Efficiency Improvement of Quantum Dot Light-Emitting Diodes via Thermal Damage Suppression with HATCN.

With many advantages including superior color saturation and efficiency, quantum dot light-emitting diodes (QLEDs) are considered a promising candidate for the next-generation displays. Emission uniformity over the entire device area is a critical factor to the overall performance and reliability of QLEDs. In this work, we performed a thorough study on the origin of dark spots commonly observed in operating QLEDs and developed a strategy to eliminate these defects. Using advanced cross section fabrication and imaging techniques, we discovered the occurrence of voids in the organic hole transport layer and directly correlated them to the observed emission nonuniformity. Further investigations revealed that these voids are thermal damages induced during the subsequent thermal deposition of other functional layers and can act as leakage paths in the device. By inserting a thermo-tolerant 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HATCN) interlayer with an optimized thickness, the thermally induced dark spots can be completely suppressed, leading to a current efficiency increase by 18%. We further demonstrated that such a thermal passivation strategy can work universally for various types of organic layers with low thermal stability. Our findings here provide important guidance in enhancing the performances and reliability of QLEDs and also other sandwich-structured devices via the passivation of heat-sensitive layers.

Test and Numerical Model of Curved Steel-Concrete Composite Box Beams under Positive Moments.

Compared with straight steel-concrete composite beams, curved composite beams exhibit more complicated mechanical behaviors under combined bending and torsion coupling. There are much fewer experimental studies on curved composite beams than those of straight composite beams. This study aimed to investigate the combined bending and torsion behavior of curved composite beams. This paper presents static loading tests of the full elastoplastic process of three curved composite box beams with various central angles and shear connection degrees. The test results showed that the specimens exhibited notable bending and torsion coupling force characteristics under static loading. The curvature and interface shear connection degree significantly affected the force behavior of the curved composite box beams. The specimens with weak shear connection degrees showed obvious interfacial longitudinal slip and transverse slip. Constraint distortion and torsion behavior caused the strain of the inner side of the structure to be higher than the strain of the outer side. The strain of the steel beam webs was approximately linear. In addition, fine finite element models of three curved composite box beams were established. The correctness and applicability of the finite element models were verified by comparing the test results and numerical calculation results for the load-displacement curve, load-rotational angle curve, load-interface slip curve, and cross-sectional strain distribution. Finite element modeling can be used as a reliable numerical tool for the large-scale parameter analysis of the elastic-plastic mechanical behavior of curved composite box beams.

Finite Beam Element for Curved Steel-Concrete Composite Box Beams Considering Time-Dependent Effect.

Curved steel-concrete composite box beams are widely used in urban overpasses and ramp bridges. In contrast to straight composite beams, curved composite box beams exhibit complex mechanical behavior with bending-torsion coupling, including constrained torsion, distortion, and interfacial biaxial slip. The shear-lag effect and curvature variation in the radial direction should be taken into account when the beam is sufficiently wide. Additionally, long-term deflection has been observed in curved composite box beams due to the shrinkage and creep effects of the concrete slab. In this paper, an equilibrium equation for a theoretical model of curved composite box beams is proposed according to the virtual work principle. The finite element method is adopted to obtain the element stiffness matrix and nodal load matrix. The age-adjusted effective modulus method is introduced to address the concrete creep effects. This 26-DOF finite beam element model is able to simulate the constrained torsion, distortion, interfacial biaxial slip, shear lag, and time-dependent effects of curved composite box beams and account for curvature variation in the radial direction. An elaborate finite element model of a typical curved composite box beam is established. The correctness and applicability of the proposed finite beam element model is verified by comparing the results from the proposed beam element model to those from the elaborate finite element model. The proposed beam element model is used to analyze the long-term behavior of curved composite box beams. The analysis shows that significant changes in the displacement, stress and shear-lag coefficient occur in the curved composite beams within the first year of loading, after which the variation tendency becomes gradual. Moreover, increases in the central angle and shear connection stiffness both reduce the change rates of displacement and stress with respect to time.

Experimental Research of the Time-Dependent Effects of Steel-Concrete Composite Girder Bridges during Construction and Operation Periods.

The present work aimed to study the effects of temperature changes and concrete creep on I-shaped steel-concrete composite continuous girder bridges during construction and operation processes. This study combined structural health monitoring data, an ANSYS finite element simulation, and the age-adjusted effective modulus method to obtain the variation laws of temperature and internal force in composite girders. Moreover, a temperature gradient model was proposed that is suitable for bridges in Hebei, China. In addition, a concrete creep experiment under unidirectional axial compression was performed using concrete specimens prepared from the concrete batch used to create the composite girder. The long-term evolution laws of the deflection and internal force of the composite girder were obtained by predicting the concrete creep effect. The measured data showed that the temperature variation trends of the steel beam and concrete slab were characterized by a sinusoidal curve without a temperature lag. The heating rate of the concrete slab was higher than the cooling rate. The prediction results showed that the internal force changes in the composite girder were characterized by three stages. The stress changes in the composite girder during the first 10 days were significant and the stress charge rate of the concrete slab, the steel girder and the shear stud can reach 5%-28%. The stress change rate decreased continuously during 10-90 days. The stress changed slowly and smoothly after 90 days. This research can provide feedback and reference for structural health monitoring and service safety control of similar I-shaped steel-concrete composite bridges.

Ammonia reduced graphene oxides as a hole injection layer for CdSe/CdS/ZnS quantum dot light-emitting diodes.

In this study, we report quantum-dot light-emitting devices (QD-LEDs) using ammonia reduced graphene oxide (rGO) as a hole injection layer (HIL). Compared with pristine GO, QD-LEDs employing rGO as a HIL show higher maximum luminance (936 cd m(-2) versus 699 cd m(-2)) and lower turn-on voltage (V th, 5.0 V versus 7.5 V). The improved performance can be attributed to the synergistic effect of the improved conductivity (1.27 µS cm(-1) versus 0.139 µS cm(-1)) and decreased work function (5.27 eV versus 5.40 eV) of the GO after the reduction process. The above results indicate that ammonia functionalized graphene may be a promising hole injection material for QD-LEDs.

Supra-(carbon nanodots) with a strong visible to near-infrared absorption band and efficient photothermal conversion.

A novel concept and approach to engineering carbon nanodots (CNDs) were explored to overcome the limited light absorption of CNDs in low-energy spectral regions. In this work, we constructed a novel type of supra-CND by the assembly of surface charge-confined CNDs through possible electrostatic interactions and hydrogen bonding. The resulting supra-CNDs are the first to feature a strong, well-defined absorption band in the visible to near-infrared (NIR) range and to exhibit effective NIR photothermal conversion performance with high photothermal conversion efficiency in excess of 50%.

[Low driving voltage in organic light-emitting diodes with NPB/MoO3/NPB as a hole transport layer].

Driving voltage of organic light-emitting diodes (OLEDs) was lowered by applying (NPB/MoO3)(x)/NPB as a hole transport layer (HTL). (NPB/MoO3)(x) was multi-layer periodic (MLP) structure with x changed from 0 to 3. Compared with the conventional device with 0-periodic structure, the driving voltage of the device with 1-periodic structure was the lowest. This was due to charge transfer (CT) complex formation between NPB and MoO3. The driving voltage of tris (8-hydroxyquinoline) aluminum (Alq3)-based organic light-emitting devices (OLEDs) could be lowered by 0. 8 V at 1 000 cd x m(-2) by using multiple structure of NPB/MoO3/NPB.