All solution‐processed white quantum‐dot light‐emitting diodes with three‐unit tandem structure

Abstract

-Quantum-dot light-emitting diodes (QLEDs) are promising candidates for next generation displays. White QLEDs which can emit red, green and blue colors are particularly important; this is because the combination of white QLEDs and color filters offers a practical solution for highresolution full-color displays. In this work, we demonstrate all-solution processed three-unit (red/ green/blue) white tandem QLEDs for the first time. The white tandem devices are achieved by serially connecting the red bottom sub-QLED, the green middle sub-QLED and the blue top sub-QLED using the inter-connecting layer (ICL) based on ZnMgO/PEDOT:PSS heterojunction. With the proposed ICL, the two-unit tandem QLEDs exhibit a high current efficiency of 22.22 cd/A, while the three-unit white QLEDs exhibit evenly separated red, green and blue emission with a CIE coordinate of (0.30, 0.44), a peak current efficiency of 4.75 cd/A and a high luminance of 4206 cd/m 2 . Displays based on the developed white QLEDs exhibit a wide color gamut of 114% NTSC. This work confirms the effectiveness of the proposed ZnMgO/PEDOT:PSS ICL and the feasibility of making all-solution processed tandem white QLEDs by using the proposed ICL.

High-Resolution Colloidal Quantum Dot Film Photolithography via Atomic Layer Deposition of ZnO

“…Lee et al successfully fabricated tandem white QLEDs by inserting a thin layer of ZnO buffer . Similarly, a charge generation layer (CGL) was also employed to enhance the device performance of the WLED, and a device EQE higher than 25% was achieved. , The solvent orthogonality concept can also be applied to fabricate WLEDs using the structure shown in Figure a. Simple DEZ treatment on pre-existing QDs provides solvent orthogonality during the spin-casting of QDs with another color, although the same solvent was used.…”

Colloidal quantum dot hybrids: an emerging class of materials for ambient lighting

“…Some previous studies also presented similar voltage-dependent spectral variance, and the smaller bandgap QDs would generally contribute less EL when devices are biased at higher working voltage. 28,98,99 Specifically, as shown in energy band diagram within multilayered WQLED, the electron injection barrier from ETL to red QD is much lower than the hole injection barrier from HTL to blue QD. Then the exciton formation zone can be at the blue QD EML.…”

“…In 2017, Zhang et al first achieved a white tandem WQLED by serially connecting R/G/B CdZnSeS/ZnS QDs EMLs using a proposed ZnMgO/ (poly (3,4-ethylenedioxythio-phene):poly(styrene sulfonate))(PEDOT: PSS) heterojunction ICL. 98 Unfortunately, the resultant WQLEDs exhibited a low CE of 4.75 cd A -1 and a CIE coordinate of (0.30, 0.44), which can be attributed to morphology deterioration between pre-deposited ZnMgO and post-deposited PEDOT: PSS associated with their hydrophilicity mismatch. Replacing hydrophilic PEDOT: PSS with other hydrophobic ICL materials or adjusting hydrophilicity by interface engineering could be one solution to this problem.…”

Technology progress on quantum dot light-emitting diodes for next-generation displays

“…4 (c), which is used to improve the efficiency of QD-LED by vertically stacking several QD-LED units with a transparent interconnecting layer (ICL). 30,[43][44][45][46][47] Each of the auxiliary layers such as HIL, HTL and ETL is characterised by the layer thickness, the carrier mobilities, the energy band alignments with the neighbouring layers as well as the interfacial morphologies. It is crucial to develop the layer structure of the device architecture and to optimize the materials and the processes of all layers to achieve high electrooptical performance.…”