In Situ Interfacial-Assembly Perovskite Quantum Dot via Marangoni and Capillary Convection Manipulation for Robust Luminescence.

In solid substrates, colloidal solutions produce irregular deposits on the surface by Marangoni flow and capillary flow during evaporation. Reportedly, perovskite quantum dots (PQDs) as a colloidal solution have irregular surfaces based on a similar principle as the coffee ring effect in QD systems when droplets evaporate from the substrate. Given that this issue is due to the direction of Marangoni and capillary flows, the substrate is tilted to change the direction of the flows. The appropriate angle is determined by controlling the angle of the substrate so that the two flows circulate similarly; this method is called "assembly-coating". Herein, we compare the PL intensity before and after the thermal evaporation of the thin films prepared by conventional and assembly-coating. Moreover, by characterizing the diode device (hole-only space charge limited current) for each coating process, the charge carrier characteristics are investigated in detail. Therefore, we suggest a facile strategy to obtain a uniform surface and thermal evaporative stability using colloidal solutions. This strategy is effective in designing surface uniformity and light-emitting layers for colloidal solution deposition and assembly.

Tuning the energy level of TAPC: crystal structure and photophysical and electrochemical properties of 4,4'-(cyclohexane-1,1-diyl)bis[N,N-bis(4-methoxyphenyl)aniline].

The energy level of a hole-transporting material (HTM) in organic electronics, such as organic light-emitting diodes (OLEDs) and perovskite solar cells (PSCs), is important for device efficiency. In this regard, we prepared 4,4'-(cyclohexane-1,1-diyl)bis[N,N-bis(4-methoxyphenyl)aniline] (TAPC-OMe), C46H46N2O4, to tune the energy level of 4,4'-(cyclohexane-1,1-diyl)bis[N,N-bis(4-methylphenyl)aniline] (TAPC), which is a well-known HTM commonly used in OLED applications. A systematic characterization of TAPC-OMe, including 1H and 13C NMR, elemental analysis, UV-Vis absorption, fluorescence emission, density functional theory (DFT) calculations and single-crystal X-ray diffraction, was performed. TAPC-OMe crystallized in the triclinic space group P-1, with two molecules in the asymmetric unit. The dihedral angles between the central amine triangular planes and those of the phenyl groups varied from 26.56 (9) to 60.34 (8)° due to the steric hindrance of the central cyclohexyl ring. This arrangement might be induced by weak hydrogen bonds and C-H...π(Ph) interactions in the extended structure. The emission maxima of TAPC-OMe showed a significant bathochomic shift compared to that of TAPC. A strong dependency of the oxidation potentials on the nature of the electron-donating ability of substituents was confirmed by comparing oxidation potentials with known Hammett parameters (σ).

Facile NiOx Sol-Gel Synthesis Depending on Chain Length of Various Solvents without Catalyst for Efficient Hole Charge Transfer in Perovskite Solar Cells.

Nickel oxide (NiOx)⁻based perovskite solar cells (PSCs) have recently gained considerable interest, and exhibit above 20% photovoltaic efficiency. However, the reported syntheses of NiOx sol-gel used toxic chemicals for the catalysts during synthesis, which resulted in a high-temperature annealing requirement to remove the organic catalysts (ligands). Herein, we report a facile "NiOx sol-gel depending on the chain length of various solvents" method that eschews toxic catalysts, to confirm the effect of different types of organic solvents on NiOx synthesis. The optimized conditions of the method resulted in better morphology and an increase in the crystallinity of the perovskite layer. Furthermore, the use of the optimized organic solvent improved the absorbance of the photoactive layer in the PSC device. To compare the electrical properties, a PSC was prepared with a p-i-n structure, and the optimized divalent alcohol-based NiOx as the hole transport layer. This improved the charge transport compared with that for the typical 1,2-ethanediol (ethylene glycol) used in earlier studies. Finally, the optimized solvent-based NiOx enhanced device performance by increasing the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF), compared with those of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)⁻based devices.

Effects of Qi-training on heart rate variability.

This study investigates changes in autonomic nervous function through Qi-training. The power spectrum of heart rate variability (HRV) was examined in 20 sedentary healthy subjects and 20 Qi-trainees. It was found that Qi-training in healthy young subjects during controlled respiration increases the high frequency (HF) power and decreases the low frequency/high frequency (LF/HF) power ratio of HRV. These results support the hypothesis that Qi-training increases cardiac parasympathetic tone. In addition, Qi-trainees were found to have higher parasympathetic heart modulation compared with their age-matched, sedentary counterparts. This augmented HRV in Qi-trainees provides further support for long-term Qi-training as a possible non-pharmacological cardio-protective maneuver. In conclusion, Qi-training may stabilize the autonomic nervous system by modulating the parasympathetic nervous system.