Short-length and high-density TiO₂ nanorod arrays for the efficient charge separation interface in perovskite solar cells

The TiO₂ nanorod arrays with the length of 70 nm, the diameter of 20 nm, and the areal density of 1000 µm⁻² were firstly prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 60 min. Over-500 nm-thickness CH₃NH₃PbI_3−xBr_x absorber layers were successfully obtained by sequential deposition routes using 1.7 M PbI₂·DMSO complex precursor solution and 0.465 M isopropanol solution of the methylammonium halide mixture with the molar ratio of CH₃NH₃I/CH₃NH₃Br=85/15. The perovskite solar cells based on the TiO₂ nanorod array and 560 nm-thickness CH₃NH₃PbI_3−xBr_x absorber layer exhibited the best photoelectric conversion efficiency (PCE) of 15.93%, while the corresponding planar perovskite solar cells without the TiO₂ nanorod array and with 530 nm-thickness CH₃NH₃PbI_3−xBr_x absorber layer gave the best PCE of 12.82% at the relative humidity of 50–54%. - Graphical abstract: The TiO₂ nanorod arrays with the length of 70 nm, the diameter of 20 nm, and the areal density of 1000 µm⁻² were prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 60 min. The optimal annealing temperature of TiO₂ nanorod arrays was 450 °C. The perovskite solar cells based on the TiO₂ nanorod array and 560 nm-thickness CH₃NH₃PbI_3−xBr_x absorber layer exhibited the best photoelectric conversion efficiency (PCE) of 15.93% and the average PCE of 13.41±2.52%, while the corresponding planar perovskite solar cells without the TiO₂ nanorod array and with 530 nm-thickness CH₃NH₃PbI_3−xBr_x absorber layer gave the best PCE of 12.82% and the average PCE of 10.54±2.28% at the relative humidity of 50–54%. - Highlights: • Preparation of TiO₂ nanorod array with length of 70 nm and density of 1000 µm⁻². • Influence of annealing temperatures on the -OH content of TiO₂ nanorod arrays. • Preparation of over-500 nm-thickness CH₃NH₃PbI_3−xBr_x absorber layer. • Combination of short-length TiO₂ nanorod array and high-thickness perovskite layer. • The best and average PCE with TiO₂ array of 15.93% and 13.41±2.52% at 50–54% RH.