Why Mixed Halides in 2D Chiral Perovskites Weaken Chirality-Induced Spin Selectivity

Area of Science:

• Materials Science
• Condensed Matter Physics
• Organic Electronics

Background:

• 2D Ruddlesden-Popper (RP) perovskites with chiral amines exhibit chirality-induced spin selectivity (CISS).
• Tuning the CISS effect via halogen alloying in methylbenzylammonium (MBA)-based RPs is challenging, as mixed-halides often show suppressed chirality.
• Circular dichroism (CD) measurements previously indicated complete chirality suppression in mixed-halide RP perovskites.

Purpose of the Study:

• To investigate the CISS effect in mixed-halide 2D RP perovskites.
• To identify the mechanism behind apparent chirality suppression in these materials.
• To explore strategies for tuning spin-polarized charge transport.

Main Methods:

• Synthesis of mixed-halide 2D RP perovskites with varying bromide content.
• Magnetic-conducting atomic force microscopy (mc-AFM) to probe spin-dependent charge transport.
• Magnetoresistance (MR) measurements to assess spin polarization.
• Analysis of lattice microstrain and hydrogen bonding interactions.

Main Results:

• Photoinduced halide segregation was identified as the cause of apparent chirality suppression.
• The CISS effect in (R/S-MBA)2PbI4(1-x)Br4x decreased non-monotonically with bromide inclusion.
• A correlation was found between lattice microstrain and spin-polarized charge transport.
• Inhomogeneity in hydrogen bond strength between organic moieties and halogens influences chirality transfer.

Conclusions:

• The study explains the weakened CISS effect in mixed-halide chiral RP perovskites.
• Hydrogen-bond-induced coupling transfers chirality from the amine to the inorganic sublattice.
• A strategy for tuning spin-polarized charge transport in these materials is proposed.