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The energy level offset at inorganic layer–organic layer interfaces and the mismatch of hole/electron mobilities of the individual layers greatly limit the establishment of balanced charge carrier injection inside the emissive layer of halide perovskite light-emitting diodes (PeQLEDs). In contrast with other types of light-emitting devices, namely OLEDs and QLEDs, various techniques such as inserting an electron suppression layer between the emissive and electron transport layer have been employed as a means of establishing charge carrier injection into their respective emissive layers. Hence, in this study, we report the use of a thin layer of Poly(4-vinylpyridine) (PVPy) (an electron suppression material) placed between the emissive and electron transport layer of a halide PeQLEDs fabricated with an inverted configuration. With ZnO as the electron transport material, devices fabricated with a thin PVPy interlayer between the ZnO ETL and CsPbBr3 -based green QDs emissive layer yielded a 4.5-fold increase in the maximum observed luminance and about a 10-fold increase in external quantum efficiency (EQE) when compared to ones fabricated without PVPy. Furthermore, the concentration and coating process conditions of CsPbBr3 QDs were altered to produce various thicknesses and film properties which resulted in improved EQE values for devices fabricated with QDs thin films of lower surface root-mean-square (RMS) values. These results show that inhibiting the excessive injection of electrons and adjusting QDs layer thickness in perovskite-inverted QLEDs is an effective way to improve device luminescence and efficiency, thereby improving the carrier injection balance. [ABSTRACT FROM AUTHOR]

A desire to achieve optimal electron transport from the electron transport layer (ETL) towards the emissive layer (EML) is an important research factor for the realization of high performance quantum dot light-emitting diodes (QD-LEDs). In this paper, we study the effect of a single, double, and electron transport layer sandwiched Poly(4-vinylpyridine) (PVPy here on) on the charge injection balance and on the overall device performance of InP-based red quantum dot light emitting diodes (red QD-LEDs). The results showed general improvement of device characteristic performance metrics such as operational life with incorporation of a PVPy interlayer. The best performance was observed at a lower concentration of PVPy (@ 0.1 mg/mL) in interlayer with continual worsening in performance as PVPy concentration in the interlayer increased in other fabricated devices. The AFM images obtained for the different materials reported improved surface morphology and overall improved surface properties, but decreased overall device performance as PVPy concentration in interlayer was increased. Furthermore, we fabricated two special devices: in the first special device, a single 0.1 mg/mL PVPy sandwiched between two ZnO ETL layers, and in the second special device, two 0.1 mg/mL PVPy interlayers were inter-sandwiched between two ZnO ETL layers. Particular emphasis was placed on monitoring the maximum obtained EQE and the maximum obtained luminance of all the devices. The first special device showed better all-round improved performance than the second special device compared to the reference device (without PVPy) and the device with a single 0.1 mg/mL PVPy interlayer stacked between ZnO ETL and the emissive layer. [ABSTRACT FROM AUTHOR]

Microscale light‐emitting diodes (µLEDs) have ushered in a new era of small‐sized high‐resolution displays by integrating numerous microscale pixels within a limited panel area. However, to realize passive‐matrix‐based high‐resolution µLED displays, it is important to prevent image diffusion (crosstalk) between the pixels. Herein, p‐type resistive‐switching (RS) electrodes are introduced in a mesa‐etched passive‐matrix‐based µLED array structure to block electrical interference between adjacent pixels and eliminate cross‐talk. To distinguish between addressed and unaddressed pixels in the µLED array structure, the resistance state of the RS electrode is modulated from low (52 Ω) to high (1.2 × 107 Ω). Moreover, the RS electrode exhibits a high on/off ratio (106), good retention (105 s), and stable endurance (104 cycles). X‐ray photoelectron spectroscopy analysis reveals that the switching mechanism in the RS electrodes is achieved by the generation and annihilation of oxygen vacancies in the conductive path. Consequently, the fabricated µLEDs with RS electrodes exhibit a 93.1% higher electroluminescence intensity and 95.3% higher light output power compared to a reference device fabricated through combined mesa‐ and isolation‐etching. [ABSTRACT FROM AUTHOR]

Inkjet printing of colloidal quantum dots (QDs) is considered a promising technology for application in full‐color quantum dot light‐emitting diode (QLED) displays. However, QLEDs that are inkjet printed in a pixel‐defining bank structure generally exhibit a low performance, mainly due to the nonuniformity in its QD morphology. In this study, an enhanced performance of inkjet‐printing‐based pixelated QLEDs is achieved by introducing small amounts of poly(methyl methacrylate) (PMMA) of different molecular weights into QD inks. When this QD–PMMA composite ink is adopted, uniform droplets are formed, originating from contact line depinning during drying. Inside the bank structure, the inkjet‐printed QD–PMMA composite film shows a smooth surface and little pileup at the bank edges. A pixelated QLED with PMMA with a molecular weight of 8 kDa exhibits the highest luminance of 73 360 cd m−2 and an external quantum efficiency of 2.8%, which are remarkably higher than that of the inkjet‐printed QLED subpixels without PMMA. The result is verified through the observation of the drying process and the QLED subpixel shapes under operation. Thus, inkjet‐printed QD–PMMA composite inks can be a promising strategy for future research on pixelated QLEDs for the fabrication process of full‐color QLED displays. [ABSTRACT FROM AUTHOR]

The article presents study which compares the efficacy of pulsed dye laser (PDL)-assisted photodynamic therapy versus light-emitting diode (LED) laser for the treatment of Bowen's disease (BD) and actinic keratosis (AK). The study has examined 50 Korean patients aging 18 years old and above who had biopsy-proven primary AK or BD diagnosed. It says that the efficacy of PDT shows a distinct result with precancerous lesions based on the selected light sources such as PDL or LED.

[Display omitted] • Multilayered HTL constructed by inserting thin MoO 3 into an organic layer. • Multilayered HTL exhibits high hole conductivity compared to monostructured HTL. • The QLEDs with multilayered HTL exhibited enhanced efficiency and lifetime. • Multilayered HTL denoted high electrical stability with 15 times enhanced lifetime. We report a multilayered hole transport layer (HTL) structure to improve the efficiencies and lifetimes of quantum dot light-emitting diodes (QD-LEDs). The HTL structure was constructed by inserting molybdenum trioxide (MoO 3) into an organic monolayer to enhance its hole conductivity. We then investigated the effects of the multilayered HTL on the performance and operating lifetimes of QD-LEDs. QD-LEDs with optimal HTL exhibit power efficiency, external quantum efficiency, and lifetime (T 80) of 10.19 lm/W, 9.66%, and 336 h, respectively. Compared to the monolayer structure, the lifetime of the multilayered HTL was enhanced by a factor of 15. This novel architecture for QD-LEDs with multilayered HTL offers a new design strategy for next-generation high-efficiency QLED displays and solid-state lighting technologies. [ABSTRACT FROM AUTHOR]