Scalable open-air deposition of compact ETL TiOx on perovskite for fullerene-free solar cells

Abstract

We report a scalable, low-temperature TiO_x electron transport layer (ETL) produced directly on top of perovskite in an inverted architecture device by an open-air chemical vapor deposition (OA-CVD) process. The OA-CVD pyrolysis of a titanium ethoxide precursor forms a fully inorganic, conformal, and compact TiO_x film. The resultant film is mechanically robust and exhibits a fracture toughness 30-fold higher than commonly used fullerene-based ETL films. The TiO_x is an effective barrier layer against environmental degradation—unencapsulated devices with the TiO_x ETL retain 60% of their initial efficiency after 1000 hours in ambient aging conditions—compared to devices with a fullerene ETL which were inoperable after 144 hours. Inverted architecture devices with an optimized TiO_x ETL thickness of 70 nm exhibited high open-circuit voltages of 1.08 V. We comment on the photocatalytic properties of TiO_x and the influence of an amorphous film on maximum power point stability.