Mechanical-load and temperature-engendered degradation of α-CsPbI3: reactive molecular dynamics simulation

Abstract

Inorganic halide perovskite materials are widely used to make efficient solar cells; however, they have a number of stability issues. Furthermore, due to the inadequate spatiotemporal resolution in experimental tests, the impact of mechanical-load and temperature-induced stresses on the degradation mechanism of halide perovskite materials is poorly understood. Here, we investigate the effect of mechanical and temperature-induced stresses on the degradation of the cubic (α) perovskite CsPbI₃ using reactive molecular dynamics. As per the detailed investigation, major structural degradation of α-CsPbI₃ was observed at around a temperature of T = 850 K. As a result, we evaluated the structural stability and subsequent relaxation over a wide range of temperatures (T = 300 K to 800 K) and external loads (F_z = 0.007 pN to 35 pN) applied along the z-axis. The number of dissociating bonds (ξ) in the structure is calculated to be in the following order at F_z = 1.74 pN and T = 300 K: ξ_{(Pb—I,Pb–Pb)} > ξ_{(Cs–Cs,I–I,Cs–Pb)} > ξ_(Cs–I). Furthermore, the ξ value of these bonds is found to be in inverse order with temperature. Moreover, it shows a saw-tooth or stick-slip pattern during bond dissociation at T = 300 K and low pulling force (<0.07 pN). It is also observed that the impact of applied force along the z-axis differs from that along the x-axis. We also investigated the bond dissociation and formation of all connected bonds over a wide range of applied forces and temperatures, as well as the subsequent relaxation process, to better understand the feasibility of restoring the perovskite structure of degraded products. The data show that, during the relaxation of the applied force and at high temperatures, the dissociated atoms of the structure aggregate and the degraded products are unable to reform the perovskite structure. We anticipate that our findings will help researchers better grasp the stability of perovskite materials under external-load and temperature-driven stresses.