Preparation And Properties Optimization Of Titanium Dioxide Microspheres-based Solar Cells

With the increasing deterioration of environmental and resouce issues since1900 s,it is urgent to develop feasible techniques to the research and development of new energy.Among various clean energy sources,solar energy has attracted much attention as an inexhaustible source of energy.Dye-sensitized solar cells(DSSCs)and quantum dots sensitized solar cells(QDSSCs)have been extensive researched because of the simple preparation process,high photoelectric conversion efficiency,and low cost.Among various semiconductors,TiO2 has been widely studied and successfully applied to photoanodes for solar cells because of its specific optoelectronic properties,low price,good stability,good corrosion resistance,and strong oxidizing characteristics.However,for solar cell application,further research is desirable because of their limited efficiencies.Thus,prepareing high quality photoanodes with good capability of light-scattering and enhanced electron-collection and transport capability is one of the key issues.In this paper,we focuesd on the preparation,doping modification,of three dimension TiO2 microspheres,solar cell applications,and properties optimization,and the main points could be summarized as follows:The niobium doped hierarchical anatase TiO2 microspheres,which are consist of a serried nano-thorns and plicate nano-ribbons with exposed(001)facet,were synthesized using hydrothermal method followed by heat treatment.The effects of niobium on the microstructures and photovoltaic performances of the dye-sensitized solar cells(DSSCs)were studied.The results revealed that Nb5+ doping replaces Ti4+cations in TiO2 lattice,and the bandgap of the films varies with increasing Nb doping concentration because of the downshift of the conduction band minimum(CBM).The niobium-doped TiO2 DSSCs with moderate loadings show enhanced performance comparing with their pure TiO2 counterparts.Optimally,the conversion efficiency of the Nb-3.5(Nb 3.5 mol%)DSSC is 4.99%.This is higher than that(4.39%)of pure TiO2 cells by 13.7%.This is due to the fact that the Nb-doped solar cells haveincreased the number of the photo-induced electrons because of their exposed(001)facets and higher specific surface area;and enhanced electrons collection and transport because of the downshifted CBM of the Nb-doped TiO2.However,heavy Nb doping results in the decrease of the performance of the niobium-doped cells due to the excessive defects within the Nb-TiO2 samples resulting in enhanced charge recombination at defects.Using three-dimensional anatase TiO2 microspheres as light scattering overlayer and commercial TiO2 nanocrystalline as connecting underlayer,novel double-layered TiO2 films were prepared by a doctor blade method for quantum dots sensitized solar cell(QDSSC)application.The Graphene quantum dots(GQDs)were introduced by dripping,and the CdS/CdSe quantum dots were deposited by continuous ion-layer adsorption(SILAR)method,respectively.CdS/CdSe quantum dots sensitized and GQDs/CdS/CdSe co-sensitized solar cells were fabricated,respectively,and the effects of GQDs and CdS quantum dots with different deposition cycles of on the microstructures and the photovoltaic performance of the double-layered TiO2 QDSSCs are investigated and discussed.The results revealed that the introduced GQDs and the CdS deposition cycle obviously influence the optical properties.The electron transfer and charge-recombination process is also affected by the CdS deposition cycle and the introduced GQDs.Optimally,the conversion efficiency of the TiO2/QGDs/CdS(4)/CdSe solar cell is 1.24% with a photocurrent density of 9.47mA/cm2.This is higher than those(0.59% and 6.22 mA/cm2,respectively)of the TiO2/CdS(4)/CdSe cell.This is due to the effective electrons transport and reduced charge recombination within the co-sensitized cell.