Freeze Metal Halide Perovskite for Dramatic Laser Tuning: Direct Observation via In Situ Cryo‐Electron Microscope

Abstract A frozen‐temperature (below −28 °C) laser tuning way is developed to optimize metal halide perovskite (MHP)’s stability and opto‐electronic properties, for emitter, photovoltaic and detector applications. Here freezing can adjust the competitive laser irradiation effects between damaging and annealing/repairing. And the ligand shells on MHP surface, which are widely present for many MHP materials, can be frozen and act as transparent solid templates for MHP's re‐crystallization/re‐growth during the laser tuning. With model samples of different types of CsPbBr ₃ nanocube arrays,an attempt is made to turn the dominant exposure facet from low‐energy [100] facet to high‐energy [111], [‐211], [113] and [210] ones respectively; selectively removing the surface impurities and defects of CsPbBr ₃ nanocubes to enhance the irradiation durability by 101 times; and quickly (tens of seconds) modifying a Ruddlesden–Popper (RP) boundary into another type of boundary like twinning, and so on. The laser tuning mechanism is revealed by an innovative in situ cryo‐transmission electron microscope (cryo‐TEM) exploration at atomic resolution.