Alkali cations modified poly(styrene sulfonate) enabling interfacial band structure regulation for efficient true-blue perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) have promised as potential light source device for display. However, interfacial barrier generated from the mismatched band structure of charge transport layer and perovskite, which leads to the charge accumulation and low charge transport efficiency at the interface, resulting in an inferior performance of true-blue PeLEDs particularly. Herein, we show the interfacial band structure regulation realized by aqueous compatible alkali cations modification on poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS), which achieves deeper highest occupied molecular orbital (HOMO) level for modified PEDOT:PSS benefiting charge transport at the interface, as well as reduces defect density of the perovskite film through improved crystallinity. Eventually, the champion device obtained on the true-blue PeLEDs based on Li cation modified PEDOT:PSS, exhibiting maximum luminance of 512.59 cd m⁻², and a maximum external quantum efficiency (EQE) of 5.43% at 479 nm. Those performance values locate at the top ranking of similar devices.