Juan Bisquert

• Distinguished Research Professor
• Research Director at Instituto de Tecnologia Química (UPV-CSIC)

The investigation of solar energy conversion materials and devices has come to the forefront of global scientific research and reached a state of maturity in the recent decades. Nonetheless, challenges that lie ahead are still enormous; substantial scientific innovation will be necessary to obtain the essential contributions and steps forward towar...

Human brain is capable of optimizing information flow and processing without energy-intensive data shuttling between processor and memory. At the core of this unique capability are billions of neurons connected through trillions of synapses—basic processing units of the brain. The action potentials or “spikes” based temporal processing using the re...

The use of the van der Waals (vdW) gap as an ion migration path, similar to cathode materials in lithium‐ion batteries, enables improved ion migration. If these materials also possess semiconductor properties, they can simultaneously control electron or hole transport. Such materials can be used in memtransistors, which combine memory and semicondu...

Memristors are key elements for building synapses and neurons in advanced neuromorphic computation. Memristors are made with a wide range of material technologies, but they share some basic functionalities to reproduce biological functions such as synapse plasticity for dynamic information processing. Here, we explain the basic neuromorphic functio...

Memristors stand out as promising components in the landscape of memory and computing. Memristors are generally defined by a conductance mechanism containing a state variable that imparts a memory effect. The current–voltage cycling causes transitions of conductance, which are determined by different physical mechanisms, such as the formation of co...

For the successful implementation of organic electrochemical transistors in neuromorphic computing, bioelectronics, and real‐time sensing applications it is essential to understand the factors that influence device switching times. This work describes a physical‐electrochemical model of the transient response to a step of the gate voltage. The mode...

Metal halide perovskites are mixed ionic‐electronic semiconductors that involve an important and particular phenomenology that negatively affects the performance and stability of next‐generation photovoltaic devices based on such material. The ionic nature of perovskites is shown to undergo not only a simple redistribution of charges but also influ...

The transient behavior of organic electrochemical transistors (OECTs) is complex due to mixed ionic‐electronic properties that play a central role in bioelectronics and neuromorphic applications. Some works applied impedance spectroscopy in OECTs for understanding transport properties and the frequency‐dependent response of devices. The transversal...

Iontronic fluidic ionic/electronic components are emerging as promising elements for artificial brain‐like computation systems. Nanopore ionic rectifiers can be operated as a synapse element, exhibiting conductance modulation in response to a train of voltage impulses, thus producing programmable resistive states. We propose a model that replicates...

Memristors stand out as promising components in the landscape of memory and computing. Memristors are generally defined by a conductance equation containing a state variable that imparts a memory effect. The current-voltage cycling causes transitions of the conductance, determined by different physical mechanisms such as the formation of conducting...

Memristors have been positioned at the forefront of the purposes for carrying out neuromorphic computation. Their tuneable conductivity properties enable the imitation of synaptic behaviour. Multipore nanofluidic memristors have shown their memristic properties and are candidate devices for liquid neuromorphic systems. Such properties are visible t...

For the successful implementation of organic electrochemical transistors in neuromorphic computing, bioelectronics, and real-time sensing applications it is essential to understand the factors that influence device switching times. Here we describe a physical-electrochemical model of the transient response to a step of the gate voltage. The model i...

The transient behaviour of organic electrochemical transistors (OECT) is complex due to mixed ionic-electronic properties that play a central role in bioelectronics, sensing and neuromorphic applications. We investigate the impedance response of ion-controlled transistors using a model that combines electronic motion along the channel and vertical...

The switching response in organic electrochemical transistors (OECT) is a basic effect in which a transient current occurs in response to a voltage perturbation. This phenomenon has an important impact on different aspects of the application of OECT, such as the equilibration times, the hysteresis dependence on scan rates, and the synaptic properti...

Multipore membranes with nanofluidic diodes show memristive and current rectifying effects that can be controlled by the nanostructure asymmetry and ionic solution characteristics in addition to the frequency and amplitude of the electrical driving signal. Here, we show that the electrical conduction phenomena, which are modulated by the interactio...

Current-voltage measurements are a standard testing protocol to determine the efficiency of any solar cell. However, perovskite solar cells display significant kinetic phenomena that modify the performance at several time scales, due to hysteresis, internal capacitances, and related mechanisms. Here, we develop a method to analyze the current-volta...

With the increasing demands and complexity of the neuromorphic computing schemes utilizing highly efficient analog resistive switching devices, understanding the apparent capacitive and inductive effects in device operation is of paramount importance. Here, we present a systematic array of characterization methods that unravel two distinct voltage-...

Based on the emergence of iontronic fluidic components for brain‐inspired computation, the general dynamical behavior of nanopore channels is discussed. The main memory effects of fluidic nanopores are obtained by the combination of rectification and hysteresis. Rectification is imparted by an intrinsic charge asymmetry that affects the ionic curre...

Halide perovskites are at the forefront of active research in many applications, such as high performance solar cells, photodetectors, and synapses and neurons for neuromorphic computation. As a result of ion transport and ionic‐electronic interactions, current and recombination are influenced by delay and memory effects that cause hysteresis of cu...

