it generates only water as a by-product of combustion. In addition, the energy mass density of hydrogen is higher than that of fossil fuel. [1][2][3] Photoelectrochemical (PEC) water splitting systems for hydrogen generation using solar energy have been intensively developed in recent years. [3] The total reactions in such systems are generally divided into the oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode. [4] To obtain green hydrogen through solar-driven water splitting reactions without external bias, the PEC cell follows a three-step process (light absorption, charge transport, and charge transfer), proceeding through four functional layers (absorption layer, buffer layer, protection layer, and co-catalyst). [3,4] Each layer performs various roles to improve the PEC performance. The absorption layer absorbs sunlight to form electronhole pairs (EHP) and separates the excited EHP. [5] This layer has a sufficiently long carrier diffusion length to allow the charge carrier to reach the surface of the electrode. Light absorption can be increased by improving conductivity through morphology control, doping, and bandgap tuning of the absorption layer. [4,6] Typically, n-type metal oxides, such as TiO 2 (3.0 eV), [7][8][9] WO 3 (2.8 eV), [10,11] BiVO 4 (2.4 eV), [12,13] and Fe 2 O 3 (2.3 eV), [14,15] have been actively studied as photoanodes for OER, while p-type photocathodes for HER have been developed based on copper-based binary or ternary oxides. [16][17][18][19] The buffer layer forms a heterojunction structure with the semiconducting absorption layer in consideration of the energy band-offset and built-in potential to efficiently deliver the photo-generated charges to the surface or catalysts through an internal electric field, where metal oxide materials, such as Al-doped ZnO (AZO), Ga 2 O 3 , and CuO, act as the buffer layer for p-type Cu 2 O photoabsorbers. [20] Furthermore, the buffer layer on photoabsorbers can increase the photovoltage and photocurrent by overcoming insufficient charge separation and transfer efficiency (TE). [21] In PEC water splitting systems, the absorbers are immersed directly in an aqueous electrolyte, resulting in Photoelectrochemical (PEC) cells using Cu 2 O, semiconductor photoabsorbers passivated by protection layers, show a trade-off between high photocurrent and stability because of the thickness of the energy band transport along the conduction band. Based on nanofilaments with non-volatile metal-like current flow characteristics in resistance-change memory devices, a strategically advanced conducting filament transport mechanism for vigorous and robust PEC operation is proposed. The breakdown-like electrochemical forming behavior effectively occurs with a rapid increase in current at ≈2 V (vs RHE). The fundamental properties of filaments, such as diameter, density, and conductivity, are controlled by varying the artificial compliance currents. This process does not require any top electrodes that obstruct light-harvesting a...

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The performance of bismuth vanadate (BiVO4) photoanodes is limited by surface defects and photo-corrosion instabilities. This paper proposes a revolutionary protection layer that overcomes these problems. Considering the role of...

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To utilize continuous ultralow intensity signals from oxide synaptic transistors as artificial synapses that mimic human visual perception, we propose strategic oxide channels that optimally utilize their advantageous functions by stacking two oxide semiconductors with different conductivities. The bottom amorphous indium–gallium–zinc oxide (a-IGZO) layer with a relatively low conductivity was designed for an extremely low initial postsynaptic current (PSCi) by achieving full depletion at a low negative gate voltage, and the stacked top amorphous indium–zinc oxide (a-IZO) layer improved the amplitude of the synaptic current and memory retention owing to the enhancement in the persistent photoconductivity characteristics. We demonstrated an excellent photonic synapse thin-film transistor (TFT) with a precise synaptic weight change even in the range of ultralow light intensity by adapting this stacking IGZO/IZO channel. The proposed device exhibited distinct ∆PSC values of 3.1 and 18.1 nA under ultralow ultraviolet light (350 nm, 50 ms) of 1.6 and 8.0 μW/cm2. In addition, while the lowest light input exhibited short-term plasticity characteristics similar to the “volatile-like” behavior of the human brain with a current recovery close to the initial value, the increase in light intensity caused long-term plasticity characteristics, thus achieving synaptic memory transition in the IGZO/IZO TFTs.