No abstract

Perovskite memristors have emerged as leading contenders in brain-inspired neuromorphic electronics. Although these devices have been shown to accurately reproduce synaptic dynamics, they pose challenges for in-depth understanding of the underlying nonlinear phenomena. Potentiation effects on the electrical conductance of memristive devices have attracted increasing attention from the emerging neuromorphic community, demanding adequate interpretation. Here, we propose a detailed interpretation of the temporal dynamics of potentiation based on nonlinear electrical circuits that can be validated by impedance spectroscopy. The fundamental observation is that the current in a capacitor decreases with time; conversely, for an inductor, it increases with time. There is no electromagnetic effect in a halide perovskite memristor, but ionic-electronic coupling creates a chemical inductor effect that lies behind the potentiation property. Therefore, we show that beyond negative transients, the accumulation of mobile ions and the eventual penetration into the charge-transport layers constitute a bioelectrical memory feature that is the key to long-term synaptic enhancement. A quantitative dynamical electrical model formed by nonlinear differential equations explains the memory-based ionic effects to inductive phenomena associated with the slow and delayed currents, invisible during the “off mode” of the presynaptic spike-based stimuli. Our work opens a new pathway for the rational development of material mimesis of neural communications across synapses, particularly the learning and memory functions in the human brain, through a Hodgkin-Huxley-style biophysical model.

This study focuses on understanding the fundamentals of energy transfer and electron transport in photovoltaic devices with uniquely designed nanostructures by analysing energy transfer in purple photosynthetic bacteria using dye-sensitised solar cell systems. F€ orster resonance energy transfer between the xanthene dye (donor of energy) and a new polymethine dye (acceptor of energy) was studied in dye-sensitised solar cells, which leads to a doubling of energy conversion efficiency in comparison to the cell with only the polymethine dye. The electron transport in the two different nanostructures of zinc oxide (nanorods and nanosheets) was investigated by spectroscopic methods (UV-vis spectrometer, time-resolved photoluminescence spectroscopy) and electrochemical potentiostat methods. The nanosheet structure of zinc oxide showed high short circuit current and long diffusion length. This fundamental study will lead to efficient artificial photosystem designs.

In this study, the effect of modification of poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) morphology on its optical, charge transport, and photovoltaic properties of organic solar cells based on the P3HT:PC60BM bulk heterojunction is presented. It is shown that the addition of isopropyl alcohol to the PEDOT:PSS polymer solution and annealing of spin‐coated PEDOT:PSS film leads to a change in its morphology, charge transport, and optical properties. By an impedance spectroscopy technique, the charge transport properties of PEDOT:PSS films were studied. It was established that the efficiency of carrier transport and the efficiency of the polymer solar cells depends on the structural features of PEDOT:PSS.