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A uniform and compact hole blocking layer is necessary for a high performance perovskite solar cells, as it not only serves as an electron collector but also represses the electron recombination by blocking direct contact between the transparent conducting oxide and the perovskite layer. So far, highly performing perovskite solar cells have been achieved using a blocking layer that requires sintering at high temperatures (> 450 °C). In this study, reactive magnetron sputtering was used to synthesise crystalline anatase TiO2 thin film blocking layer at a moderate temperature (150 °C). The influence of block layer thickness on the photovoltaic performance is scrutinised. A high performance of 8.7% power conversion efficiency was obtained for perovskite solar cells with a 76 nm thick TiO2 blocking layer. This low temperature synthesis method will extend the choice of substrate to cheap and flexible polymer substrates. The surface plasma treatment prior to the blocking layer deposition was also found to affect the performance of the solar cells.

Oxygen plasma treatment of TiO2 films has been used to improve the efficiency of dye sensitized solar cells. Both a commercial TiO2 sample and a TiO2 thin film synthesized by a sol-gel technique were treated using a custom built inductively coupled plasma apparatus. X-ray photoelectron spectroscopy revealed that oxygen-plasma treatment increased the number of oxygen functional groups (hydroxyl groups) and introduced some Ti3 + species on the surface of TiO2. A sample solar cell with plasma treated TiO2 showed an overall solar-to-electricity conversion efficiency of 4.3%, about a 13% increase over untreated TiO2. The photon conversion efficiency for the plasma treated TiO2 was 34% higher than untreated TiO2. This enhanced cell-performance is partly due to increased dye adsorption from an increase in surface oxygen functional groups and also may be partly due to Ti3 + states on the surface of TiO2.