Application Of CeO₂ Based Upconversion Hollow Structured Material In The Photoanode Of Dye-sensitized Solar Cells

Energy is necessary for human society survival and development,energy is also the foundation of the national economy and social development.As the fossil energy depletion and global awareness of the "greenhouse effect",the development and utilization of clean and renewable energy is becoming a theme of present and future world energy technology development.Photovoltaic technology can transfer solar energy directly into electricity,which is clean and renewable,and since decades ago has been attracted great attention,and fast developed.As the cost reduction of photovoltaic power generation and the increasing demand for clean energy,solar energy products are gradually come into our daily lives.As a new type of clean and low cost solar photovoltaic,dye-sensitized solar cells mimics photosynthesis mechanism are receiving more and more attention worldwide.Photoanode is the core component of dye-sensitized solar cells,and also key to the efficiency of the solar cell.The shortcomings of conventional P25 photoanode is either less light scattering due to small size of P25 particles,or solar light absorption spectrum limited to ultraviolet region.In recent years,various methods for photoanode modification,optimization has been developed,we mainly studies the Ceria?CeO₂?-based materials for bilayer structured photoanode.Based on the assumption of light scattering effect and upconversion effect,we study the synthesis and performance of hollow-structured CeO₂@TiO₂ and Er,Yb-CeP2 for dye sensitized solar cells.Because of its special morphology and particle size,the light scattering was enhanced,and doping Er3+/Yb3+ into CeO₂,forming materials with upconversion properties,enable the photoanode absorb infrared light convert to visible light,expanded anode light spectral response range,thus improve the photoelectric conversion efficiency of the solar cell.This paper focused on application of CeO₂-based hollow-structured core-shell CeO₂@TiO₂ and upconversion CeO₂:Er3+/Yb3+ materials as photoanode materials for DSSC,which was shown as follows:?1?CeO₂@TiO₂ hollow-structured composite material was synthesized as follows:first,CeO₂ was coated on the carbon-sphere which served as template to get C@CeO₂ by hydrothermal method.Then,TiO₂ shell was coated again to form C@CeO₂@TiO₂ by sol-gel method under a water-bath reflux condition.Finally,carbon-sphere template was removed by calcination to form the target product CeO₂@TiO₂ with core-shell hollow structure.The morphology,valence state,and crystal structure of the obtained samples were characterized through a series of instruments such as TEM,SEM,XRD,EDS and UV-Vis.The obtained CeO₂@TiO₂ was coated on to P25 photoanode to form a bilayer-structured thin film photoanode,then the assembled DSSC went through a series of solar performance test.The results shown that hollow-structured CeO₂@TiO₂ thin film has both bigger size and larger surface area which simultaneously enhance the dye-adsorption and light scattering.Thus efficiency of DSSCs was improved.Furthermore,through Electrochemical Impedance Spectroscopy,we found that electrons in the CeO₂ film behaves both longer life-time and longer diffusion length,which promotes the collection of electrons,results in the increase of photoelectric conversion efficiency to 7.9%,far better than the ho llow-structured TiO₂ thin film material.This study proves the CeO₂@TiO₂ hollow-structured composite material would serve as a superior candidate material for application in thin film photoanode of DSSCs.?2?Er,Yb-CeO₂ ho llow-structured composite material was synthesized as follows:first,CeO₂ was coated on the carbon-sphere which served as template and doped Er3+/Yb3+ to get C@ Er,Yb-CeO₂ by hydrothermal method.Then,carbon-sphere template was removed by calcination to form the target hollow-structured Er,Yb-CeO₂.The crystal structure,morphology,and valence state of the obtained samples were characterized through a series of instruments such as SEM,TEM,XRD,EDS and UV-Vis.Both the undoped ho llow-structured CeO₂ and doped upconversion CeO₂:Er3+/Yb34+ was coated on to P25 photoanode to form a bilayer-structured thin film photoande,separately,results in an efficiency of 6.4%,and 7.0%,respectively.Which far better than pure P25 photoanode without upconversion materials.To explain,at one hand,hollow-structured undoped CeO₂ and Er,Yb-CeO₂ thin film has both special mrphology and larger surface area which simultaneously enhance the light scattering and dye adsorption;at another hand,upconversion materials transform infrared light of solar spectrum into visible light and expanding spectral response range.It is because of the upconversion and scattering effect,the photoelectric conversion efficiency of dye-sensitised cells signifcantly enhanced.