Yu-Fen Wang

Hydrothermal fabrication of hierarchically anatase TiO2 nanowire arrays on FTO glass for dye-sensitized solar cells.

Hierarchical anatase TiO2 nano-architecture arrays consisting of long TiO2 nanowire trunk and numerous short TiO2 nanorod branches on transparent conductive fluorine-doped tin oxide glass are successfully synthesized for the first time through a facile one-step hydrothermal route without any surfactant and template. Dye-sensitized solar cells based on the hierarchical anatase TiO2 nano-architecture array photoelectrode of 18 μm in length shows a power conversion efficiency of 7.34% because of its higher specific surface area for adsorbing more dye molecules and superior light scattering capacity for boosting the light-harvesting efficiency. The present photovoltaic performance is the highest value for the reported TiO2 nanowires array photoelectrode.

Hierarchical Oriented Anatase TiO2 Nanostructure arrays on Flexible Substrate for Efficient Dye-sensitized Solar Cells

The vertically oriented anatase single crystalline TiO2 nanostructure arrays (TNAs) consisting of TiO2 truncated octahedrons with exposed {001} facets or hierarchical TiO2 nanotubes (HNTs) consisting of numerous nanocrystals on Ti-foil substrate were synthesized via a two-step hydrothermal growth process. The first step hydrothermal reaction of Ti foil and NaOH leads to the formation of H-titanate nanowire arrays, which is further performed the second step hydrothermal reaction to obtain the oriented anatase single crystalline TiO2 nanostructures such as TiO2 nanoarrays assembly with truncated octahedral TiO2 nanocrystals in the presence of NH4F aqueous or hierarchical TiO2 nanotubes with walls made of nanocrystals in the presence of pure water. Subsequently, these TiO2 nanostructures were utilized to produce dye-sensitized solar cells in a backside illumination pattern, yielding a significant high power conversion efficiency (PCE) of 4.66% (TNAs, JSC = 7.46 mA cm−2, VOC = 839 mV, FF = 0.75) and 5.84% (HNTs, JSC = 10.02 mA cm−2, VOC = 817 mV, FF = 0.72), respectively.

Sonochemical Preparation of Hierarchical ZnO Hollow Spheres for Efficient Dye‐Sensitized Solar Cells

Hierarchical ZnO hollow spheres (400-500 nm in diameter) consisting of ZnO nanoparticles with a diameter of approximately 15 nm have been successfully prepared by a facile and rapid sonochemical process. The formation of hierarchical ZnO hollow spheres is attributed to the oriented attachment and subsequent Ostwald ripening process according to time-dependent experiments. The as-prepared ZnO hollow spheres are used as a photoanode in dye-sensitized solar cells and exhibit a highly efficient power conversion efficiency of 4.33%, with a short-circuit current density of 9.56 mA cm(-2), an open-circuit voltage of 730 mV, and a fill factor of 0.62 under AM 1.5 G one sun (100 mW cm(-2)) illumination. Moreover, the photovoltaic performance (4.33%) using the hierarchical ZnO hollow spheres is 38.8% better than that of a ZnO nanoparticle photoelectrode (3.12%), which is mainly attributed to the efficient light scattering for the former.

