Passivating Surface Iodide Defects Slows the CsPbI3 Phase Transformation

Efforts to improve halide perovskite solar cell stability require detailed understanding of all of the various degradation modes that can occur in a device. One degradation mode of note is the perovskite to nonperovskite phase transition. In this work, we demonstrate a simple method to track the kinetics of this in CsPbI3 thin films. We demonstrate that this phase transition is first order with respect to atmospheric water. Moreover, we show the ability to decrease the phase transition rate from 7.5×10–3 s−1 to 1.4×10–3 s−1 by surface iodide treatment of the films. This insight will help the design of more robust perovskite films and continued understanding of this phase transformation will likely be important for efforts aimed at extrapolating accelerated lifetime tests.