The all-inorganic halide perovskite CsPbBr3 has attracted significant attention for applications of high-performance and stable solar cells, light-emitting diodes (LEDs), and photoelectric and X-/γ-ray detectors. The discrepant photoelectric properties are confusing, which strongly implies that the perovskite is sensitive to defects. Here, novel and ubiquitous defects, “twin domains”, are reported in solution-grown CsPbBr3 single crystals on the basis of X-ray diffraction techniques, optical microscopy, and transmission electron microscopy (TEM). Two kinds of orthorhombic domain structures, {121} reflection twins and 90° rotations along [101̅], are identified in as-grown CsPbBr3 crystals. In situ TEM results indicate that these domains are ferroelastic, which are related to the spontaneous strain induced by a phase transition. During a phase transition from parent cubic (m3̅m) to tetragonal (4/mmm), the loss of cubic {110} reflection planes, the 4-fold rotation axis (4), or the 3-fold rotoinversion axis (3̅) could act as a twin law and account for the appearance of domain walls. Further reduction of symmetry to orthorhombic (mmm) and the losses of the tetragonal 4-fold rotation axis (4) and mirror plane {101} lead to the emergence of [101̅] rotations and {101} reflection twins, respectively. Our work not only enhances the understanding of defects in CsPbBr3, which opens the door for the further optimization of photoelectric applications, but also provides a way to tailor it.

The ferroic domain, in metal halide perovskites (MHPs) at a low symmetry phase, was reported to affect optoelectronic properties. Building the relationship between ferroic domains and optoelectronic properties of MHPs will be a non-trivial task for understanding the charge transport mechanism. Here, high-quality CsPbBr3 single-crystal films (SCFs) were successfully grown by a cast-capping method. Through the phase transition process by heating and cooling the sample, dense domains in CsPbBr3 SCFs were formed and observed by an in situ polarized optical microscope. These domains were identified as 90° rotation twins by electron backscattered diffraction and transmission electron microscopy. Interestingly, the photocurrent response was dramatically enhanced after introducing ferroelastic domains. The highest responsivity, external quantum efficiency, and detectivity are 380 mA/W, 130%, and 12.9 × 1010 Jones, respectively, which are surprisingly 25.03, 25, and 7.8 times higher than those of the as-grown CsPbBr3 SCF, respectively, which may be attributed to the function of the domain wall of separating electrons and holes.

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