Ionotronic Halide Perovskite Drift-Diffusive Synapses for Low-Power Neuromorphic Computation.

Emulation of brain-like signal processing is the foundation for development of efficient learning circuitry, but few devices offer the tunable conductance range necessary for mimicking spatiotemporal plasticity in biological synapses. An ionic semiconductor which couples electronic transitions with drift-diffusive ionic kinetics would enable energy-efficient analog-like switching of metastable conductance states. Here, ionic-electronic coupling in halide perovskite semiconductors is utilized to create memristive synapses with a dynamic continuous transition of conductance states. Coexistence of carrier injection barriers and ion migration in the perovskite films defines the degree of synaptic plasticity, more notable for the larger organic ammonium and formamidinium cations than the inorganic cesium counterpart. Optimized pulsing schemes facilitates a balanced interplay of short- and long-term plasticity rules like paired-pulse facilitation and spike-time-dependent plasticity, cardinal for learning and computing. Trained as a memory array, halide perovskite synapses demonstrate reconfigurability, learning, forgetting, and fault tolerance analogous to the human brain. Network-level simulations of unsupervised learning of handwritten digit images utilizing experimentally derived device parameters, validates the utility of these memristors for energy-efficient neuromorphic computation, paving way for novel ionotronic neuromorphic architectures with halide perovskites as the active material.

High ionic conductivity P(VDF-TrFE)/PEO blended polymer electrolytes for solid electrochromic devices.

Solid polymer electrolytes with excellent ionic conductivity (above 10(-4) S cm(-1)), which result in high optical modulation for solid electrochromic (EC) devices are presented. The combination of a polar host matrix poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) and a solid plasticized of a low molecular weight poly(ethylene oxide) (PEO) (M(w)≤ 20,000) blended polymer electrolyte serves to enhance both the dissolution of lithium salt and the ionic transport. Calorimetric measurement shows a reduced crystallization due to a better intermixing of the polymers with small molecular weight PEO. Vibrational spectroscopy identifies the presence of free ions and ion pairs in the electrolytes with PEO of M(w)≤ 8000. The ionic dissolution is improved using PEO as a plasticizer when compared to liquid propylene carbonate, evidently shown in the transference number analysis. Ionic transport follows the Arrhenius equation with a low activation energy (0.16-0.2 eV), leading to high ionic conductivities. Solid electrochromic devices fabricated with the blended P(VDF-TrFE)/PEO electrolytes and polyaniline show good spectroelectrochemical performance in the visible (300-800 nm) and near-infrared (0.9-2.4 µm) regions with a modulation up to 60% and fast switching speed of below 20 seconds. The successful introduction of the solid polymer electrolytes with its best harnessed qualities helps to expedite the application of various electrochemical devices.

Toward electrochromic device using solid electrolyte with polar polymer host.

Polymer electrolyte is an important component in many multilayer devices such as batteries, fuel cells, and electrochromic devices. The effects of polymer electrolyte solidification on the ionic movement and device performance are presented based on near-infrared (IR) (860-2500 nm) electrochromic (EC) devices using the conducting polymer polyaniline. EC devices using electrolyte with polar polymer host of P(VDF-TrFE) show stable and reversible light modulation up to 65% in gel state and 30% in solid state. This is significantly improved when compared to devices with solidified nonpolar polymer host which retains less than 10% light modulation. Electrochemical impedance combined with in situ light modulation measurement identifies various key characteristics exerted by the electrolyte states on device performance. Gel-state devices are affected by the amount of dissociated ions while ionic movement in the electrolyte bulk and through the electrolyte/EC material interface dictates the light modulation in semisolid devices. For solid-state devices, electronic leakage, ionic dissociation, and interaction with electrochrome molecules have been found to limit the operation.