Memristors are devices in which the conductance state can be alternately switched between a high and a low value by means of a voltage scan. In general, systems containing a...

We demonstrate that nanofluidic diodes in multipore membranes show a memristive behavior that can be controlled not only by the amplitude and frequency of the external signal but also by series and parallel arrangements of the membranes. Each memristor consists of a polymeric membrane with conical nanopores that allow current rectification due to t...

Halide perovskite materials have reached important milestones in the photovoltaic field, positioning them as realistic alternatives to conventional solar cells. However, unavoidable kinetic phenomena have represented a major concern for reliable steady-state performance assessment from standard current–voltage measurements. In particular, the dynam...

Hysteresis observed in the current-voltage curves of both electronic and ionic devices is a phenomenon where the curve's shape is altered on the basis of the measurement speed. This effect is driven by internal processes that introduce a time delay in the response to an external stimulus, leading to measurements being dependent on the history of th...

Organic electrochemical transistors (OECTs) are effective devices for neuromorphic applications, bioelectronics, and sensors. Numerous reports in the literature show persistent dynamical hysteresis effects in the current–voltage curves, attributed to the slow ionic charging of the channel under the applied gate voltage. Here we present a model that...

Metal halide perovskites are archetypal ionic‐electronic materials with great prospects for optoelectronic applications. Among the rich variety of physics exhibited by ionic‐electronic conduction, here, those most relevant to optoelectronic devices in which ionic mechanisms introduce a kinetic delay in the electronic phenomena are analyzed. The att...

Resistive switching in memristors is being amply investigated for different applications in nonvolatile memory, neuromorphic computing, and programmable logic devices. Memristors are conducting devices in which the conductance depends on one or more slow internal state variables, and they exhibit strongly nonlinear properties and intense memory eff...

The rapid expansion of artificial intelligence (AI) technologies necessitates the resolution of data handling and storage limitations inherent in the von Neumann computer architecture. Drawing inspiration from biology, which initially sparked the development of artificial neural networks, we explore a new avenue in computer architecture known as ne...

Neurons, which are made of biological tissue, exhibit cognitive properties that can be replicated in various material substrates. To create brain-inspired computational artificial systems, we can construct microscopic electronic neurons that mimic natural systems. In this paper, we discuss the essential material and device properties needed for a s...

Memristor devices have been investigated for their properties of resistive modulation that can be used in data storage and brain-like computation elements as artificial synapses and neurons. Memristors are characterized by an onset of high current values under applied voltage that produces a transition to a low resistance state or successively to d...

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 at...

Despite the impressive progress, the perovskite solar cells are still under the stage of laboratory research, mainly because of their inferior operational stability. To improve the device lifetime, one of the most important strategies is to eliminate the undesirable side reactions between the functional layers. In this study, we present the thermal...

The kinetics of light emission in halide perovskite LEDs and solar cells is composed of a radiative recombination of voltage‐injected carriers mediated by additional steps such as carrier trapping, redistribution of injected carriers, and photon recycling that affect the observed luminescence decays. We investigate these processes in high performan...

Hysteresis effects in ionic-electronic devices are a valuable resource for the development of switching memory devices that can be used in information storage and brain-like computation. Halide perovskite devices show frequent hysteresis in current-voltage curves that can be harnessed to build effective memristors. These phenomena can be often desc...

Many chemical and physical systems show self-sustained oscillations that can be described by a set of nonlinear differential equations. The system enters oscillatory behavior by an intrinsic instability that leads to bifurcation. We analyze conducting systems that present oscillating response under application of external voltage or current. Phenom...

Since the inception of the unprecedented rise of halide perovskites for photovoltaic research, ion migration has shadowed this material class with undesirable hysteresis and degradation effects, limiting its practical implementations. Unfortunately, the localized doping and electrochemical reactions triggered by ion migration cause many more undesi...

Metal halide perovskite (MHP) devices often show different types of hysteresis in separate voltage domains. At low voltage, the impedance response is capacitive, and the cell gives regular hysteresis. At high voltage, the hysteresis is inverted, corresponding to an inductive response that causes a negative capacitance feature. We calculate the hyst...

The recombination lifetime is a central quantity of optoelectronic devices, as it controls properties such as the open-circuit voltage and light emission rates. Recently, the lifetime properties of halide perovskite devices have been measured over a wide range of the photovoltage, using techniques associated with a steady state by small perturbatio...

The current–voltage curves of memristors exhibit significant hysteresis effects of use for information storage and computing. Here, we provide a comparison of different devices based on MAPbI3 perovskite with different contact configurations, from a 15% efficient solar cell to a pure memristor that lacks directional photocurrent. Current–voltage cu...

The internal crossfire of ionic and electronic effects in perovskite devices forms a complex analysis problem that has not been fully solved yet. Specifically, halide photovoltaic perovskites show a photoinduced ionic inductance behavior in current transient measurements, evidenced by ubiquitous negative spikes. Here, we provide a consolidated inte...

