Effective Interfaces between Fullerene Derivatives and CH3NH3PbI3 to Improve Perovskite Solar Cell Performance

Inverted hybrid perovskite solar cells using fullerene derivatives as an electron transport layer show high energy photo conversion efficiency and improvements in stability. In practice, a wide variety of fullerene derivative functional groups have been proposed, but there is still no clear understanding of the influence of this structure on solar cell behavior. Using density functional theory calculations, we study the conditions that allow the transport of electrons without energetic barriers in the interface formed between the surfaces of CH3NH3PbI3 and the derivatives of fulleropyrrolidine and PCBM. Representative atomistic models of the interfaces are provided, and the self-consistent electronic structures obtained with hybrid functionals were analyzed. It is shown that only the perovskite surface terminated in a layer rich in methylammonium iodide offers electron transport without energy barriers for fullerene derivatives. Moreover, the lead iodide (PbI2)-terminated surface is not passivated with fullerene derivatives. The surface state disappears if the PbI2-terminated surface is treated with ammonium salts or zwitterionic compounds, such as methylammonium chloride and sulfamic acid. Therefore, these modified surfaces favor the performance of the solar cells if the interfaces remain aligned, without barriers, for the transport of electrons. Our study offers these interface models to contribute to the optimal design of perovskite solar cells.

Automated summary

In this study, density functional theory calculations were used to investigate the influence of fullerene derivatives as an electron transport layer in inverted hybrid perovskite solar cells. It was found that only the perovskite surface terminated in a layer rich in methylammonium iodide provides electron transport without energy barriers for fullerene derivatives, while the lead iodide (PbI2)-terminated surface is not passivated with fullerene derivatives. The surface state disappears if the PbI2-terminated surface is treated with ammonium salts or zwitterionic compounds. Thus, the optimal design of perovskite solar cells should consider the barrier-free electron transport between interfaces.