Interfacial Chemistry Limits the Stability of Deep Blue Perovskite LEDs Revealed by Operando Characterization.

To commercialize lead halide perovskites as light-emitting diodes (LEDs), the operational device lifetime needs to be drastically improved. For this to be achieved, an understanding of degradation behavior under bias is crucial. Herein, we perform operando measurements of the structural, chemical, and electronic changes using synchrotron-based grazing-incidence wide-angle X-ray scattering and hard X-ray photoelectron spectroscopy on full-stack deep blue mixed bromide/chloride lead halide perovskite LEDs. While a clear drop in optoelectronic performance is recorded under electrical bias, the accompanying X-ray scattering data reveals only minor changes in structural properties. However, photoelectron spectroscopy reveals substantial chemical changes at the electron-injecting interface after bias is applied, including the formation of unwanted metallic lead and a new chlorine species that is not in the perovskite structure. These operando approaches give important structural and interfacial perspectives to reveal the degradation mechanisms in these LEDs and highlight the need to address the top electron-injecting interface to realize step-changes in operational stability.