Dynamic Competition between Photodegradation and Self-Healing in Perovskite Nanocrystals Dictated by Microstructure.

Metal halide perovskite nanocrystals (PNCs) are exceptional light emitters for next-generation display technologies, yet their practical deployment is critically hindered by poor photostability. A long-standing puzzle is the contradictory report of either photodegradation or photobrightening under illumination, suggesting a dynamic competition between these opposing processes; however, the underlying determinant factor remains elusive. Here, we demonstrate that the intrinsic microstructure of PNC films dictates this dynamic competition. We engineer CsPbBr3 PNC films with identical chemical composition yet distinct microstructures (discrete nanoparticles versus sintered networks) as two well-defined initial states. Under continuous-wave illumination relevant to the operational conditions, discrete films undergo progressive photodegradation, whereas sintered films display enhanced photoluminescence. As revealed by systematic spectroscopic, photoelectric, and morphological analyses, the microstructure dictates the competition between photodegradation and photobrightening by determining whether light exposure predominantly creates or passivates trap states. Building on these mechanistic insights, we develop a sequential thermal annealing-light exposure strategy yielding close-packed PNC films with unprecedented photostability, showing less than 1% photoluminescence fluctuation under intense irradiation in air. This work establishes the microstructure as the decisive factor controlling the competition between photodegradation and self-healing, providing a fundamental mechanistic framework and a practical engineering pathway toward stable PNC-based color conversion layers for high-power light-emitting applications.