Perovskites　are　promising　environmentally　sustainable　materials　for　circularly　polarized　electroluminescence　(CPEL).　While　another　chiral　nonemissive　layer　is　required　for　the　developed　perovskite-based　CPEL,　we　report　herein　a　highly　efficient　circularly　polarized　electroluminescence　based　on　a　single　layer　of　quasi-2D　perovskite　with　achiral　phenethylammonium　iodide　(PEAI)　and　chiral　S/R-1-(1-naphthyl)ethylammonium　iodide　(S/R-NEAI)　as　dual　spacer　cations.　The　quasi-2D　perovskite　was　further　passivated　by　carbazole-functionalized　phosphonium.　The　as-fabricated　film　exhibits　not　only　a　circular　dichroism　(CD)　signal　but　also　prominent　circularly　polarized　luminescence　(CPL)　activity　with　a　maximum　photoluminescence　dissymmetry　factor　(glum)　of　∼2.1　×　10-3.　More　importantly,　a　highly　efficient,　spin-polarized　light-emitting　diode　(LED)　was　fabricated　based　on　the　in　situ　passivated　quasi-2D　perovskite　with　a　peak　external　quantum　efficiency　of　3.7%　and　a　maximum　electroluminescence　dissymmetry　factor　(gEL)　of　∼4.0　×　10-3　©　2023　American　Chemical　Society