Future brain-machine interfaces, prosthetics, and intelligent soft robotics will require integrating artificial neuromorphic devices with biological systems. Due to their poor biocompatibility, ...circuit complexity, low energy efficiency, and operating principles fundamentally different from the ion signal modulation of biology, traditional Silicon-based neuromorphic implementations have limited bio-integration potential. Here, we report the first organic electrochemical neurons (OECNs) with ion-modulated spiking, based on all-printed complementary organic electrochemical transistors. We demonstrate facile bio-integration of OECNs with Venus Flytrap (Dionaea muscipula) to induce lobe closure upon input stimuli. The OECNs can also be integrated with all-printed organic electrochemical synapses (OECSs), exhibiting short-term plasticity with paired-pulse facilitation and long-term plasticity with retention >1000 s, facilitating Hebbian learning. These soft and flexible OECNs operate below 0.6 V and respond to multiple stimuli, defining a new vista for localized artificial neuronal systems possible to integrate with bio-signaling systems of plants, invertebrates, and vertebrates.
Bismuth‐based ternary halides have recently gained a lot of attention as lead‐free perovskite materials. However, photovoltaic performances of these devices remain poor, mostly due to their ...low‐dimensional crystal structure and large bandgap. Here, a dynamic hot casting technique to fabricate silver bismuth iodide‐based perovskite solar cells under an ambient atmosphere with power conversion efficiencies above 2.5% is demonstrated. Silver bismuth iodides are 3D analogs of complex ternary bismuth halides with a suitable bandgap for a single junction solar cell. As far as it is known, these results represent the highest efficiency for solution processed air‐stable lead‐free perovskite solar cells. The enhanced solar cell performance via this dynamic hot casting technique can be attributed to long carrier lifetimes, micrometer‐sized crystalline grains, and pinhole free thin‐film formation with uniform morphology. This work provides a new direction for fabrication of solution‐processed lead‐free perovskite solar cells with a rapid fabrication strategy irrespective of the processing environment.
A dynamic hot casting technique is presented to fabricate silver bismuth iodide‐based perovskite solar cells under an ambient atmosphere with power conversion efficiencies above 2.5%. The enhanced solar cell performance can be ascribed to pin‐hole free thin‐film formation with uniform morphology, micrometer‐sized crystalline grains, and long carrier lifetime.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Organic electrochemical transistors (OECTs) are being researched for various applications, ranging from sensors to logic gates and neuromorphic hardware. To meet the requirements of these ...diverse applications, the device fabrication process must be compatible with flexible and scalable digital techniques. Here, we report a direct-write additive process to fabricate fully 3D-printed OECTs, using 3D printable conducting, semiconducting, insulating, and electrolyte inks. These 3D-printed OECTs, which operate in the depletion mode, can be fabricated on flexible substrates, resulting in high mechanical and environmental stability. The 3D-printed OECTs have good dopamine biosensing capabilities (limit of detection down to 6 µM without metal gate electrodes) and show long-term (~1 h) synapse response, indicating their potential for various applications such as sensors and neuromorphic hardware. This manufacturing strategy is suitable for applications that require rapid design changes and digitally enabled direct-write techniques.
Future brain–computer interfaces will require local and highly individualized signal processing of fully integrated electronic circuits within the nervous system and other living tissue. New devices ...will need to be developed that can receive data from a sensor array, process these data into meaningful information, and translate that information into a format that can be interpreted by living systems. Here, the first example of interfacing a hardware‐based pattern classifier with a biological nerve is reported. The classifier implements the Widrow–Hoff learning algorithm on an array of evolvable organic electrochemical transistors (EOECTs). The EOECTs’ channel conductance is modulated in situ by electropolymerizing the semiconductor material within the channel, allowing for low voltage operation, high reproducibility, and an improvement in state retention by two orders of magnitude over state‐of‐the‐art OECT devices. The organic classifier is interfaced with a biological nerve using an organic electrochemical spiking neuron to translate the classifier's output to a simulated action potential. The latter is then used to stimulate muscle contraction selectively based on the input pattern, thus paving the way for the development of adaptive neural interfaces for closed‐loop therapeutic systems.
A modular circuit constructed mainly of organic electrochemical transistors is used to classify patterns written on a 4 × 4 pixel array, translate a positive classification to a signal that is interpretable by biological systems, and interface with the ventral nerve cord of a medicinal leech to actuate muscle contraction upon encountering a positive classification.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Double perovskite halides are a class of materials with diverse chemistries that are amenable to solution-based synthesis routes, and display a range of properties for a variety of potential ...applications. Starting from a consideration of the octahedral and tolerance factors of ∼2000 candidate double perovskite compounds, we compute structural, electronic, and transport properties of ∼1000 using first-principles calculations based on density-functional-theory methods. The computational results have been assembled in a database that is accessible through the Materials Project online. As one potential application, double perovskites are candidates in the search for lead-free halide photovoltaic absorbers. We present the application of our database to aid the discovery of new double perovskite halide photovoltaic materials, by combining the results with optical absorption and phonon stability calculations. From three distinct classes of chemistries, 11 compounds were identified as promising solar absorbers and the complex chemical trends for band gap within each of these are analyzed, to provide guidelines for the use of substitutional alloying as a means of further tuning the electronic structure. Other possible applications of the database are also discussed.
