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Wurtzite Zn1-xTMxO nanostructures were solution processed for treating industrial effluents and as photo electrocatalysts for water splitting reactions. The influence of transition metals (TM: Ni, Cr, Co, Mn and Hf) on the physical and chemical properties of host semiconductor was initially adjudged through several analytical tools. The morphological evolution of Zn1-xTMxO nanostructures was noted to be evolved in form of nanoparticles and nanorods, depending on the traits of substituting ions. The nature of substitution and interaction of dopant metal ions within Zn1-xTMxO was evaluated through X-ray photoelectron spectroscopic (XPS) measurements. Absorbance data suggested the tunability in optical band gap and absorbance values of Zn 1-xTMxO as a function of the dopant ions. Likewise, the emission spectra affirmed the potential of dopant ions to suppress the defect related emissions in Zn1-xTMxO. The photocatalytic efficacy was noted to be significantly higher in Co doped samples from the results obtained through comparative dye degradation studies using all the processed nanomaterials. A similar trend was also observed in the PEC investigations through time-dependent photocurrent density outputs. The electrochemical impedance data collectively emphasized the Co ions to induce the effective separation of charge carriers in Zn1-xTMxO via improved electronic conductivity.

Here in, we report the fabrication of thin two dimensional (2D) ZnO nanosheets (NSs) flexible piezo-phototronic ultraviolet (UV) photodetector (PD). The morphological and optical properties of the as-synthesized ZnO NSs is characterized in detail. The flexible Ag–ZnO NSs-Ag lateral PDs are fabricated on the polyethylene terephthalate (PET) substrate. A striking photoresponse is observed for 2D-ZnO under UV illumination. Furthermore, by introducing a strain (in the form of bending) the photocurrent and responsivity of this PD can be modulated via piezo-phototronic effect, emerging from the ZnO nanosheets. The photocurrent enhancement under bending could be attributed to the piezo polarization charges produced at ZnO/Ag interface due to strain. This piezo polarization charges result in the modulation of Schottky barrier (SB) height at the semiconductor/metal interface and induce improved photogenerated charge carriers and reduced recombination probability to result enhanced performances from the ZnO NSs photodetector. The physical mechanism involved in the enhancement of photocurrent via piezo-phototronic is proposed to explain change in SB height at semiconductor/metal interface using the band diagrams. This results demonstrates an efficient prototype of the piezo-phototronic PD based on thin ZnO NSs, which provides an effective pathway to enhance the performance of optoelectronic devices.

A visible-light-driven self-powered photoelectrochemical (PEC) aptasensor was developed for ampicillin (AMP) detecting based on carbon dots (CDs) hybrid MIL-68(In)-derived In2O3 In2S3 hollow tubular heterojunction (CDs/In2O3 In2S3). In2S3 nanosheets uniformly grew in-situ on the surface of In2O3 hollow tubes, forming a close contact heterogeneous interface, which significantly promoted the transfer and separation of photo-generated carriers, and provided a large specific surface area and rich active sites for the PEC aptasensing platform. Furthermore, the CDs/In2O3 In2S3/ITO electrode, which was obtained by dipping assembly, showed remarkable and stable photoelectric signals at zero-bias under visible light irradiation. The amino-functionalized AMP aptamer was fixed on the working electrode as a biological recognition element, and the concentration of AMP was determined by observing the change in photocurrent intensity caused by the specific capture of AMP molecules in solution. Under optimized conditions, the developed PEC aptasensor displayed a relatively wide linear range from 0.001 ng mL−1 to 300 ng mL−1, as well as a low detection limit (LOD) of 0.06 pg mL−1. Besides, the novel self-powered PEC AMP-aptasensor exhibited excellent reproducibility, good stability and selectivity, which open a potential avenue for antibiotic residues detection in environmental media.

Graphical abstract, Highlights • A hybrid stochastic/deterministic model of mouse rod phototransduction is presented. • Rod photocurrent to photovoltage conversion in darkness is accurately characterized. • Photoresponses to dim and bright stimuli and in various mutants are well reproduced. • Recently debated molecular mechanisms of the phototransduction cascade are examined., The phototransduction cascade is paradigmatic for signaling pathways initiated by G protein-coupled receptors and is characterized by a fine regulation of photoreceptor sensitivity and electrical response to a broad range of light stimuli. Here, we present a biochemically comprehensive model of phototransduction in mouse rods based on a hybrid stochastic and deterministic mathematical framework, and a quantitatively accurate description of the rod impedance in the dark. The latter, combined with novel patch clamp recordings from rod outer segments, enables the interconversion of dim flash responses between photovoltage and photocurrent and thus direct comparison with the simulations. The model reproduces the salient features of the experimental photoresponses at very dim and bright stimuli, for both normal photoreceptors and those with genetically modified cascade components. Our modelling approach recapitulates a number of recent findings in vertebrate phototransduction. First, our results are in line with the recently established requirement of dimeric activation of PDE6 by transducin and further show that such conditions can be fulfilled at the expense of a significant excess of G protein activated by rhodopsin. Secondly, simulations suggest a crucial role of the recoverin-mediated Ca2+-feedback on rhodopsin kinase in accelerating the shutoff, when light flashes are delivered in the presence of a light background. Finally, stochastic simulations suggest that transient complexes between dark rhodopsin and transducin formed prior to light stimulation increase the reproducibility of single photon responses. Current limitations of the model are likely associated with the yet unknown mechanisms governing the shutoff of the cascade.

