Tuning Chiroptical Properties of Chiral 2D Hybrid Organic-Inorganic Perovskites Through Mixing Halogen

Chiral 2D halide perovskites have attracted increasing attention due to their exceptional photoluminescence properties, tunable bandgap, and various crystallized structure. However, tuning chiroptical properties of chiral 2D hybrid halide organic-inorganic perovskites have not yet been extensively studied. Here, we report the chirality of chiral 2D halide perovskites through circular dichroism(CD) and circularly polarized photoluminescence(CPL). By varying the mixing ratio of chlorine, bromide, and iodide anions in S- or R-(MBA)2 PbI4(1−x)Br4x or S- or R-(MBA)2 PbBr4(1−y)Cl4y, the mixing of halide ions allows a tunable band gap of the chiral OIHPs, leading to a shift of the CD signal from 495 to 320 nm and the CPL signal from 530 to 485nm. Moreover, it is noticed that the CD signal ascends from x=0 to x=1 and descends from x=1 to x=4. Successively, the CD signal ascends from y=0 to y=4. This difference can be explained that the phase transition of the crystalline structure occurred. Chiral optical asymmetry (g-factor) at y=4 has a maximum value of 0.015 compared to other mixing ratios. The CPL signal becomes greatly small after the phase transition because of structural distortion in the inorganic framework and instability. Additionally, the CD sign conversion is discovered as well through mixing halogen. These properties can take advantage of the structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices. Spin organic light-emitting diodes were achieved by using chiral 2D hybrid halide perovskites film as the spin filter layer. Circularly polarized electroluminescence was observed at room temperature in the absence of an external magnetic field.