Engineering Architecture of Quantum Dot-Based Light-Emitting Diode for High Device Performance with Double-Sided Emission Fabricated by Nonvacuum Technique

Abstract

The CdSe/ZnS quantum dots (QDs) have drawn the attention of the researchers due to their superior photophysical properties and their applications in QD-based light-emitting diodes (QLEDs). The conventional CdSe/ZnS-based QLED uses a highly conductive electron-transport layer, low-mobility hole-transporting layers (HTLs), and a vacuum-deposited opaque metal electrode at the top. This structure renders unbalanced charge injection into the emissive layer and also allows the device to emit light only at the bottom side, which affects the device output luminance and stability. Moreover, in the vacuum-deposition technique, the fabrication process is more complex, expensive, and time-consuming. To address all these issues, we fabricated an all-solution processable double-sided emitting QLED by a nonvacuum technique using high mobility multi-HTLs with a cascade structure, an insulating layer, and a transparent silver nanowire (AgNW) electrode for balanced charge injection for obtaining higher luminance at the top-side AgNW electrode. The as-fabricated QLED exhibited a very low turn-on voltage and high luminance of 2.2 V and 41,010 cd m −2 , respectively. The QLED has also shown a high current efficiency of 15.2 cd A −1 , a luminous efficiency of 16.2 lm W −1 , and an external quantum efficiency of 8.2% at the top-side. These results indicate that the double-sided emitting QLED device opens up a pathway for designing next-generation lighting and display devices.

Significant enhancement in quantum-dot light emitting device stability via a ZnO:polyethylenimine mixture in the electron transport layer

“…Solution-coated ZnO ETLs however have structural and stochiometric defects that can act as exciton quenching sites and thereby reduce device EQE. 21,22 Therefore, to passivate the ZnO surface and/or prevent excitons from reaching it a thin layer of a wide band-gap material, such as Al 2 O 3 13 or a polymeric material [22][23][24][25][26] is often introduced in between the ZnO ETL and the EML. Polymers containing aliphatic amine groups, such as polyethylenimine (PEI) and its ethoxylated derivative (PEIE), are often used for this purpose 27,28 .…”

Ultrastable and High-Efficiency Deep Red QLEDs through Giant Continuously Graded Colloidal Quantum Dots with Shell Engineering

“…QLEDs emitting photons with wavelengths beyond 630 nm are highly desirable in order to reach a wide color gamut. However, the emission wavelength of red QLEDs with record EQE and operation lifetime had been limited to the range of 600–630 nm due to the challenge of synthesizing high-quality CdSe QDs emitting beyond 630 nm. ,,,,− One reason is the difficulty in increasing their size while maintaining the high PLQY. This difficulty is caused by the decrease in radiative decay rate with increasing size, while the defect-related nonradiative decay rate remains nearly unchanged. − Additionally, the number of internal and surface defects acting as nonemitting centers is proportional to the QDs’ volume and surface area. − Another challenge is the growth of a high-quality, defect-free passivating shell around larger seeds.…”

Customizable Stretchable Transparent Electrodes Based on AgNW/CNT Hybrids via Tailoring Sizes of Building Blocks

“…Stretchable transparent electrodes (STEs) are attracting increasing attention in next-generation stretchable electronic, optoelectronic, and wearable devices. − Typically, STEs are composed of a stretchable transparent elastic substrate with compliant conductive elements coated on its surface or embedded in . One of the main requirements for STEs is the maintenance of stable conductivity and transparency under various mechanical deformations, including stretching, bending, folding, twisting, crumpling, flipping, and so forth .…”