Narrow-Bandgap Tellurium-Based Chiral Hybrid Perovskite Single Crystals with Rashba–Dresselhaus Effect and Piezoelectricity

Chiral
hybrid perovskites have aroused great interest due to their
unique versatile properties. However, designing chiral perovskites
with narrow bandgaps is challenging, with their electronic properties
such as the Rashba–Dresselhaus effect and piezoelectricity
remaining unclear. Herein, single crystals of zero-dimensional (0D)
tellurium-based chiral hybrid perovskite, (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 (PEA
= phenylethylammonium), with sizes of over 5 mm are grown by seed-crystal-assisted
solution-temperature-lowering. The optical bandgaps are about 1.60
and 2.18 eV for the iodide and bromide analogues, respectively, which
are the lowest among various chiral lead-free hybrid perovskites with
the same halide ions in the X-site to the best of our knowledge. First-principles
calculations reveal that (R-/S-α-PEA)2TeBr6 shows a larger Rashba–Dresselhaus
spin-splitting than (R-/S-α-PEA)2TeI6, probably thanks to the greater distortion
of [TeBr6] octahedra. Moreover, the piezoelectric coefficients d33 of (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 are about 2.6
and 1.8 pC N–1, respectively. This work deepens
the understanding of physical properties of 0D tellurium-based chiral
perovskites with potential multifunctionality, including spintronic
and piezoelectric performances.