Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability, however, remains a major obstacle to broad application because of the poorly understood degradation pathways. Here, we apply integrated luminescence and electron microscopy (iLEM) on perovskites for the first time. Simultaneously applying light illumination and electron beam (e-beam) scanning, the integrated microscopy allows us to monitor in situ morphology evolution alongside changes in optical properties upon perovskite degradation.

Interestingly, morphology, photoluminescence (PL), and cathodoluminescence (CL) of perovskite film samples evolve differently upon degradation driven by e-beam or by light. The scanning e-beam induce an instant drop in PL. Nevertheless, PL gradually recovers after extended period scanning of e-beam. The recovery in PL under e-beam is accompanied with blue-shifts in spectra and with enhancement in CL intensities. Light driven degradation, on the other hand, results in little shift in spectrum. Next to differences in PL changes by e-beam and by light, distinctly different structural evolution are observed. E-beam leads to thinning of films, while light breaks the films into particle-like residues.

The different observations on light and e-beam driven degradation are due to differences in electric currents that drive ion migration in perovskite. A transversal electric current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degradation results in material decomposition to scattered particles and shows little PL spectral shifts. The differences in degradation can be ascribed to different electric currents that drive ion migration. Moreover, solution-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphology. Our results reveal the essential role of ion migration in perovskite degradation and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphology and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degradation and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using scanning electron microscopy or transmission electron microscopy techniques.