The effect of solution process control on the formation of the α-FAPbI3 perovskite: FAPbI3 versus MAPbI3 solar cells

This study aims at the fabrication of hole-conductor-free perovskite solar cells by the sequential deposition method. To develop the cells, MAPbI(3) (CH3NH3PbI3) and FAPbI(3) (HC(NH2)(2)PbI3) perovskites were used as light-absorbing materials. It is difficult to achieve a black alpha-FAPbI(3) perovskite due to the unwanted yellow delta-FAPbI(3) phase that is usually first formed at a low temperature and then converted into a black alpha-FAPbI(3) perovskite at a high annealing temperature. A high annealing temperature can also lead to the uncontrollable degradation of the alpha-FAPbI(3) perovskite. Here, we report the effect of various temperatures of a dipping solution of formamidine iodide (FAI) in isopropanol on the formation of black alpha-FAPbI(3) perovskites from the initial stage. The effects of various annealing temperatures on the surface morphology and the optical properties of the perovskite layer are also studied. The optimum temperatures of the FAI solution and annealing for making an FAPbI(3) perovskite were 80 degrees C and 170 degrees C respectively. A stable black FAPbI(3) perovskite layer was formed in these optimum conditions. Moreover, the short-circuit current density and the efficiency of the fabricated FAPbI(3) and MAPbI(3) perovskite solar cells were approximately the same.