Rationally reconstructing the surface microstructure of a chemical bath deposited electron transport layer for efficient and stable perovskite solar cells†

In perovskite solar cells (PSCs), chemical bath deposition (CBD) is promising as the core technique for preparing a commercial electron transport layer (ETL) because the film prepared by CBD exhibits excellent uniform and conformal coverage of the substrate. However, metal oxide (MO_x) films prepared through CBD often have defects on the surface like oxygen vacancies and hydroxyl that limit the PSCs efficiency and degrade the long-term stability. To address this obstacle to the scaled PSCs application, we here reconstructed the surface microstructure of a CBD tin dioxide (SnO₂) ETL by post-treatment with dilute H₂SO₄ solution to terminate the oxygen vacancies from the MO_x surface while effectively removing the hydroxyl groups. Concurrently, the potent oxidizing property of H₂SO₄ facilitates the transformation from Sn(II) to Sn(IV), thereby enhancing the alignment of the energy level between SnO₂ and the perovskite (PVK) layer within the ETL architecture. Moreover, the interaction between SO₄²⁻ and the perovskite precursor mitigates the difference in crystallization velocity between the perovskite upper and buried surfaces, enabling the formation of films with homogeneous phase distribution and good crystallization. Ultimately, with the assistance of this facile surface microstructure reconstruction, the power conversion efficiency (PCE) improves from 22.48% to 24.29%.