A high-quality organolead trihalide perovskite film with large-sized crystalline grains and smooth surfaces is required to obtain efficient perovskite solar cells (PSCs). Herein, high-quality (FAPbI3)0.97(MAPbBr3)0.03 perovskite films were fabricated using trimesic acid (TMA) additives in a halide perovskite precursor solution to obtain efficient PSCs. The X-ray diffraction analysis and scanning electron microscopy of the films revealed that the TMA had a significant effect on the roughness of the films by acting as a surface link, thus reducing the surface defects and recombination at the grain boundaries. In addition, with the addition of the TMA additive, a smooth perovskite film with a flat surface and no pinholes was obtained. The perovskite film was used to fabricate a PSC device, and the device exhibited a high power conversion efficiency of 17.26%, which was higher than that of the control device (15.15%) under the same conditions. This study demonstrates a facile method to passivate defects on the perovskite layer via surface modification.

The electron transport layer (ETL) of organic–inorganic perovskite solar cells plays an important role in their power conversion efficiency (PCE). In this study, TiO2 hollow nanospheres with a diameter of 150 nm were prepared by a facile synthesis method. The synthesized TiO2 hollow nanospheres had a highly porous structure with a surface area of 85.23 m2 g−1, which is significantly higher than commercial TiO2 (P25) (54.32 m2 g−1), indicating that they can form an ideal mesoporous layer for Formamidinium iodide-based perovskite solar cells (PSCs). In addition, the nanospheres achieved a remarkable perovskite performance, and the average PCE increased from 12.87% to 14.27% with a short circuit current density of 22.36 mAcm−2, an open voltage of 0.95 V, and a fill factor of 0.65. The scanning electron microscopy images revealed that the enhanced PCE could be due to the improved carrier collection and transport properties of the nanosphere, which enabled efficient filtration of perovskite into the TiO2 mesoporous ETL. The TiO2 hollow nanospheres fabricated in this study show high potential as a high-quality ETL material for efficient (FAPbI3)0.97(MAPbBr3)0.03-based PSCs.

In the proposed method, we could complete the synthesis with only 3 h of thermal treatment, which is relatively fast in comparison to the previously reported procedure, without an expensive gascontrolled chamber system. The compound comprises Re2O3 and NiO3 powders that were mixed thoroughly in a stoichiometric ratio in a ball mill for 24 h and then dried in an oven at a 100 °C. The powder mixture was quickly calcined at various temperature for at least 3 h in an oxygen gas flow compared to conventional annealing method. After calcination at 1100 °C, the detected XRD peaks matched well with peaks of the standard ABO3 perovskite structure. Moreover, EDX and FT-IR spectral analysis results confirmed that the mixture had formed stoichiometry ReNiO3. All prepared samples comprised plate-like grains with a random orientation, and their average particle size was in the range of 1 to 3 μm calculated from FE-SEM images.

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