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Mixed Sn/Pb perovskite solar cells offer a suitable alternative pathway to reduce lead toxicity and regulate optical band gap and therefore have significant potential for the development of clean and renewable energy technologies. In this study, the optical and electrical properties of CH 3 NH 3 Sn x Pb 1−x I 3 [0 ≤ x ≤ 1] solar cells under dark conditions were investigated. The compressive strain values of perovskite layers were measured and reported by analyzing the shift of their active Raman modes. Electrical characterizations under dark conditions showed that the values of the threshold voltage (V th ) and inverse saturation current (I 0 ) of the cells decrease and increase with increasing Sn concentration, respectively. Examination of the behavior of the space charge limited current (SCLC) of cells showed that the presence of Sn atoms increases the ability of the electrical carrier mobility (μ) of cells. Based on the results and calculations, the charge transport mechanism indices including the ideality factor (n), trap-filled limit voltage (V TFL ), trap-state density (n trap ), and the lifetime of minor carriers (τ n ) in each of the samples were characterized and reported.

Compositional engineering is one of the ways of controlling the phase structure and improving the stability of perovskite solar cells. This study is the investigation of how adding cesium (Cs) to formamidium lead iodide (FAPbI 3 ) perovskite affects the structure, morphology, performance and stability of hole-transport-free (HTF) mesoporous solar cells. It was shown that this addition leads to decrease in the lattice constant and the tolerance factor and causes perovskite band gaps to vary. The x-ray diffraction analysis also showed the removal of the non-photovoltaic perovskite phase and the conversion of the trigonal black phase to tetragonal structure. As 15% of Cs was added, the average efficiency of 7.41% and the highest efficiency of 11.78% were achieved for the HTF solar cells. Finally, FA 0.85 Cs 0.15 PbI 3 perovskite cells proved to be more stable than FAPbI 3 reference cells at 150 • C and the humidity of 90%.