ALD-grown tin oxide as an electron selective layer for perovskite/silicon tandem cells

This work presents a comparative study between tin(IV) oxide (SnO2) thin films deposited by spin coating or Atomic Layer Deposition (ALD) to be used as an electron selective layer (ESL) in perovskite/silicon tandem solar cells. This study is motivated by the usually lower performances of ESL made of ALD-grown SnO2 compared to ones made via solution-based processes. Chemical, electrical, optical and topographical properties of each type of film were investigated. In an attempt to link thin film properties to device characteristics, single-junction perovskite solar cells and perovskite/silicon tandem solar cells were fabricated. Despite the high-quality electronic and optical properties of ALD-grown SnO2, perovskite-based solar cells employing such film showed limited performances. Characterization of perovskite films properties grown on both type of SnO2 did not rise significant differences and tends to indicate some hindering factors at the ALD-grown SnO2/perovskite interface. Kelvin force probe microscopy characterisation unveiled a larger workfunction for ALD-grown SnO2, which could create a potential barrier for electron extraction from the perovskite.