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Perovskite quantum dots (PeQDs) are promising nanoscale emitters in a generation of high-performance, large-area, and low-cost light-emitting diodes (LEDs) due to their superior emissive properties and excellent solution processability. Despite the tremendous advancement in luminescence efficiency in PeQDs, the design principle of the hole-transporting layer for PeQDs-based LEDs is still limited. Here, we investigate the discrepancy in electroluminescence properties of PeQDs-based LEDs with two widely used hole-transporting layers, namely, poly-[bis-(4-phenyl)-(2,4,6-trimethylphenyl)-amine] (PTAA) and poly-(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine) (TFB). The results show that the TFB-based PeQD-LEDs exhibit much inferior performance than the PTAA-based device (7% vs 18% for external quantum efficiency) although the PeQDs show better optical properties when depositing on TFB hole-transporting layers. Theoretical calculation and comprehensive spectroscopic analysis indicate a weaker interaction between PeQDs and TFB polymers, which is attributed to the larger steric hindrance of TFB than that of PTAA. As a result, electrical characterizations identify a poor hole injection efficiency from the TFB to the PeQDs emissive layer when compared with the PTAA hole-transporting layers, thus leading to poor device performance. This work reveals the interaction between the hole-transporting layer and PeQDs on the performance of electroluminescence beyond the energy level and mobility of hole-transporting materials, which promotes an understanding of the hole injection mechanism in PeQDs-based LEDs. [ABSTRACT FROM AUTHOR]

Achieving excellent optical properties and stability is crucial for the practical utilization of perovskite emitters. Herein, ultra-stable CsPbBr3-DPSI/MS composites with a high photoluminescence quantum yield (PLQY) of 93.2% are obtained through passivation of the surface of CsPbBr3 quantum dots (QDs) by 3-(decyldimethylammonio)-propane-sulfonate inner salt (DPSI) and encapsulating these QDs using silica molecular sieve (MS) templates. After aging for 1000 hours under harsh synergistic conditions (i.e., temperature of 60 °C, relative humidity of 90%, and blue light irradiation with a power density of 3500 W m−2), these composites still retain 90% of their initial photoluminescence (PL) intensity. To the best of our knowledge, these CsPbBr3-DPSI/MS composites represent the most stable CsPbBr3 emitters in an accelerated aging test under these synergistic humidity–heat–light conditions. The liquid crystal display (LCD) backlight module utilizing these stable composites shows a wide color gamut of 111.7% NTSC. Furthermore, these CsPbBr3-DPSI/MS composites exhibit exceptional X-ray scintillator performance and impressive radiation hardness, delivering a high X-ray imaging spatial resolution of up to ≈16 lp mm−1 and a low detection limit of 339 nGyair s−1. [ABSTRACT FROM AUTHOR]

High‐performance pure red perovskite light‐emitting diodes (PeLEDs) with an emission wavelength shorter than 650 nm are ideal for wide‐color‐gamut displays, yet remain an unprecedented challenge to progress. Mixed‐halide CsPb(Br/I)3 emitter‐based PeLEDs suffer spectral stability induced by halide phase segregation and CsPbI3 quantum dots (QDs) suffer from a compromise between emission wavelength and electroluminescence efficiency. Here, we demonstrate efficient pure red PeLEDs with an emission centered at 638 nm based on PbClx‐modified CsPbI3 QDs. A nucleophilic reaction that releases chloride ions and manipulates the ligand equilibrium of the colloidal system is developed to synthesize the pure red emission QDs. The comprehensive structural and spectroscopic characterizations evidence the formation of PbClx outside the CsPbI3 QDs, which regulates exciton recombination and prevents the exciton from dissociation induced by surface defects. In consequence, PeLEDs based on PbClx‐modified CsPbI3 QDs with superior optoelectronic properties demonstrate stable electroluminescence spectra at high driving voltages, a record external quantum efficiency of 26.1 %, optimal efficiency roll‐off of 16.0 % at 1000 cd m−2, and a half lifetime of 7.5 hours at 100 cd m−2, representing the state‐of‐the‐art pure red PeLEDs. This work provides new insight into constructing the carrier‐confined structure on perovskite QDs for high‐performance PeLEDs. [ABSTRACT FROM AUTHOR]

