Hierarchical TiO2 microspheres: synthesis, structural control and their applications in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs), as a type of promising energy conversion device, have received much attention in the past two decades due to their high efficiency and low cost. In order to achieve higher energy conversion efficiency, different TiO2 structures have been employed to fulfill the requirements of large surface area, light scattering capability and effective electron collection. In recent years, TiO2 hierarchical microspheres (HMSs) emerged as a class of robust photoanode materials to integrate the above-mentioned qualities, taking advantage of their unique structures. This review summarises the vast array of methods for the fabrication and structural control of the TiO2 HMSs. Subsequently, it focuses on illustrating the structural advantages of the HMSs, such as high surface area, submicron-sized diameter and interconnected primary building blocks over their performances when used in DSSCs. Finally, in the perspective, we intensively discuss the reasons preventing the HMS based DSSC from making striking improvements in power conversion efficiency. Moreover, the further optimization of the HMSs and their potential applications in other solar energy conversion devices are also discussed.