Efficient methylammonium lead trihalide perovskite solar cells with chloroformamidinium chloride (Cl-FACl) as an additive

Mixed halide perovskite (MAPbI_3-xCl_x) solar cells have been widely researched because of their excellent photoelectronic properties. However, Cl doping is difficult to obtain due to the low formation energy and low boiling point of MAPbCl₃ which can decompose into PbCl₂ and MACl. MACl can leave the perovskite film during the annealing process leading to the loss of Cl and undesirable pinholes or cracks. Here, we present the chloroformamidinium chloride (Cl-FACl) as a "stabilizer" to stabilize Cl ions and thus restrain the removal of Cl avoiding the undesirable defects. With the introduction of Cl-FACl, improvement of film quality and reduction of defects result in a longer TRPL decay time and thus more stable devices. High-efficiency methylammonium lead trihalide (MAPbI_3-xCl_x) perovskite solar cells with an efficiency up to 20.36% have been achieved with negligible hysteresis.