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

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 CsPbBr3 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 CsPbBr3 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. A frozen‐temperature laser tuning method (below −28 °C) is developed to achieve giant functionality optimization and stability enhancement (>100 times) of metal halide perovskites (MHPs) for various applications. Freezing allows precise control over laser effects, enhancing CsPbBr3 nanocube arrays. The laser tuning mechanism is revealed by in situ cryo‐TEM at atomic resolution.