Hierarchical Tin Oxide Octahedra for Highly Efficient Dye‐Sensitized Solar Cells

Since the great breakthrough made in 1991 by O Regan and Gr tzel , dye-sensitized solar cells (DSSCs) have attracted tremendous interest and are becoming one of the most promising candidates for practical photovoltaic applications due to their low production cost and efficient photovoltaic performance. Up to now, more than 11 % power conversion efficiency has been reported for DSSCs based on TiO2 nanocrystalline photoelectrodes. [3] It is well known that the composition and structure of the photoelectrode material play an important role in the photovoltaic performance and stability of DSSCs. As an efficient photoelectrode, the material should have a large surface area to adsorb larger amounts of dye and highly ordered nanoarrays or densely packed microstructure for fast electron transport and light scattering. Among the photoelectrodes, one interesting structure is the double-layer electrode containing a dye adsorption layer (10–15 mm thick, consisting of 20 nm particles) and a light-scattering layer (3–5 mm thick, consisting of a few hundreds of nanometer particles); this has been found to improve the photovoltaic performance. Another novel photoelectrode is the hierarchically structured film consisting of submicron spheres that are made up of 10–20 nm particles. The photoelectrode consists of this kind of bifunctional material with both the dye adsorption layer (nanoparticles) and the light-scattering layer (submicron spheres), which results in a significant enhancement of power conversion efficiency. However, most of the works have been only focused on the hierarchical TiO2 or ZnO spheres. [5,6]

Hydrothermal Fabrication of Quasi‐One‐Dimensional Single‐Crystalline Anatase TiO2 Nanostructures on FTO Glass and Their Applications in Dye‐Sensitized Solar Cells

One-dimensional and quasi-one-dimensional semiconductor nanostructures are desirable for dye-sensitized solar cells (DSSCs), since they can provide direct pathways for the rapid collection of photogenerated electrons, which could improve the photovoltaic performance of the device. Quasi-1D single-crystalline anatase TiO(2) nanostructures have been successfully prepared on transparent, conductive fluorine-doped tin oxide (FTO) glass with a growth direction of [101] through a facile hydrothermal approach. The influences of the initial titanium n-butoxide (TBT) concentration, hydrothermal reaction temperature, and time on the length of quasi-1D anatase TiO(2) nanostructures and on the photovoltaic performance of DSSCs have been investigated in detail. A power conversion efficiency of 5.81% has been obtained based on the prepared TiO(2) nanostructure photoelectrode 6.7 μm thick and commercial N719 dye, with a short-circuit current density of 13.3 mA cm(-2) , an open-circuit voltage of 810 mV, and a fill factor of 0.54.

Synthesis of hierarchical SnO2 octahedra with tailorable size and application in dye-sensitized solar cells with enhanced power conversion efficiency

Following the previous report on the fabrication of three-dimensional hierarchical SnO2 octahedra consisting of nanoparticles via a rapid sonochemical process (Wang et al., Chem.–Eur. J., 2010, 16, 8620–8625), the influences of ultrasonic time, amplitude, ratio of H2O–diethylene glycol (DEG), and different Sn salts on the morphology and size of SnO2 have been further investigated in the present article. The hierarchical SnO2 octahedra with average edge lengths of 0.5, 0.8, 1.0, 1.5 and 1.8 μm composed of 30–40 nm SnO2 nanoparticles have been successfully obtained. The power conversion efficiencies of dye-sensitized solar cells (DSSCs) based on the hierarchical SnO2 octahedra photoanodes varied from 5.57%, 5.82%, 6.40%, 6.45% to 6.80% with the corresponding octahedron sizes of 0.5, 0.8, 1.0, 1.5 and 1.8 μm, respectively. Intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated voltage spectroscopy (IMVS) and UV-vis diffuse spectroscopy were used to investigate the influences of the SnO2 octahedron size on the photovoltaic performances of DSSCs.

Macroporous SnO2 Synthesized via a Template-Assisted Reflux Process for Efficient Dye-Sensitized Solar Cells

Macroporous SnO2 composed of small SnO2 nanoparticles with diameters around 10 nm is prepared via a reflux process. This novel structure is designed as the photoanode in dye-sensitized solar cells (DSSCs), intending to improve the light utilization efficiency with its excellent light scattering ability. Though the dye adsorption of macroporous SnO2 (14.00 × 10(-8) mol cm(-2)) is lower than that of SnO2 nanoparticles (19.24 × 10(-8) mol cm(-2)), the photovoltaic performance of the DSSCs based on the former is 4.87% compared to 4.41% for SnO2 nanoparticles, showing over 10% increment than the latter. This improvement is mainly due to the enhanced light scattering ability and charge collection efficiency of the macroporous structure, both of which contribute to a higher short current density and hence for the better power conversion efficiency. Furthermore, a double-layer structure composed of SnO2 nanoparticles (active layer) and macroporous SnO2 (scattering layer) possess both large dye adsorption (22.82 × 10(-8) mol cm(-2)) and scattering property, thus leads to a significant overall conversion efficiency of 5.78%.

