Abstract To realize economically feasible electrochemical CO 2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the ...hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO 2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm ‒2 ), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO 2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO 2 RR instead of HER. We analyze catalyst degradation and cathode flooding during CO 2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO 2 electrolysis.
The optoelectronic devices based on colloidal lead sulfide quantum dots (PbS QDs) have suffered from electronic trap states in bandgap. The trap state is a source for accelerating carrier ...recombination and degrading the performance of optoelectronic devices. Here, we treated PbS QD electrochemically using cyclic voltammetry to modulate the density of trap states. The reduction of the trap density in the QD layer after electrochemical treatment was confirmed by the impedance analyzing technique, the thermal admittance spectroscopy. The XPS spectra showed that the QD films are oxidized after the electrochemical treatment, implying that the oxidation of the QD surface regulated the trap density through the electrochemical treatment.
Abstract
Colloidal InAs quantum dots (QDs) are emerging candidates for NIR-SWIR optoelectronic applications because of their excellent electrical and optical properties. However, the syntheses of ...InAs QDs, which demand strongly reducing atmospheres or highly reactive precursors, are difficult because of their highly covalent bonding and lack of Group 15 precursors. While the coreduction method with commercially available arsenic precursors enables facile syntheses of InAs QDs, it results in broad size distributions requiring subsequent size-selection processes. In this study, we introduced zinc ions in the form of coordination complexes during coreduction of the indium and arsenic precursors. The Zn ions chemically passivated the surfaces of the InAs QDs, narrowed the size distribution and removed surface defects. When the InAs QDs were integrated into infrared photodiodes as IR absorbers, the surface-attached Zn ions electrically modulated the energy level and carrier concentration. Infrared photodiodes with the InAs:Zn QD layers exhibited dark currents and photoresponses that were two orders of magnitude lower and approximately twice as fast, respectively, as those seen for bare InAs QDs.
Human behavior (e.g., the response to any incoming information) has very complex forms and is based on the response to consecutive external stimuli entering varied sensory receptors. Sensory ...adaptation is an elementary form of the sensory nervous system known to filter out irrelevant information for efficient information transfer from consecutive stimuli. As bioinspired neuromorphic electronic system is developed, the functionality of organs shall be emulated at a higher level than the cell. Because it is important for electronic devices to possess sensory adaptation in spiking neural networks, the authors demonstrate a dynamic, real‐time, photoadaptation process to optical irradiation when repeated light stimuli are presented to the artificial photoreceptor. The filtered electrical signal generated by the light and the adapting signal produces a specific range of postsynaptic states through the neurotransistor, demonstrating changes in the response according to the environment, as normally perceived by the human brain. This successfully demonstrates plausible biological sensory adaptation. Further, the ability of this circuit design to accommodate changes in the intensity of bright or dark light by adjusting the sensitivity of the artificial photoreceptor is demonstrated. Thus, the proposed artificial photoreceptor circuits have the potential to advance neuromorphic device technology by providing sensory adaptation capabilities.
Sol–gel‐derived neurotransistors integrated with perovskite‐based photodetectors are designed to serve as an artificial optoelectronic device array, which experimentally demonstrates the emulation of the dynamic adaptation process of the biological visual nervous system. The fundamental properties of biological adaptation, such as accuracy and desensitization behaviors, are characterized. These results enable post‐synaptic responses to be manipulated to obtain external‐environment‐dependent encoded images.
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•The impact of Fermi level pinning on energy level alignment in PbS quantum dot is examined.•UPS analyses indicate that energetic position of PbS QD’s gap-state to be c.a. 4.0 eV.•The ...pinning factors (S) for PbS QD-EDT and PbS-TBAI are empirically determined by UPS and LEIPES.•Higher S for PbS-EDT indicate the TBAI more effectively passivates the gap-state of PbS QD.
