Ion migration or diffusion under light or bias is a frequently observed electrochemical phenomenon in halide perovskites. Such intrinsic instability in their chamical distribution under working condition poses questions and challenges for real application of halide materials. We investigated the effect of large-sized cation of guanidinium (GA) at the A site in the CsPbIBr₂ perovskite on the ion migration and device stability. Moreover, we employed one photon and multiphoton spectroscopy to investigate the underlying mechanism of polaron-induced ion migration. One can find that halogen ion migration of CsPbIBr₂ perovskite under laser illumination results in the shift of photoluminescence (PL) peak wavelength due to phase segregation. A series of “probe-set-probe” operation is designed to visualize the ion migration through PL spectrum and PL mapping. The experimental data demonstrate that the excitation intensity, as well as duration, has an impact on the ion migration induced phase segregation. After incorporating the GA cation in the CsPbIBr₂ perovskite, local lattice distortion is formed in the perovskite crystal due to a size mismatch between Cs and GA, which impedes the ion migration to some extend. Such distortion reduces the formation of strain in GA_xCs_1−xPbIBr₂ perovskite film under illumination, which inhibits the ion migration. Inhibition of the ion migration leads to a stable PL emission spectrum and enhanced devices stability under light stimulations. The physical insight of bias-induced migration of mobile ions in the perovskite active layer effectuating the observed non-linearity in the increased magnitude of electroluminescence (EL) and luminous efficiency (LE) as a function of current density for PeLEDs will also be discussed.