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.

Surface plasmon-enhanced electroluminescence (EL) has been demonstrated by incorporating gold (Au) nanoparticles (NPs) in quantum dot light-emitting diode (QLED). Time-resolved photoluminescence (TRPL) spectroscopy reveals that the EL enhancement is ascribed to the near-field enhancement through an effective coupling between excitons of the quantum dot emitters and localized surface plasmons around Au NPs. It is found that the size of Au NPs and the distance between the Au NPs and the emissive layer have significant effects on the performance of QLED. The enhancement can be maximized as the SP resonance wavelength of Au NPs matches well with the PL emission wavelength of the QD film and the distance between Au NPs and the emissive layer maintains 15 nm. The photoluminance (PL) and EL intensity can be enhanced by 4.4 and 1.7 folds with the incorporation of Au NPs. The maximum current efficiency of 4.56 cd/A can be achieved for the resulting QLEDs by incorprating Au NPs with an enhancement factor of 2.0. In addition, the enhancement ratio of 2.2 can be achieved for the lifetime of resulting QLED.

A highly efficient QLED achieving white emission at a low driving voltage is obtained by employing Zn0.95Mg0.05O as the electron transport layer.

In this paper, we have synthesized ZnCdSeS quantum dots (QDs)-gold nanoparticle (Au NPs) hybrids in aqueous solution via bi-functional linker mercaptoacetic acid (MPA). The absorption peaks of ZnCdSeS QDs and Au are both located at 520 nm. It is investigated that PL intensity of QD-Au hybrid can be affected by the amounts of Au and pH value of hybrid solution. The located surface plasmon resonance (LSPR) effect of QD-Au NPs has been demonstrated by increased fluorescence intensity. The phenomenon of fluorescence enhancement can be maximized under the optimized pH value of 8.5. LSPR-enhanced photoluminescence property of QD-Au hybrid will be beneficial for the potential applications in the area of biological imaging and detection.

We report an inverted and multilayer quantum dot light emitting diode (QLED) which boosts high efficiency by tuning the energy band alignment between charge transport and light emitting layers. The electron transport layer (ETL) was ZnO nanoparticles (NPs) with an optimized doping concentration of cesium azide (CsN) to effectively reduce electron flow and balance charge injection. This is by virtue of a 0.27 eV upshift of the ETL's conduction band edge, which inhibits the quenching of excitons and preserves the superior emissive properties of the quantum dots due to the insulating characteristics of CsN. The demonstrated QLED exhibits a peak current efficiency, power efficiency and external quantum efficiency of up to 13.5 cd A, 10.6 lm W and 13.4% for the red QLED, and correspondingly 43.1 cd A, 33.6 lm W and 9.1% for green, and 4.1 cd A, 2.0 lm W and 6.6% for the blue counterparts. Compared with QLEDs without optimization, the performance of these modified devices shows drastic improvement by 95.6%, 39.4% and 36.7%, respectively. This novel device architecture with heterogeneous energy levels reported here offers a new design strategy for next-generation high efficiency QLED displays and solid-state lighting technologies.