Oxidation, reduction, and inert gases plasma-modified defects in TiO2 as electron transport layer for planar perovskite solar cells

Abstract The bulk defects in the electron transport layers (ETLs) and the interface defects between the ETLs and the perovskite film are detrimental for charge transfer and transport from the perovskite film to the ETLs, which degrade the performance of the planar heterojunction perovskite solar cells (PSCs). Here, low temperature plasma technique with a few types of atmospheres including representative oxidation, reduction, and inert gases is proposed to modify the bulk and surface defects of TiO 2 films. TiO 2 film treated by CO 2 plasma demonstrates a more low-density of defect state in both of surface and bulk than the as-fabricated one. Consequently, the efficiency of PSC is significantly improved from 16.47% of the PSC with the as-fabricated ETL to 18.10% of the PSC with the treated ETL. However, the He and H 2 plasma treatments cause the increase in the oxygen-related defects on the surface of TiO 2 film or/and in the TiO 2 bulk. As a result, the He and H 2 plasma-treated ETLs-based PSCs exhibit poor performance. This study highlights that, to tailor metal oxide ETLs for highly efficient PSCs, the plasma technique by the PECVD approach with suitable gas source should be well considered.