In this work, Zr-Mo co-doping was successfully employed on electrochemically deposited BiVO4 photoanodes, and tested for photoelectrochemical (PEC) water oxidation. Zr doping induced the formation of relatively smaller morphological features resulting in improved light absorption and PEC activity. Mo doping resulted in structural damage that enhanc...

Impedance Spectroscopy (IS) has proven to be a powerful tool for the extraction of significant electronic parameters in a wide variety of electrochemical systems, such as solar cells or electrochemical cells. However, this has not been the case with perovskite solar cells, which have the particular ionic-electronic combined transport that complicat...

The synchronization of populations of interacting spiking neurons is a topic of interest for understanding the operation of the brain and for developing oscillatory‐based biomimetic computation. The analysis of the operation of neurons by models such as Hodgkin‐Huxley and FitzHugh‐Nagumo (FHN) is based on electrical and electrochemical concepts. Th...

A large body of literature reports that both bismuth vanadate and haematite photoanodes are semiconductors with an extremely high doping density between 1018 and 1021 cm-3. Such values are obtained from Mott-Schottky plots by assuming that the measured capacitance is dominated by the capacitance of the depletion layer formed by the doping density w...

A multitude of chemical, biological, and material systems present an inductive behavior that is not electromagnetic in origin. Here, it is termed a chemical inductor. We show that the structure of the chemical inductor consists of a two-dimensional system that couples a fast conduction mode and a slowing down element. Therefore, it is generally def...

Electrochemical hydrogen peroxide (H2O2) production via the two-electron oxygen reduction reaction (ORR) has received much consideration as a substitute to the well-known industrial anthraquinone method. The present challenge in this area is developing appropriate cost-efficient materials with excellent electrocatalytic properties, durability, and...

An investigation of the kinetic behavior of MAPbI3 memristors shows that the onset voltage to a high conducting state depends strongly on the voltage sweep rate, and the impedance spectra generate complex capacitive and inductive patterns. We develop a dynamic model to describe these features and obtain physical insight into the coupling of ionic a...

Spontaneous oscillations in a variety of systems, including neurons, electrochemical, and semiconductor devices, occur as a consequence of Hopf bifurcation in which the system makes a sudden transition to an unstable dynamical state by the smooth change of a parameter. We review the linear stability analysis of oscillatory systems that operate by c...

Lead free tin perovskite solar cells (PKSCs) are the most suitable alternative candidate for conventional lead perovskite solar cells. However, the efficiency and the stability are insufficient, mainly because of the poor film quality and numerous defects. Here we introduce an efficient strategy based on a simple trimethylsilyl halide surface passi...

A large body of literature reports that both bismuth vanadate and haematite photoanodes are semiconductors with an extremely high doping density between 10^18-10^21 cm^-3. Such values are obtained from Mott-Schottky plots by assuming that the measured capacitance is dominated by the capacitance of the depletion layer formed by the doping density wi...

Impedance spectroscopy (IS) provides a detailed understanding of the dynamic phenomena underlying the operation of photovoltaic and optoelectronic devices. Here we provide a broad summary of the application of IS to metal halide perovskite materials, solar cells, electrooptic and memory devices. IS has been widely used to characterize perovskite so...

The dynamics of neurons consist of oscillating patterns of a membrane potential that underpin the operation of biological intelligence. The FitzHugh-Nagumo (FHN) model for neuron excitability generates rich dynamical regimes with a simpler mathematical structure than the Hodgkin-Huxley model. Because neurons can be understood in terms of electrical...

This chapter is a summary of the understanding of the dynamic response of lead halide perovskite materials and devices when measured by electrical and electro‐optical techniques. We first review the properties of conduction, analyzing the electronic and ionic conduction properties. Then, we summarize the different types of capacitances that are fou...

Environment-friendly tin perovskite solar cells (T-PKSCs) are the most suitable alternative candidate for lead-free PKSCs. However, the photovoltaic performance of such T-PKSCs is far below those of lead-based perovskite solar cells due to an energetic mismatch between the perovskite layer and charge transport layers. Herein, it is shown that, by p...

The correlation of different methods of measurement can become an important tool to identify the dominant physical elements that govern the electronic and ionic dynamics in perovskite solar cells. The diverse phenomena underlying the response of halide perovskite materials to different stimuli are reflected in time-domain measurements, where transi...

Perovskite solar cells show a number of internal electronic–ionic effects that produce hysteresis in the current–voltage curves and a dependence of the temporal response on the conditions of the previous stimulus applied to the sample. There are many models and explanations in the literature, but predictive methods that may lead to an assessment of...

The impedance of diffusion is an important tool to investigate a wide variety of systems, including electrochemical devices such as Li-ion batteries, porous electrodes, and solar cells. The classical impedance model for diffusion in a thin layer with a blocking boundary contains two separate regimes: Warburg diffusion at high frequency and capaciti...

Reabsorption and reemission of photons, or photon recycling (PR) effect, represents an outstanding mechanism to enhance the carrier and photon densities in semiconductor thin films. This work demonstrates the propagation of recycled photons over several mm by integrating a thin film of CsPbBr3 nanocrystals into a planar waveguide. An experimental s...