Application Of Upconversion Luminescence In Dye-sensitized Solar Cells

Mankind begins to realize the fact that extreme growth of energy demand in the world is one of the most important problems which needs to be solved.Exploitation and utilization of renewable energy has recently been proposed as a main solution.Solar energy as a free, clean and abundant source of energy that can be directly converted into electricity in photovoltaic cells has to be utilized widely. Since the first report of dye-sensitized solar cells（DSSCs） in 1991,DSSCs have been considered as one of the promising candidates for new generation solar cells due to their relatively high conversion efficiency and low cost.In the last decade, tremendous progress has been made in improving the performance of DSSCs.However, the infrared and near-infrared spectral parts of sunlight, which comprise almost half of the energy of the sun’s radiation, have not been utilized.In order to achieve a higher DSSC efficiency,one feasible way is to expand the light absorption in visible region to NIR spectral region.Up-converting phosphor, which can transform lower energy photons（>900 nm）into high-energy visible photons（<750 nm） that are absorbable by the dye.Rare-earth ions(Re³⁺) doped β-Na YF₄ phosphors have been reported to be the most efficient NIR-to-vis UC host materials.Luminescent materials of different sizes and shapes had been fabricated via hydrothermal method and solvothermal method with different experimental conditions.The as-synthesized samples were characterized by XRD, SEM, TEM and PL.Up-conversion and down-conversion luminescent materials were added to the Ti O2 photoanodes of dye-sensitized solar cells to improve the efficiency of the solar cells.The main contents are as follow:（1）A novel and facile oxalate-assisted hydrothermal approach has been developed for the shape and size-selective synthesis of Na YF₄:Yb³⁺,Er³⁺. The shape of six-party rod had the highest luminescence property and photoelectric efficiency of 7.3137%,which is a noticeable improvement of 11.78% compared to the cell without the luminescent materials.（2）A novel and facile citrate-assisted hydrothermal approach has been developed for the shape and size-selective synthesis of Na YF₄:Yb³⁺,Er³⁺.Na YF₄:Yb³⁺,Er³⁺prepared with 2 : 1 molar ratio of Cit3-–Re³⁺at p H4 was selected to prepare the Na YF₄:Yb³⁺,Er³⁺ @Si O2 with single layer core-shell structure and Na YF₄:Yb³⁺,Er³⁺@Si O2@Ti O2 with double layer core-shell structure. The efficiency of7.5660%, 6.9188%, 6.1111% and 6.5459% were obtained by testing Na YF₄:Yb³⁺,Er³⁺@Si O2@Ti O2,Na YF₄:Yb³⁺,Er³⁺@Si O2,Na YF₄:Yb³⁺,Er³⁺ doping and undoping dye-sensitized solar cells.（3） To achieve efficient dual-mode luminescence in a well-defined core-shell nanostructure,Na YF₄:Yb³⁺,Er³⁺@Na YF₄:Eu³⁺ nanoparticles were successfully synthesized through a solvothermal strategy.The performance of dye-sensitized solar cell was significantly enhanced, resulting in an efficiency of 7.3730%, which is a noticeable improvement of 37.33% compared to the cell with Na YF₄:Yb³⁺,Er³⁺ doping,12.64% compared to the cell without the luminescent materials.