Formamidine Engineering the Lattice Distortion of Chiral Halide Perovskites for Efficient Blue Circularly Polarized Emission

Abstract Chiral halide perovskites have emerged as promising circularly polarized light sources due to their great potential applications in 3D displays, optical data storage, and optical communication devices. However, to date, chiral halide perovskites with efficient blue circularly polarized luminescence (CPL) are scarcely unearthed. Herein, through formamidine engineering to decrease lattice distortion, the first new types of chiral corrugated 2D halide perovskites are presented (R/S)‐(BPEA)FAPbBr₄·H₂O (2‐R/S) (BPEA = 4‐bromophenylethylaminium, FA = formamidinium). Interestingly, driven by the incorporation of FA organic cations, the chiral perovskite layer realizes the transformation from (100)‐oriented (R/S)‐(BPEA)₂PbBr₄·H₂O (1‐R/S) to (110)‐oriented 2‐R/S accompanying with reduced lattice distortion. More importantly, (110)‐oriented chiral perovskites 2‐R exhibit remarkable blue CPL with large asymmetry factors (g_lum =8.4 × 10⁻³). This work offers an exciting approach to realizing efficient blue CPL and promotes their further applications in photoelectronic devices.