Research Progress on Spiro-Type Small Molecule Hole Transport Materials in Perovskite Solar Cells

The performance of hole transport materials directly affects the transport of holes in perovskite solar cells and the recombination of electrons and holes. This, in turn, determines the performance improvement of the cells. The spiro-type structure has a unique orthogonal molecular conformation. This makes the molecules form good contact on the perovskite film easily. It also leads to uniform charge transport characteristics and a higher glass transition temperature. This material has been widely used as a highly efficient hole transport material skeleton unit in perovskite solar cells. This paper summarizes the research progress of spiro-type hole transport materials. The focus is mainly on the optimization of spiro-type small molecule hole transport material terminal functional groups and spiro-type core regulation. It summarizes the impact of molecular structure changes on material photophysics, electrochemistry, thermal stability, hole transport characteristics, and performance in perovskite solar cells. At the same time, this paper also predicts the development of this field. It looks at the development and research trend of high-performance spiral-type hole transport materials.