3.1. Fundamental Characterization 6672 3.2. Photocurrent Action Spectroscopy 6673 3.3. Optical Characterization 6673 3.4. Characterization of Electron Transfer 6673 4. Electron Transport in Metal Oxide Films 6674 4.1. Mechanism of Photoinduced Carrier Transport 6674 4.2. Characterization of Diffusion Length 6675 4.3. One-Dimensional (1-D) Transport Architectures 6675 4.4. Electrolyte Interactions 6676 5. Recent Trends in Liquid-Junction Solar Cells 6676 5.1. Dye Sensitized Solar Cells 6677 5.2. Quantum Dot Sensitized Solar Cells 6678 5.3. Carbon Nanostructure Based Photochemical Solar Cells 6679

Beyond Photovoltaics: Semiconductor Nanoarchitectures for Liquid-Junction Solar Cells

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

Compound Copper Chalcogenide Nanocrystals

The rapid development of information technology has led to urgent requirements for high efficiency and ultralow power consumption. In the past few decades, neuromorphic computing has drawn extensive attention due to its promising capability in processing massive data with extremely low power consumption. Here, we offer a comprehensive review on emerging artificial neuromorphic devices and their applications. In light of the inner physical processes, we classify the devices into nine major categories and discuss their respective strengths and weaknesses. We will show that anion/cation migration-based memristive devices, phase change, and spintronic synapses have been quite mature and possess excellent stability as a memory device, yet they still suffer from challenges in weight updating linearity and symmetry. Meanwhile, the recently developed electrolyte-gated synaptic transistors have demonstrated outstanding energy efficiency, linearity, and symmetry, but their stability and scalability still need to be optimized. Other emerging synaptic structures, such as ferroelectric, metal–insulator transition based, photonic, and purely electronic devices also have limitations in some aspects, therefore leading to the need for further developing high-performance synaptic devices. Additional efforts are also demanded to enhance the functionality of artificial neurons while maintaining a relatively low cost in area and power, and it will be of significance to explore the intrinsic neuronal stochasticity in computing and optimize their driving capability, etc. Finally, by looking into the correlations between the operation mechanisms, material systems, device structures, and performance, we provide clues to future material selections, device designs, and integrations for artificial synapses and neurons.

A comprehensive review on emerging artificial neuromorphic devices

Functional nanostructured materials have attracted great attention over the past several decades owing to their unique physical and chemical properties, while their applications have been proven to be advantageous not only in fundamental scientific areas, but also in many technological fields. Spray pyrolysis (SP), which is particularly facile, effective, highly scalable and suitable for on-line continuous production, offers significant potential for the rational design and synthesis of various functional nanostructured materials with tailorable composition and morphology. In this review, we summarize the recent progress in various functional nanostructured materials synthesized by SP and their potential applications in energy storage and conversion. After a brief introduction to the equipment, components, and working principles of the SP technique, we thoroughly describe the guidelines and strategies for designing particles with controlled morphology, composition, and interior architecture, including hollow structures, dense spheres, yolk–shell structures, core–shell structures, nanoplates, nanorods, nanowires, thin films, and various nanocomposites. Thereafter, we demonstrate their suitability for a wide range of energy storage and conversion applications, including electrode materials for rechargeable batteries, supercapacitors, highly active catalysts for hydrogen production, carbon dioxide reduction and fuel cells, and photoelectric materials for solar cells. Finally, the potential advantages and challenges of SP for the preparation of nanostructured materials are particularly emphasized and discussed, and several perspectives on future research and development directions of SP are highlighted. We expect that this continuous, one-pot, and controllable synthetic technology can serve as a reference for preparing various advanced functional materials for broader applications.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion.

Routes to copper zinc tin sulfide Cu2ZnSnS4 a potential material for solar cells.

We report dual ion beam sputtering fabrication of an Al/ZnO/Al memristor displaying forming-free bipolar resistive switching characteristics with memristive behavior without necessitating any post-processing steps. A nearly amorphous ZnO thin film and an appropriate concentration of oxygen vacancies play a significant role in imparting forming-free, stable, and reliable behavior to memory cells. Besides, sufficient non-lattice oxygen ions in the film play a crucial role in the resistive switching process. The AlOx interface layer is observed to strongly affect the switching mechanism in the memory device by altering the barrier at the Al/ZnO interface. The device shows stable switching behavior for >250 cycles with good retention and stable set/reset voltages.

