C.K. Hong

Effect of TiO2 rutile nanorods on the photoelectrodes of dye-sensitized solar cells

In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO2 nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO2 thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells.

PHOTOVOLTAIC PROPERTIES OF TiO2 PHOTOELECTRODE PREPARED BY USING LIQUID PEG-EEM BINDER

We present one of the central and basic factors related to the TiO2 photoanodes of optimal absorption site. Binder is of particular importance for surfaces and interfaces that involve organic dye and TiO2 layer. We introduced monodispersed liquid copolymer binders; poly(ethylene glycol)-ethyl ether methacrylate (PEG-EEM) instead of solid PEG to increase TiO2 electrodes surface area. We attempt to investigate the morphology of the photoanodes and photovoltaic effects using field emission scanning electron microscopy (FE-SEM), BET and photovoltaic properties under illumination with AM 1.5 simulated sunlight. We achieve 167% enhanced power conversion efficiency when the optimal content of liquid PEG-EEM binder was 4 wt.% than that of PEG binder. We show that the performance of Dye-sensitized solar cell (DSSC) can be strongly improved using liquid type binder.

Enhanced efficiency of dye-sensitized solar cells doped with green phosphors LaPO4:Ce, Tb or (Mg, Zn)Al11O19:Eu

We have successfully introduced green phosphors LaPO4:Ce, Tb (G4) or (Mg, Zn)Al11O19:Eu (G2) into TiO2 photoelectrode of dye-sensitized solar cells. The conversion efficiency of the G4-doped device was enhanced by 30% compared with the pristine TiO2 photoelectrode. The green phosphor doped at 5-wt.% ratio contributed to the reduction of resistances of the surface and interface of the photoelectrode and to the great enhancement of the absorption spectrum in UV-visible and near-infrared regions. The internal resistances and absorbance of the photoelectrode directly affect the power conversion efficiency. Green phosphor plays an important role towards the realization of high-efficiency dye-sensitized solar cells.

Mesoporous architecture of TiO2 microspheres via controlled template assisted route and their photoelectrochemical properties

Anatase titanium dioxide (TiO2) microspheres were successfully synthesized via a controlled chemical route using carbon spheres as sacrificial templates. The morphology has been controlled by varying the deposition time of carbonaceous (c) spheres from 4 to 16xa0h with the interval of 4xa0h, which affect the size of TiO2 spheres. The structural, morphological, optical, compositional and photoelectrochemical properties of the TiO2 thin films were studied. X-ray diffraction (XRD) pattern confirms the formation of anatase TiO2 with the tetragonal crystal structure. Field emission scanning electron microscopy analysis revealed that the synthesized anatase TiO2 microspheres has average diameter of ~330–510xa0nm. The blueshift in optical absorption is observed due to Mie scattering. The indirect optical band gap energy of TiO2 was varied over 3.05–3.16xa0eV, with the increase in deposition time. The HRTEM and SAED results show the polycrystalline nature of the sample which is in good agreement with the XRD. The anatase TiO2 hollow spheres with mesoporous walls and high specific surface area i.e. 41xa0m2xa0g−1 was obtained using this simple method. The films were photoelectrochemically active with maximum current density 531xa0µA/cm2 under 100xa0mW/cm2 illuminations.

Compact nanoarchitectures of lead selenide via successive ionic layer adsorption and reaction towards optoelectronic devices

Thin films of Lead Selenide (PbSe) having compact nanoarchitectures were synthesized by a facile and cost-efficient successive ionic layer adsorption and reaction (SILAR) technique. The structural, morphological, optical and compositional properties were studied using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), UV–vis spectrophotometer, and X-ray photoelectron spectroscopy (XPS) techniques. Moreover, the effect of SILAR cycles on the morphology of PbSe thin films was investigated. XRD patterns revealed the formation of crystalline PbSe with the cubic crystal structure. FESEM images show shape evolution from nanoparticulate to merged pyramidal—like structure with variation in size from ~200 to 430xa0nm. The optical direct band gap energy of PbSe were varies from 1.32 to 1.20xa0eV with the increase in deposition cycles. The HRTEM and SAED results show the crystalline nature of the sample which is in good agreement with the XRD. The electrical characterizations were performed in order to obtain the ohmic behavior in the metal–semiconductor interface. The deposited thin films show a good ohmic behavior.

Novel synthesis of efficient counter electrode by facile arrested precipitation technique (APT)

In the present investigation, we have successfully synthesized nanogranular thin film of copper sulfoselenide Cu2(S, Se) as efficient counter electrode to CdS0.7Se0.3 photoanode by facile arrested precipitation technique (APT). The deposited photoanode was annealed at 150xa0°C in vacuum oven and used for further characterization. Optical absorption study suggested the band gap energy of photoanode is 1.75xa0eV. X-ray diffraction results indicate that APT is a favorable technique to synthesize pure nanocrystalline CdS0.7Se0.3 thin films having hexagonal crystal structure. An electrochemical impedance spectroscopy analysis confirms the charge transfer resistance. X-ray photoelectron spectroscopy reveals stoichiometry at valance state of Cu2(S, Se) counter and CdS0.7Se0.3 photoanode. The enhanced photoconversion efficiency achieved was 0.42xa0% for this counter electrode due to systematic study.