Predeposited Multifunctional Carbon Nanotube:SnO2 on the PbI2 Film for Efficient an d Stable Two-Step-Processed Perovskite Solar Cells

Compared with one-step-processed perovskite solar cells (PSCs), there are few reports on improving the power conversion efficiency (PCE) of two-step-processed PSCs by reducing the nonradiative recombination caused by defects through interface engineering. Herein, a new strategy is proposed, that is, by predepositing multifunctional inorganic SnO2 quantum dots-modified single-walled carbon nanotubes (CNT:SnO2) on PbI2 film to form perovskite/CNT: SnO2 heterojunction in the top region within two-step-processed perovskite films. The CNT:SnO2 not only promotes the crystallization of perovskite and improves the quality of perovskite films, but also passivates perovskite defects, and effectively suppresses nonradiative recombination. Meanwhile, CNT:SnO2 leads to the change of the Fermi energy level of the perovskite film, which optimizes the interface energy band arrangement and leads to an additional potential in the perovskite/CNT:SnO2 heterojunction region, which further accelerate the charge separation and transport. In addition, the CNT:SnO2 suppresses the migration of halogen anions in the perovskite film and improves the hydrophobicity of the perovskite film. Consequently, the PCE of CNT:SnO2-based PSCs is significantly increased from 20.10% to 22.25%. They also exhibit improved stability; for instance, the unencapsulated cell maintains 75% of its original PCE even after 600 h of thermal aging at 85 degrees C.