Chiral Two-Dimensional Perovskites for Highly Selective Room-Temperature Spin-Polarized Light-Emitting Diodes

Circularly polarized light (CPL) is an essential light source with a broad range of potential applications, including magnetic recording, three-dimensional displays, and information processing. In this work, we introduce core−shell heterostructured perovskite quantum dots (QDs) for room-temperature spin-polarized light-emitting diodes (spin-LEDs). Specifically, 2-dimensional (2D) chiral organic−inorganic hybrid perovskite shell was deposited onto the achiral 3D inorganic CsPbBr₃ perovskite core. It is demonstrated that (R)- and (S)-1-(2-(naphthyl)ethylamine) chiral cations can enhance the degree of spin polarization due to their robust chiroptical properties. Owing to the chiral-induced spin selectivity (CISS) effect, the spin state of the injected charge carriers is biased when they are transmitted through the 2D chiral shell. Such spin-controlled carriers then undergo radiative recombination within the CsPbBr₃ core, resulting in the CPL emission. The spin-LEDs fabricated with core−shell QDs attained a maximum external quantum efficiency (EQE) of 5.47% and exhibited circularly polarized electroluminescence with an outstanding polarization degree (P_CP-EL) for both left- and right-handed 2D chiral perovskites at room temperature.
Furthermore, blue spin-LEDs are demonstrated by incorporating (R)- and (S)-2-fluoro-methylbenzylamine (R/S-2F-MBA) chiral cation into the surface of Br/Cl-mixed halide perovskite thin-films. It was found that small ionic radii of bromide and chloride ions strengthened the hydrogen bonding between ammonium functional groups of chiral cation and halide anions in inorganic octahedra, enhancing circular dichroism of 2D chiral perovskites by ~4 fold. Due to the increased chiroptical properties as well as spin selectivity, the resulting blue spin-LEDs exhibited a remarkable circularly polarized electroluminescence dissymmetry factor. Also, halide vacancies inside perovskite films were effectively passivated due to a high polarity of R/S-2F-MBA chiral cations, thereby achieving a notable EQE.