Separating Crystal Growth from Nucleation Enables the In Situ Controllable Synthesis of Nanocrystals for Efficient Perovskite Light-Emitting Diodes.

Colloidal perovskite nanocrystals (PNCs) display bright luminescence for light-emitting diode (LED) applications; however, they require post-synthesis ligand exchange that may cause surface degradation and defect formation. In situ-formed PNCs achieve improved surface passivation using a straightforward synthetic approach, but their LED performance at the green wavelength is not yet comparable with that of colloidal PNC devices. Here, it is found that the limitations of in situ-formed PNCs stem from uncontrolled formation kinetics: conventional surface ligands confine perovskite nuclei but fail to delay crystal growth. A bifunctional carboxylic-acid-containing ammonium hydrobromide ligand that separates crystal growth from nucleation is introduced, leading to the formation of quantum-confined PNC solids exhibiting a narrow size distribution. Controlled crystallization is further coupled with defect passivation using deprotonated phosphinates, enabling improvements in photoluminescence quantum yield to near unity. Green LEDs are fabricated with a maximum current efficiency of 109 cd A-1 and an average external quantum efficiency of 22.5% across 25 devices, exceeding the performance of their colloidal PNC-based counterparts. A 45.6 h operating half-time is further documented for an unencapsulated device in N2 with an initial brightness of 100 cd m-2 .

Efficient Semitransparent Organic Solar Cells Enabled by Ag Grid Electrodes and Optical Coupling Layers.

Semitransparent organic solar cells (ST-OSCs) show great promise for building integrated photovoltaic systems. The balance between power conversion efficiency (PCE) and average visible transmittance (AVT) is a key point of ST-OSCs. We developed a novel semitransparent organic solar cell (ST-OSC) with high PCE and AVT for building integrated renewable energy applications. We used photolithography to fabricate Ag grid bottom electrodes with high figures of merit of 292.46. We also used an optimized active layer of PM6 and Y6, achieving a PCE of 10.65% and an AVT of 22.78% for our ST-OSCs. By adding optical coupling layers of CBP and LiF alternately, we further increased the AVT to 27.61% and the PCE to 10.87%. Importantly, the balance of PCE and AVT can be achieved by the integrated optimization of the active and optical coupling layers, which leads to a significant increase in light utilization efficiency (LUE). These results are of great importance for particle applications of ST-OSCs.

A Review of Recent Advances in Vital Signals Monitoring of Sports and Health via Flexible Wearable Sensors.

In recent years, vital signals monitoring in sports and health have been considered the research focus in the field of wearable sensing technologies. Typical signals include bioelectrical signals, biophysical signals, and biochemical signals, which have applications in the fields of athletic training, medical diagnosis and prevention, and rehabilitation. In particular, since the COVID-19 pandemic, there has been a dramatic increase in real-time interest in personal health. This has created an urgent need for flexible, wearable, portable, and real-time monitoring sensors to remotely monitor these signals in response to health management. To this end, the paper reviews recent advances in flexible wearable sensors for monitoring vital signals in sports and health. More precisely, emerging wearable devices and systems for health and exercise-related vital signals (e.g., ECG, EEG, EMG, inertia, body movements, heart rate, blood, sweat, and interstitial fluid) are reviewed first. Then, the paper creatively presents multidimensional and multimodal wearable sensors and systems. The paper also summarizes the current challenges and limitations and future directions of wearable sensors for vital typical signal detection. Through the review, the paper finds that these signals can be effectively monitored and used for health management (e.g., disease prediction) thanks to advanced manufacturing, flexible electronics, IoT, and artificial intelligence algorithms; however, wearable sensors and systems with multidimensional and multimodal are more compliant.

Quinonoid Zwitterion: An Amphiphilic Cathode Interlayer with Initial Thickness-Insensitive and Self-Organizing Properties for Inverted Polymer Solar Cells.

Orthogonal solvent processability is generally considered as one of the key requirements for an efficient interfacial material. Here, we showed that in inverted polymer solar cells (PSCs), solvent orthogonality is not required for an effective and reliable cathode interlayer. A quinonoid zwitterionic molecule with amphiphilic property [dissolved in both methanol and o-dichlorobenzene (o-DCB)] named ZW-Bu was first applied as the cathode interlayer in inverted PSCs. For three different photoactive systems, the devices with ZW-Bu cathode buffer layers (CBLs) exhibited better performance than those with commonly used ZnO CBLs. Most importantly, the device efficiency was fairly insensitive to the initial thickness of ZW-Bu. In addition, due to the high surface energy of the ZW-Bu film, it was successfully used as a self-organized CBL in poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) systems, yielding a desirable efficiency compared to the PSCs fabricated via the layer-by-layer deposition method.

Self-assembly of copper-free maltoheptaose-block-polystyrene nanostructured thin films in real and reciprocal space.

The promising carbohydrate-based block copolymer maltoheptaose-block-polystyrene (MH-b-PS) has been used for high-performance memory transistors and next generation nanolithography. In order to realize the potential of MH-b-PS especially in microelectronic applications, we firstly improved its synthetic method for obtaining large amount of copper-free MH-b-PS. The main improvement relies on the removal of the residual copper catalyst by using a chelating resin. Then, the microphase separation of copper-free MH-b-PS in both thin film and bulk states under different solvent vapor annealing conditions were investigated comprehensively and compared with our previous report by using both real-space and reciprocal-space techniques. A phase transition of MH-b-PS from hexagonal close-packed horizontal cylinders to face-centered cubic were observed when increasing the amount of tetrahydrofuran in the mixture annealing solvent of tetrahydrofuran and H2O. More details about self-assembled MH-b-PS nanostructures were analyzed by comparing grazing incidence small angle X-ray scattering patterns with corresponding atomic force microscopy phase images.

