Predeposited Multifunctional Carbon Nanotube:SnO2 on the PbI2 Film for Efficient and 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 SnO 2 quantum dots‐modified single‐walled carbon nanotubes (CNT:SnO 2 ) on PbI 2 film to form perovskite/CNT:SnO 2 heterojunction in the top region within two‐step‐processed perovskite films. The CNT:SnO 2 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:SnO 2 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:SnO 2 heterojunction region, which further accelerate the charge separation and transport. In addition, the CNT:SnO 2 suppresses the migration of halogen anions in the perovskite film and improves the hydrophobicity of the perovskite film. Consequently, the PCE of CNT:SnO 2 ‐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 °C.