ABSTRACT
A comparative study of doping aliovalent ions, Zr- or Al-, into Ni-rich Li(Ni,Co,Mn)O2 cathode materials is conducted in terms of the electrochemical properties and chemical analysis, especially on the surface region. The solubility and chemical composition for the given sol-gel treatment matches well with the computational results with which the infinitesimal Zr-coating is identified as exhibiting increased charge capacity with prolonged cycle life. Specifically, the whole process can be understood by the suppressed lithium-ion charge transfer resistance (RCT) during the cycles, which can be facilitated by the decreased NiO formation during the cyclic reactions.
ABSTRACT
Many research groups have been interested in the quartz crystal microbalance (QCM)-based gas sensors due to their superb sensitivity originated from direct mass sensing at the ng level. Despite such high sensitivities observed from QCM sensors, their ability to identify gas compounds still needs to be enhanced. Herein, we report a highly facile method that utilizes microcolumns integrated on a QCM gas-responsive system with enhanced chemical selectivity for sensing and ability to identify volatile organic compound single gases. Graphene oxide (GO) flakes are coated on the QCM electrode to substantially increase the adsorption of gas molecules, and periodic polydimethylsiloxane microcolumns with micrometer-scale width and height were installed on the GO-coated QCM electrode. The observed frequency shifts upon sensing of various single gas molecules (such as ethanol, acetone, hexane, etc.) can be analyzed accurately using a simple exponential model. The QCM sensor system with and without the microcolumn both exhibited high detection response values above 50 ng/cm2 for sensing of the gases. Notably, the QCM sensor equipped with the microcolumn features gas identification ability, which is observed as distinct diverging behavior of time constants upon detection of different gases caused by the difference in diffusional transfer of molecules through the microcolumns. For example, the difference in the calculated time constant between ethanol and acetone increased from 22.6 to 92.1 s after installation of the microcolumn. This approach provides an easy and efficient method for identification of single gases, and it may be applied in various advanced sensor systems to enhance their gas selectivity.
ABSTRACT
We herein report an investigation of the device performance capabilities and impedance characteristics of solution-processed organic light-emitting devices (OLEDs) with all-water-processable triple-stacked hole-selective layers (HSLs) on an indium-tin-oxide (ITO) anode, fabricated using a simple coating technique. Highly smooth and homogeneous triple-stacked layers were deposited via horizontal-dip- (H-dip-) coating using aqueous dispersions of graphene oxide (GO), molybdenum oxide (MoO3), and poly(ethylenedioxy thiophene):poly(styrene sulfonate) ( PEDOT: PSS). From the triple-stacked GO/MoO3/ PEDOT: PSS HSLs used as hole-injection layers (HILs) in the OLEDs, which outperform a conventional single HIL of PEDOT: PSS, it was found that OLEDs with triple-stacked HILs exhibited characteristic impedance properties, including low parallel resistance with trap-free space-charge-limited conductivity. Furthermore, it was shown that the relaxation frequency of a sample OLED with triple-stacked GO/MoO3/ PEDOT: PSS HILs was much higher than that of a reference device with a single PEDOT: PSS HIL. These impedance behaviors indicate that carrier (hole) injection in the sample OLED is more efficient than that in any of the other devices tested here. The results presented here clarify that the triple-stacked GO/MoO3/ PEDOT: PSS layers can act as efficient HILs on an ITO anode, representing a remarkable advance in relation to the mass production of high-performance solution-processable OLEDs.