Efficient and chromaticity-stable flexible white organic light-emitting devices based on organic-inorganic hybrid color-conversion electrodes.

We have developed a novel organic-inorganic hybrid color conversion electrode composed of Ag NWs/poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) via a solution process, which is the first report on a color conversion electrode for applications in flexible optoelectronics. Using the Ag NWs/MEH-PPV composite film as the anode on polyethylene terephthalate substrate and combined with a blue organic light emitting devices (OLEDs) unit employing bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(iii)) (Flrpic) in 1,3-bis(carbazol-9-yl)benzene (mCP) as the emitting layer, a highly efficient and chromaticity-stable color-conversion flexible white OLEDs (WOLEDs) is achieved with a maximum current efficiency of 20.5 cd A-1. To the best of our knowledge, this is the highest efficiency reported for color-conversion based flexible WOLEDs. Our work provides an approach to achieving high-performance flexible WOLEDs devices and demonstrates great potential for lighting and display applications.

Carbohydrate-Based Block Copolymer Thin Films: Ultrafast Nano-Organization with 7 nm Resolution Using Microwave Energy.

Block copolymers (BCP) can self-assemble into nanoscale patterns with a wide variety of applications in the semiconductor industry. The self-assembly of BCPs is commonly accomplished by solvent vapor or thermal annealing, but generally these methods require long time (few hours) to obtain nanostructured thin films. In this contribution, a new and ultrafast method (using microwaves) is proposed-high temperature solvent vapor annealing (HTSVA), combining solvent vapor annealing with thermal annealing, to achieve fast and controllable self-assembly of amphiphilic BCP thin films. A promising carbohydrate-based BCP capable of forming cylindrical patterns with some of the smallest feature sizes is used for demonstrating how to obtain a highly ordered vertical cylindrical pattern with sub-10 nm feature sizes in few seconds by HTSVA. HTSVA provides not only a simple way to achieve BCP fast self-assembly in practical applications but also a tool to study the self-assembly behavior of BCPs under extreme conditions.

Electrosprayed molybdenum trioxide aqueous solution and its application in organic photovoltaic cells.

A molybdenum trioxide thin film with smooth surface and uniform thickness was successfully achieved by an electrospray deposition method using an aqueous solution with a drastically low concentration of 0.05 wt%. Previous papers demonstrated that an additive solvent technique is useful for depositing the thin film by the electrospray deposition, and the high vapor pressure and a low surface tension of an additive solvent were found to be important factors. As a result, the smooth molybdenum trioxide thin film was obtained when the acetonitrile was used as the additive solvent. Furthermore, the vapor pressure of acetone is much higher than that of aqueous solution, and this indicates that the acetone is easily evaporated after spraying from the glass capillary. By optimizing a concentration of acetone in the molybdenum aqueous solution, a minimum root mean square roughness of the MoO3 thin film became 3.7 nm. In addition, an organic photovoltaic cell was also demonstrated using the molybdenum trioxide as a hole transport layer. Highest photoconversion efficiency was 1.72%, a value comparable to that using conventional thermal evaporation process even though the aqueous solution was used for the solution process. The photovonversion efficiency was not an optimized value, and the higher value can be achieved by optimizing the coating condition of the active layer.

Diameter control of ultrathin zinc oxide nanofibers synthesized by electrospinning.

Electrospinning is a versatile technique, which can be used to generate nanofibers from a rich variety of materials. We investigate the variation of a zinc oxide (ZnO)-polyvinylpyrrolidone (PVP) composite structure in morphology by electrospinning from a series of mixture solutions of ZnO sol-gel and PVP. Calcination conditions for the crystallization of ZnO nanofibers and removal of the PVP component from the ZnO-PVP composite nanofibers were also studied. The progression of the ZnO-PVP composite structure from grains to nanofibers was observed, and ZnO-PVP nanofibers as thin as 29.9 ± 0.8 nm on average were successfully fabricated. The size of the resultant ZnO-PVP composite nanofibers was considerably affected by two parameters: the concentrations of zinc acetate and PVP in the precursor solution. The concentration of zinc acetate particularly influenced the diameter distribution of the ZnO-PVP nanofibers. The ZnO-PVP nanofibers could be subsequently converted into ZnO nanofibers of a pure wurtzite phase via calcination in air at 500°C for 2 h.

[Highly efficient and chromatic-stability yellow organic light emitting diodes using double ultra thin yellow emissive layers].

The authors investigated the efficiency and chromatic-stability characteristics of organic light emitting devices (OLEDs) with ultra-thin yellow emissive layers of 0.1 nm 5,6,11,12,-tetraphenylnaphthacene (rubrene) and hole block layer of BCP. The OLEDs with double thin rubrene layers and BCP layer were found to exhibit a high luminance and electroluminescence (EL) efficiency. The maximum EL efficiency and luminance reached 6. 35 cd x A(-1) at 6 V and 7 068 cd x m(-2) at 10 V respectively. Moreover, Commission International De L'Eclairage (CIE) coordination maintained unchanged (0.49, 0.49) in the wide range of applied voltages. The enhanced efficiency and good chromatic stability were attributed to a balanced injection and transport of electrons and holes and the expected confinement and balanced recombination of the emission region in the ultra-thin rubrene layers.