Atomic-layer-deposited ultra-thin VOx film as a hole transport layer for perovskite solar cells

In this study, we report the use of ultra-thin VOx film deposited by low temperature (50 degrees C) atomic layer deposition (ALD) as a hole transport layer (HTL) for perovskite solar cells (PSCs). High efficient PSCs with a power conversion efficiency of 11.53% are achieved with a similar to 1 nm VOx layer. It is found that compared to the pristine ALD-VOx films, UV post-treatment significantly enhances the hole transportation ability of the VOx films To understand the hole transporting mechanism in the VOx films, the ALD-VOx films grown on fluorine-doped tin oxide are investigated by photoelectron spectroscopy. Our investigation confirms that the defect states below the Fermi level of the VOx facilitate hole extractions, and that a greater V5+ oxidation state ratio is found in the UV-treated VOx films This work shows the potential of using low temperature inorganic VOx films as the HTLs for the application of flexible and large-area PSCs.