Application Of Polyoxometalates And Their Derivatives In Dye/Quantum Dot Sensitized Solar Cells

Energy problem has become one of the most concerned problems in the world today,and the effective way to solve the energy problem is to make full use of solar energy.Solar cells,the most direct way to use solar energy,can convert solar energy directly into electricity.The dye/quantum dot sensitized solar cell?DSSCS/QDSCS?has developed rapidly as a third generation low-cost and new material solar cell,and obtained great research progress.However,some problems still exist,which restricts the further improvement of efficiency of solar cells,such as the serious electron recombination in the devices;development of wide spectrum and pure inorganic photosensitizer;development of platinum-free counter electrode materials with high catalytic activity and so on.Polyoxometalate is a kind of inorganic molecular cluster composed of high yield elements.They have many excellent properties and functions,such as natural nanometer size,adjustable band gap energy,wide spectral absorption,strong electron acceptor ability,reversible multi-electron redox activity,etc.In addition,polyoxometalates are precursors to other excellent nanomaterials.In this article,we will focus on the excellent physical and chemical properties of polyoxometalates and apply them in DSSCS/QDSCS to further improve the efficiency and reduce the cost of the solar cells.1.CdSe quantum dot as photosensitizer of QDSCs is not very efficient because of the defects of absorption in visible area.For the first time,the wide spectrum and pure inorganic D-A type K₆H₄[a-SiW₉O₃₇Co₃?H₂O?₃]·17H₂O?SiW₉Co₃?was used in QDSCs as a collaborative cosensitizer with CdSe,which can compensate for the optical absorption defects of CdSe in the solar cells and increase utilization of sunlight.The experimental results show that SiW₉Co₃ can improve the photoelectric response of the QDSCs in the visible area.The optimized efficiency of QDSCs can reach 6.59%,which is 32.33%higher than that of the pure CdSe-sensitized solar cells?4.98%?.2.The Dawson type?NH₄?₈[P₂Mo₁₈^VIO₆₂](P₂Mo₁₈^VI)and its 2 electron reduction product?NH₄?₈[P₂Mo₂^VMo₁₆^VI](P₂Mo₂^VMo₁₆^VI)heteropoly blue were assembled into the photoanode of DSSCs by simple sol-gel method.After introducing P₂Mo₁₈^VI and P₂Mo₂^VMo₁₆^VI to DSSCs,the efficiency of the DSSCs are 7.17%and 6.75%,respectively,which are 24.48%and 17.19%higher than that without adding polyoxometalate.The experimental results show that the introduction of P₂Mo₁₈^VI and P₂Mo₂^VMo₁₆^VI into DSSCs can reduce the electron recombination and increase the lifetime of electrons in the device,thus further improving the efficiency of DSSCs.3.In QDSCs,serious electron recombination is an important reason that hinders the improvement of its efficiency.We propose a simple method to further reduce the electron recombination in the QDSCS,that is,by adding a layer?POM/TiO₂?₃ electronic interface layer between the mesoporous TiO₂ and the FTO conductive glass using the LbL method.By using strong electron acceptor ability of the polyoxometalate,it can suppress the recombination between conduction electrons of TiO₂ and ground state of quantum dot or electrolyte.We have studied the performance and mechanism of QDSCs in detail.The most important is that the energy conversion efficiency of QDSCs containing?POM2/TiO₂?₃electronic interface layer can reach 8.13%(J_s=23.08 mA·cm^-2,Voc=0.58,FF=0.62),which is 23.0%higher than that without?POM2/TiO₂?₃ electronic interface layer.This work provides a new idea for reducing the internal electron recombination in QDSCs.4.Polyoxometalates have a natural nanometer size and excellent water solubility,which will help them to form composite materials with other materials.Co₃O₄ and WC materials have attracted wide attention recently in photocatalysis and electrocatalytic,but they have less research in DSSCs,and each has its own advantages and disadvantages.We will combine their respective strengths,and the nanomaterial Co₃O₄-WC-CN/r GO has been prepared by the high temperature calcination of the Na₆H₂W₁₂O₄₀·H₂O embedded metal-organic framework.It shows high catalytic activity as the counter electrode in DSSCs,which is due to the excellent catalytic activity of Co₃O₄-WC and high conductivity of rGO.This work provides a new idea for the preparation of nanocomposites.5.Polyoxometalates?POMs?,as a kind of molecular inorganic semiconductors,have been widely used in the DSSCs to reduce the cost and improve the efficiency due to their excellent photosensitivity,redox,and catalytic properties.This chapter is on the basis of the research achievements of the scholars in DSSCs and our research accumulations both on POMs and DSSCs in recent years.We have summarized the following:the energy level regulation of POMs,the principle of POMs acted as the electron acceptors in DSSCs,the photosensitive properties of POMs in DSSCs,the redox and catalytic properties of POMs in DSSCs.More importantly,the structure-property relationship of POMs in DSSCs has been deeply explored,which may be the guide for us to directionally synthesize the POMs with better photoelectric properties for DSSCs.