Impact of Crystal Orientations on the Circular and Linear Dichroism Signals in Chiral Perovskite

Chiral perovskites owing to their broken mirror symmetry exhibit selective absorption of circularly polarized light manifesting a strong circular dichroism (CD). CD spectroscopy is a key technique to understand chiral perovskites. However, there is a debate on whether the observed CD is intrinsic to the chiral crystal structures or is modulated by extrinsic phenomena particularly linear dichroism (LD) and linear birefringence (LB) effects. This work investigates the chiroptical properties of (R‐/S‐MBA) 2 CuCl 4 (MBA = Methylbenzyl ammonium) by thoroughly studying the contribution from LD and LB to the observed CD signals. We further compare similar material system to extend the scope and key findings. The comparison of highly oriented and randomly oriented films exhibits notable LD and LB contributions to the observed CD, which are caused by orientation‐dependent electric‐field interactions and local anisotropy. Both randomly and highly orientated films exhibit distinct CD responses. The randomly films retain a significantly larger intrinsic CD contribution (∼60%), whereas highly oriented films show primarily LDLB‐induced contributions (∼90%) with only a minor intrinsic CD component (∼10%). Our findings demonstrate that careful consideration of crystal orientation and structural effects is necessary for appropriate interpretation of CD spectra in chiral perovskite thin films.