Bifunctional Spacer Cation Enables High-Efficiency Chiral Red Quasi-2D Perovskite Light-Emitting Diodes via Defect Passivation and Chirality Enhancement

Quasi-two-dimensional (quasi-2D) perovskites are promising candidates for circularly polarized luminescence (CPL) materials and spin light-emitting diodes (LEDs), owing to their strong spin–orbit coupling, tunable chiral-inducing structures, and device compatibility. However, achieving high dissymmetry factors and efficient spin-LED performance remains challenging due to the limited chirality transfer and poor optical properties of existing chiral quasi-2D perovskites. In this work, we introduce a bifunctional achiral organic spacer, 2-phenoxyethanamine (POEA+) into quasi-2D perovskites, resulting in mixed chiral and achiral spacer cations. The incorporation of POEA+ not only passivates defects and improves the optical properties of the perovskite films but also enhances the chirality-induced spin selectivity (CISS) by facilitating efficient chirality transfer within the mixed spacer cation system and promoting a more effective energy transfer process. Additionally, the presence of POEA+ promotes the formation of intermediate phases, which act as energy transfer channels, thereby enabling more efficient energy funneling and a stronger CISS effect. As a result, the mixed spacer cation perovskite film exhibits a significantly enhanced CPL signal at ∼701 nm, with a maximum photoluminescence dissymmetry factor of 5.4 × 10–3 at room temperature. Furthermore, LEDs based on the optimized film demonstrate a high external quantum efficiency of 4.22%. This work proposes an effective strategy to simultaneously enhance the chiroptical properties of quasi-2D perovskites and improve the quality of the films, which shows great potential for future applications in chiroptoelectronics and spintronics.