Signal Filtering Enabled by Spike Voltage-Dependent Plasticity in Metalloporphyrin-Based Memristors.

Neural systems can selectively filter and memorize spatiotemporal information, thus enabling high-efficient information processing. Emulating such an exquisite biological process in electronic devices is of fundamental importance for developing neuromorphic architectures with efficient in situ edge/parallel computing, and probabilistic inference. Here a novel multifunctional memristor is proposed and demonstrated based on metalloporphyrin/oxide hybrid heterojunction, in which the metalloporphyrin layer allows for dual electronic/ionic transport. Benefiting from the coordination-assisted ionic diffusion, the device exhibits smooth, gradual conductive transitions. It is shown that the memristive characteristics of this hybrid system can be modulated by altering the metal center for desired metal-oxygen bonding energy and oxygen ions migration dynamics. The spike voltage-dependent plasticity stemming from the local/extended movement of oxygen ions under low/high voltage is identified, which permits potentiation and depression under unipolar different positive voltages. As a proof-of-concept demonstration, memristive arrays are further built to emulate the signal filtering function of the biological visual system. This work demonstrates the ionic intelligence feature of metalloporphyrin and paves the way for implementing efficient neural-signal analysis in neuromorphic hardware.

Cation-Modulated HER and OER Activities of Hierarchical VOOH Hollow Architectures for High-Efficiency and Stable Overall Water Splitting.

Atom-scale modulation of electronic regulation in nonprecious-based electrocatalysts is promising for efficient catalytic activities. Here, hierarchically hollow VOOH nanostructures are rationally constructed by partial iron substitution and systematically investigated for electrocatalytic water splitting. Benefiting from the hierarchically stable scaffold configuration, highly electrochemically active surface area, the synergistic effect of the active metal atoms, and optimal adsorption energies, the 3% Fe (mole ratio) substituted electrocatalyst (VOOH-3Fe) exhibits a low overpotential of 90 and 195 mV at 10 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, respectively, superior than the other samples with a different substituted ratio. To the best of current knowledge, 195 mV overpotential at 10 mA cm-2 is the best value reported for V or Fe (oxy)hydroxide-based OER catalysts. Moreover, the electrolytic cell employing the VOOH-3Fe electrode as both the cathode and anode exhibits a cell voltage of 0.30 V at 10 mA cm-2 with a remarkable stability over 60 h. This work heralds a new pathway to design efficient bifunctional catalysts toward overall water splitting.

4,5-Diazafluorene-Based Donor-Acceptor Small Molecules as Charge Trapping Elements for Tunable Nonvolatile Organic Transistor Memory.

Three diazafluorene derivatives triphenylamine (TPA)(PDAF) n (n = 1, 2, 3) serving as small molecular elements are designed and synthesized via concentrated sulfuric acid mediated Friedel-Crafts reaction. With highly nonplanar topological configuration, TPA(PDAF)3 shows weaker intermolecular interaction in the solid states and thus exhibits single nanomolecular behavior, which is crucial for charge stored and retained in an organic field-effect transistor (OFET) memory device. Furthermore, diazafluorene derivatives possess a completely separate highest occupied molecular orbital/lowest unoccupied molecular orbital, which offers ideal hole and electron trapping sites. As charge storage elements, triphenylamine groups provide the hole trapping sites, while diazafluorene units provide the electron trapping sites and act as a hole blocking group to restrain the leakage of stored holes trapped in triphenylamine. The pentacene-based OFET memory device with solution-processing TPA(PDAF)3 shows a good hole-trapping ability, high hole trapping density (4.55 × 1012 cm-2), fast trapping speed (<20 ms), a large memory window (89 V), and a tunable ambipolar memory behavior. The optimized device shows a large ON/OFF current ratio (2.85 × 107), good charge retention (>104 s), and reliable endurance properties. This study suggests that diazafluorene based donor-acceptor small molecular elements have great promise for high-performance OFET memory.

Side-chain Engineering of Benzo[1,2-b:4,5-b']dithiophene Core-structured Small Molecules for High-Performance Organic Solar Cells.

Three novel small molecules have been developed by side-chain engineering on benzo[1,2-b:4,5-b']dithiophene (BDT) core. The typical acceptor-donor-acceptor (A-D-A) structure is adopted with 4,8-functionalized BDT moieties as core, dioctylterthiophene as π bridge and 3-ethylrhodanine as electron-withdrawing end group. Side-chain engineering on BDT core exhibits small but measurable effect on the optoelectronic properties of small molecules. Theoretical simulation and X-ray diffraction study reveal the subtle tuning of interchain distance between conjugated backbones has large effect on the charge transport and thus the photovoltaic performance of these molecules. Bulk-heterojunction solar cells fabricated with a configuration of ITO/PEDOT:PSS/SM:PC71BM/PFN/Al exhibit a highest power conversion efficiency (PCE) of 6.99% after solvent vapor annealing.

Design and photovoltaic characterization of dialkylthio benzo[1,2-b:4,5-b']dithiophene polymers with different accepting units.

Three dialkylthio benzo[1,2-b:4,5-b']dithiophene (S-BDT) based polymers have been developed using different accepting units to tune their bandgaps. The polymer:PC71BM solar cells achieved the highest power conversion efficiency (PCE) of 4.51% without any post-treatment (such as annealing and solvent additive) in conventional single-cell devices. Joint photophysical, electrical and computational studies on the polymer based solar cells revealed the considerable impact of molecular planarity on polymer design. The polymer:PC71BM devices processed with 1,8-diiodooctane for improving their morphology afforded an improved PCE value of 5.63%, with a Voc of 0.83, a Jsc of 10.24 mA cm(-2) and a FF of 66.3%.