Domain　distribution,　defect　density　as　well　as　carrier　transport　all　exert　some　great　impact　on　the　performance　of　quasi-two-dimensional　(quasi-2D)　perovskites　light　emitting　diodes　(PeLEDs).　Herein,　the　novelty　multifunctional　metformin　hydrochloride　(MFCl)　buried　passivated　layer　was　introduced　to　optimize　the　crystal　dynamics,　surface　morphology,　and　electro-luminescent　properties　of　the　quasi-2D　perovskites.　On　the　one　hand,　MF　ion　to　some　extent　optimized　the　domain　distribution　just　by　both　decreasing　the　n　=　2　phase　and　increasing　the　three-dimensional　(3D)　phase,　which　facilitated　the　charge　funnelling.　On　the　other　hand,　by　combining　MFCl　with　PSS　or　PSS-Na,　the　energy　level　of　the　hole　transport　layer　was　effectively　adjusted,　resulting　in　an　obvious　reduction　of　the　injection　barrier.　As　a　result,　the　MFCl-optimized　blue　quasi-2D　PeLEDs　with　the　maximum　external　quantum　efficiency　of　5.22　%　was　achieved,　which　is　3.6　times　higher　than　that　of　the　device　without　the　MFCl　treatment.　This　work　provided　favourable　strategy　for　the　performance　enhancement　of　blue　quasi-2D　PeLEDs,　in　which　a　multifunction　interface　was　introduced　to　synchronously　improve　the　phase　distribution　as　well　as　the　defect　passivation　of　quasi-2D　perovskite,　meanwhile　all　of　those　further　promoted　the　charge　transportation.　©　2024　Elsevier　B.V.