With the continuous development of artificial intelligence technology and the exponential growth in the number of images, image detection and recognition technology is becoming more widely used. Image knowledge management is extremely urgent. The data source of a knowledge graph is not only the text and structured data but also the visual or auditory data such as images, video, and audio. How to use multimodal information to build an information management platform is a difficult problem. In this paper, a method is proposed to construct the result of image recognition as a knowledge graph. First of all, based on the improvement in the BlendMASK algorithm, the hollow convolution kernel is added. Secondly, the effect of image recognition and the relationships between all kinds of information are analyzed. Finally, the image knowledge graph is constructed by using the relationship between the image entities. The contributions of this paper are as follows. (1) The hollow convolution kernel is added to reduce the loss from extracting feature information from high-level feature images. (2) In this paper, a method is proposed to determine the relationship between entities by dividing the recognition results of entities in an image with a threshold, which makes it possible for the relationships between images to be interconnected. The experimental results show that this method improves the accuracy and F1 value of the image recognition algorithm. At the same time, the method achieves integrity in the construction of a multimodal knowledge graph. [ABSTRACT FROM AUTHOR]

Perovskite light-emitting diodes (PeLEDs) provide excellent opportunities for low-cost, color-saturated, and large-area displays. However, the performance of blue PeLEDs lags far behind that of their green and red counterparts. Here, we show that the external quantum efficiencies (EQEs) of blue PeLEDs scale linearly with the photoluminescence quantum yields (PL QYs) of CsPb(Br x Cl 1- x ) 3 nanocrystals emitting at 460 to 480 nm. The recombination efficiency of carriers is highly sensitive to the chlorine content and the related deep-level defects in nanocrystals, causing notable EQE drops even with minor increases in chlorine defects. Minor adjustments of chlorine content through rubidium compensation on the A-site effectively suppress the formation of nonradiative defects, improving PL QYs while retaining desirable bandgaps for blue-emitting nanocrystals. Our PeLEDs with record-high efficiencies span the blue spectrum, achieving peak EQEs of 12.0% (460 nm), 16.7% (465 nm), 21.3% (470 nm), 24.3% (475 nm), and 26.4% (480 nm). This work exemplifies chlorine-defect control as a key design principle for high-efficiency blue PeLEDs.

Quasi-2D perovskites exhibit impressive optoelectronic properties and hold significant promise for future light-emitting devices. However, the efficiency of perovskite light-emitting diodes (PeLEDs) is seriously limited by defect-induced nonradiative recombination and imbalanced charge injection. Here, the defect states are passivated and charge injection balance is effectively improved by introducing the additive cyclohexanemethylammonium (CHMA) to bromide-based Dion-Jacobson (D-J) structure quasi-2D perovskite emission layer. CHMA participates in the crystallization of perovskite, leading to high quality film composed of compact and well-contacted grains with enhanced hole transportation and less defects. As a result, the corresponding PeLEDs exhibit stable pure blue emission at 466 nm with a maximum external quantum efficiency (EQE) of 9.22%. According to current knowledge, this represents the highest EQE reported for pure-blue PeLEDs based on quasi-2D bromide perovskite thin films. These findings underscore the potential of quasi-2D perovskites for advanced light-emitting devices and pave the way for further advancements in PeLEDs., (© 2024 Wiley‐VCH GmbH.)

