Probing impact of interface mixing on the charge carrier dynamics of a solution-processed organic light emitting diode via impedance spectroscopy.

Recently, several studies have revealed that the thermal annealing process induces intermixing at the interfaces of multilayered solution-processed organic light emitting diodes (OLEDs) and enhances their device performance. Depth profiling measurements, such as neutron reflectometry, have meticulously shown that significant intermixing occurs when the annealing temperature exceeds the glass transition temperature (Tg) of OLED materials. However, electrical characterization to unveil the physical origins of the correlation between interfacial characteristics and device performance is still lacking. Here, we introduce impedance spectroscopy (IS) analysis to examine the thermally induced modifications of charge carrier dynamics in a solution-processed bilayer OLED, consisting of an emission layer and an electron transporting layer (ETL). The characteristic relaxation frequency and capacitance extracted from the capacitance-frequency spectra of the OLEDs thermally annealed at varying temperatures were utilized to separately assess the conductance of the ETL and interfacial carrier accumulation, respectively. The results show that the improved charge transport of the ETL upon thermal annealing is mainly responsible for the performance enhancement since annealing the OLEDs at a temperature above the Tg of the ETL, at which significant intermixing occurs, promotes non-radiative trap-assisted recombination and thereby deteriorates the current efficiency. The proposed IS analysis exhibits that IS can separately probe the charge transport, interfacial charge accumulation and recombination process which are crucial for accurate analysis of charge carrier dynamics in solution-processed OLEDs and can thus be utilized to identify the key factors limiting the device performance.

Identification of Droplet-Flow-Induced Electric Energy on Electrolyte-Insulator-Semiconductor Structure.

Recently, various energy transducers driven by the relative motion of solids and liquids have been demonstrated. However, in relation to the energy transducer, a proper understanding of the dynamic behavior of ions remains unclear. Moreover, the energy density is low for practical usage mainly due to structural limitations, a lack of material development stemming from the currently poor understanding of the mechanisms, and the intermittently generated electricity given the characteristics of the water motion (pulsed signals). Here, we verify a hypothesis pertaining to the ion dynamics which govern the operation mechanism of the transducer. In addition, we demonstrate enhanced energy transducer to convert the mechanical energy of flowing water droplets into continuous electrical energy using an electrolyte-insulator-semiconductor structure as a device structure. The output power per droplet mass and the ratio of generated electric energy to the kinetic energy of water drops are 0.149v2 mW·g-1·m-2·s2 and 29.8%, respectively, where v is the speed of the water droplet.

Use of acidifier and solubilizer in tadalafil solid dispersion to enhance the in vitro dissolution and oral bioavailability in rats.

The purpose of this study is to improve the solubility, in vitro dissolution, and oral bioavailability in rats of tadalafil (TDF) by using SD technique with a weak acid and a copolymer. TDF-SD was prepared via solvent evaporation, coupled with the incorporation of an acidifier and solubilizer. Tartaric acid enhanced the solubility of TDF over 5-fold in DW, and Soluplus® enhanced the solubility of TDF over 8.7-fold and 19.2-fold compared to that of TDF (pure) in DW and pH 1.2 for 1h, respectively. The optimal formulation of TDF-SD3 was composed of TDF vs Tartaric acid vs Soluplus® vs Aerosil=1:1:3:3. The in vitro dissolution rate of TDF-SD3 in DW, pH 1.2 and pH 6.8 buffer (51.5%, 53.3%, and 33.2%, respectively) was significantly higher than that of the commercial product (Cialis®) powder (16.5%, 15.2%, and 14.8%, respectively). TDF was completely transformed to an amorphous form as shown in SEM, DSC and PXRD data. The stability of TDF-SD3 included drug contents and in vitro dissolution for 1 month were similar to those of Cialis®, and the amorphous form of TDF-SD3 was well maintained for 6 months. The TDF-SD3 formulation improved the relative bioavailability (BA) and peak plasma concentration (Cmax) compared to that of Cialis® powder after oral administration in rats as 117.3% and 135.7%, respectively. From the results, we found that the acidifier increased the wettability of TDF, and the solubilizer improved solubility through hydrogen bonding with TDF, thereby increasing the solubility, dissolution and oral bioavailability of TDF in TDF-SD3.

