Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes.

Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.This work was partially supported by Samsung Research Funding Center of Samsung Electronics under Project Number SRFC-MA-1402-07. A.S. was partially supported by the Engineering and Physical Sciences Research Council (UK).This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the American Association for the Advancement of Science

Multicolored Organic/Inorganic Hybrid Perovskite Light-Emitting Diodes

Bright organic/inorganic hybrid perovskite light-emitting diodes (PrLEDs) are realized by using CH3NH3PbBr3 as an emitting layer and self-organized buffer hole-injection layer (Buf-HIL). The PrLEDs show high luminance, current efficiency, and EQE of 417 cd m(-2), 0.577 cd A(-1), and 0.125%, respectively. Buf-HIL can facilitate hole injection into CH3NH3PbBr3 as well as block exciton quenching.X11473381sciescopu

Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes

Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions

Blending of n‑type Semiconducting Polymer and PC₆₁BM for an Efficient Electron-Selective Material to Boost the Performance of the Planar Perovskite Solar Cell

The highly efficient CH₃NH₃PbI₃ perovskite solar cell (PeSC) is simply achieved by employing a blended electron-transport layer (ETL) consisting of PC₆₁BM and P­(NDI2OD-T2). The high molecular weight of P­(NDI2OD-T2) allows for a thinned ETL with a uniform morphology that optimizes the PC₆₁BM ETL more effectively. As a result of this enhancement, the power conversion efficiency of a PC₆₁BM:P­(NDI2OD-T2)-based PeSC is 25% greater than that of the conventional PC₆₁BM based-PeSC; additionally, the incorporation of P­(NDI2OD-T2) into PC₆₁BM attenuates the dependence of the PeSC on the ETL-processing conditions regarding its performance. It is revealed that, in addition to the desirable n-type semiconducting characteristics of PC₆₁BM:P­(NDI2OD-T2)including a higher electron-mobility and a more-effective electron selectivity of a blended ETL for an efficient electron extractionthe superior performance of a PC₆₁BM:P­(NDI2OD-T2) device is the result of a thinned and uniformly covered ETL on the perovskite layer

Highly Efficient, Color-Reproducible Full-Color Electroluminescent Devices Based on Red/Green/Blue Quantum Dot-Mixed Multilayer

Over the past few years the performance of colloidal quantum dot-light-emitting diode (QLED) has been progressively improved. However, most of QLED work has been fulfilled in the form of monochromatic device, while full-color-enabling white QLED still remains nearly unexplored. Using red, green, and blue quantum dots (QDs), herein, we fabricate bichromatic and trichromatic QLEDs through sequential solution-processed deposition of poly(9-vinlycarbazole) (PVK) hole transport layer, two or three types of QDs-mixed multilayer, and ZnO nanoparticle electron transport layer. The relative electroluminescent (EL) spectral ratios of constituent QDs in the above multicolored devices are found to inevitably vary with applied bias, leading to the common observation of an increasing contribution of a higher-band gap QD EL over low-band gap one at a higher voltage. The white EL from a trichromatic device is resolved into its primary colors through combining with color filters, producing an exceptional color gamut of 126% relative to National Television Systems Committee (NTSC) color space that a <i>state-of-the-art</i> full-color organic LED counterpart cannot attain. Our trichromatic white QLED also displays the record-high EL performance such as the peak values of 23 352 cd/m² in luminance, 21.8 cd/A in current efficiency, and 10.9% in external quantum efficiency

Palladium-Decorated Hydrogen-Gas Sensors Using Periodically Aligned Graphene Nanoribbons

Polymer residue-free graphene nanoribbons (GNRs) of 200 nm width at 1 μm pitch were periodically generated in an area of 1 cm² via laser interference lithography using a chromium interlayer prior to photoresist coating. High-quality GNRs were evidenced by atomic force microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy measurements. Palladium nanoparticles were then deposited on the GNRs as catalysts for sensing hydrogen gases, and the GNR array was utilized as an electrically conductive path with less electrical noise. The palladium-decorated GNR array exhibited a rectangular sensing curve with unprecedented rapid response and recovery properties: 90% response within 60 s at 1000 ppm and 80% recovery within 90 s in nitrogen ambient. In addition, reliable and repeatable sensing behaviors were revealed when the array was exposed to various gas concentrations even at 30 ppm