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

Perovskite solar cells (PSCs) based on the SnO2 electron transport layer (ETL) have achieved remarkable photovoltaic efficiency. However, the commercial SnO2 ETLs show various shortcomings. The SnO2 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 SnO2 and the perovskite. And, few studies designed SnO2-based ETLs to promote crystal growth of PbI2, a crucial prerequisite for obtaining high-quality perovskite films via the two-step method. Herein, we proposed a novel bilayer SnO2 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-SnO2, it can effectively modulate the roughness of FTO substrate, enhance the quality of ETL, and induce the growth of PbI2 crystal phase to develop the crystallinity of perovskite layer. Furthermore, a created built-in field of the bilayer SnO2 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.