Controlling interfacial reactions is critical for zinc oxide (ZnO)-based inverted perovskite light-emitting diodes (PeLEDs), boosting the external quantum efficiency (EQE) of the near-infrared device to above 20%. However, violent interfacial reactions between the bromine-based perovskites and ZnO-based films severely limit the performance of inverted green PeLEDs, whose efficiency and stability lag far behind those of their near-infrared counterparts. Here, a controllable interfacial amidation between the bromine-based perovskites and magnesium-doped ZnO (ZnMgO) film utilizing caprylyl sulfobetaine (SFB) is realized. The SFB molecules strongly interact with formamidinium bromide, decelerating the amidation reaction between formamidinium and carboxylate groups on the ZnMgO film, thus regulating the crystallization of FAPbBr 3 . Combined with the passivation of benzylamine, a FAPbBr 3 bulk film directly deposited on a ZnMgO substrate with single-crystal characteristics is obtained, exhibiting a high photoluminescence quantum yield of above 80%. The resultant PeLEDs demonstrate a peak EQE of exceeding 20% at a high luminance of 120,000 cd m -2 and a half lifetime of 26 min at 11,000 cd m -2 , representing the state-of-the-art inverted green electroluminescence. This work resolves the crucial issues of violent interfacial reactions and provides a strategy toward inverted green PeLEDs with outstanding performance.

Developing green perovskite light-emitting diodes (PeLEDs) with a high external quantum efficiency (EQE) and low efficiency roll-off at high brightness remains a critical challenge. Nanostructured emitter-based devices have shown high efficiency but restricted ascending luminance at high current densities, while devices based on large-sized crystals exhibit low efficiency roll-off but face great challenges to high efficiency. Herein, we develop an all-inorganic device architecture combined with utilizing tens-of-nanometers-sized CsPbBr 3 (TNS-CsPbBr 3 ) emitters in a carrier-confined heterostructure to realize green PeLEDs that exhibit high EQEs and low efficiency roll-off. A typical type-I heterojunction containing TNS-CsPbBr 3 crystals and wide-bandgap Cs 4 PbBr 6 within a grain is formed by carefully controlling the precursor ratio. These heterostructured TNS-CsPbBr 3 emitters simultaneously enhance carrier confinement and retain low Auger recombination under a large injected carrier density. Benefiting from a simple device architecture consisting of an emissive layer and an oxide electron-transporting layer, the PeLEDs exhibit a sub-bandgap turn-on voltage of 2.0 V and steeply rising luminance. In consequence, we achieved green PeLEDs demonstrating a peak EQE of 17.0% at the brightness of 36,000 cd m -2 , and the EQE remained at 15.7% and 12.6% at the brightness of 100,000 and 200,000 cd m -2 , respectively. In addition, our results underscore the role of interface degradation during device operation as a factor in device failure.

High-performance pure red perovskite light-emitting diodes (PeLEDs) with an emission wavelength shorter than 650 nm are ideal for wide-color-gamut displays, yet remain an unprecedented challenge to progress. Mixed-halide CsPb(Br/I) 3 emitter-based PeLEDs suffer spectral stability induced by halide phase segregation and CsPbI 3 quantum dots (QDs) suffer from a compromise between emission wavelength and electroluminescence efficiency. Here, we demonstrate efficient pure red PeLEDs with an emission centered at 638 nm based on PbCl x -modified CsPbI 3 QDs. A nucleophilic reaction that releases chloride ions and manipulates the ligand equilibrium of the colloidal system is developed to synthesize the pure red emission QDs. The comprehensive structural and spectroscopic characterizations evidence the formation of PbCl x outside the CsPbI 3 QDs, which regulates exciton recombination and prevents the exciton from dissociation induced by surface defects. In consequence, PeLEDs based on PbCl x -modified CsPbI 3 QDs with superior optoelectronic properties demonstrate stable electroluminescence spectra at high driving voltages, a record external quantum efficiency of 26.1 %, optimal efficiency roll-off of 16.0 % at 1000 cd m -2 , and a half lifetime of 7.5 hours at 100 cd m -2 , representing the state-of-the-art pure red PeLEDs. This work provides new insight into constructing the carrier-confined structure on perovskite QDs for high-performance PeLEDs., (© 2024 Wiley-VCH GmbH.)