Highly Efficient Deep Blue Cd‐Free Quantum Dot Light‐Emitting Diodes by a p‐Type Doped Emissive Layer

Abstract

Environmentally friendly ZnSe/ZnS core/shell quantum dots (QDs) as an alternative blue emission material to Cd‐based QDs have shown great potential for use in next‐generation displays. However, it remains still challenging to realize a high‐efficiency quantum dot light‐emitting diode (QLED) based on ZnSe/ZnS QDs due to their insufficient electrical characteristics, such as excessively high electron mobility (compared to the hole mobility) and the deep‐lying valence band. In this work, the effects of QDs doped with hole transport materials (hybrid QDs) on the electrical characteristics of a QLED are investigated. These hybrid QDs show a p‐type doping effect, which leads to a change in the density of the carriers. Specifically, the hybrid QDs can balance electrons and holes by suppressing the overflow of electrons and improving injection of holes, respectively. These electrical characteristics help to improve device performance. In detail, an external quantum efficiency (EQE) of 6.88% is achieved with the hybrid QDs. This is increased by 180% compared to a device with pure ZnSe/ZnS QDs (EQE of 2.46%). This record is the highest among deep‐blue Cd‐free QLED devices. These findings provide the importance of p‐type doping effect in QD layers and guidance for the study of the electrical properties of QDs.

Heavy-metal-free blue-emitting ZnSe(Te) quantum dots: synthesis and light-emitting applications

“…However, ZnSe-based QLEDs are influenced by the imbalance carrier injection caused by the large hole injection barrier, with a maximum EQE of 13.6%, 24 and the emission peak is mainly concentrated in the high-energy blue-violet regions (≤450 nm). 25–27 ZnSeTe QDs formed by alloying ZnTe with a narrow bandgap (2.25 eV) and ZnSe can extend the emission spectrum to the blue region by regulating the Se/Te ratio. Therefore, ZnSe(Te) QDs, including binary ZnSe and ternary ZnSeTe QDs, are expected to realize full spectral coverage in the blue light waveband.…”

Quantum Mechanical Analysis Based on Perturbation Theory of CdSe/ZnS Quantum-Dot Light-Emission Properties

“…Given these advantages, there have been continuous efforts to develop high-performance QDs and light-emitting diodes using QD EMLs, with the aim of replacing organic light-emitting diodes (OLEDs) with quantum-dot light-emitting diodes (QLEDs) [ 6 , 7 , 8 , 9 , 10 ]. However, research on QDs and QLEDs is in the early stage; thus, their lifetime [ 11 , 12 ] and efficiency [ 13 , 14 ] should be improved further before commercial application of QLEDs. A detailed analysis of the energy levels of QDs is required, as these determine the optoelectronic characteristics.…”

8‐5: Inkjet‐Printed Quantum Dot/Organic Semiconductor Nanohybrids for Efficient InP‐based Quantum Dot Light‐Emitting Diodes

“…Additionally, choosing the right charge transport materials for the efficient charge carrier balance in the Cd-free QD-LEDs is also critical to realize stable and efficient devices [11,12]. Recently, to overcome these issues, mixing QDs with the organic charge transporting materials to form QD/organic semiconductor nanohybrids or composite has gained the interest in particular [13][14][15][16][17][18]. In comparison to the QD-only film, QDs embedded in organic matrix has several advantages as an emitting layer.…”