Highly Distorted Chiral Two-Dimensional Tin Iodide Perovskites for Spin Polarized Charge Transport

Incorporating
chiral organic molecules into organic/inorganic hybrid
2D metal-halide perovskites results in a novel family of chiral hybrid
semiconductors with unique spin-dependent properties. The embedded
chiral organic moieties induce a chiroptical response from the inorganic
metal–halide sublattice. However, the structural interplay
between the chiral organic molecules and the inorganic sublattice,
as well as their synergic effect on the resulting electronic band
structure need to be explored in a broader material scope. Here we
present three new layered tin iodide perovskites templated by chiral
(R/S-)­methylbenzylammonium (R/S-MBA), i.e., (R-/S-MBA)2SnI4, and their racemic phase (rac-MBA)2SnI4. These MBA2SnI4 compounds exhibit the largest level of octahedral bond distortion
compared to any other reported layered tin iodide perovskite. The
incorporation of chiral MBA cations leads to circularly polarized
absorption from the inorganic Sn–I sublattice, displaying chiroptical
activity in the 300–500 nm wavelength range. The bandgap and
chiroptical activity are modulated by alloying Sn with Pb, in the
series of (MBA)2Pb1–xSnxI4. Finally, we show that
vertical charge transport through oriented (R-/S-MBA)2SnI4 thin films is highly spin-dependent,
arising from a chiral-induced spin selectivity (CISS) effect. We demonstrate
a spin-polarization in the current–voltage characteristics
as high as 94%. Our work shows the tremendous potential of these chiral
hybrid semiconductors for controlling both spin and charge degrees
of freedom.