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) 2 TeI 6 and ( R -/ S -α-PEA) 2 TeBr 6 (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) 2 TeBr 6 shows a larger Rashba-Dresselhaus spin-splitting than ( R -/ S -α-PEA) 2 TeI 6 , probably thanks to the greater distortion of [TeBr 6 ] octahedra. Moreover, the piezoelectric coefficients d 33 of ( R -/ S -α-PEA) 2 TeI 6 and ( R -/ S -α-PEA) 2 TeBr 6 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.