Laser-accelerated phase transformation in cesium lead iodide perovskite

•Photoexcitation significantly accelerates the moisture-induced phase transformation •A photodarkened state is observed prior to the high-T to low-T phase transformation •Defects created by photoexcitation are still present even after the laser is off High-temperature phase CsPbI3 has garnered increased attention due to its suitable band gap for photovoltaics, but its structural instability under ambient conditions limits its long-term application. While there have been studies on its structural stability under heat and moisture, insight on the influence of light absorption is limited. We demonstrate that, under ambient moisture, illumination by an above-band gap laser transforms high-temperature CsPbI3 into its low-temperature phase at rates that are orders of magnitude larger than that of the moisture-induced phase transformation alone, likely due to additional surface vacancy creation and/or migration. Without moisture, laser illumination does not trigger the phase transformation, but introduces defects that lower the material’s photoluminescence intensity and accelerate the high-temperature to low-temperature phase transformation when the sample is exposed to moisture. These results expand our understanding of the influence of light exposure on CsPbI3 and highlight the interdependencies at play when subjecting CsPbI3 to combined environmental stimuli. High-temperature phase CsPbI3 has garnered increased attention due to its suitable band gap for photovoltaics, but its structural instability under ambient conditions limits its long-term application. While there have been studies on its structural stability under heat and moisture, insight on the influence of light absorption is limited. We demonstrate that, under ambient moisture, illumination by an above-band gap laser transforms high-temperature CsPbI3 into its low-temperature phase at rates that are orders of magnitude larger than that of the moisture-induced phase transformation alone, likely due to additional surface vacancy creation and/or migration. Without moisture, laser illumination does not trigger the phase transformation, but introduces defects that lower the material’s photoluminescence intensity and accelerate the high-temperature to low-temperature phase transformation when the sample is exposed to moisture. These results expand our understanding of the influence of light exposure on CsPbI3 and highlight the interdependencies at play when subjecting CsPbI3 to combined environmental stimuli.