Novel Bilayer SnO2 Electron Transport Layers with Atomic Layer Deposition for High‐Performance α‐FAPbI3 Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) based on the SnO 2 electron transport layer (ETL) have achieved remarkable photovoltaic efficiency. However, the commercial SnO 2 ETLs show various shortcomings. The SnO 2 precursor is prone to agglomeration, resulting in poor morphology with numerous interface defects. Additionally, the open circuit voltage ( V oc ) would be constrained by the energy level mismatch between the SnO 2 and the perovskite. And, few studies designed SnO 2 ‐based ETLs to promote crystal growth of PbI 2 , a crucial prerequisite for obtaining high‐quality perovskite films via the two‐step method. Herein, we proposed a novel bilayer SnO 2 structure that combined the atomic layer deposition (ALD) and sol‐gel solution to well address the aforementioned issues. Due to the unique conformal effect of ALD‐SnO 2 , it can effectively modulate the roughness of FTO substrate, enhance the quality of ETL, and induce the growth of PbI 2 crystal phase to develop the crystallinity of perovskite layer. Furthermore, a created built‐in field of the bilayer SnO 2 can help to overcome the electron accumulation at the ETL/perovskite interface, leading to a higher V oc and fill factor. Consequently, the efficiency of PSCs with ionic liquid solvent increases from 22.09% to 23.86%, maintaining 85% initial efficiency in a 20% humidity N2 environment for 1300 h.