The current work investigates the morphology, crystallinity and photoelectrochemical (PEC) performance of bismuth sulfide/silver sulfide/zinc oxide nanorods (Bi2S3/Ag2S/ZnO NRAs) photoelectrodes as prepared at different annealing temperature. ZnO NRAs was initially grown hydrothermally, deposited in sequence with Ag2S and Bi2S3 via successive ionic layer adsorption and reaction (SILAR) method before undergoing the annealing treatment. The optimised photoelectrode (Bi2S3/Ag2S/ZnO NRAs-400 °C) possesses an optical bandgap of 1.60 eV extending the absorption edge of ZnO to visible light spectrum. The current-voltage characterization of Bi2S3/Ag2S/ZnO NRAs photoelectrodes revealed that the photocurrent density and photoconversion efficiency were strongly dependent on the annealing temperature. The PEC study shows that the photoelectrode annealed at 400 °C achieved impressive photocurrent density of 12.95 mA/cm2 at +0.5 V (vs Ag/AgCl/saturated KCl) under 100 mW/cm2 illumination with superior photoconversion efficiency of 12.63%. This improvement is due to the cascade-designed band structure alignment of Bi2S3/Ag2S/ZnO/ITO and to the brilliant role of Ag2S as an intermediate layer that reduced random chance of electron-hole (e−-h+) pairs recombination and improved the electrons collection efficiency. This work is highly anticipated to give contribution on further utilisation of Bi2S3/Ag2S/ZnO NRAs as a promising semiconductor material in PEC related applications.

In the present work, we have endeavored the utilization of wet-chemically synthesized copper oxide nanoparticles (CuO-NPs) as the active layer in hybrid bulk heterojunction (BHJ) solar cells. The BHJs with CuO-NPs display significantly different physics from customary BHJs, and prove a noteworthy improvement in their performance. It is noted that with the addition of CuO-NPs, the morphology of the photoactive layer endures significant changes. Incorporating CuO-NPs is an additional paradigm for BHJs solar cells which enhances the photocurrent density from 9.43 mA/cm2 to 11.32 mA/cm2 and the external quantum efficiency as well. Also the power-conversion efficiency (PCE) improved from 2.85% to 3.82% without harming the open circuit voltage and the fill factor. The enhancement in PCE achieved here makes it worthy to design high-performance organic solar cells holding inorganic nanoparticles. Keywords: Bulk heterojunction, Solar cells, Copper oxide nanoparticles, Thin films, Photo current density, External quantum efficiency

Constructing plasmonic-semiconductor nanoarchitecture provides a photocatalytic platform for enhancing solar energy conversion. The excitation and extraction of energetic carriers are critical for improving energy efficiency, which can be affected by the geometric features of plasmonic structures. An extensive study on morphology dependent hot electron utilization is desirable but challenging. In this paper, we applied photocurrent response from the microscale reaction region on Au-TiO2 photoanode to evaluate the influence of plasmonic morphology in water splitting. We compared the photocurrent of two structures, gold nanospheres and nanorods, under visible illumination. We experimentally proved that the nanorods demonstrate better energy performance. The possible origins of this enhancement are ascribed to the sharp curvature at tips, where strong hot spots boost the generation and injection efficiency of hot electrons. These results may pave a way for a rational geometry design for plasmonic enhanced photocatalysis.

Broadband photodetectors have attracted substantial attention in recent years. The ternary chalcogenide Ta2NiSe5 is a layered material with a direct narrow-band gap (Eg ~ 0.33 eV) which possesses greatly potential to broadband photodetectors. Here, high-quality bulk Ta2NiSe5 was synthesized by Chemical Vapor Transport (CVT) method. We demonstrate a photodetector based on exfoliated Ta2NiSe5 nanoflake, which exhibits a broadband photo-response from 405 nm to 4300 nm. Meanwhile, its main characteristics are superior to other typical 2D materials: high responsivity ~198.1 A W−1 at 1350 nm and ultrafast response time of ~27.4 µs. Long-time photocurrent reproducibility shows that the photodetector has excellent stability under atmosphere. Furthermore, the scanning photocurrent mapping reveals the photoconductive mechanism of Ta2NiSe5 photodetector. In addition, the anisotropic ratio of the photocurrent is ~1.46. The broadband photodetection, high responsivity, anisotropic and environmental stability achieved simultaneously in Ta2NiSe5 photodetector, which are promising for neotype electronics and optoelectronics field.