Fabric Active Transducer Stimulated by Water Motion for Self-Powered Wearable Device.

The recent trend of energy-harvesting devices is an adoption of fabric materials with flexible and stretchable according to the increase of wearable electronics. But it is a difficult process to form a core structure of dielectric layer or electrode on fabric materials. In particular, a fabric-based energy-harvesting device in contact with water has not been studied, though there are many challenging issues including insulation and water absorption in a harsh environment. So we propose an effective method to obtain an electrical energy from the water contact using our new fabric energy harvesting device. Our water motion active transducer (WMAT) is designed to obtain electrical energy from the variable capacitance through the movement and contact of water droplet. In this paper, we succeeded in generating an electrical energy with peak to peak power of 280 µW using a 30 µL of water droplet with the fabric WMAT device of 70 mm × 50 mm dimension. Furthermore, we specially carried out spray-coating and transfer processes instead of the conventional spin-coating process on fabric materials to overcome the limitation of its uneven morphology and porous and deformable assembly.

Preparation of Nano-Porous Activated Carbon Aerogel Using a Single-Step Activation Method for Use as High-Power EDLC Electrode in Organic Electrolyte.

Carbon aerogel was chemically activated with KOH using two different activation methods (conventional activation method and single-step activation method) to yield the nano-porous activated carbon aerogel. Both nano-porous activated carbon aerogels exhibited a better capacitive behavior than carbon aerogel in organic electrolyte. However, a drastic decrease in the specific capacitance with increasing current density was observed in the ACA_C (activated carbon aerogel prepared by a conventional activation method), which is a general tendency of carbon electrode for EDLC in organic electrolyte. Interestingly, the specific capacitance of ACA_S electrode (activated carbon aerogel prepared by a single-step activation method) decreased slowly with increasing current density and its CV curve maintained a rectangular shape well even at a high scan rate of 500 mV/s. The enhanced electrochemical performance of ACA_S at a high current density was attributed to its low ionic resistance caused by the well-developed pore structure with appropriate pore size for easy moving of organic electrolyte ion. Therefore, it can be concluded that single-step activation method could be one of the efficient methods for preparation of nano-porous activated carbon aerogel electrode for high-power EDLC in organic electrolyte.

Fluidic Active Transducer for Electricity Generation.

Flows in small size channels have been studied for a long time over multidisciplinary field such as chemistry, biology and medical through the various topics. Recently, the attempts of electricity generation from the small flows as a new area for energy harvesting in microfluidics have been reported. Here, we propose for the first time a new fluidic electricity generator (FEG) by modulating the electric double layer (EDL) with two phase flows of water and air without external power sources. We find that an electric current flowed by the forming/deforming of the EDL with a simple separated phase flow of water and air at the surface of the FEG. Electric signals between two electrodes of the FEG are checked from various water/air passing conditions. Moreover, we verify the possibility of a self-powered air slug sensor by applying the FEG in the detection of an air slug.

Influences of Surface and Ionic Properties on Electricity Generation of an Active Transducer Driven by Water Motion.

In this Letter, we discuss the surface, ionic properties, and scale-up potential of an active transducer that generated electricity from natural water motion. When a liquid contacts a solid surface, an electrical double layer (EDL) is always formed at the solid/liquid interface. By modulating the EDL, the active transducer could generate a peak voltage of ∼3 V and a peak power of ∼5 µW. Interestingly, there were specific salinities of solution droplets that showed maximum performance and different characteristics according to the ions' nature. Analyzing the results macroscopically, we tried to figure out the origins of the active transducing precipitated by ions dynamics. Also, we demonstrated the scale-up potential for practical usage by multiple electrode design.