20%. It has reached a level comparable to the mature organic light emitting diodes (OLEDs) on the market. Even the slowest-developing blue PeLEDs have an EQE of more than 10%. This article only briefly introduces the material characteristics, photoelectric properties and research progress of perovskite electroluminescent diodes, so that readers have a better understanding of perovskite electroluminescent diodes.

Metal halide perovskite materials show the promising application prospects in solid lighting and display, owing to their tunable band-gap, narrow emission, high carrier mobility, and high photoluminescence quantum yield. The external quantum efficiencies of red and green perovskite emitting-diodes (PeLEDs) have exceeded 20% by optimizing perovskite film composition and device structure. Compared with the red and green PeLEDs, the development of blue PeLEDs is far lagging behind, as a result of the wide bandgap blue perovskite emitters possess poor stability, high defect-state density, and poor charge injection ability. Therefore, this article reviews recent methods to solve these problems in three main perovskite blue emitters, including three-dimensional perovskite, quasi-two-dimensional perovskite, and perovskite quantum dots. Finally, the opportunities and challenges of blue PeLEDs have prospected.

Recently, blue perovskite light emitting diodes (PeLEDs) is becoming a research hot spot. However, the electroluminescence (EL) spectra of blue PeLEDs based on Cl/Br mixed perovskites will be redshifted under bias, due to the ion migration of Cl and Br anions, which badly hinders the commercialization of blue PeLEDs. In this work, the cesium trifluoroacetate (CsTFA) is introduced to the CsPbClBr2 perovskite precursor to enhance the nucleation density, leading to the formation of small nanoparticle-based perovskite films and thus enhancing the film morphology. Most importantly, the C=O bonds in CsTFA can function effectively in passivating the defects at grain boundaries and preventing the ion migration of halide anions, which largely stabilize the EL spectra. The EL spectra can maintain even under high driven voltage. The maximum luminance and the external quantum efficiency (EQE) is enhanced by 31- and 8-fold compared with control devices, respectively.

Recently, the newly-emerging lead-halide perovskite materials have received extensive attention in optoelectronic devices due to their high photoluminescence quantum yield (PLQY), high color purity, and tunable bandgap, etc. However, the toxicity of heavy metal lead seriously hinders their large-scale production and commercialization. Therefore, the development of lead-free perovskite materials with low toxicity has become an urgent research direction in this field. In this work, a lead-free copper-based Rb2CuBr3 material is synthesized by hot-injection method. The effects of Rb+/Cu+ molar ratio and reaction time on the purity and crystallinity of Rb2CuBr3 are investigated. Transmission electron microscopy show that the microstructure of Rb2CuBr3 is a one-dimensional rod-like morphology, which is consistent with their intrinsic one-dimensional crystal structure. Moreover, the as-synthesized Rb2CuBr3 exhibits a bright violet emission located at 390 nm, and a high PLQY of 9175% is obtained. Furthermore, the temperature-dependent photoluminescence (PL) and time-resolved PL decay measurements confirm that the large Stokes shift and broad emission spectra originate from the self-trapped excitons-related radiative recombination. These results indicate that the lead-free Rb2CuBr3 material with high-efficiency luminescence has great application potential in lighting and display fields in the future.

Hole Transport Layer (HTL) is an important factor affecting carrier transport balance in metal halide Perovskite Light-emitting Diodes (Pero-LEDs). Poly(3,4-ethylenedioxythiophene)∶Poly (styrene sulfonate) (PEDOT∶PSS) films are widely used as the HTL of Pero-LEDs due to their excellent conductive properties, light transmittance and simple solution preparation. However, the gap between the valence band of perovskite and the highest occupied molecular orbital (HOMO) energy level of PEDOT∶PSS film is large, which increases the hole injection barrier and thus reduces the device efficiency. Herein, a simple method of directly adding cesium chloride (CsCl) into PEDOT∶PSS aqueous solution improved the hole transport capacity of PEDOT∶PSS film significantly, making the carrier transport more balanced. Based on the modified PEDOT∶PSS film, the best device reaches high brightness of 124 012 cd/m2, and the maximum external quantum efficiency (EQE) reaches 1039%, respectively. Compared with the undoped samples, the maximum brightness increased by 2549%, and the maximum EQE increased by 63.88%.

