Strategic Buried Defect Passivation of Perovskite Emitting Layers by Guanidinium Chloride for High‐Performance Pure Blue Perovskite Light Emitting Diodes

Perovskite light‐emitting diodes (PeLEDs) show promise for high‐definition displays due to their exceptional electroluminescent properties. However, the performance of pure blue PeLEDs is hindered by the unfavorable ionic behavior of halides and the presence of defective antisites in blue‐emitting perovskite materials. An unstable buried interface between charge transport layers and the perovskite emitting layer is a major issue that limits carrier transport and recombination behavior in PeLEDs. In this study, effective buried defect passivation of pure blue perovskite emitting layers by introducing guanidinium chloride (GACl) as a bottom‐passivating layer is demonstrated. The GACl bottom layer not only passivates the point defects present at the buried interface but also provides chloride anions to suppress ion migration and halide vacancy formation. Along with the defect passivation, GACl also enforces phase purity of 2D layered structure in the perovskite emitting layers to improve crystallinity and optoelectronic properties. As a result, the PeLEDs with high brightness (1200 cd m −2 ) and excellent external quantum efficiency (6.61%) are achieved at a spectrally stable pure blue electroluminescence at 471 nm (band width = 17.63 nm). This study offers insights into the straightforward way for effective buried passivation for preparing high‐performance PeLEDs.