Efficient and Stable Quantum‐Dot Light‐Emitting Diodes Enabled by Tin Oxide Multifunctional Electron Transport Layer

Abstract

theoretical limit. In order to achieve efficient and stable QLEDs, each functional layer needs to be elaborately designed and optimized, especially for the charge transport layers. [1][2][3] At present, the most commonly used electron transport layer (ETL) material in QLEDs is zinc oxide (ZnO) or Mg-doped ZnO (ZnMgO) nanoparticles (NPs). As a wide bandgap semiconductor, ZnO exhibits exceptional properties, including high mobility, high transparency, and tunable conductivity, which are helpful to realize highly efficient QLEDs. Now, ZnO NPs are ubiquitous in all record-breaking QLED devices. [1][2][3][4][5][6][7][8][9] Although ZnO ETLs are widely employed and considered to be the basis for high-efficiency QLEDs, the large number of defects in ZnO often lead to the nonradiate quenching of excitons and the low stability of QLEDs. [1,[10][11][12] In addition, a unique phenomenon named positive aging has also been suggested to be associated with ZnO defects. [11][12][13] Despite the fact that people endeavor to optimize ZnO NPs, including doping, adjusting the thickness, and regulating the energy band, [14][15][16] there is still no perfect solution to eliminate the defects of ZnO, which limits the commercialization of QLEDs.To address these problems, a promising solution is to develop a novel ETL material, such as titanium oxide (TiO 2 ), tin oxide (SnO 2 ), and organic compounds to replace ZnO. [17][18][19] Among them, SnO 2 is a solution-processable n-type semiconductor similar to ZnO, but compared with ZnO (≈3.4 eV), SnO 2 has a wider bandgap (≈3.8 eV), higher transmittance, higher mobility, and better stability. [20,21] These unique characteristics facilitate SnO 2 as an ideal ETL for perovskite solar cells (PSCs). [22][23][24][25] Despite substantial advances in the application of SnO 2 for PSCs, the application of SnO 2 NPs in QLEDs has rarely been studied. [18] In this work, we prepared SnO 2 NPs by aqueous synthesis and the obtained SnO 2 NPs exhibit high conductivity, good transparency, excellent stability, and low defect density. With such unique characteristics, SnO 2 NPs can act as the multifunctional ETLs for various structured QLEDs, e.g., 1) as a phase tuning layer to improve the efficiency of inverted QLEDs, 2) as a thick protection layer to improve the stability of noninverted QLEDs, 3) as a sputtering buffer layer to protect the functional layer from ion bombardment damage in transparent QLEDs, and 4) as an internal light extraction layer to enhance the light coupling efficiency of top-emitting QLEDs. With SnO 2 ETLs, Zinc oxide (ZnO) based nanoparticles (NPs) are the most commonly used electron transport layer (ETL) materials in quantum dot light-emitting diodes (QLEDs). However, numerous defects, severe quenching, and poor stability of ZnO NPs limit the commercialization of QLEDs. Herein, tin oxide (SnO 2 ) NPs are prepared as a substitute to ZnO. The obtained SnO 2 NPs exhibit high conductivity, good transparency, and excellent stability, thus enabling them to be applied as multifunctional ETLs ...

Solution-processed quantum-dot light-emitting diodes combining ultrahigh operational stability, shelf stability, and luminance

“…The buffer layer used here is assembled of SnO 2 NPs, an n-type ETL material with similar electronic levels but less surface activity. Notably, the function of SnO 2 proposed here significantly differs from previous reports 17,20 . Through the post-treatment in tetramethylammonium hydroxide (TMAH) solution, NPs can decently disperse in ethanol (see TEM images in Supplementary Fig.…”

Tailored ZnO Functional Nanomaterials for Solution‐Processed Quantum‐Dot Light‐Emitting Diodes

“…For example, Z. Chen et al used SnO 2 NPs as ETL as an alternative to ZnO. [ 118 ] According to their study, due to its high conductivity, high transparency, and high stability, SnO 2 could be used as a multifunctional ETL in a variety of architectures such as inverted, noninverted, transparent, and top‐emitting QLEDs. In addition, M. Chen et al studied the stabilization of SnO 2 ETL in the QLED with tetramethylammonium hydroxide (TMAH) that prevented the agglomeration of the SnO 2 NPs and increased the operational lifetime and EL efficiency of their QLEDs.…”

Photonics design theory enhancing light extraction efficiency in quantum dot light emitting diodes

“…Therefore, there are multiple boundaries the photons have to go through for the light to make its way into the air. The EL-QLED structure is very similar to that of an OLED, with the difference coming from the EML being made out of QDs and the ETL being made out of inorganic materials, mostly metal oxides such as ZnO, SnO 2 and TiO 2 [23][24][25]. The typical parameters of different QLED layers used in this work can be seen in table 1.…”