High‐Luminance Blue Quasi‐2D Perovskite Light‐Emitting Diodes by Engineering Polarity‐Controlled Solvent‐Film Interaction

Blue perovskite light‐emitting diodes (PeLEDs) operating in the 460–480 nm spectral range remain limited by insufficient luminance and rapid degradation under high current densities. In quasi‐two‐dimensional (quasi‐2D) perovskite emitters, excessive lower‐ n phases and organic‐rich surface components hinder efficient carrier transport and accelerate nonradiative recombination, leading to early luminance saturation. Here, we demonstrate a polarity‐controlled solvent post‐treatment that selectively regulates surface‐emissive pathways after forming quasi‐2D perovskite films without altering the composition. A systematic solvent screening based on solvent‐perovskite interactions correlated with dielectric constants identified isopropyl alcohol (IPA) as the ideal post‐treatment solvent. IPA treatment facilitates a dynamic redistribution of emission sources from lower‐ n to more stable higher‐ n domains. The IPA treatment effectively reduced surface‐associated organic species and defect‐mediated non‐radiative losses while preserving the quasi‐2D lattice framework. Consequently, the IPA‐treated quasi‐2D PeLEDs exhibited a record‐high peak luminance of 8,600 cd∙m −2 at 478 nm, outperforming previously reported blue quasi‐2D PeLEDs. This enhancement was complemented by facilitated charge transport and mitigated efficiency roll‐off, ultimately resulting in superior operational stability. This work establishes solvent post‐treatment as a straightforward and processing‐compatible strategy to overcome intrinsic luminance limitations in blue quasi‐2D PeLEDs by regulating surface‐dominated recombination dynamics under high‐current operation.