Metal-organic Framework Thin Films And Derived Materials For Solar Energy Conversion

Metal-organic framework materials are a class of porous polymer materials that are coordinated by metal and organic ligands.They have advantages in material sources,porous structures,and simple preparation.Metal-organic frameworks have been widely used in gas adsorption separation,battery,supercapacitor,catalysis and other fields in recent years.The unique structure and morphology of metal-organic frameworks allow them to serve as precursors for the preparation of hybrid nanostructured materials.The preparation of novel metal-organic framework films enables the use of metal-organic framework materials for solar energy conversion.Due to this series of excellent properties,metal-organic framework materials attracted the attention of scientists.In this paper,two kinds of organic ligands with different functions were designed and synthesized.H₂DAP molecule with porphyrin-like structure and mononuclear ruthenium organic ligands were used to prepare metal-organic framework films by liquid phase epitaxy method.The applications of metal-organic framework films in solar energy conversion were studied as light-absorbing materials and photoelectrocatalytic materials,respectively.Finally,the application of metal-organic framework derived material in dye-sensitized batteries was studied.First,H₂DAP metal-organic framework films are used as light-absorbing materials in solid-state thin film solar cells.The conditions for the preparation of metal-organic framework films are optimized,and highly ordered metal-organic framework films are prepared under moderate humidity.Different thicknesses of the metal-organic framework films were obtained by depositing different times,and the highest photoelectric conversion efficiency was obtained when five layers were deposited.Using P3HT as a hole transport material for solar cells,the P3HT film not only accelerates the hole derivation rate,but also covers defects of the metal-organic framework film and increases the photocurrent.The last achieved efficiency is 0.065%.Second,metal-organic framework thin films based on mononuclear ruthenium organic ligands are used in photoelectrocatalytic water oxidation.Using the characteristics of epitaxial growth of metal-organic framework thin film materials,molecular catalyst materials were modified on BiVO₄.Because of its highly ordered flaky skeleton structure,the contact area with water is increased,so that the reactive sites are increased,and the efficiency of the photoelectric water oxidation of the BiVO₄ electrode is significantly improved.In addition,the loading of the catalyst can be adjusted by changing the number of depositions of the metal-organic framework material.The results show that the novel method for loading molecular catalysts developed in this work has a good universality,and it is easy to form heterostructures with other materials using epitaxial growth method.Finally,metal-organic framework derived materials are prepared into thin films for use in dye sensitized solar cells.The ZIF-67 is carbonized in a hydrogen atmosphere to form a structure in which carbon nanotubes encapsulate cobalt nanoparticles.The use of metal-organic framework derived carbon counter electrode material has the advantages of low preparation cost and good catalytic effect.The cobalt particles coated by carbon nanotubes greatly increase the reactive sites of the reaction,and increase the ability of electrocatalytic reduction of I₃^-,thereby improving the photoelectric conversion efficiency of the dye-sensitized solar cell.Compared to the DSSC based on platinum counter electrode,photoelectric conversion efficiency was improved by 9%.