Due
to the inherent toxicity of cadmium selenide (CdSe)-based quantum
dots (QDs), Cd-free alternatives are being widely investigated. Indium
phosphide (InP) QDs have shown great potential as a replacement for
CdSe QDs in display applications. However, the performance of InP-based
quantum dot light-emitting diodes (QLEDs) is still far behind that
of the CdSe-based devices. In this study, we wanted to show the effects
of different approaches to improving the performance of InP-based
QLED devices. We investigated the effect of magnesium (Mg) doping
in ZnO nanoparticles, which is used as an n-type electron transport
layer, in balancing the charge transfer in InP-based QLED devices.
We found that an increasing Mg doping level can broaden ZnO band gap,
shift its energy levels, but most importantly, increase its resistivity;
as a result, the electron current density is significantly reduced
and the device efficiency is improved. We also investigated the effect
of high-photoluminescence quantum yield emitters and different QLED
architectures on the device performance. Through optimizing QD structures
and devices, red InP QLEDs with the current efficiencies as high as
11.6 cd/A were fabricated.
Quantum Dot Light Emitting diodes (QLED) show promise in the development of next‐generation displays due to their unique properties, such as cost‐effective, large‐area, wide‐color‐gamut and long life‐time. However, the most studied bottom‐emitting device structure can't meet the requirements of high resolution and high information‐content active matrix (AM) display in the future. Here, top‐emitting blue QLEDs with capping layer (CPL) on top metal cathode were fabricated and characterized. The introduction of CPL can influence both the optical and electrical properties of the device, resulting in a remarkable current efficiency improvement. By optimizing the CPL thickness, we have achieved an almost 12‐fold efficiency improvement of top‐emitting blue QLEDs.
The unique features of solution‐processed quantum dots (QDs) including emission tunability in the visible range, high‐quality saturated color and outstanding intrinsic stability in environment are highly desired in various application fields. Especially, quantum dot light‐emitting diodes (QLEDs) are promising light sources for applications in displays. However, the imbalance injection of holes and electrons have always been a challenging issue of QLED. In this study, the modified ligands which is synthesized by ourselves are incorporated into QDs through solution ligand exchange. The highest occupied molecular orbital (HOMO) of QDs is upshifted from ‐5.65eV to ‐5.35eV, leading to the decrement of the energy gap between the HOMO of QDs and the HOMO of hole transport layer. Through the successful ligands exchange, improvement by factors of 7.5 is achieved in maximum external quantum efficiency (EQE) compared with QLED with OA ligands.
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