Very thin thermally stable TiO2 blocking layers with enhanced electron transfer for solar cells

Abstract Very thin TiO 2 blocking layers (BLs) are important components for achieving high solar power conversion efficiencies (PCEs) in the dye-sensitized solar cells, and particularly perovskite solar cells (PSCs). When reasonably thin, TiO 2 BLs prevent recombination of photogenerated charges at the conductive fluorine-doped tin oxide (FTO) glass substrate used in these devices. However, all previous attempts to generate efficient TiO 2 BLs have been hampered by an insufficient charge transfer rate at quasi-amorphous TiO 2 and very low thermal stability, leading to the loss of blocking properties after thermal calcination. In this work, we report the deposition of homogenous very thin (∼30 nm) TiO 2 BLs by combining advanced high impulse power magnetron sputtering (HiPIMS) and additional bipolar medium-frequency (MF) magnetron co-sputtering. The as-deposited TiO 2 films were shown to provide excellent blocking properties which were preserved even after thermal treatment at 450 °C. Moreover, TiO 2 BLs thermally treated at 450 °C show a well-developed rutile structure and 70 times higher photocurrents compared to the as-deposited layers. This work opens possibilities for the utilization of very thin TiO 2 layers in solar cell technologies providing a double mode of action: blocking functionality and efficient electron transport.