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.