Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Room-Temperature-Processed Ga-Doped ZnO Nanoparticles as the Electron Transport Layer

Abstract

Colloidal ZnO nanoparticle (NP) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QD-LEDs) with good stability and high efficiency. However, because of the inherently high work function of such films, spontaneous charge transfer occurs at the QD/ZnO interface in such a QD-LED, thus leading to reduced performance. Here, to improve the QD-LED performance, we prepared Ga-doped ZnO NPs with low work functions and tailored band structures via a room-temperature (RT) solution process without the use of bulky organic ligands. We found that the charge transfer at the interface between the CdSe/ZnS QDs and the doped ZnO NPs was significantly weakened because of the incorporated Ga dopants. Remarkably, the as-assembled QD-LEDs, with Ga-doped ZnO NPs as the ETLs, exhibited superior luminances of up to 44 000 cd/m and efficiencies of up to 15 cd/A, placing them among the most efficient red-light QD-LEDs ever reported. This discovery provides a new strategy for fabricating high-performance QD-LEDs by using RT-processed Ga-doped ZnO NPs as the ETLs, which could be generalized to improve the efficiency of other optoelectronic devices.

Beyond OLED: Efficient Quantum Dot Light‐Emitting Diodes for Display and Lighting Application

“…Liu and co-workers introduced a double-layer HTL structure by combining poly(9-vinlycarbazole) (PVK) and poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))-diphenylamine)] (TFB) together, and thus a stepwise energy level for hole injection is formed by this means. [34] The improved hole injection was verified by the enhanced current density of the hole-only device with double-layer HTL, which stemmed from the reduced hole injection barrier and the [36], [40] and [43]) . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 high mobility of TFB (~1.0 3 10 À2 cm 2 /(V s)).…”

“…[41] In this regard, group III elements including Al, Ga and In, are more suitable to serve as the ntype dopants to adjust the work functions (WFs) of ZnO hosts compared with their group II counterparts such as Mg. [42] Thus, Al-doped and Ga-doped ZnO ETLs were also developed in recent years and the QLEDs based on these ternary metal oxides exhibited higher efficiency than ZnObased QLEDs. [43] The higher performance were enabled via lowering the WFs of as-grown ZnO by the dopants, which could weaken the interfacial charge transfer process and thus make the QDs remain neutrality.…”

Zinc oxide light-emitting diodes: a review

“…170 Various groups have recently fabricated LEDs that make use of ZnO quantum dots as an emission layer, an electron transport layer or both. Cao et al 171 have reported on the fabrication of highly efficient CdSe/ZnS quantum dot LEDs incorporating a gadolinium-doped ZnO quantum dot electron transport layer. Magnesium-doped ZnO quantum dots have also been used as the electron transport layer in a layered LED made completely out of functional quantum dot layers.…”

2.1: Highly Efficient Quantum‐dot Light Emitting Diodes with Metal‐oxide Transport Layer

“…Various dopings in ZnO NPs have been carried out to control band gap and resistivity for LED and solar cell. Alkali metals such as magnesium (Mg), gallium (Ga) and calcium (Ca) could be used as dopants to widen ZnO bandgap [14][15][16][17] . Thus, the electron injection from ETL to QDs can be controlled.…”