Characterizing the Circular Polarization-Dependent Refractive Index of Low-Dimensional Chiral Perovskites

Hybrid organic-inorganic perovskites (HOIPs) have recently emerged as promising materials with remarkable light-absorbing and luminescent properties. In two-dimensional hybrid perovskites (2DHPs), chiral ligands can endow the chirality to perovskites and further enable chiral optoelectronic applications such as chiral photoluminescence and chiral photodetection. Currently, the degree of chirality in 2DHPs is represented by their circular dichroism (CD), defined as difference in absorption between left-handed (A_L) and right-handed (A_R) circularly polarized light. However, such characterizations are typically performed on thin film samples in transmission measurements, and the results can be blurred by material thickness and film morphology. Here, we propose and demonstrate the use of chiral complex refractive index (n and k) as a more intrinsic parameter to evaluate the degree of chirality of 2DHPs. From reflectance spectroscopy and the transfer matrix method, we characterize the chirality-dependent n and k for archetypal chiral 2DHPs. Our study provides fundamental insights regarding how chiral ligands impact the intrinsic material optical property and provide guiding principles for the design of chiral perovskites optoelectronic devices.