Mechanisms of Electron Beam-Induced Damage in Perovskite Thin Films Revealed by Cathodoluminescence Spectroscopy

Electron-beam-induced damages in methylammonium lead triiodide (MAPbI₃) perovskite thin films were studied by cathodoluminescence (CL) spectroscopy. We find that high-energy electron beams can significantly alter perovskite properties through two distinct mechanisms: (1) defect formation caused by irradiation damage and (2) phase transformation induced by electron-beam heating. The former mechanism causes quenching and broadening of the excitonic peaks in CL spectra, whereas the latter results in new peaks with higher emission photon energy. The electron-beam damage strongly depends on the electron-beam irradiation conditions. Although CL is a powerful technique for investigating the electronic properties of perovskite materials, irradiation conditions should be carefully controlled to avoid any significant beam damage. In general, reducing acceleration voltage and probing current, coupled with low-temperature cooling, is more favorable for CL characterization and potentially for other scanning electron-beam-based techniques as well. We have also shown that the stability of perovskite materials under electron-beam irradiation can be improved by reducing defects in the original thin films. In addition, we investigated effects of electron-beam irradiation on formamidinium lead triiodide (FAPbI₃) and CsPbI₃ thin films. FAPbI₃ shows similar behavior as MAPbI₃, whereas CsPbI₃ displays higher resistance to electron-beam damage than its organic-inorganic hybrid counterparts. Using CsPbI₃ as a model material, we observed nonuniform luminescence in different grains of perovskite thin films. We also discovered that black-to-yellow phase transformation of CsPbI₃ tends to start from the junctions at grain boundaries.