Controlling the Film Properties of SnO2 in Perovskite Solar Cells using Scalable Spatial Atomic Layer Deposition

Nowadays, Atomic Layer Deposition (ALD) is routinely used to deposit tin oxide (SnO2) layers in perovskite solar cells (PSC’s). SnO2 is amongst others used as a buffer layer on the C60 layer to prevent it from sputtering damage of the subsequent Transparent Conductive Oxide (TCO) coating. In this contribution we investigate whether the film density of SnO2 layer deposited on the C60 layer by Spatial ALD (s-ALD) can improve the water barrier performance. During the manufacturing of a tandem PSC, tin oxide can protect the underlying perovskite from the water based PEDOT:PSS coating which is required for the narrow band gap perovskite coating on top. First, we systematically explore the s-ALD process parameters, as for example temperature, water dosage and process speed, and analyze their effect on film thickness and refractive index using spectroscopic ellipsometry. Higher refractive index values are generally associated with denser coatings and thus better moisture barriers. Second, 20 nm thick SnO2 layers are deposited directly on the C60 coating using the process parameters explored. Two types of perovskite (PSK) stacks consisting of a dual cation PSK-C60 surface and triple cation PSK-TEAClC60 surface are investigated. The barrier performance of SnO2 layers are analyzed by mimicking the PEDOT:PSS coating by a water based coating process using a spin coater. The 20 nm thick SnO2 layers deposited on the dual cation PSK-C60-SnO2 cells all survived the water exposure. However, some of the triple cation PSK-TEACl-C60- SnO2 cells clearly degrade upon water exposure.