Solution-Processed Self-Stratifying Layer with Controllable Dielectric Polarization for High-Luminance Organic Light-Emitting Diodes

Spin-coated poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layers are well known to show a PSS-rich surface layer. Such a self-stratifying PEDOT:PSS layer has been applied for improving maximum external quantum efficiency (EQE) of organic light-emitting diodes (OLEDs). However, such devices typically show much reduced high-luminance performance affecting practical applications of such a self-stratifying interlayer (SSL). In this work, we demonstrate that a simple ionization process can eliminate the adverse effects at high luminance while maintaining high maximum EQE. It is shown that ions of the salt can interact with hydroxyl groups of the PSS polymer and thus disorder the orientation polarization. This implies that the ionization process enables active tuning of the dielectric properties of the PEDOT:PSS layer. It reduces carrier accumulation caused by orientation polarization of the SSL and thus suppresses both exciton annihilation and electric stress across the emitting layer in OLEDs. With this strategy, the device using the self-stratifying PEDOT:PSS layer shows a wide window of operating current density which is nearly 6 times compared with that of the corresponding device without the treatment. This enables 5 times of luminance and operation lifetime enhancements

Ultrasonic Spray Processed, Highly Efficient All-Inorganic Quantum-Dot Light-Emitting Diodes

All-inorganic and low-cost quantum-dot light-emitting diodes (QLEDs) are always desired considering the easy processing and outstanding physical and chemical stability of inorganic oxides. Herein, efficient all-inorganic QLEDs are demonstrated by using NiO and ZnO as the charge transport layers fabricated via ultrasonic spray processes. Excellent device performance is achieved thanks to the introduction of an Al₂O₃ interlayer between quantum dots (QDs) and an amorphous NiO layer. Transient photoluminescence and electricity measurements indicate that the Al₂O₃ layer can suppress the exciton quenching induced by the NiO layer and reduce the electron leakage from QDs to NiO. In consequence, relative to that of a device without an Al₂O₃ layer, the efficiency of an Al₂O₃-containing device is enhanced by a factor of 539%, increasing from 3.8 cd/A to 20.5 cd/A, and it exhibits color-saturated green emission (peak at 530 nm) and high luminescence (>20 000 cd/m²). These are the best performances for all-inorganic QLEDs reported to date. Meanwhile, it is demonstrated that ultrasonic spray is a feasible and cost-effective technology to construct efficient all-inorganic QLEDs. We anticipate that these results will spur the progress toward realization of high performance and mass production of all-inorganic QLEDs as a platform for QD-based full-color displays

Coffee-Ring-Free Ultrasonic Spray Coating Single-Emission Layers for White Organic Light-Emitting Devices and Their Energy-Transfer Mechanism

Ultrasonic spray coating (USC) process is an alternative for low-cost solution-processed white organic light-emitting devices (OLEDs). However, complicated flow behaviors in the thick liquid layer, especially in multicomponent solution, result in the existence of ripples (coffee rings) in organic films. The ripples keep the USC process from being generally recognized as an efficient solution process for white OLEDs. Therefore, a slope method is proposed to avoid the emergence of ripples during the USC process. In the method, just like centrifugal force in a spin-coating process, gravity is used to remove redundant solution so that the remaining liquid layer can stay uniform under the control of substrate surface forces. Based on this, uniform organic films consisting of multiple components are obtained, and they are used as emitting layers to realize efficient white OLEDs. The white OLEDs based on the USC binary doping and ternary doping single-emission layer exhibit excellent electroluminescent performances. Furthermore, to clarify the energy transfer in the multicomponent emitting layers, their transient emission spectra are built based on the transient photoluminescent decay curves. And the detailed energy-transfer mechanism of the device is discussed

Cyanide-Bridged Rope-like Chains Based on Trigonal-Bipyramidal [Fe₂Cu₃] Subunits

Extending a selected cyanometalate block into a higher dimensional framework continues to present intriguing challenges in the fields of chemistry and material science. Here, we prepared two rope-like chain compounds of {[(Tp*Me)­Fe­(CN)3]2Cu2X2(L)}·sol (1, X = Cl, L = (MeCN)0.5(H2O/MeOH)0.5, sol = 2MeCN·1.5H2O; 2, X = Br, L = MeOH, sol = 2MeCN·0.75H2O; Tp*Me = tris­(3, 4, 5-trimethylpyrazole)­borate) in which the cyanide-bridged trigonal-bipyramidal [Fe2Cu3] subunits were linked with the adjacent ones via two vertex Cu­(II) centers, providing a new cyanometallate chain archetype. Direct current magnetic study revealed the presence of ferromagnetic couplings between Fe­(III) and Cu­(II) ions and uniaxial anisotropy due to a favorable alignment of the anisotropic tricyanoiron­(III) units. Moreover, compound 1 exhibits single-chain magnet behavior with an appreciable energy barrier of 72 K, while 2 behaves as a metamagnet, likely caused by the subtle changes in the interchain interactions