Application Of LiNbO₃ Upconversion Luminescent Materials In Dye-sensitized Solar Cells

Since 21th century,the main task of mankind is to find other renewable energy sources because the world's conventional energy sources will exhausted in next few decades.Solar energy,which is clean,infinite,free and extensive,could be converted into electricity by the solar cell.Due to its low price,clean and easy to produce,many reacheres facus on the dye-sensitized solar cell and improves continuously its performance from 1991.However,dye-sensitized solar cell only absorbs sunlight in the visible range of 300-800nm.The infrared light,which accounts for about 43%of sunlight,has been wasted in the form of heat energy.In order to effectively utilize sunlight,the rare earth upconversion luminescent materials are used in the dye-sensitized solar cell,which could convert the infrared light into visible light absorbed by the dye and overcome the defects of the dye-sensitized solar cell.The nano-sized LiNbO₃:Yb³⁺/Er³⁺upconversion material had been synthesized via hydrothermal method,in which LiNbO₃ is used as host material and rare earth ions Yb³⁺and Er³⁺are the luminescence ions.The LiNbO₃:Yb³⁺/Er³⁺nanoparticles exhibite the cube structure and gradually are grown with the increasing reaction time.After 72 hours,the pure phase LiNbO₃:Yb³⁺/Er³⁺is successfully obtained.After calcining at the high temperature,the LiNbO₃:Yb³⁺/Er³⁺particles are agglomerated.It has been found that calcined LiNbO₃:Yb³⁺/Er³⁺particles could the green and red upconversion emissions under980 nm lasers excitation,but there are no upconversion emissions obtained in the uncalcined samples.In order to synthesize the LiNbO₃:Yb³⁺/Er³⁺@SiO₂ core-shell particles,the surface of LiNbO₃:Yb³⁺/Er³⁺nanoparticles are coated with a layer of SiO₂.The as-prepared LiNbO₃:Yb³⁺/Er³⁺@SiO₂ core-shell particles still maintain the cube structure,and the SiO₂layer is around 15 nm in thickness.Through the fluorescence test,the upconversion performances of LiNbO₃:Yb³⁺/Er³⁺@SiO₂ core-shell particles are better than those of LiNbO₃:Yb³⁺/Er³⁺particles.A series of mass ratio of LiNbO₃:Yb³⁺/Er³⁺@SiO₂ powder is mixed in pure TiO₂ paste to assemble the a dye-sensitized solar cell.When the mass ratio of LiNbO₃:Yb³⁺/Er³⁺@SiO₂ powder is 16 wt.%,the efficientcy of dye-sensitized solar cell is up to 6.81%,which is 16%higher than that of the cell assembled with pure TiO₂.The double-shell LiNbO₃:Yb³⁺/Er³⁺@SiO₂@TiO₂ is consist of the surface of LiNbO₃:Yb³⁺/Er³⁺@SiO₂ core-shell coated by a layer of TiO₂ by using different amounts of titanium tetraisopropanolate.The TiO₂ particles and LiNbO₃:Yb³⁺/Er³⁺@SiO₂@TiO₂particles are coexisted in double-shell LiNbO₃:Yb³⁺/Er³⁺@SiO₂@TiO₂ because of the excess titanium tetraisopropanolate.The scattering layer of the photoelectrode is prepared with different double-shell LiNbO₃:Yb³⁺/Er³⁺@SiO₂@TiO₂.When the dosage of titanium tetraisopropanolate is 1.6 mL,the assembled dye-sensitized solar cell exhibits the highest efficiency of 8.63%,which is 14.6%higher than that of dye-sensitized solar cell with titanium tetraisopropanolate of 0.4 mL,and is also 8.3%higher than that of dye-sensitized solar cell with pure TiO₂.