High power conversion efficiency and device stabilization are two major challenges for CH3NH3PbI3 (MAPbI3) perovskite solar cells to be commercialized. Herein, we demonstrate a diffusion-engineered perovskite synthesis method using MAI/ethanol dipping, and compared it to the conventional synthesis method from MAI/iso-propanol. Diffusion of MAI/C2H5OH into the PbCl2 film was observed to be more favorable than that of MAI/C3H7OH. Facile perovskite conversion from ethanol and highly-crystalline MAPbI3 with minimized impurities boosted the efficiency from 5.86% to 9.51%. Additionally, we further identified the intermediates and thereby the reaction mechanisms of PbCl2 converting into MAPbI3. Through straightforward engineering to enhance the surface morphology as well as the crystallinity of the perovskite with even faster conversion, an initial power conversion efficiency of 11.23% was obtained, in addition to superior stability after 30 days under an ambient condition.

Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at −0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature.

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Non-classical crystallization, in which charged nanoparticles (NPs) are the building blocks of film growth, has been extensively studied in chemical vapor deposition (CVD). Recently, a similar mechanism of film growth has been reported during radio frequency (RF) sputtering with a Ti target and DC magnetron sputtering using an Ag target. In this study, the effect of pressure on the generation of Ti NPs and on the film deposition was studied during RF sputtering with a Ti target. Ti NPs were captured on transmission electron microscopy (TEM) membranes with the electric biases of −30, 0, and +50 V under 20 and 80 mTorr. The number densities of the Ti NPs were 134, 103, and 21 per 100 × 100 nm2, respectively, with the biases of −30, 0, and +50 V under 20 mTorr and were 196, 98, and 0 per 100 × 100 nm2, respectively, with the biases of −30, 0, and +50 V under 80 mTorr, which was analyzed by TEM. The growth rate of Ti films deposited on Si substrates was insensitive to the substrate bias under 20 mTorr but was sensitive under 80 mTorr, with the thicknesses of 132, 133, 97, and 29 nm, respectively, after being deposited for 15 min with the substrate biases of −30, −10, 0, and +50 V. This sensitive dependence of the film growth rate on the substrate bias under 80 mTorr is in agreement with the sensitive dependence of the number density of Ti NPs on the substrate bias under 80 mTorr.

LiFePO4 electrodes using three dimensional NiCrAl alloy metal foam of different electrode thickness are prepared. In order to improve the electrochemical and cycle-life performance of lithium ion batteries, it is important to optimize the electrode thickness and mass loading of active material. As compared to those with thick electrode, the cells with thin electrode exhibit high rate performance and cycle-life behavior, due to the shorter diffusion length of lithium-ion and improved kinetic behavior. Also, cyclic voltammetry curves and electrochemical impedance spectroscopy analysis indicate that the redox reaction for the thinner electrode occurs much faster, and the charge transfer resistance is much lower. The results of same current density (mA cm-2) show that 450 μm-thickness electrode exhibits superior electrochemical and power performance. It is because the 300 μm-thickness electrode which has the lowest mass loading of active material meant that it carried the highest current rate, and thicker electrodes show higher internal resistance and much poorer kinetic property. Namely, electrode thickness and an amount of active material are difference according to the intended use.

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The development of ferroelectric random-access memory (FeRAM) technology with control of grain boundaries would result in a breakthrough for new nonvolatile memory devices. The excellent piezoelectric and electrical properties of bulk ferroelectrics are degraded when the ferroelectric is processed into thin films because the grain boundaries then form randomly. Controlling the nature of nucleation and growth are the keys to achieving a good crystalline thin-film. However, the sought after high-quality ferroelectric thin-film has so far been thought to be impossible to make, and research has been restricted to atomic-layer deposition which is extremely expensive and has poor reproducibility. Here we demonstrate a novel epitaxial-like growth technique to achieve extremely uniform and large rectangular-shaped grains in thin-film ferroelectrics by dividing the nucleation and growth phases. With this technique, it is possible to achieve 100-μm large uniform grains, even made available on Si, which is large enough to fabricate a field-effect transistor in each grain. The electrical and reliability test results, including endurance and retention test results, were superior to other FeRAMs reported so far and thus the results presented here constitute the first step toward the development of FeRAM using epitaxial-like ferroelectric thin-films.

LiFePO 4 electrodes using three-dimensional NiCrAl metal foam of different conductive carbon content were prepared. Increasing the carbon black content greatly enhanced the rate performance, with a severe capacity fade shown for lower carbon black content with increases current rate. The electrode with no addition of carbon black showed very poor electrochemical performance, due to the high charge transfer resistance (R ct ) and high diffusion limitation of Li-ion. The electrodes of increased carbon black loadings enhanced the kinetic performance and dramatically decreased the R ct , due to the large effective contact area between the conductive carbon material and the LiFePO 4 particles. However, lower carbon black loading resulted in much higher areal capacity (mAh cm −2 ) at 0.2 and 0.5 C, due to increases in the amount of LiFePO 4 particles from reducing the carbon black loading. According to the results for 8 mA cm −2 , the specific capacity of 15 wt.%-electrode was higher than 10 wt.%-electrode. However, electrode polarization of 15 wt.%-electrode was more high than for 10 wt.%-electrode, due to high over-potential by the high current rate. That is to say the optimal conductive carbon content differs according to the intended use.