Low-Temperature Processed Nanostructured Rutile TiO2 Array Films for Perovskite Solar Cells With High Efficiency and Stability

The rutile TiO2 array (RTA) films consisting of vertically oriented nanoneedles and/or nanosheets are grown on a fluorine-doped tin oxide (FTO) glass substrate via a chemical bath deposition (CBD) process at 70 degrees C, and are utilized as electron transport layer (ETL) for CH3NH3PbI3-based perovskite solar cells (PSCs). The morphology and microstructure of the RTA films can be tuned by varying the CBD time. A mixed nanoneedles/nanosheets array film (similar to 250 nm thickness) derived from 60 min CBD process achieve a power conversion efficiency (PCE) up to 15.4% with reduced hysteresis, improved reproducibility, and stability as compared to those PSCs based on traditional mesoscopic-TiO2 or planar-TiO2 ETLs, which is due to the lower charge recombination, more efficient hole-blocking, and electron transport. After aging and storage in the dark, the optimal PSC exhibits a slightly improved PCE (16.3%), which is the highest one among those CH3NH3PbI3-based PSCs fabricated with low-temperature processed RTAs reported previously. This work is the first example of vertically oriented nanosheets and/or nanoneedles RTA film grown on a conductive glass to serve as ETL of PSC, and the low-temperature procedure of the RTA film paves a promising low-cost way for fabricating large-scale PSCs.