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

Abstract

Very thin TiO2 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, TiO2 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 TiO2 BLs have been hampered by an insufficient charge transfer rate at quasi-amorphous TiO2 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 (∼30nm) TiO2 BLs by combining advanced high impulse power magnetron sputtering (HiPIMS) and additional bipolar medium-frequency (MF) magnetron co-sputtering. The as-deposited TiO2 films were shown to provide excellent blocking properties which were preserved even after thermal treatment at 450°C. Moreover, TiO2 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 TiO2 layers in solar cell technologies providing a double mode of action: blocking functionality and efficient electron transport.