The Construction And Research Of Dye-sensitized Solar Cells Based On Polyoxometalate For All-weather Energy Collection

Nowadays,energy is an important material foundation for the national development of economy.With the improvement of people’s quality of life,the increasing demand for energy of human beings has made the storage of non-renewable energy on the planet gradually in short supply.Therefore,the development and utilization of renewable energy is one of the topics we are currently focusing on.Solar energy,as a rich renewable energy,has great development value and utilization potential.Solar cell is an optical device which can transform solar energy into electric energy.Its research and application is one of the important ways to effectively utilize solar energy.Dye-sensitized solar cells（DSSCs）,as the third generation of new photovoltaic devices,have attracted the attention of scholars all over the world due to their simple manufacturing process,environmentally friendly and high efficiency.But now,in the process of DSSCs production and research,it is found that there are still some defects affecting the further improvement of battery efficiency.On the one hand,when the dye is illuminated,the photo generated electrons will return in the process of transferring between the photoanode and the electrolyte interface,and at the same time,they will react with the redox electric pair in the electrolyte,which makes it difficult to improve the photoelectric conversion efficiency（PCE）of DSSCs;on the other hand,the generating mechanism of DSSCs requires that it should be placed under the condition of sufficient illumination to generate enough electric energy,but it is difficult to generate electricity in rainy days or at night when the light intensity is relatively weak,which limits the application scope of DSSCs.Therefore,the key to solve the above problems is to restrain the complex reaction in the cells and construct an all-weather DSSCs,then we can further improve the PCE of DSSCs.As we all know,polyoxometalates（POMs）are a kind of environmental friendly molecular metal oxygen cluster composed of tungsten,molybdenum,vanadium and other metal atoms.As a multifunctional material with excellent stability and adjustable energy level,polyoxometalates can be used as electron acceptors,which can accelerate the electron transfer rate and inhibit the electron recombination.Therefore,polyoxometalates can be used in the photoanode of DSSCs to further improve the PCE of DSSCs.At the same time,when the light intensity is weakened,the all-weather solar cell can continue to generate electricity,but when the incident light intensity is reduced,the electron density in the cell will also be reduced,which increases the probability of electron recombination reactions.Therefore,wecan take the advantage of polyoxometalates which can accelerate the electron transmission rate,then mix it into the photoanode when building the all-weather DSSCs,which makes the effect increasing possible.Therefore,they play an important role in photovoltaic devices.The main contents of this paper are as follows:（1）We have added long-lasting phosphor（LPP）and H₃[α-PW₁₂O₄₀]·21H₂O(PW₁₂)into photo-anode of DSSCs through the grinding method for the first time.At the same time,compared with the traditional spin coating method,we only added 5% LPP into the photoanode to build a new all-weather DSSCs.As an optical energy storage material,LPP can store the light energy that can not be absorbed by photoanode and N719（dye）under the condition of illumination.Once the light intensity is weakened or dark,LPP can release fluorescence,and then N719 can continue to absorb the light energy to generate photoelectric current.However,the fluorescence produced by LPP is too weak compared with sunlight,so the probability of electron recombination reactions between photoanode and electrolyte interface will be greatly increased,so 5%PW₁₂ is introduced to reduce electron reflux.The experimental results show that the PCE of DSSCs is 6.9%（the efficiency of DSSCs assembled by photoanode of P25 is 5.8%）and the maximum output power（Pmax）is 79.8μW·cm-2 under dark conditions.This strategy provides a new method for building a new all-weather DSSCs which is easy to prepare and efficient.（2）Because of its excellent electron transport and catalytic properties,the sandwich polyoxometalate can be used as the first choice to improve the efficiency of DSSCs.The intramolecular charge transfer mechanism of K₁₅{K₃[(A-α-PW₉O₃₄)₂Fe₂（C₂O₄）₂]}29H2O was studied.Meanwhile,LUMO energy level（-0.06 V）and band gap（2.8 V）of the sandwich polyoxometalates were determined by solid-state UV diffuse reflectance and cyclic voltammetry test.Because its LUMO is lower than titanium dioxide’s conduction band（CB）,the photo generated electrons on titanium dioxide can be transferred to the POM,and then to the external circuit,at the same time,it can inhibit the electron reflux and improve the PCE of DSSCs.We used the sol-gel method to incorporate sandwich polyoxometalate（5%）into the DSSCs anode.By electrochemical testing,the efficiency of DSSCs added to the POM reached 6.33%,which was 20% higher than that of the pure P25 anode DSSCs（5.52%）,which further proved that the POM had the function of accelerating the electron transmission rate and reducing the electron recombination reactions,thus increasing the PCE of DSSCs.This work also provides a new idea for the application of functional sandwiched polyoxometalates in photoelectric conversion,and widens the development space of dye-sensitized solar cells.