PbS quantum dots capped by ethanedithiol (PbS QD-EDT) and tetrabutylammonium iodide (PbS QD-TBAI) and supported by different substrates were examined in terms of Fermi level pinning (FLP), gap states, and electron and hole barriers (Φe and Φh, respectively) using ultraviolet and low-energy inverse photoemission spectroscopy. The former analysis showed that TBAI and EDT differed in their ability to induce gap-state passivation, with the corresponding energy difference determined as 4.0 eV. Two FLP regimes were identified: at substrate work function (Фsub) < 4.0 eV, both ligands showed perfect FLP (S ≈ 0 for holes and electrons), whereas at Фsub > 4.0 eV, the pinning strength of PbS QD-EDT (S of Фb,h and Фb,e = 0.19 and 0.24, respectively) exceeded that of PbS QD-TBAI (S of Фb,h and Фb,e = 0.53 and 0.57, respectively). Thus, the gap states were more effectively passivated in the case of PbS QD-TBAI. Our results indicate the importance of considering FLP strength when working with high-work-function substrates for the design of optimized QD-based devices.
We fabricated a 1 × 10 PbS QD photodiode array with multiple stacked QD layers with high-resolution patterning using a customized photolithographic process. The array showed the average responsivity ...of 5.54 × 10 −3 A/W and 1.20 × 10 −2 A/W at 0 V and -1 V under 1310- nm short-wavelength infrared (SWIR) illumination. The standard deviation of the pixel responsivity was under 10%, confirming the uniformity of the fabrication process. The response time was 2.2 ± 0.13 ms, and the bandwidth was 159.1 Hz. A prototype 1310-nm SWIR imager demonstrated that the QD photodiode-based SWIR image sensor is a cost-effective and practical alternative for III-V SWIR image sensors.
Optoelectronic Device Arrays
In article number 2105485, Tae‐Yeon Seong and co‐workers experimentally demonstrate dynamic photoadaptation behavior of an integrated optoelectronic device array that ...mimics the functionality of the biological visual nervous system. The device array, which is designed to adapt to repeated optical stimuli that change according to external conditions, exhibits excellent performance. This autonomic response to stimuli is essential to the improvement of next‐generation bionic electronics.
There is a growing demand for human-eye-invisible short-wave infrared (SWIR) detection due to its potential in applications in areas such as medical diagnostics, environmental monitoring, and night ...vision. PbS colloidal quantum dots (QDs) are a promising light absorber for SWIR detection. Herein, we report on a PbS QD/InGaZnO (IGZO) heterostructure-based phototransistor and flat-panel imager for human-eye-safe SWIR photodetection and high-resolution imaging. Such hybrid phototransistors show good electrical performance and obvious photoresponse behaviors with a maximum responsivity of 104 A/W and specific detectivity of 1012 Jones under 1310 nm SWIR illumination. We found that PbS QD ligand molecules significantly impact the environmental stability. Phototransistors featuring a tetrabutylammonium iodide (TBAI) ligand exhibit excellent air stability with no serious degradation after exposure to air for 3 weeks, while phototransistors with ethanedithiol (EDT) ligands lose their SWIR detecting capability within 2 weeks. Such an improved air stability may be correlated with the TBAI ligand passivation effect that is confirmed by X-ray photoemission spectroscopy analyses. PbS QDs are patterned on the flexible IGZO transistor array by photolithographic lift-off method for implementing a more practical imaging pixel array. Furthermore, we demonstrate a prototype of 1.3 μm SWIR flat-panel image sensor array, establishing its potential application in advanced developments as a gate-tunable, highly sensitive, high-resolution, and large area flat-panel SWIR imager.
We report the effect of oxidation on PbS quantum dot (QD) photodetectors using rapid thermal annealing (RTA) and furnace annealing in air at different durations and temperatures. Air-annealed QD ...films using RTA had an improved specific detectivity of up to 1.51 × 1012 Jones with a responsivity of up to 1.895 × 103 A/W at 1 kHz. We used transient photocurrent decay measurements, X-ray photoelectron spectroscopy, and frequency response measurements to investigate the origin of this effect. We found that short-term annealing with RTA in air increases the product of carrier mobility and carrier lifetime (μτ) of the QD photoconductors, which leads to high photoconductive gain and bandwidth.
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