Hybrid MoO/HAT-CN is employed as a hole injection layer (HIL) in green inverted colloidal quantum dot light-emitting devices (QLEDs). The hybrid HILs can be easily prepared and have been found to effectively improve the electroluminescent properties. The best performance device had an HIL of 1.5 nm-thick MoO/2.5 nm-thick HAT-CN and showed a turn-on voltage of 1.9 V, a maximum current efficiency (CE) of 41.3 cd A, and maximum external quantum efficiency of 9.72%. Compared to the corresponding devices with the single MoO or HAT-CN interlayer, the CE of the hole-only devices was improved by 1.6 or 1.5 times, respectively. The measured electrical performance shows that hole-only devices with hybrid HILs have a smaller leakage current density at low driving voltage and much enhanced hole injection current than the devices with single interlayers. It indicates that much improved electroluminescent efficiency in green inverted QLEDs with hybrid MoO/HAT-CN orginates from the significant enhancement of hole injection efficiency and suppression of space charge accumulation in the quantum dot-emitting region due to the improved balance of the charge carriers. The hybrid HILs can be extended to other color inverted QLEDs, which are favorable to achieve bright, highly efficient, and color saturation devices for display applications.
Although tremendous efforts have been devoted to investigating planar single-conductor circuits, it remains challenging to provide tight confinement of electromagnetic field and compatibility with active semi-conductor components such as amplifier, harmonic generator and mixers. Single-conductor spoof surface plasmon polariton (SSPP) structure, which is one of the most promising planar single-conductor transmission media due to the outstanding field confinement, still suffers from the difficulty in integrating with the active semi-conductor components. In this paper, a new kind of odd-modemetachannel (OMM) that can support odd-mode SSPPs is proposed to perform as the fundamental transmission channel of the single-conductor systems. By introducing zigzag decoration, the OMM can strengthen the field confinement and broaden the bandwidth of odd-mode SSPPs simultaneously. More importantly, the active semi-conductor amplifier chip integration is achieved by utilizing the intrinsic potential difference on OMM, which breaks the major obstacle in implementing the single-conductor systems. As an instance, an amplifier is successfully integrated on the single-conductor OMM, which can realize both loss compensation and signal amplification. Meanwhile, the merits of OMM including crosstalk suppression, low radar cross section (RCS), and flexibility are comprehensively demonstrated. Hence, the proposed OMM and its capability to integrate with the active semi-conductor components may provide a new avenue to future single-conductor conformal systems and smart skins.
Frequency-dependent characteristic impedance extraction and compact excitation of spoof surface plasmon polariton (SSPP) waveguides are achieved in this work. The behavior of SSPP waveguides cannot be directly described using the transmission-line model due to the non-transverse electromagnetic modes. By investigating the near-field distribution of a typical SSPP waveguide, we find a special position where the field component in the longitudinal direction is nearly equal to zero, and the reflection is completely caused by impedance mismatch rather than mode mismatch. Then, the characteristic impedance curve of the SSPP waveguide is extracted. Based on the obtained characteristic impedance and the special excitation position, transition between the microstrip and SSPP waveguide in the desired frequency bands can be achieved without using an additional gradient-corrugation transition structure. Compared to the conventional gradient-corrugation strategy, the proposed transition has a much more compact size and better transition performance. Meanwhile, the accuracy of the proposed method is not impacted by the internal discontinuities and local couplings of typical or atypical SSPP waveguides, which is a complicated problem in other methods. The simulated and measured results demonstrate the validity of the presented method. Hence, the characteristic impedance extracted by the presented method is accurate and makes compact transformation and systematic integration of SSPP waveguides more practicable.
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