Fig. 1: Oxygen vacancies in TiO2 ETLs.
From: Metal chalcogenide electron extraction layers for nip-type tin-based perovskite solar cells
a Schematic diagram of the buried interface between the TiO2 ETL and Sn-based perovskite layer. Oxygen desorption from OVs in the TiO2 ETL accelerates the oxidation of Sn2+ to Sn4+ within the Sn-based perovskite. b EPR spectra of the TiO2 ETL, confirming the existence of OVs. c High-resolution XPS spectra in the O 1 s region of the TiO2 ETL, further supporting the existence of OVs. High-resolution XPS spectra of Sn-based perovskite films on (d) FTO and (e) FTO/TiO2 substrates after aging for 14 days, respectively. This distinct difference observed suggests that desorbed oxygen from TiO2 films leads to severe oxidation in Sn-based perovskites.
