Investigation Of Surface States Based On TiO₂ Hierarchical Microspheres

Due to the good chemical stability,suitable band structure,high surface area,excellent photoelectric properties,TiO₂ nanomaterials has become one of the promising direction for many researchers,and it have been widely used in the field of functional materials,catalyst,sensors and solar cells.The TiO₂ microspheres composed of TiO₂ nanoparticles not only possessed a large specific surface area,but also own a higher light scatting property.In recent years,the TiO₂ microspheres have been widely used in various types of optoelectronic devices,such as in the perovskite solar cells,dye-sensitized solar cells.On the other hand,In the process of solar cells,there are many interfacial charge transfer and phase transfer process,and the energy loss of each interface has a great influence on the photoelectric conversion efficiency.However,the high specific surface area of TiO₂ microspheres inevitably leads to a large number of surface states in the mid-gap region,which would influence the electron transport in TiO₂ network directly.The surface states of TiO₂ microspheres are still to be investigated in details.The main work of this paper is carried out from the experimental and mechanism.The surface states and electron transport process in this paper was analyzed by cyclic voltammetry,electrochemical impedance spectroscopy,intensity modulated photocurrent/photovoltage spectrum,open circuit photovoltage decay method and charge extraction in detail.By studying the surface states,band edge and the electron transfer kinetics,we have found that the surface energy distribution of TiO₂ microspheres is shallower than TiO₂ particles,which leads to a higher electron collection efficiency in the TiO₂ microspheres film.Then,the microstructure of TiO₂ microspheres?porosity,diameter?has been improved from the aspects of surface states and electron transfer kinetics.At last,the synthesis conditions of TiO₂ microspheres were also optimized by the results of surface states and the density of states.This work explains the excellent performance of the TiO₂ microspheres from the aspects of surface states,and exhibits the detail working mechanism of surface states to electron transfer kinetics.This paper provided a gist for high efficiency DSSCs research.It laid the foundation for prediction and enhances the performance of the DSSCs,and provide significant scientific contributions to the further understanding of the detailed working mechanism of DSSCs.