Ultrasmooth Quantum Dot Micropatterns by a Facile Controllable Liquid-Transfer Approach: Low-Cost Fabrication of High-Performance QLED

Fabrication of a high quality quantum dot (QD) film is essentially important for a high-performance QD light emitting diode display (QLED) device. It is normally a high-cost and multiple-step solution-transfer process where large amounts of QDs were needed but with only limited usefulness. Thus, developing a simple, efficient, and low-cost approach to fabricate high-quality micropatterned QD film is urgently needed. Here, we proposed that the Chinese brush enables the controllable transfer of a QD solution directly onto a homogeneous and ultrasmooth micropatterned film in one step. It is proposed that the dynamic balance of QDs was enabled during the entire solution transfer process under the cooperative effect of Marangoni flow aroused by the asymmetric solvent evaporation and the Laplace pressure different by conical fibers. By this approach, QD nanoparticles were homogeneously transferred onto the desired area on the substrate. The as-prepared QLED devices show rather high performances with the current efficiencies of 72.38, 26.03, and 4.26 cd/A and external quantum efficiencies of 17.40, 18.96, and 6.20% for the green, red, and blue QLED devices, respectively. We envision that the result offers a low-cost, facile, and practically applicable solution-processing approach that works even in air for fabricating high-performance QLED devices

Photoluminescence Temperature Dependence, Dynamics, and Quantum Efficiencies in Mn²⁺-Doped CsPbCl₃ Perovskite Nanocrystals with Varied Dopant Concentration

A series of Mn²⁺-doped CsPbCl₃ nanocrystals (NCs) was synthesized using reaction temperature and precursor concentration to tune Mn²⁺ concentrations up to 14%, and then studied using variable-temperature photoluminescence (PL) spectroscopy. All doped NCs show Mn²⁺ ⁴T_1g → ⁶A_1g d–d luminescence within the optical gap coexisting with excitonic luminescence at the NC absorption edge. Room-temperature Mn²⁺ PL quantum yields increase with increased doping, reaching ∼60% at ∼3 ± 1% Mn²⁺ before decreasing at higher concentrations. The low-doping regime is characterized by single-exponential PL decay with a concentration-independent lifetime of 1.8 ms, reflecting efficient luminescence of isolated Mn²⁺. At elevated doping, the decay is shorter, multiexponential, and concentration-dependent, reflecting the introduction of Mn²⁺–Mn²⁺ dimers and energy migration to traps. A large, anomalous decrease in Mn²⁺ PL intensity is observed with decreasing temperature, stemming from the strongly temperature-dependent exciton lifetime and slow exciton-to-Mn²⁺ energy transfer, which combine to give a strongly temperature-dependent branching ratio for Mn²⁺ sensitization

Blue Quantum Dot Light-Emitting Diodes with High Electroluminescent Efficiency

High-efficiency blue CdSe/ZnS quantum dots (QDs) have been synthesized for display application with emission peak over 460 nm with the purpose of reducing the harmful effect of short-wavelength light to human eyes. To reach a better charge balance, different size ZnO nanoparticles (NPs) were synthesized and electrical properties of ZnO NPs were analyzed. Quantum dot light-emitting diodes (QLEDs) based on as-prepared blue QDs and optimized ZnO NPs have been successfully fabricated. Using small-size ZnO NPs, we have obtained a maximum current efficiency (CE) of 14.1 cd A^–1 and a maximum external quantum efficiency (EQE) of 19.8% for QLEDs with an electroluminescence (EL) peak at 468 nm. To the best of our knowledge, this EQE is the highest value in comparison to the previous reports. The CIE 1931 color coordinates (0.136, 0.078) of this device are quite close to the standard (0.14, 0.08) of National Television System Committee (NTSC) 1953. The color saturation blue QLEDs show great promise for use in next-generation full-color displays