Simultaneous Improvement\nin Blue-Light Emission and\nOperational Stability of Nanometer-Thick Perovskite Light-Emitting\nDiodes by Incorporating Multiple Organic/Inorganic Chloride Salts

Although recent advancements in organic–inorganic\nhybrid\nperovskites have captivated not only the community of photovoltaics\nbut also the field of display technologies, the development of perovskite-based\nlight-emitting diodes (PeLEDs) with pure-blue emission has lagged\nbehind that of their green- or red-emitting counterparts in terms\nof optoelectronic properties and operational stability. In this study,\nwe report a comprehensive strategy to enforce pure-blue emission of\nPeLEDs with high quantum efficiency and operational stability by introducing\nmultiple cationic chlorides in perovskite layers. First we demonstrate\nthe gradual induction of a distinct hypsochromic shift to the blue\nregion in green-emissive CsFAPbBr<sub>3</sub> perovskite films by\nincorporating bulky ammonium bromide and chloride. This shift is accomplished\nthrough dimensional and lattice structure engineering. Second, small\nA-site cationic chlorides are introduced to further tune the band\ngap and optoelectronic properties of the pure-blue PeLEDs. Finally,\nyttrium(III) chloride is introduced as an additive to hamper severe\nphase segregation and ion migration in the perovskite emitting layers.\nAs a result of these deliberate modifications, the proper inclusion\nof multiple inorganic chloride salts enforced the hypsochromic shift\nof the perovskite layer with a minimized defect density, leading to\npure-blue electroluminescence at 472 nm with an exceptionally narrow\nbandwidth of 17.91 nm and an external quantum efficiency of 4.22%.\nThe optimized chlorides also achieve superior operational stability\nwith an electroluminescence half-life of 23 min at an initial luminance\nof 350 cd/m<sup>2</sup> in an ambient atmosphere. This suggests a\nstraightforward way to prepare practical pure-blue PeLEDs for achieving\nfull-color perovskite display technologies.