Bing-Xin Lei

Oriented hierarchical single crystalline anatase TiO2 nanowire arrays on Ti-foil substrate for efficient flexible dye-sensitized solar cells

Hierarchical anatase TiO2 nanowire (HNW) arrays consisting of long single crystalline nanowire trunks and short single crystalline nanorod branches have been synthesized on Ti-foil substrate via a two-step hydrothermal growth process. The formation of the HNW arrays based on anatase TiO2 nanowire (NW) arrays can be ascribed to the crystallographic relationship between trunk and branch. The power conversion efficiency of dye-sensitized solar cells (DSSCs) based on such a HNW photoelectrode (4.51%) shows a significant enhancement compared to TiO2 nanowire (NW) array photoelectrode (3.12%) with similar thickness (∼15 μm in nanowire length), which can be attributed to more dye loading, superior light scattering ability and comparable electron transport rate for the former. Furthermore, flexible DSSC using TiO2 HNW arrays on Ti substrate as working electrode and transparent PEDOT/ITO-PET prepared via in situelectrodeposition as counter electrode shows a comparable photovoltaic performance to the rigid Pt/FTO-glass cell. A power conversion efficiency as high as 4.32% (Jsc = 7.91 mA cm−2, Voc = 796 mV, FF = 0.69) is obtained for the first time for fully flexible DSSC based on hierarchical TiO2 nanowire arrays and Pt-free counter electrode.

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.

Tri-functional hierarchical TiO2 spheres consisting of anatase nanorods and nanoparticles for high efficiency dye-sensitized solar cells

Hierarchical anatase TiO2 spheres consisting of nanorods and nanoparticles are successfully prepared via a simple acid thermal method using titanium n-butoxide and acetic acid, which will overcome the kinetic and light-scattering limitations of nanoparticles and the surface area limitations of one-dimensional nanostructures, as photoelectrodes for dye-sensitized solar cells. The as-prepared and calcined hierarchical spheres were characterized by transmission electron microscopy, scanning electron microscopy and X-ray powder diffraction. The DSSC based on hierarchical TiO2 spheres as the photoelectrode shows a highly efficient power conversion efficiency (10.34%) accompanied by 18.78 mA cm−2 in short-circuit photocurrent density and 826 mV in open-circuit voltage. The great improvements of photocurrent density and power conversion efficiency for hierarchical TiO2 spheres compared to P25 nanoparticle photoelectrodes are mainly attributed to a considerable surface area, a higher light scattering ability, and faster electron transport rates and slower recombination rates for the former.

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.

Highly efficient CdTe/CdS quantum dot sensitized solar cells fabricated by a one-step linker assisted chemical bath deposition

We report on an interesting and efficient one-step linker assisted chemical bath deposition method to synthesise CdTe or CdTe/CdS quantum dot sensitized TiO2 photoelectrodes. The CdTe or CdTe/CdS core/shell quantum dots with different size and structure can be easily obtained by controlling the hydrothermal temperature. The QDs are covalently linked to TiO2 nanocrystallites by thioglycolic acid (TGA) bifunctional molecule which also acts as stabilizer and sulfur source in this one-step fabrication. In this sensitized electrode, CdTe has higher light absorptivity while the CdS shell plays a crucial role in the sensitive CdTe QDs protection and photo-generated charges separation. Both effects push the power conversion efficiency of the quantum dot sensitized solar cells (QDSSCs) up to 3.8% and 5.25% under AM 1.5 G one sun (100 mW cm−2) and 0.12 sun illumination, respectively.

High performance and reduced charge recombination of CdSe/CdS quantum dot-sensitized solar cells

CdSe and CdSe/CdS quantum dots (QDs) with narrow size distribution are attached onto TiO2 electrodes by linker-assisted chemical bath deposition (LACBD). Preparation is carried out at 60 °C or 160 °C, which results in the formation of CdSe or CdSe/CdS QDs onto the TiO2 nanoparticles connected by thioglycolic acid (TGA). The solar cell based on a CdSe/CdS QD-sensitized TiO2 photoelectrode shows higher JSC, VOC and power conversion efficiency comparing to single CdSe QD-sensitized TiO2, which can be ascribed to superior light absorption, faster electron transport and slower charge recombination for the former. Furthermore, the effects of a ZnS passivation layer and thermal annealing on the photovoltaic performance have been investigated by UV-vis spectra, incident photo-to-current conversion efficiency (IPCE) and electrochemical impedance spectra (EIS). As a result, a quantum dot-sensitized solar cell (QDSSC) based on a TiO2–CdSe/CdS–ZnS photoanode (400 °C, 300 s calcination), polysulfide electrolyte and Cu2S counter electrode achieves a power conversion efficiency of 4.21% under AM 1.5 G one sun illumination.

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.

Hiearchical ZnO rod-in-tube nano-architecture arrays produced via a two-step hydrothermal and ultrasonication process

Vertically aligned hierarchical ZnO rod-in-tube nano-architecture arrays are produced via a two-step process including an initial hydrothermal reaction followed by ultrasonication growth. The ZnO nanorod arrays grow firstly on FTO glass through a hydrothermal process and then act as templates for the fabrication of rod-in-tube nano-architectures during ultrasonication. The as-prepared ZnO rod-in-tube nano-architectures are assembled by the self-stacking of hexagonal nanorings along with orientation of ZnO nanorod templates. Both hexamethylenetetramine and sodium citrate are found to play key roles in the formation of the novel ZnO rod-in-tube nano-architectures. The power conversion efficiency of dye-sensitized solar cell based on hierarchical ZnO rod-in-tube nano-architectures photoelectrode (0.91%) exhibits a significant improvement (75%) compared to that of ZnO nanorods (0.52%).

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.

Highly Catalytic Carbon Nanotube/Pt Nanohybrid-Based Transparent Counter Electrode for Efficient Dye-Sensitized Solar Cells

Low-cost transparent counter electrodes (CEs) for efficient dye-sensitized solar cells (DSSCs) are prepared by using nanohybrids of carbon nanotube (CNT)-supported platinum nanoparticles as highly active catalysts. The nanohybrids, synthesized by an ionic-liquid-assisted sonochemical method, are directly deposited on either rigid glass or flexible plastic substrates by a facile electrospray method for operation as CEs. Their electrochemical performances are examined by cyclic voltammetry, current density-voltage characteristics, and electrochemical impedance spectroscopy (EIS) measurements. The CNT/Pt hybrid films exhibit high electrocatalytic activity for I(-)/I(3)(-) with a weak dependence on film thickness. A transparent CNT/Pt hybrid CE film about 100 nm thick with a transparency of about 70% (at 550 nm) can result in a high power conversion efficiency (η) of over 8.5%, which is comparable to that of pyrolysis platinum-based DSSCs, but lower cost. Furthermore, DSSC based on flexible CNT/Pt hybrid CE using indium-doped tin oxide-coated polyethylene terephthalate as the substrate also exhibits η=8.43% with J(sc)=16.85 mA cm(-2), V(oc)=780 mV, and FF=0.64, and this shows great potential in developing highly efficient flexible DSSCs.