Size Tunable ZnO Nanoparticles To Enhance Electron Injection in Solution Processed QLEDs

Abstract

Quantum dot (QD) light-emitting diodes (LEDs) are a promising candidate for high-efficiency, color-saturated displays. This work reports on the size effect of sol−gel synthesized ZnO nanoparticles (NPs) in which sizes of 2.9, 4.0, and 5.5 nm, were used as an electron transfer layer in QLEDs. The size of the NPs was estimated by transmission electron microscopy (TEM) and its effect on QLED performance was investigated by photoluminescence decay lifetime and electron mobility of ZnO NPs. It was found that as the size of the NP decreased from 5.5 to 2.9 nm, the conductivity increased, whereby the electron mobility was enhanced from 7.2 × 10 −4 cm 2 /V•s to 4.8 × 10 −3 cm 2 /V•s and electron decay lifetime increased from 5.11 to 6.68 ns. A comparison of NP size effects shows that the best performance is achieved with the 2.9 nm sized ZnO, which yields a turn on voltage of 3.3 V, a maximum current efficiency of 12.5 cd/A, power efficiency of 4.69 lm/W and external quantum efficiencies (EQE) of 4.2%. This is most likely due to the higher electron mobility in the smaller ZnO NPs, which facilitates electron transfer from the NPs to QDs, along with the slow exciton dissociation in the QD layer as a result of more favorable energy level alignment at the interface of smaller ZnO NPs and the adjacent emissive layer.

P‐9.7: Stable Quantum Dot Light‐Emitting Diodes via Adopting Solution‐Processed All‐Inorganic Heterostructure

“…The QDs was synthesized according to our previous publication. 7 The nickel oxide precursor was synthesized according to the literature 8 with some modification. Nickel acetate tetrahydrate and ethanolamine were dissolved in methanol to form the nickel ink precursor.…”

54‐5: New Technologies for Colouring in Displays

“…Inverted structure also provides more chance to utilizing various HTL deposited by thermal evaporation, which can reduce hole injection barrier more effectively compared to conventional structure. In addition, the electron injection barriers in the inverted structure can be easily compensated by applying various inorganic ETL such as ZnO [17], ZrO 2 [18] , SnO 2 [19] and TiO 2 [20] .…”

48-2:Invited Paper: N- and P-type Metal-Oxides for Quantum Dot Light Emitting Diodes

“…ZnO and TiO x are well known n-type metal oxide and can be adopted as electron injection and transporting layers (EILs and ETLs). [7][8] Recently, ZnO nanoparticles (NPs) are widely used as n-type ETL having a high electron mobility of 10 -3 cm 2 /Vs. [9] On the other hand, a sol-gel processed metal oxide is also used as ETL.…”