Recent Advances on Cyan‐Emitting (480 ≤ λ ≤ 520 nm) Metal Halide Perovskite Materials

Efficient and tunable emission CsPbClxBr3-x quantum dot glass for overcoming the lack of cyan gap in WLED

Recently, the photoluminescence (PL) performance and stability of cyan emission perovskite quantum dot (PQD) were found to be inferior to other color emitting PQDs, which greatly limits their practical applications. In this Letter, CsPbClxBr3-x PQD glass with excellent hydrothermal stability is successfully synthesized by a high-temperature melting method. Results review that the vacancy defects in [PbBr6]4- octahedra can be effectively compensated by excessive halogen doping, resulting in an improvement in the photoluminescence quantum yield (PLQY) of PQDs from 24.73% to 65.62%. In addition, compared to white light emitting diode (WLED) synthesized with commercial fluorescent powders, the introduction of CsPbCl2Br1 PQD glass effectively fills the cyan gap. Moreover, the WLED displays the color-rendering index (CRI) of 87 at correlated color temperature (CCT) of 5257 K, and the color gamut area reaches 126% of the National Television System Committee (NTSC). This work provides an effective way for improving the PL performance of PQDs and brings CsPbClxBr3-x PQD glass significant prospect in the optoelectronic applications.

Modifying PTAA/Perovskite Interface via 4-Butanediol Ammonium Bromide for Efficient and Stable Inverted Perovskite Solar Cells

Inverted perovskite solar cells (IPSCs) have witnessed an impressive development in recent years. However, their efficiency is still significantly behind theoretical limits, and device instabilities hinder their commercialization. Two main obstacles to further enhancing their performance via one-step deposition are: 1) the unsatisfactory film quality of perovskite and 2) the poor surface contact. To address the above issues, 4-butanediol ammonium Bromide (BD) is utilized to passivate Pb²⁺ defects by forming PbN bonds and fill vacancies of formamidinium ions at the buried surface of perovskite. The wettability of poly [bis (4-phenyl) (2,4,6-triMethylphenyl) amine] films is also improved due to the formation of hydrogen bonds between PTAA and BD molecules, resulting in better surface contacts and enhanced perovskite crystallinity. As a result, BD-modified perovskite thin films show a significant increase in the mean grain size, as well as a dramatic enhancement in the PL decay lifetime. The BD-treated device exhibits an efficiency of up to 21.26%, considerably higher than the control device. Moreover, the modified devices show dramatically enhanced thermal and ambient stability compared to the control ones. This methodology paves the way to obtain high-quality perovskite films for fabricating high-performance IPSCs.

Synthesis of Efficient and Stable Tetrabutylammonium Copper Halides with Dual Emissions for Warm White Light-Emitting Diodes

In order to achieve a high color-rendering index (CRI) and low correlated color temperature (CCT) indoor lighting, single-component phosphors with broad-band dual emission are in high demand for white-light-emitting diodes (WLEDs). However, phosphors with such fluorescent properties are rare at present. Herein, we report a facile solid-state chemical method for the synthesis of single-component phosphor with broad-band emission and a large Stokes shift that can meet the requirements of future white-light sources. These new tetrabutylammonium copper halides phosphors have excellent warm white emission characteristics, and their luminescence peaks are located at 494 and 654 nm. The optimized photoluminescence (PL) quantum yield can reach 93.7 %. The typical CIE coordinate of the as-fabricated WLED is at (0.3620, 0.3731) with a CRI of 89 and low CCT of 4516 K.

Light Emission of Self-Trapped Excitons in Inorganic Metal Halides for Optoelectronic Applications

Self-trapped excitons (STEs) have recently attracted tremendous interest due to their broadband emission, high photoluminescence quantum yield, and self-absorption-free properties, which enable a large range of optoelectronic applications such as lighting, displays, radiation detection, and special sensors. Unlike free excitons, the formation of STEs requires strong coupling between excited state excitons and the soft lattice in low electronic dimensional materials. The chemical and structural diversity of metal halides provides an ideal platform for developing efficient STE emission materials. Herein, an overview of recent progress on STE emission materials for optoelectronic applications is presented. The relationships between the fundamental emission mechanisms, chemical compositions, and device performances are systematically reviewed. On this basis, currently existing challenges and possible development opportunities in this field are presented.

Highly Plasticized Lanthanide Luminescence for Information Storage and Encryption Applications

The development of new storage media to meet the demands for diverse information storage scenarios is a great challenge. Here, a series of lanthanide-based luminescent organogels with ultrastrong mechanical performance and outstanding plasticity are developed for patterned information storage and encryption applications. The organogels possessing outstanding mechanical properties and tunable luminescent colors are prepared by electrostatic and coordinative interactions between natural DNA, synthetic ligands, and rare earth (RE) ions. The organogel-REs can be stretched by 180 times and show an ultrastrong breaking strength of 80 MPa. A series of applications with both information storage and encryption, such as self-information pattern, quick response (QR) code, and barcode, are successfully demonstrated by the organogel-REs. The developed information storage systems have various advantages of good processability, high stretchability, excellent stability, and versatile design of information patterns. Therefore, the organogel-RE-based information storage systems are suitable for applications under different scenarios, such as flexible devices under repeating rude operations. The advancements will enable the design and development of luminescent organogel-REs as information storage and encryption media for various scenarios.

