Optimization of a SnO2-Based Electron Transport Layer Using Zirconium Acetylacetonate for Efficient and Stable Perovskite Solar Cells

SnO2 is a promising material for use as an electron transfer layer (ETL) in perovskite photovoltaic devices due to its suitable energy level alignment with the perovskite, high electron mobility, excellent optical transmission, and low-temperature processability. The development of high-quality SnO2 ETLs with a large coverage and that are pinhole-free is crucial to enhancing the performance and stability of the perovskite solar cells (PSCs). In this work, zirconium acetylacetonate (ZrAcac) was introduced to form a double-layered ETL, in which an ideal cascade energy level alignment is obtained. The surface of the resulting ZrAcac/SnO2 (Zr-SnO2) layer is compact and smooth and had a high coverage of SnO2, which enhances the electron extractability, improves ion blocking, and reduces the charge accumulation at the interface. As a result, the fill factor (FF, 80.99%), power conversion efficiency (PCE, 22.44%), and stability of the Zr-SnO2 device have been significantly improved compared to PSCs with only a SnO2 ETL. In addition, the PCE of the Zr-SnO2 device is maintained at more than 80% of the initial efficiency after 500 h of continuous illumination.