Effect of Residual Chloride in FAPbI₃ Film on Phase Stability and Photovoltaic Performance of Perovskite Solar Cell

The chloride ion in additive is found to have beneficial effect on enhancing photovoltaic performance due to the grain growth of FAPbI₃ perovskite. However, we found that the residual Cl incorporated in crystal lattice can aggravate the crystal phase and device stability. Thus, it is necessary to find an effective way to remove chloride ion from the perovskite film without sacrificing the photovoltaic performance. Here, we report a methodology to improve the stability of perovskite solar cell via elimination of the residual chloride ion. The extended X-ray absorption microstructure (EXAFS) combined with X-ray diffraction (XRD) reveal that the lattice distortion of PbI₆ octahedra is reduced due to the increased (Pb-I) bond distance after removal of chloride ion. The absence of chloride ion, confirmed by X-ray photoelectron spectroscopy (XPS), improves charge carrier lifetime, leading to higher power conversion efficiency (PCE) from 21.57 % for the perovskite film with residual chloride ion to 22.76%, mainly due to the enhancement of open-circuit voltage from 1.129 V to 1.168 V. Long-term stability test for over 1000 h under relative humidity of about 45% shows clearly that the device employing the chloride-removed perovskite film is much less degraded than the control one with perovskite film having residual chloride.