In order to obtain deep-red perovskite light-emitting diodes (LEDs) with high color purity, high luminous efficiency, and simple preparation method, Ethylammonium iodide (EAI) is selected as an organic additive. EAI is doped in CsPbBr0.5I2.5 perovskite precursor solution with the solvent of N’N-dimethylformamide (DMF). In this method, spin-coating is used without using anti-solvent to obtain perovskite films with different EAI doping ratios. It is found that when the doping molar ratio is 0.5∶1 (EAI∶Pb2+), a flat and compact perovskite film is obtained, and the perovskite grains after passivation are reduced to 40 nm. Based on this perovskite film as the light-emitting layer, a deep-red perovskite LED with the structure of ITO (90 nm)/ PVK (30 nm)/ perovskite (40 nm)/ TPBi (55 nm)/ CsF (1.2 nm)/ Al (120 nm) was fabricated, giving a turn-on voltage of 2.7 V, a maximum luminance of 320 cd/m2, a maximum external quantum efficiency (EQE) of 7 %, and a bright red electroluminescence peak of 680 nm with a Commission Internationale del′Eclairage (CIE) coordinates of (0.71, 0.28). Therefore, the organic additive EAI can effectively inhibit the growth of large perovskite grains while reducing the density of defect states. Simple solution processing technology and molecular-scale self-assembly technology are used to obtain high-quality thin films for preparing excellent deep-red perovskite LED.

As a non-contact, mask-free digital printing technology, inkjet printing is widely used in the fields of printed circuit boards, photovoltaic modules and display devices. In recent years, Metal Halide Perovskites, as a new type of direct band gap ionic semiconductor materials, have received extensive attention and research from researchers. The use of inkjet printing technology can accurately control the distribution and deposition process of perovskite ink droplets, providing a feasible process route for the industrialization of perovskite optoelectronic devices. Starting from the working principle of inkjet printing, the development process of inkjet printing perovskite optoelectronic devices from the perspectives of ink engineering and process engineering is summarized, and the current challenges of inkjet printing perovskite are analyzed. At the same time, the functional layers and electrodes of perovskite optoelectronic devices prepared based on inkjet printing technology are summarized, and on this basis, the future development prospects and industrialization exploration of inkjet printing perovskite optoelectronic devices are prospected.

Colloidal quantum dots (QDs) are a new type of high-quality optoelectronic material with a radius close to the Bohr radius of the exciton. Its special size effect enables QDs to achieve high-purity three primary color luminescence, continuously adjustable emissions and wide color gamut by adjusting the size of QDs. In addition, the special core-shell structure ensures that QDs have good photo / thermal stability. At the same time, QDs also have excellent solution-processable properties. Since being discovered in 1990s, QDs have become popular research materials in the field of display. Quantum dot light-emitting diodes (QLEDs) based on QDs have also been regarded as the most promising technology to replace organic light-emitting diodes. In the past few decades, QLEDs have achieved such great success to be regarded as one of the most promising materials in the display field. Therefore, researching, analyzing and optimizing the performance of QLEDs devices are of great significance for accelerating their commercial marketization. From the perspective of QLEDs devices optimization to the large-area QLEDs production, the research progresses of domestic and foreign researchers in the direction of constructing efficient and stable QLEDs for display applications are summarized, and the difficulties and challenges we are going to face in the future development of QLEDs are aralyzed.

Quantum dots have a series of advantages of spectrum adjustable with size, high luminous efficiency, good light, thermal and chemical stability, and good solution processability, making them have a wide range of application prospects in lighting, display and other fields and they have become a hot spot in recent years. This paper firstly introduces the types of quantum dot materials, then summarizes the three structures and preparation methods of core-shell quantum dot materials, and systematically describes their three different core-shell structures, and then systematically describes and compares the research progress of quantum dot white light-emitting diodes (QD-WLED) in recent years, focusing on the analysis of white light produced by quantum dots. Finally, it summarizes the application of QD-WLED in visible light communication, health lighting, plant lighting and photodynamic therapy, and expounds the challenges and the future development prospects of this field.

Quantum dots and their light-emitting diodes have a great potential in the display industry. However, cadmium-based quantum dots and perovskite nanocrystals, which contain cadmium and lead, posing a great threat to the environment and human health, which limits their large-scale application. Cadmium-free and lead-free quantum dots and their light-emitting diodes show greater potential. At present, there are many researches on red and green emitting, but few reports on blue light emitting. The research progress of several cadmium-free and lead-free environment-friendly blue quantum dots and light-emitting diodes are summarized in this paper, such as indium phosphide (InP), zinc selenide (ZnSe) and copper halide-based perovskite (Cs3Cu2I5). The structure design, fabrication process of materials and the structure optimization and performance characterization of devices are summarized and analyzed. The future development of cadmium-free and lead-free environment-friendly blue quantum dots and their light-emitting diodes are prospected. The further exploration and development directions are proposed from two aspects of materials and devices.