ABSTRACT
Full-color matrix devices based on perovskite light-emitting diodes (PeLEDs) formed via inkjet printing are increasingly attractive due to their tunable emission, high color purity, and low cost. A key challenge for realizing PeLED matrix devices is achieving high-quality perovskite films with a favorable emission structure via inkjet printing techniques. In this work, a narrow phase distribution, high-quality quasi-two-dimensional (quasi-2D) perovskite film without a "coffee ring" was obtained via the introduction of a phenylbutylammonium cation into the perovskite and the use of a vacuum-assisted quick-drying process. Relatively efficient emissions of red, green, and blue (RGB) uniform quasi-2D perovskite films with high photoluminescence quantum yields were cast by the inkjet printing technique. The RGB monochrome perovskite matrix devices with 120 pixel-per-inch resolution exhibited electroluminescence, with maximum external quantum efficiencies of 3.5, 3.4, and 1.0% (for red, green, and blue light emissions, respectively). Furthermore, a full-color perovskite matrix device with a color gamut of 102% (NTSC 1931) was realized. To the best of our knowledge, this is the first report of a full-color perovskite matrix device formed by inkjet printing.
ABSTRACT
We report the effects of ultraviolet (UV) irradiation and storage on the performance of ZnO-based inverted quantum-dot light-emitting diodes (QLEDs). The effects of UV irradiation on the electrical properties of ZnO nanoparticles (NPs) were investigated. We demonstrate that the charge balance was enhanced by improving the electron injection. The maximum external quantum efficiency (EQE) and power efficiency (PE) of QLEDs were increased by 26% and 143% after UV irradiation for 15 min. In addition, we investigated the storage stabilities of the inverted QLEDs. During the storage period, the electron current from ZnO gradually decreased, causing a reduction in the device current. However, the QLEDs demonstrated improvements in maximum EQE by 20.7% after two days of storage. Our analysis indicates that the suppression of exciton quenching at the interface of ZnO and quantum dots (QDs) during the storage period could result in the enhancement of EQE. This study provides a comprehension of the generally neglected factors, which could be conducive to the realization of high-efficiency and highly storage-stable practical applications.
ABSTRACT
An environment-friendly inverted indium phosphide red quantum dot light-emitting diode (InP QLED) was fabricated using Mg-doped zinc oxide (ZnMgO) as the electron transport layer (ETL). The effects of ZnMgO ETL on the performance of InP QLED were investigated. X-ray diffraction (XRD) analysis indicated that ZnMgO film has an amorphous structure, which is similar to zinc oxide (ZnO) film. Comparison of morphology between ZnO film and ZnMgO film demonstrated that Mg-doped ZnO film remains a high-quality surface (root mean square roughness: 0.86 nm) as smooth as ZnO film. The optical band gap and ultraviolet photoelectron spectroscopy (UPS) analysis revealed that the conduction band of ZnO shifts to a more matched position with InP quantum dot after Mg-doping, resulting in the decrease in turn-on voltage from 2.51 to 2.32 V. In addition, the ratio of irradiation recombination of QLED increases from 7% to 25% using ZnMgO ETL, which can be attributed to reduction in trap state by introducing Mg ions into ZnO lattices. As a result, ZnMgO is a promising material to enhance the performance of inverted InP QLED. This work suggests that ZnMgO has the potential to improve the performance of QLED, which consists of the ITO/ETL/InP QDs/TCTA/MoO3/Al, and Mg-doping strategy is an efficient route to directionally regulate ZnO conduction bands.
ABSTRACT
A unique technique to passivate both bottom and top sides of perovskite has been successfully developed to achieve highly efficient inverted perovskite light-emitting diodes (PeLEDs). For the bottom passivation, an organic/inorganic hybrid electron transporting layer (ETL) replaces the widely adopted inorganic ETL to overcome the disadvantages of the pure inorganic ETL. The ZPM (ZnO-in-polymer matrix) ETL, which consists of ZnO nanoparticles blended into polyvinylpyrrolidone, not only passivates the surface defects of ZnO nanoparticles, but also improves the morphology and stability of FAPbBr3 film. For the top passivation, smaller grains and a FAPbBr3/PEA2PbBr4 3D/2D hybrid structure are obtained by applying a small amount of PEABr solution. The synergetic interplay of organic/inorganic hybrid ETL and organic halide salt surface modification substantially shrinks the grain size to facilitate radiative recombination, and suppresses non-radiative recombination both at the interface of ETL/perovskite and HTL/perovskite, and in the perovskite layer. As a result, the highly efficient green PeLED sets a new record of device performance for FAPbBr3-based inverted PeLEDs, with current efficiency of 39.7 cd A-1, external quantum efficiency of 9.0%, power efficiency of 46.4 lm W-1, maximum luminance of 6.03 × 104 cd m-2, and half-lifetime of 297 minutes at an initial brightness of â¼100 cd m-2.
ABSTRACT
All-solution-processed pure formamidinium-based perovskite light-emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr3 device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution-processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution-processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W-1 , a peak current efficiency of 21.3 cd A-1 , and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 105 cd m-2 . A record lifetime T50 of 436 s is achieved at the initial brightness of 10 000 cd m-2 . Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn-on voltage is attributed to Auger-assisted energy up-conversion process.
ABSTRACT
In all-solution processed inverted quantum dots based light emitting diodes (QLEDs), the solvent erosion on the quantum dot (QD) layer prevents devices from reaching high performance. By employing an orthogonal solvent 1,4-dioxane for the hole transport layer (HTL) poly(9-vinlycarbazole) (PVK), the external quantum efficiencies (EQE) of red QLED is increased 4-fold, while the luminous efficiencies (LE) of blue QLED is enhanced by 25 times, compared to the previous devices' record. To further improve the device efficiency and reduce the efficiency roll-off, solution processed PVK/poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] (TFB) double-layer HTL is introduced to facilitate hole injection with stepwise energy level. By reducing the hole injection barrier, the turn-on voltage of QLEDs decreases from 3.4 to 2.7 V for red, from 5.1 to 2.7 V for green, and from 5.3 to 4.1 V for blue. The peak LE reach 22.1 cd/A, 21.4 cd/A, and 1.99 cd/A, while the maximum EQE reach 12.7%, 5.29%, and 5.99%, for red, green, and blue QLEDs, respectively. To the best of our knowledge, the red and blue QLEDs exhibit the best device performance among all the all-solution processed inverted QLEDs. In addition, the blue QLED is the champion among all the inverted QLEDs, including the devices fabricated by thermal evaporation.
