Ruddlesden-Popper (RP) phase perovskite quantum wells (QWs) offer the potential for achieving deep blue emission. However, the RP perovskite consists of bilayers of monovalent alkylammonium ions arranged back-to-back between the separated perovskite octahedral layers. The weak van der Waals interactions between these bilayers cause an inherent tendency for dissociation, facilitating the generation of mixed phases and promoting the decomposition of the perovskite. Herein, we propose a spacer molecule management strategy to achieve size-homogenized and strongly confined stable Dion-Jacobson (DJ) phase CsPbBr