a Ambient stability of the control perovskite film (left) and target perovskite film (right) based on the evolution of the XRD patterns of the perovskite films stored in an ambient environment for various times. b The average relative humidity during the aging process in Lausanne, Switzerland. c Maximum power point tracking measured with the unencapsulated device under full solar illumination (AM 1.5 G, 100 mW cm−2 in N2, 25 °C). d Thermal stability of perovskite devices at an elevated temperature of 85 °C. e Assessment of lead leakage upon immersing solar cells into water. The PCE refers to the steady-state efficiency. The concentration of lead in water was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) measurement.