Chiral three-dimensional organic-inorganic lead iodide hybrid semiconductors.

Chiral hybrid metal halides (CHMHs) have received a considerable amount of attention in chiroptoelectronics, spintronics, and ferroelectrics due to their superior optoelectrical properties and structural flexibility. Owing to limitations in synthesis, the theoretical prediction of room-temperature stable chiral three-dimensional (3D) CHFClNH3PbI3 has not been successfully prepared, and the optoelectronic properties of such structures cannot be studied. Herein, we have successfully constructed two pairs of chiral 3D lead iodide hybrids (R/S/Rac-3AEP)Pb2I6 (3R/S/Rac, 3AEP = 3-(1-aminoethyl)pyridin-1-ium) and (R/S/Rac-2AEP)Pb2I6 (2R/S/Rac, 2AEP = 2-(1-aminoethyl)pyridin-1-ium) through chiral introduction and ortho substitution strategies, and obtained bulk single crystals of 3R/S/Rac. The 3R/S exhibits optical activity and bulk photovoltaic effect induced by chirality. The 3R crystal device exhibits stable circularly polarized light performance at 565 nm with a maximum anisotropy factor of 0.07, responsivity of 0.25 A W-1, and detectivity of 3.4 × 1012 jones. This study provides new insights into the synthesis of chiral 3D lead halide hybrids and the development of chiral electronic devices.

Room-Temperature Anisotropic Actuation Driven by a Synergistic Order-Disorder and Displacive Phase Transition in a Ferroelectric Crystal.

Actuating materials convert different forms of energy into mechanical responses. To satisfy various application scenarios, they are desired to have rich categories, novel functionalities, clear structure-property relationships, fast responses, and, in particular, giant and reversible shape changes. Herein, we report a phase transition-driven ferroelectric crystal, (rac-3-HOPD)PbI3 (3-HOPD = 3-hydroxypiperidine cation), showing intriguingly large and anisotropic room-temperature actuating behaviors. The crystal consists of rigid one-dimensional [PbI3] anionic chains running along the a-axis and discrete disk-like cations loosely wrapping around the chains, leaving room for anisotropic shape changes in both the b- and c-axes. The shape change is switched by a ferroelectric phase transition occurring at around room temperature (294 K), driven by the exceptionally synergistic order-disorder and displacive phase transition. The rotation of the cations exerts internal pressure on the stacking structure to trigger an exceptionally large displacement of the inorganic chains, corresponding to a crystal lattice transformation with length changes of +24.6% and -17.5% along the b- and c-axis, respectively. Single crystal-based prototype devices of circuit switches and elevators have been fabricated by exploiting the unconventional negative temperature-dependent actuating behaviors. This work provides a new model for the development of multifunctional mechanically responsive materials.

Tuning ferroelectric phase transition temperature by enantiomer fraction.

Tuning phase transition temperature is one of the central issues in phase transition materials. Herein, we report a case study of using enantiomer fraction engineering as a promising strategy to tune the Curie temperature (TC) and related properties of ferroelectrics. A series of metal-halide perovskite ferroelectrics (S-3AMP)x(R-3AMP)1-xPbBr4 was synthesized where 3AMP is the 3-(aminomethyl)piperidine divalent cation and enantiomer fraction x varies between 0 and 1 (0 and 1 = enantiomers; 0.5 = racemate). With the change of the enantiomer fraction, the TC, second-harmonic generation intensity, degree of circular polarization of photoluminescence, and photoluminescence intensity of the materials have been tuned. Particularly, when x = 0.70 - 1, a continuously linear tuning of the TC is achieved, showing a tunable temperature range of about 73 K. This strategy provides an effective means and insights for regulating the phase transition temperature and chiroptical properties of functional materials.