Ke Fu

Rare earth ion doped phosphors for dye-sensitized solar cells applications

Dye-sensitized solar cells (DSSCs) have attracted extensive attention as one of the promising alternatives to silicon solar cells. However, DSSCs have a maximum absorption in the visible light of solar spectrum, which confines their power conversion efficiency. Lots of research efforts have been focused on extending light absorption to enhance the conversion efficiency. Rare earth ion doped up/down conversion materials is an available approach to compensate for the non-absorbable wavelength region of DSSCs via converting ultraviolet and near-infrared radiation to visible emission. In addition to the light-harvesting enhancement, light-scattering effect and recombination loss can also be achieved in DSSCs by utilizing upconversion (UC) or downconversion (DC) materials. Moreover, the introduction of UC or DC facilitates to improve the stability of solar cells. In this review paper, the performance of dye-sensitized solar cells based on up or down conversion materials will be introduced.

Reduced interfacial recombination in dye-sensitized solar cells assisted with NiO:Eu3+,Tb3+ coated TiO2 film

Eu3+,Tb3+ doped and undoped NiO films were deposited on TiO2 by a sol-gel spin-coating method as the photoanodes of dye sensitized solar cells (DSSCs). A comparative study with different structures including TiO2, TiO2/NiO and TiO2/NiO:Eu3+,Tb3+ as the photoanodes was carried out to illustrate the photovoltaic performance of solar cells. NiO could enhance the performance of DSSCs ascribed to acting as a barrier for the charge recombination from the fluorine doped tin oxide (FTO) to electrolyte and forming a p-n junction (NiO/TiO2). Moreover, Eu3+, Tb3+ co-doped NiO could accelerate the electron transfer at TiO2/dye/electrolyte interface, which further benefited the performance of solar cells. The solar cells assembled with the photoelectrodes consisting of NiO:Eu3+,Tb3+ and TiO2 exhibited short-circuit current density (JSC) of 17.4 mA cm−2, open-circuit voltage (VOC) of 780 mV and conversion efficiency of 8.8%, which were higher than that with TiO2/NiO and pure TiO2. The mechanisms of the influence of NiO and NiO:Eu3+,Tb3+ on the photovoltaic performance of DSSCs were discussed.

Improving the photovoltaic performance of dye sensitized solar cells based on a hierarchical structure with up/down converters

A hierarchical structure composed of porous TiO2:Al2O3:Eu3+ nanoparticles (NPs) and vertically grown one-dimensional TiO2:Er3+,Yb3+ nanorods (NRs) on fluorine doped tin oxide (FTO) substrates coated with a TiO2:graphene (G) seed layer was investigated for use in photoanodes for dye sensitized solar cells (DSSCs). The DSSCs assembled with this hierarchical structure exhibit an outstanding power conversion efficiency of 4.58%, which is superior to that of the devices based on pure TiO2. This high performance can be attributed to the spectrum modifications achieved by utilizing the upconversion (UC) material TiO2:Er3+,Yb3+ and the downconversion (DC) material Al2O3:Eu3+, which facilitate the light harvesting of solar cells via converting near infrared (NIR) and ultraviolet (UV) radiation to visible emission, respectively. Moreover, the TiO2:G layer provides faster electron transport from TiO2 to FTO for the high carrier mobility of G. Moreover, the one-dimensional nanorod structure can offer direct electrical pathways for photogenerated electrons as well as enhance the light scattering capabilities of photoanodes. This study indicates that the TiO2:G/TiO2:Er3+,Yb3+ NRs/TiO2:Al2O3:Eu3+ hierarchical structure has the potential to improve the performance of DSSCs.

Fabrication of TiO2 Nanosheet Aarrays/Graphene/Cu2O Composite Structure for Enhanced Photocatalytic Activities

TiO2 NSAs/graphene/Cu2O was fabricated on the carbon fiber to use as photocastalysts by coating Cu2O on the graphene (G) decorated TiO2 nanosheet arrays (NSAs). The research focus on constructing the composite structure and investigating the reason to enhance the photocatalytic ability. The morphological, structural, and photocatalytic properties of the as-synthesized products were characterized. The experimental results indicate that the better photocatalytic performance is ascribed to the following reasons. First, the TiO2 NSAs/graphene/Cu2O composite structure fabricated on the carbon cloth can form a 3D structure which can provide a higher specific surface area and enhance the light absorption. Second, the graphene as an electron sink can accept the photoelectrons from the photoexcited Cu2O which will reduce the recombination. Third, the TiO2 nanosheet can provide more favorable carrier transportation channel which can reduce the recombination of carriers. Finally, the Cu2O can extend the light absorption range.

Hybrid nanostructures of TiO2 nanorod array/Cu2O with a CH3NH3PbI3 interlayer for enhanced photocatalytic activity and photoelectrochemical performance

TiO2 nanorod arrays (NRAs) filled with CH3NH3PbI3 were coated by Cu2O, which was fabricated on carbon fiber to form the photocatalyst TiO2 NRAs/CH3NH3PbI3/Cu2O. The morphology and structure of the as-obtained samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The ultraviolet-visible (UV-vis) absorption measurements and photocurrent test revealed that the CH3NH3PbI3 layer can provide a greatly enhanced light harvesting efficiency. The I–V curves and electrochemical impedance spectra (EIS) analysis confirmed that the TiO2 NRAs/CH3NH3PbI3/Cu2O hybrid structure favors electron transfer. The TiO2 NRAs/CH3NH3PbI3/Cu2O structure exhibits enhanced photocatalytic activity with good recyclability under Xe lamp irradiation. The experimental results indicate that the better photocatalytic performance is ascribed to the higher carrier separation and transportation, higher specific surface area and the broadened absorption spectrum.

Enhanced Efficiency of Dye-Sensitized Solar Cells Benefited from Graphene Modified by Ag Nanoparticles

In this paper, graphene modified by Ag nanoparticles was successfully applied into dye sensitized solar cells. The morphologies and compositions of graphene and graphene-Ag nanoparticles were characterized by scanning electron microscope and energy dispersive X-ray spectroscopy. The optical and electrical properties were evaluated by UV-vis-NIR absorption spectroscopy, electrochemical impedance spectroscopy and current-voltage curve. The results indicated that the incorporation of graphene or graphene-Ag nanoparticles can improve the light absorption and decrease the charge recombination. The solar cells with graphene-Ag nanoparticles exhibited short-circuit current density of 14.34 mA cm-2, open-circuit voltage of 709 mV and conversion efficiency of 6.01%, which were higher than those of DSSCs with graphene or pure TiO2.