The remarkable optoelectronic features of halide perovskite promote their potential applications in semiconductor devices beyond solar cells, which require high-quality single crystals with controlled defect levels. Herein, we investigated the synthesis mechanism of chemical vapor deposited single-crystalline all-inorganic perovskite microplates (MPs), and reported a defect-modulated photocurrent which is closely related to the growth sequence of the MPs. The MP synthesis initiates from island-like nano-disks, and subsequently transits to a layer-by-layer fashion, resulting in a defect-rich area at the center of the MPs. At elevated temperatures, these central defects may be thermally activated and become highly mobile, leading to photoluminescence quenching and degression of local and overall optoelectronic attributes, as evidenced by the spatial resolved optical and electrical scanning probe microscopy. Overall, this work shines light on the formation, proliferation and dynamics of defects in perovskites, and offers guidance for preparation of high-quality perovskites micro-crystals for functional semiconductor devices with high temperature stability.