Beyond Rigid Octahedra: Asymmetric Lattice Dynamics in a Thermally‐Activated Incommensurate Perovskite Phase Toward Optoelectronic Exploitation

ABSTRACT Hybrid perovskites have emerged as revolutionary optoelectronic materials, yet their structural instabilities, particularly the enigmatic intermediate‐phase behaviors, remain poorly understood. These transitional states often hold the key to carrier dynamics control but are notoriously difficult to characterize due to their transient nature. Herein, we develop a ResNet‐18‐based deep learning framework that achieves 97% accuracy in automated identification of modulated structures, enabling screening of structural complexity in disordered systems. Leveraging this model, we explore a stable incommensurate modulation structure in MAPbBr 3 single crystals within a well‐defined temperature window (120–142 K), resolving a long‐overlooked structural instability in these materials. Through X‐Ray‐based crystallographic analysis, we uncover that this modulation stems from cooperative [BX 6 ] 4 − octahedral tilt distortions, exhibiting striking asymmetry, i.e., bromide ions dominate the distortion (index = 0.279) while lead ions remain relatively rigid (index = 0.046). Furthermore, we engineer a perovskite photodetector with two‐orders‐of‐magnitude enhancement in photo response rate at low temperatures, underscoring the functional relevance of structural nonuniformity in optoelectronic applications. This work not only deciphers the atomistic origins of incommensurate phases in hybrid perovskites but also provides a generalizable strategy for harnessing structural modulation to tailor carrier dynamics and device performance.