Hierarchical Macroporous Zn2SnO4–ZnO Nanorod Composite Photoelectrodes for Efficient CdS/CdSe Quantum Dot Co-Sensitized Solar Cells

A hierarchical macroporous Zn2SnO4-ZnO nanorod composite film is prepared through a drop-casting process of PS@Zn2SnO4 and subsequent hydrothermal growth of ZnO nanorod. CdS/CdSe co-sensitized solar cells based on the macroporous Zn2SnO4-ZnO nanorod composite photoelectrode exhibits an enhancement of 34.4% in power conversion efficiency (1.68%) compared to the pristine macroporous Zn2SnO4 photoelectrode (1.25%). Especially worth noting is that the growth of ZnO nanorods contributes greatly to the enlargement of surface area and improvement of light scattering ability of the composite film, which dominates the increase of Jsc values and eventual power conversion efficiency. QDSSCs based on the optimized 9 μm thick composite photoanode film exhibits a power conversion efficiency of 2.08%, which is the highest value for the reported QDs sensitized solar cells based on the Zn2SnO4 photoelectrode.

Facile Fabrication of Hierarchical SnO2 Microspheres Film on Transparent FTO Glass

Hierarchical SnO(2) microspheres consisting of nanosheets on the fluorine-doped tin oxide (FTO) glass substrates are successfully prepared via a facile hydrothermal synthesis process. The as-prepared novel microsphere films were characterized in detail by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy. Moreover, SnO(2) nanoparticles with 30-80 nm in size covered on the surface of nanosheets/microspheres were also obtained by optimizing the hydrothermal reaction temperature, time, or volume ratio of acetylacetone/H(2)O. The detailed investigations disclose the experimental parameters, such as acetylacetone, NH(4)F, and seed layer play important roles in the morphology of hierarchical SnO(2) microspheres on the FTO glass. The formation process of SnO(2) microspheres is also proposed based on the observations of time dependent samples.

Fabrication of a double layered photoanode consisting of SnO2 nanofibers and nanoparticles for efficient dye-sensitized solar cells

Hierarchical one-dimensional SnO2 nanofibers (NFs) consisting of nanoparticles (NPs) have been synthesized and employed as an efficient light scattering layer to fabricate double layered dye-sensitized solar cells (DSSCs). The photovoltaic performance (5.44%) of the DSSC based on the SnO2 NPs (14.5 μm)/NFs (4.0 μm) double layered photoanode showed a 26.3% enhancement compared to that of a SnO2 NPs photoanode (18.5μm, 4.30%). Intensity modulation photocurrent spectroscopy (IMPS), intensity-modulated voltage spectroscopy (IMVS) and open-circuit voltage decay (OCVD) spectroscopy were used to investigate the kinetic process of electron transport and recombination within SnO2 NPs or NPs/NFs based DSSCs, revealing a faster electron transport rate and a lower recombination rate in the SnO2 NPs/NFs photoanode. The UV-vis diffuse reflectance spectroscopy results showed that the SnO2 NPs/NFs possess better light scattering ability which enhanced their photovoltaic performance compared to the SnO2 NPs. Furthermore, an overall power conversion efficiency of 6.31% (with a Jsc of 16.78 mA cm−2, Voc of 711 mV and FF of 0.53) was achieved for the SnO2 NPs/NFs double layered photoanode with an additional SnO2 blocking layer, which suppressed electron recombination between the FTO glass and the electrolyte.