Orientational Dependence of Electron Beam Irradiation Damage in Lead-Free Halide Double Perovskite Cs2AgBiBr6

Irradiation damage in halide perovskites usually enhances ion migration, decomposition, formation of intermediate phases, etc., which further decrease the working stability of halide perovskite optoelectronic devices. For example, due to the beam-sensitive nature of halide perovskites, the artifact information about local structures and microstructures is difficult to avoid during transmission electron microscopy (TEM) characterization. The interaction mechanism between high-energy electron beams and halide perovskites is still unclear. In this work, the electron-beam irradiation effect on solution-grown halide double perovskite Cs2AgBiBr6 crystals was systematically investigated by TEM. Depending on the different orientations of Cs2AgBiBr6, two kinds of electron beam irradiation damage were observed. When the irradiation on Cs2AgBiBr6 is along the [110]pc zone axis, a new phase Cs2Ag0.5BiBr6 with a vacancy-ordered superstructure forms, which is attributed to the "knock-on displacement" mechanism. In contrast, when the electron beams are along the [111]pc zone axis of Cs2AgBiBr6, an amorphous phase is gradually generated due to the "radiolysis" mechanism. Our finding clearly reveals the characteristics of irradiation damage in representative halide perovskites and further provides a new understanding of the working instability of halide perovskite optoelectronic devices.