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.
Quasi-one-dimensional (quasi-1D) van der Waals crystal fibrous red phosphorus (RP) exhibits pronounced in-plane optical anisotropy, positioning it as a potential candidate for polarization-related micro-nano devices. Unfortunately, a comprehensive investigation into the complex refractive index of fibrous RP and the structure-activity relationship connecting the distinctive quasi-1D structure with optical anisotropy is currently deficient. Herein, we have collectively determined the complex refractive index of the fibrous RP flakes within the ab-plane through Kramers-Kronig (KK) analysis and theoretical calculation. Notably, the maximum birefringence of fibrous RP reaches 0.642@475 nm with an absolute extinction coefficient of only 0.08, superior to the reported traditional optical crystals and the emerging low-dimensional materials as well. The remarkable birefringence can be attributed to the synergistic influence of the large electronic dipole polarizability, anisotropic electron density distribution and the distortion of stereochemically active lone pair (SCALP). This work demonstrates the potential of fibrous RP for polarization-sensitive devices, illuminating possibilities to exploit novel giant birefringent crystals based on the structure-activity relationship.
Fibrous red phosphorus (RP) has triggered growing attention as an emerging quasi-one-dimensional (quasi-1D) van der Waals crystal recently. Unfortunately, it is difficult to achieve substrate growth of high-quality fibrous RP flakes due to their inherent quasi-1D structure, which impedes their fundamental property exploration and device integration. Herein, we demonstrate a bottom-up approach for the growth of fibrous RP flakes with (001)-preferred orientation via a chemical vapor transport (CVT) reaction in the P/Sn/I2 system. The formation of fibrous RP flakes can be attributed to the synergistic effect of Sn-mediated P4 partial pressure and the SnI2 capping layer-directed growth. Moreover, we investigate the optical anisotropy of the as-grown flakes, demonstrating their potential application as micro phase retarders in polarization conversion. Our developed bottom-up approach lays the foundation for studying the anisotropy and device integration of fibrous red phosphorus, opening up possibilities for the two-dimensional growth of quasi-1D van der Waals materials.
The lead-free hybrid perovskite piezoelectrics possess advantages of easy processing, light weight, and low-toxicity over inorganic ceramics. However, the lack of understanding in structure-property relationships hinders exploration of new molecular piezoelectric crystals with excellent performances. Herein, by introducing chiral α-phenylethylammonium (α-PEA+ ) cations into bismuth-based hybrid halides, centimeter-sized (R-α-PEA)4 Bi2 I10 and (S-α-PEA)4 Bi2 I10 single crystals with a superior piezoelectric voltage coefficient g22 of 309 mV m N-1 , are obtained. Structural rigidity in crystals leads to a remarkable electrostrictive coefficient Q22 of 25.8 m4 C-2 , nearly 20 times higher than that of poly(vinylidene fluoride) (PVDF), which is beneficial to improve piezoelectricity with the synergistic effect of chirality. Moreover, the as-grown crystals show outstanding phase stability from 173 K to ≈470 K. This work suggests a design strategy based on rigidity and chirality to exploit novel piezoelectrics among hybrid metal halides.
Ternary hybrid perovskite solid solutions have shown superior optoelectronic properties and better stability than their ABX3 simple perovskite counterparts under ambient conditions. However, crystal growth and identification of the accurate composition of these complex crystalline compounds remain challenging, and their stability under extreme conditions such as in highly moist atmosphere is unknown. Herein, large-size (up to 2â cm) single crystals of ternary perovskite 0.80FAPbI3 â x'FAPbBr3 â y'CsPbI3 (x'+y'=0.20) are grown. An elemental analysis method based on wavelength dispersive X-ray fluorescence is proposed to determine their accurate compositions. Among these single crystals, the composition with y'=0.12 shows the best moisture stability at 90 % relative humidity for 15â days. Other components with richer or poorer Cs+ ions undergo different phase segregation behaviours. The performance and stability of photodetectors based on these single crystals are tested. This work offers a deeper insight into phase stability of ternary hybrid perovskite solid solution crystals in highly moist atmosphere.
