420 nm thick CH₃NH₃PbI_3-xBr_x capping layers for efficient TiO₂ nanorod array perovskite solar cells

The rutile TiO₂ nanorod arrays with 240 nm in length, 30 nm in diameter, and 420 μm^-2 in areal density were prepared by the hydrothermal method to replace the typical 200-300 nm thick mesoporous TiO₂ thin films in perovskite solar cells. The CH₃NH₃PbI_3-xBr_x capping layers with different thicknesses were obtained on the TiO₂ nanorod arrays using different concentration PbI₂· DMSO complex precursor solutions in DMF and the photovoltaic performances of the corresponding solar cells were compared. The perovskite solar cells based on 240 nm long TiO₂ nanorod arrays and 420 nm thick CH₃NH₃PbI_3-xBr_x capping layers showed the best photoelectric conversion efficiency (PCE) of 15.56% and the average PCE of 14.93±0.63% at the relative humidity of 50%-54% under the illumination of simulated AM 1.5 sunlight (100 mW· cm^-2).