Two-dimensional ferroelectrics is attractive for synaptic device applications because of its low power consumption and amenability to high-density device integration. Here, we demonstrate that tin monosulfide (SnS) films less than 6 nm thick show optimum performance as a semiconductor channel in an in-plane ferroelectric analogue synaptic device, whereas thicker films have a much poorer ferroelectric response due to screening effects by a higher concentration of charge carriers. The SnS ferroelectric device exhibits synaptic behaviors with highly stable room-temperature operation, high linearity in potentiation/depression, long retention, and low cycle-to-cycle/device-to-device variations. The simulated device based on ferroelectric SnS achieves ∼92.1% pattern recognition accuracy in an artificial neural network simulation. By switching the ferroelectric domains partially, multilevel conductance states and the conductance ratio can be obtained, achieving high pattern recognition accuracy.

Hybrid organic−inorganic perovskites (HOIPs) are a new generation of high-performance materials for solar cells and light emitting diodes. Beyond these applications, ferroelectricity and spin-related properties of HOIPs are increasingly attracting interests. The presence of strong spin−orbit coupling, allied with symmetry breaking ensured by remanent polarization, should give rise to Rashbatype splitting of electronic bands in HOIP. However, the report of both ferroelectricity and Rashba effect in HOIP is rare. Here we report the observation of robust ferroelectricity and Rashba effect in two-dimensional Dion-Jacobson perovskites.

Dion−Jacobson (DJ) phase organic−inorganic hybrid perovskites (OIHPs) have emerged as promising alternatives to Ruddlesden−Poppers perovskites because of their chemical stability and ferroelectric phase. Here we fabricate a ferroelectricitymodulated photodetector based on the n = 2 homologue of the ferroelectric two-dimensional DJ-OIHP (AMP)(MA)Pb 2 I 7 (DJP n=2 , AMP = 4-(aminomethyl)piperidinium; MA = methylammonium), which shows an out-of-plane polarization and a saturated polarization (P s ) value of 3.7 μC/cm 2 . The coercive field of DJP n=2 (0.34 kV/cm) is lower than that for the n = 1 homologue (AMP)PbI 4 (DJP n=1 ,0.4 kV/cm). DJP n=2 has a much longer carrier lifetime and absorption edge (580 nm, 2.13 eV) in comparison to DJP n=1 (523 nm, 2.37 eV); thus, DJP n=2 can be used for efficient photodetection in the visible range, in which a responsivity of 0.16 mA/W was achieved at 532 nm. The influence of remnant polarization on the direction and magnitude of the photocurrent was also demonstrated.

Hybrid organic-inorganic perovskites have recently emerged as potential disruptive photovoltaic technology. However, the toxicity of lead used in state-of-the-art hybrid perovskites solar cell prevents large-scale commercialization, which calls for lead-free alternatives. Sn-based perovskites have been considered as alternatives but they are limited by rapid oxidation and decomposition in ambient air. Here, an Sn-based two-dimensional hybrid organic-inorganic perovskites [A 2 B (n-1) Sn n I (3n+1) ] (n = 1 and 2) are reported with improved air stability, using bulky stilbene derivatives as the organic cations (2-(4-(3-fluoro)stilbenyl)ethanammonium iodide (FSAI)). The moisture stability of the [(FSA) 2 SnI 4 ] perovskites is attributed to the hydrophobic properties of fluorine-functionalized organic chains (FSA), as well as the strong cohesive bonding in the organic chains provided by H bonds, CH···X type H bonds, weak interlayer F···F interaction, and weak face-to-face type π-π interactions. The photodetector device fabricated on exfoliated single crystal flake of [(FSA) 2 SnI 4 ] exhibits fast and stable photoconductor response.

Ligand‐induced surface restructuring with heteroatomic doping is used to precisely modify the surface of a prototypical [Au25(SR1)18]− cluster (1) while maintaining its icosahedral Au13 core for the synthesis of a new bimetallic [Au19Cd3(SR2)18]− cluster (2). Single‐crystal X‐ray diffraction studies reveal that six bidentate Au2(SR1)3 motifs (L2) attached to the Au13 core of 1 were replaced by three quadridentate Au2Cd(SR2)6 motifs (L4) to create a bimetallic cluster 2. Experimental and theoretical results demonstrate a stronger electronic interaction between the surface motifs (Au2Cd(SR2)6) and the Au13 core, attributed to a more compact cluster structure and a larger energy gap of 2 compared to that of 1. These factors dramatically enhance the photoluminescence quantum efficiency and lifetime of crystal of the cluster 2. This work provides a new route for the design of a wide range of bimetallic/alloy metal nanoclusters with superior optoelectronic properties and functionality.