Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO2 nanofibers in a TiO2 film as electrode.

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO2 nanofiber [TN] and Ag-doped TiO2 nanofiber [ATN] have been extended to be included in TiO2 films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO2 photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO2 films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.

Increases in solar conversion efficiencies of the ZrO2 nanofiber-doped TiO2 photoelectrode for dye-sensitized solar cells.

In this paper, in order to improve the efficiency of dye-sensitized solar cells, we introduced zirconia [ZrO2] nanofibers into a mesoporous titania [TiO2] photoelectrode. The photoelectrode consists of a few weight percent of ZrO2 nanofibers and a mesoporous TiO2 powder. The mixed ZrO2 nanofibers and the mesoporous TiO2 powder possessed a larger surface area than the corresponding mesoporous TiO2 powder. The optimum ratio of the ZrO2 nanofiber was 5 wt.%. The 5 wt.% ZrO2-mixed device could get a short-circuit photocurrent density of 15.9 mA/cm2, an open-circuit photovoltage of 0.69 V, a fill factor of 0.60, and a light-to-electricity conversion efficiency of 6.5% under irradiation of AM 1.5 (100 mW/cm2).

Visible light-responsive titanium dioxide thin film prepared by reactive sputtering.

TiO2 is a wide band-gap semiconductor (3.4 eV) and can only absorb about 5% of sun light in the ultraviolet light region, which largely limits its practical applications because of the lower utility of sun light and quantum yield. In order to move the absorption edge of TiO2 films to visible spectrum range, we have made the impurity level within a band-gap of TiO2 thin film by introduction of oxygen vacancy. Oxygen-defected TiO2 photo-catalyst have prepared by reactive sputtering with the partial pressure of Ar:O2 = 76.7:23.3 approximately 98.5:1.5 ratios. As a result, we could have the impurity level of about 2.75 eV on condition that oxygen partial pressure is 2.9%. And the photocatalytic activity was realized at 400 nm wavelength.

Electrochemical characteristics of lithium iron phosphate with multi-walled carbon nanotube for lithium polymer batteries.

In this study, we prepared phospho-olivine LiFePO4 nanoparticles as cathode materials for lithium polymer batteries by hydrothermal reaction at 150 degrees C. Multi-walled carbon nanotube (MWCNT) was added to enhance the electrical conductivity of LiFePO4. LiFePO4-MWCNT nanoparticles (0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt% and 10 wt%) were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). LiFePO4-MWCNT/SPE/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm(-2) in a range between 2.5 and 4.3 V versus Li/Li+, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO4 was 103 mA h g(-1). The discharge capacity of LiFePO4-MWCNT/SPE/Li cell with 7 wt% MWCNT was 129 mA h g(-1) at the first cycle and 130 mA h g(-1) after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO4-MWCNT/SPE/Li cell with 7 wt% MWCNT was better than that of LiFePO4/SPE/Li cell.

Performance improvement of dye-sensitized glass powder added TiO2 solar cells.

The effect of two different types of glass powder added TiO2 hydride photoelectrode in performance of dye sensitize solar cell (DSSC) had been studied at different wt.%. TiO2 particles diffusion and possible attachment with Si atoms was observed with field-emission scanning electron microscopy (FE-SEM) and it strongly depends on characteristics of glass. Short circuit current (I(sc)) was increased with increasing the wt.% up to 5% of glass powder and further increase in wt.% ratio had decreased the I(sc). Maximum increase upto 32 and 45% in the efficiently was observed at 5 wt.% of glass powder in TiO2 for low temperature (LTG) and high temperature glass (HTG) powder, respectively. Adding glass powder in TiO2 can increase light scattering properties of hybrid electrode and can also create an energy barriers of SiO2 which prevents the recombination reactions, hence; an increase in efficiency observed.

Nanosized LiFePO4 cathode materials for lithium ion batteries.

In this study, we prepared nano-particles of LiFePO4 as cathode material for lithium ion batteries by the solid-state reaction. A simple one-step heat treatment has been employed with control of heating temperature and heated LiFePO4 at 650 degrees C exhibited higher 125 mA h/g of the discharge capacity than 600 degrees C, 700 degrees C. To improve conductivity of the inter-particle, carbon coating was carried out by raw carbon or pyrene as carbon sources and their morphological properties of particles on the carbon coating was compared with by FE-SEM, TEM. From the FE-SEM results, the particles of carbon added LiFePO4 have much smaller size than LiFePO4 as below 300 nm. When adding pyrene (10 wt%), the carbon surrounded non-uniformly with surface of the particles compared with adding raw carbon which wrapped uniformly with carbon web and it was exhibited 152 mA h/g of the discharge capacity on LiFePO4/C composite cells at 10th cycle.

Improved electrochemical performance of LiCoPO4 nanoparticles for lithium ion batteries.

Single phase LiCoPO4 nanoparticles were synthesized by solid-state reaction. LiCoPO4/Li batteries were fabricated in an argon-filled glove box, and their electrochemical properties were analyzed by cyclic voltammetry (CV) and charge-discharge tests. The structural performance of LiCoPO4 nanoparticles was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD result demonstrated that LiCoPO4 nanoparticles had an orthorhombic olivine-type structure with a space group of Pmnb. The charge-discharge tests indicated that the initial discharge capacity and coulombic efficiency of LiCoPO4/Li batteries were 110 mA h/g and 48% in cut-off voltage range of 3.0-5.3 V, 90 mA h/g and 54% in cut-off voltage range of 3.0-5.1 V, 70 mA h/g and 60% in cut-off voltage range of 3.0-5.0 V, respectively. After 30 cycles, the coulombic efficiency was 78% for 3.0-5.3 V, 88% for 3.0-5.1 V, 91% for 3.0-5.0 V, respectively. These results indicated that the coulombic efficiency of LiCoPO4/Li battery increased upon cycling and upon decreasing in charge upper limit voltage, respectively.