Forming-free high-endurance Al/ZnO/Al memristor fabricated by dual ion beam sputtering

Cu2ZnSnS4 (CZTS) thin films were prepared by simultaneous sputtering of metallic targets and sulfurizing a metallic precursor under elemental sulfur atmosphere in a sealed tube. Subsequently, they were applied to the fabrication of thin film solar cells. The precursors with desired compositional ratio and thickness were obtained by controlling the area ratio of sputtering targets and also sputtering parameters. We have succeeded in obtaining high-quality polycrystalline CZTS thin films by sulfurization under a sulfur vapor pressure higher than atmospheric pressure. A CZTS-based solar cell with 3.7% conversion efficiency was obtained from CZTS films sulfurized at 590 °C for 7 min.

https://iopscience.iop.org/article/10.1143/JJAP.50.01BG09/pdf

Cu2ZnSnS4 Thin Film Solar Cells Utilizing Sulfurization of Metallic Precursor Prepared by Simultaneous Sputtering of Metal Targets

A cadmium-free Cu2ZnSnS4/ZnO hetrojunction solar cell with conversion efficiency of 4.29% has been obtained. The Cu2ZnSnS4 absorber film was formed utilizing sulfurization of laminated metallic precursors, and the ZnO buffer layer was then deposited on it by ultrasonic spray pyrolysis. In comparison with a conventional Cu2ZnSnS4/CdS hetrojunction solar cell, the open circuit voltage as well as the relative quantum efficiency at the short-wavelength regions was increased. The in-plane homogeneity of p–n junction was improved by depositing the ZnO layer on Cu2ZnSnS4 film via ultrasonic spray pyrolysis.

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A Cadmium-Free Cu2ZnSnS4/ZnO Hetrojunction Solar Cell Prepared by Practicable Processes

Single synaptic device with inherent learning and memory functions is demonstrated based on a forming-free amorphous Y2O3 (yttria) memristor fabricated by dual ion beam sputtering system. Synaptic functions such as nonlinear transmission characteristics, long-term plasticity, short-term plasticity and 'learning behavior (LB)' are achieved using a single synaptic device based on cost-effective metal-insulator-semiconductor (MIS) structure. An 'LB' function is demonstrated, for the first time in the literature, for a yttria based memristor, which bears a resemblance to certain memory functions of biological systems. The realization of key synaptic functions in a cost-effective MIS structure would promote much cheaper synapse for artificial neural network.

https://iopscience.iop.org/article/10.1088/1361-6528/aaa0eb/pdf

Realization of synaptic learning and memory functions in Y2O3 based memristive device fabricated by dual ion beam sputtering.

Submicron single crystals of ZnO were grown by spray pyrolysis: the mist of an aqueous solution was generated by ultrasonic agitation and then pyrolyzed on a heated glass substrate. Hexagonal platelets of ZnO 10–90 nm thick were obtained when ammonium acetate was incorporated into the precursor solution of zinc acetate. Single-crystalline wires and rods, which were 50–150 and 300–4000 nm thick respectively, were obtained when indium nitrate was co-incorporated into the solution as a metal catalyst. The crystallographic direction of wires and rods was parallel to one of the [0001], [1010], or [1120] axis of wurtzite. As substrate temperature increased, the aspect ratio of the crystal thus tended to decrease. Structural and compositional analyses of these crystals were performed by scanning electron microscopy, scanning ion microscopy, transmission electron microscopy and electron diffraction, X-ray diffraction, X-ray photoelectron spectrocopy, and energy dispersive X-ray spectroscopy.

Myo Than Htay

Papers

Forming-free high-endurance Al/ZnO/Al memristor fabricated by dual ion beam sputtering

Cu2ZnSnS4 Thin Film Solar Cells Utilizing Sulfurization of Metallic Precursor Prepared by Simultaneous Sputtering of Metal Targets

A Cadmium-Free Cu2ZnSnS4/ZnO Hetrojunction Solar Cell Prepared by Practicable Processes

Realization of synaptic learning and memory functions in Y2O3 based memristive device fabricated by dual ion beam sputtering.

Growth of ZnO Submicron Single-Crystalline Platelets, Wires, and Rods by Ultrasonic Spray Pyrolysis