Biodegradable, Breathable Leaf Vein-Based Tactile Sensors with Tunable Sensitivity and Sensing Range

Resistive pressure sensors have been widely studied for application in flexible wearable devices due to their outstanding pressure-sensitive characteristics. In addition to the outstanding electrical performance, environmental friendliness, breathability, and wearable comfortability also deserve more attention. Here, a biodegradable, breathable multilayer pressure sensor based piezoresistive effect is presented. This pressure sensor is designed with all biodegradable materials, which show excellent biodegradability and breathability with a three-dimensional porous hierarchical structure. Moreover, due to the multilayer structure, the contact area of the pressure sensitive layers is greatly increased and the loading pressure can be distributed to each layer, so the pressure sensor shows excellent pressure-sensitive characteristics over a wide pressure sensing range (0.03-11.60 kPa) with a high sensitivity (6.33 kPa^-1 ). Furthermore, the sensor is used as a human health monitoring equipment to monitor the human physiological signals and main joint movements, as well as be developed to detect different levels of pressure and further integrated into arrays for pressure imaging and a flexible musical keyboard. Considering the simple manufacturing process, the low cost, and the excellent performance, leaf vein-based pressure sensors provide a good concept for environmentally friendly wearable devices.

Ligand-modified synthesis of shape-controllable and highly luminescent CsPbBr3 perovskite nanocrystals under ambient conditions

The intrinsic insights of ligand-modified shape-transformation of CsPbBr3 nanocrystals between nanocubes and nanorods are revealed systematically, which can accelerate their practical applications in the optoelectronic field.

Cyan Emission in Two-Dimensional Colloidal Cs2CdCl4:Sb3+ Ruddlesden-Popper Phase Nanoplatelets

Metal halide perovskites are one of the most investigated materials in optoelectronics, with their lead-based counterparts being renowned for their enhanced optoelectronic performance. The 3D CsPbX₃ structure has set the standard with many studies currently attempting to substitute lead with other metals while retaining the properties of this material. This effort has led to the fabrication of metal halides with lower dimensionality, wherein particular 2D layered perovskite structures have captured attention as inspiration for the next generation of colloidal semiconductors. Here we report the synthesis of the Ruddlesden-Popper Cs₂CdCl₄:Sb³⁺ phase as colloidal nanoplatelets (NPs) using a facile hot injection approach under atmospheric conditions. Through strict adjustment of the synthesis parameters with emphasis on the ligand ratio, we obtained NPs with a relatively uniform size and good morphological control. The particles were characterized through transmission electron microscopy, synchrotron X-ray diffraction, and pair distribution function analysis. The spectroscopic characterization revealed most strikingly an intense cyan emission under UV excitation with a measured PLQY of ∼20%. The emission was attributed to the Sb³⁺-doping within the structure.

Dendritic CsSnI3 for Efficient and Flexible Near-Infrared Perovskite Light-Emitting Diodes

All-inorganic and lead-free CsSnI₃ is emerging as one of the most promising candidates for near-infrared perovskite light-emitting diodes (NIR Pero-LEDs), which find practical applications including facial recognition, biomedical apparatus, night vision camera, and Light Fidelity. However, in the CsSnI₃ -based Pero-LEDs, the holes injection is significantly higher than that of electrons, resulting in unbalanced charge injection, undesired exciton dissipation, and poor device performance. Herein, it is proposed to manage charge injection and recombination behavior by tuning the interface area of perovskite and charge-transporter. A dendritic CsSnI₃ structure is prepared on the hole-transporter, only making a bottom contact with the hole-transporter and exposing all other available crystal surfaces to the electron-transporter. In other words, the interface area of perovskite/electron-transporter is significantly higher than that of perovskite/hole-transporter. Moreover, the embedding interface of perovskite/electron-transporter can spatially confine holes and electrons, increasing the radiation recombination. By taking advantage of the dendritic structure, efficient lead-free NIR Pero-LEDs are achieved with a record external quantum efficiency (EQE) of 5.4%. More importantly, the dendritic structure shows great superiorities in flexible devices, for there is almost no morphology change after 2000-cycles of bends, and the fabricated Pero-LEDs can keep 93.4% of initial EQEs after 50-cycles of bends.

Interfacial "Anchoring Effect" Enables Efficient Large-Area Sky-Blue Perovskite Light-Emitting Diodes

While tremendous progress has recently been made in perovskite light-emitting diodes (PeLEDs), large-area blue devices feature inferior performance due to uneven morphologies and vast defects in the solution-processed perovskite films. To alleviate these issues, a facile and reliable interface engineering scheme is reported for manipulating the crystallization of perovskite films enabled by a multifunctional molecule 2-amino-1,3-propanediol (APDO)-triggered "anchoring effect" at the grain-growth interface. Sky-blue perovskite films with large-area uniformity and low trap states are obtained, showing the distinctly improved radiative recombination and hole-transport capability. Based on the APDO-induced interface engineering, synergistical boost in device performance is achieved for large-area sky-blue PeLED (measuring at 100 mm2 ) with a peak external quantum efficiency (EQE) of 9.2% and a highly prolonged operational lifetime. A decent EQE up to 6.1% is demonstrated for the largest sky-blue device emitting at 400 mm2 .