Characterizations of tin oxide thin films prepared by different methods for perovskite solar cell applications

Tin oxide thin is a promising electron transport layer (ETL) for perovskite solar cells due to its excellent electronic properties and high thermal stability of SnO2. In addition, unlike TiO2 and ZnO, SnO2 does not have high photocatalytic activity and therefore would improve device stability under illumination compared to devices with titania or ZnO ETLs, and it can be deposited at low temperatures which makes it compatible with flexible devices. However, surface roughness, conformal coating, surface defects of SnO2, as well as its energy level alignment with the perovskite layer, affect the performance and stability of perovskite solar cells. In this study, we utilized ALD, sol-gel deposition and nanoparticle spin coating method to prepare SnO2 thin films and apply them as ETLs for planar perovskite solar cells. The obtained results indicate that the method of preparation of SnO2 significantly affects the solar cell performance. To improve the device performance, we investigated SnO2 bilayers to attempt to combine advantages of individual coating approaches. For an optimized order of layers to achieve efficient charge extraction across the interface, improved performance can be obtained compared to single layer SnO2 electron transport layers. Reasons for the performance improvement are discussed.