Photostability and Photodegradation Processes in Colloidal CsPbI₃ Perovskite Quantum Dots

All-inorganic CsPbI₃ perovskite quantum dots (QDs) have attracted intense attention for their successful application in photovoltaics (PVs) and optoelectronics that are enabled by their superior absorption capability and great photoluminescence (PL) properties. However, their photostability remains a practical bottleneck and further optimization is highly desirable. Here, we studied the photostability of as-obtained colloidal CsPbI₃ QDs suspended in hexane. We found that light illumination does induce photodegradation of CsPbI₃ QDs. Steady-state spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and transient absorption spectroscopy verified that light illumination leads to detachment of the capping agent, collapse of the CsPbI₃ QD surface, and finally aggregation of surface Pb⁰. Both dangling bonds containing surface and Pb⁰ serve as trap states causing PL quenching with a dramatic decrease of PL quantum yield. Our work provides a detailed insight about the correlation between the structural and photophysical consequences of the photodegradation process in CsPbI₃ QDs and may lead to the optimization of such QDs toward device applications.