Highly Stable All‐Inorganic Perovskite Quantum Dots Using a ZnX₂‐Trioctylphosphine‐Oxide: Application for High‐Performance Full‐Color Light‐Emitting Diode

Abstract

realistic colors can be expressed, and the contrast can be deepened, giving a 3D immersive experience. [1] To implement higher resolution quality displays, the pixel size should be more compact and smaller. Therefore, quantum dots with only a few nanometers of particle size are very suitable for the purpose. In particular, among the quantum dots, perovskite quantum dots (PeQDs) have high quantum efficiency and narrow emission spectra (full width at half maximum, FWHM) due to low trap density, and as a result, can express more realistic colors with high color reproducibility. [2] For these reasons, PeQDs have been in the spotlight as promising next-generation display materials. Perovskites generally have an ABX 3 chemical composition and their structure and stability can be predicted by calculating the Goldschmidt tolerance factor with ionic radius. [3][4][5][6] They also have the advantages of easy color tuning through halide exchange and very short synthesis time. [7,8] Currently, perovskites have been studied in depth from bulk to nanomaterials because of their wide range of applications such as LEDs, [4,9,10] solar cells, [11][12][13] lasers, [14][15][16] sensors, [17][18][19] and other applications. However, perovskites have suffered from the serious problem of low stability because structures with the ABX 3 form have weak ionic bonds and easily decompose through moisture, heat, or light exposure. [20] Unlike general semiconductor quantum dots including CdSe [21] and InP, [22] it is difficult to build a shell on the perovskite surface. Considerable research on perovskite stability has been in progress to address these issues. Recently, Li et al. fabricated CsPbBr 3 PeQD silica/ alumina monoliths through the sol-gel reaction using inorganic precursors. [23] In addition, Sun et al. showed that the photoluminescence of PeQD synthesized using octylphosphonic acid (OPA) remained in the ambient atmosphere for 3 d. [24] Herein, we synthesized PeQDs using zinc halide (ZnX 2 ) and trioctylphosphine-oxide (TOPO) as surface capping agents to improve the stability of PeQDs. The use of ZnX 2 as a precursor has already been reported. First, Jeong et al. used ZnX 2 as a halide precursor for PeQDs and explained that the stability of the PeQDs was enhanced by the halide on the surface. [25] They Perovskite is a very promising material that is being extensively studied at the bulk and nanosize scales because it has outstanding optical properties, including high quantum efficiency and narrow emission spectra. However, perovskite has stability issues related to heat, air, and light. To overcome these, highly stable perovskite quantum dots (PeQDs) are developed using excess Zn precursor and trioctylphosphine-oxide (TOPO). In particular, it is clarified that Zn and TOPO are combined and these complexes are attached to the surface of the PeQDs through 31 P NMR. They not only have high quantum efficiency and sharp full width at half maximum values (15-30 nm) but also have improved long-term stability at high temperature. Additionall...

Using Thermally Crosslinkable Hole Transporting Layer to Improve Interface Characteristics for Perovskite CsPbBr3 Quantum-Dot Light-Emitting Diodes

“…To satisfy consumers’ requirement for a higher resolution of display, the pixel size of OLEDs should be more compact and smaller. Therefore, quantum dots (QDs) with only a few nanometers of particle size are very suitable for the purpose [ 8 , 9 , 10 , 11 ]. Among them, perovskite QDs have a high quantum efficiency and narrow emission spectra (i.e., full width at half maximum (FWHM)) due to a low trap density, and thus can express more realistic colors with high color reproducibility [ 12 ].…”

Three-Color White Photoluminescence Emission Using Perovskite Nanoplatelets and Organic Emitter

“…In bulk-type perovskite materials, the emission intensity is weak; however, with the addition of an organic ammonium salt to induce a nanoplatelet shape through dimensional engineering and reduce the grain size, the exciton-binding energy can be increased, and the emission efficiency can be improved [37][38][39]. In the case of perovskite nanocrystals, the emission intensity can be improved by converting a bulk perovskite material into its corresponding perovskite quantum-dot form using long-chain organic ligands such as oleic acid and oleylamine [40,41]. The TPE derivatives used in the present study have not been previously used as a passivation additive.…”

“…Because a perovskite film can be prepared by a solution process and exhibits excellent optical properties, white-light-emitting devices with perovskite and organic light-emitting materials are being actively developed. However, blue-light-emitting perovskite materials exhibit weak luminous efficiency and poor stability compared with red-and green-lightemitting perovskite materials [11,41]. In addition, the emission band of blue-light emitting perovskites has a narrow FWHM, making white-light emission difficult.…”

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

“…Compared with impurity-doped red and green PeLEDs, relatively little attention has been paid to impurity-doped blue PeLEDs. This may be because it is more difficult to synthesize high-performance blue perovskites together with the fact that it becomes harder to manipulate the device engineering due to the wide bandgap of blue emitters [ 305 , 306 , 307 , 308 ]. Encouragingly, B-site doping has been found to be a crucial way to fulfill high-performance blue PeLEDs [ 309 ].…”