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IJS, KILJ, NUK, PNG, UL, UM
Biointegrated neuromorphic hardware holds promise for new protocols to record/regulate signalling in biological systems. Making such artificial neural circuits successful requires minimal ...device/circuit complexity and ion-based operating mechanisms akin to those found in biology. Artificial spiking neurons, based on silicon-based complementary metal-oxide semiconductors or negative differential resistance device circuits, can emulate several neural features but are complicated to fabricate, not biocompatible and lack ion-/chemical-based modulation features. Here we report a biorealistic conductance-based organic electrochemical neuron (c-OECN) using a mixed ion-electron conducting ladder-type polymer with stable ion-tunable antiambipolarity. The latter is used to emulate the activation/inactivation of sodium channels and delayed activation of potassium channels of biological neurons. These c-OECNs can spike at bioplausible frequencies nearing 100 Hz, emulate most critical biological neural features, demonstrate stochastic spiking and enable neurotransmitter-/amino acid-/ion-based spiking modulation, which is then used to stimulate biological nerves in vivo. These combined features are impossible to achieve using previous technologies.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Lead-free halide perovskite semiconductors are necessary due to the atmospheric instability and lead toxicity associated with the 3D lead halide perovskites. However, a stable lead-free perovskite ...with an ideal band gap (1.2–1.4 eV) for photovoltaics is still missing. In this work, we synthesized organic–inorganic gold halide double perovskites ((CH3NH3)2Au2 X 6, X = Br, I) through a solution-processed route that offers an ideal direct band gap for photovoltaic applications. Density functional theory calculations confirm the direct nature of the band gap with reasonable absorption coefficients in the visible range and excellent charge transport properties. In addition, the Au-halide perovskites show high chemical stability and photoresponse. These combined properties demonstrate that Au-based halide perovskites can be a promising group of compounds for optoelectronic applications.
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IJS, KILJ, NUK, PNG, UL, UM
Realization of reduced ionic (cationic and anionic) defects at the surface and grain boundaries (GBs) of perovskite films is vital to boost the power conversion efficiency of organic–inorganic halide ...perovskite (OIHP) solar cells. Although numerous strategies have been developed, effective passivation still remains a great challenge due to the complexity and diversity of these defects. Herein, a solid‐state interdiffusion process using multi‐cation hybrid halide perovskite quantum dots (QDs) is introduced as a strategy to heal the ionic defects at the surface and GBs. It is found that the solid‐state interdiffusion process leads to a reduction in OIHP shallow defects. In addition, Cs+ distribution in QDs greatly influences the effectiveness of ionic defect passivation with significant enhancement to all photovoltaic performance characteristics observed on treating the solar cells with Cs0.05(MA0.17FA0.83)0.95PbBr3 (abbreviated as QDs‐Cs5). This enables power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h.
Introduction of multi‐cation hybrid halide perovskite quantum dots reduces ionic defects at the surface and grain boundaries via a solid‐state interdiffusion process. The enhanced moisture and photostability enable power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Organic electrochemical transistors formed by in operando electropolymerization of the semiconducting channel are increasingly becoming recognized as a simple and effective implementation of synapses ...in neuromorphic hardware. However, very few studies have reported the requirements that must be met to ensure that the polymer spreads along the substrate to form a functional conducting channel. The nature of the interface between the substrate and various monomer precursors of conducting polymers through molecular dynamics simulations is investigated, showing that monomer adsorption to the substrate produces an increase in the effective monomer concentration at the surface. By evaluating combinatorial couples of monomers baring various sidechains with differently functionalized substrates, it is shown that the interactions between the substrate and the monomer precursor control the lateral growth of a polymer film along an inert substrate. This effect has implications for fabricating synaptic systems on inexpensive, flexible substrates.
Evolvable organic electrochemical transistors rely on the ability of an electropolymerized conducting polymer to bridge the gap between two metal electrodes on an insulating substrate. This work presents a systematic investigation, supported by molecular dynamics simulations, of the monomer and substrate complementarity that is required to produce functional conducting channels.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Bismuth-based double perovskite Cs
AgBiBr
is regarded as a potential candidate for low-toxicity, high-stability perovskite solar cells. However, its performance is far from satisfactory. Albeit being ...an indirect bandgap semiconductor, we observe bright emission with large bimolecular recombination coefficient (reaching 4.5 ± 0.1 × 10
cm
s
) and low charge carrier mobility (around 0.05 cm
s
V
). Besides intermediate Fröhlich couplings present in both Pb-based perovskites and Cs
AgBiBr
, we uncover evidence of strong deformation potential by acoustic phonons in the latter through transient reflection, time-resolved terahertz measurements, and density functional theory calculations. The Fröhlich and deformation potentials synergistically lead to ultrafast self-trapping of free carriers forming polarons highly localized on a few units of the lattice within a few picoseconds, which also breaks down the electronic band picture, leading to efficient radiative recombination. The strong self-trapping in Cs
AgBiBr
could impose intrinsic limitations for its application in photovoltaics.
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