In this work, we report for the first time a novel graphitic carbon nitride (CN) composited with different weight percentages (5–15%) of La(OH)3 (CN@La(OH)3) for photocatalytic reduction of hexavalent chromium (Cr(VI)) in aqueous solution. In situ fabrication of the CN@La(OH)3 photocatalysts were carried out via a hydrothermal method. The La(OH)3 nanoparticles were deposited onto the surface of CN nanosheets to form heterojunction, as confirmed by series of techniques. Compared to the pure CN and different weight percentages of CN@La(OH)3 nanocomposite, the CN@La(OH)3(10%) nanocomposite exhibited remarkable photocatalytic reduction performance for Cr(VI) under visible light illumination. Such excellent photocatalytic reduction activity ascribed to the more photocatalytic active sites, high visible light harvesting capacity and improved electron-hole separation and transfer efficiency which was confirmed by photocurrent, impedance and photoluminescence results. The photoreduction efficiency and the reduction rate constant was 98.7% and 0.0263 min−1 within 50 min. A possible reaction mechanism for the effective reduction of carcinogenic Cr(VI) is put forward tentatively. Moreover, the developed CN@La(OH)3(10%) nanocomposite also possessed high structural stability and recyclability after five photocatalytic cycles. This work may open up the way into the robust photocatalysis of Cr(VI) in wastewater treatment application.

Metal-Organic Frameworks (MOFs) are a group of compounds with high porosity and diverse capabilities in photoelectrochemistry. The use of these compounds as photocatalysts and photoelectrodes is still a strong challenge due to bulk and surface recombination issues. To solve this problem, we applied a dual strategy to simultaneously enhance charge separation and catalytic activity in MIL-125-NH2 and UIO-66-NH2 MOF photocatalysts. Mesoporous TiO2 was used as electron-selective contact on the MOF surface (MOF/TiO2) to minimize bulk recombination. On the other hand, to increase the MOF catalytic activity for water oxidation, a well-matched Co3(PO4)2 (CoPi) co-catalyst (CoPi/MOF/TiO2) was used. The obtained results showed that CoPi and TiO2 were introduced in the MOF structure. The (CoPi/MOF/TiO2) photoelectrodes showed a photocurrent density 26 times higher compared to the reference MOF at 1.23 V vs. RHE for PEC water oxidation of artificial seawater, validating the developed strategy for further photocatalytic and photoelectrochemical applications. Funding for open access charge: CRUE-Universitat Jaume I We acknowledge with appreciation the financial support from the University of Isfahan and Ministry of Science, Research and Technology Center for International Scientific Studies and Collaboration (CISSC). SG acknowledges the financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain through funded project ENE2017-85087-C3-1-R.

The growing consumption of global energy has posed serious challenges to environmental protection and energy supplies. A promising solution is via introducing clean and sustainable energy sources, including photoelectrochemical hydrogen fuel production. 2D materials, such as transition metal trichalcogenphosphites (MPCh3), are gaining more and more interest for their potential as photocatalysts. Crystals of transition metal selenophosphites, namely MnPSe3, FePSe3 and ZnPSe3, were tested as photocatalysts for the hydrogen evolution reaction (HER). ZnPSe3 is the one that exhibited the lowest overpotential and the higher response to the light during photocurrent experiments in acidic media. For this reason, among the crystals in this work, it is the most promising for the photocatalyzed production of hydrogen.

Achieving both high onset potential and photocurrent in photoelectrodes is a key challenge while performing unassisted overall water splitting using tandem devices. We propose a simple interface modification strategy to maximize the performance of polycrystalline Sb2Se3 photocathodes for photoelectrochemical (PEC) water splitting. The para-aminobenzoic acid (PABA) modification at Sb2Se3/TiO2 interface enhanced both the onset potential and photocurrent of the Sb2Se3 photocathodes. The surface defects in the polycrystalline Sb2Se3 limited the photovoltage production, lowering the onset potential of the photocathode. Surface restoration using the conjugated PABA molecules efficiently passivated the surface defects on the Sb2Se3 and enabled the rapid photoelectron transport from the Sb2Se3 to the TiO2 layer. The PABA treated Sb2Se3 photocathode exhibited substantially improved PEC performance; the onset potential increased from 0.35 to 0.50 V compared to the reversible hydrogen electrode (VRHE), and the photocurrent density increased from 24 to 35 mA cm−2 at 0 VRHE.

The series of Cd1-xZnxS (x = 0–1.0) photocatalysts and Cd1-xZnxS/FTO thin film photoelectrodes were prepared. The obtained samples were studied by X-ray diffraction method (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and N2 low temperature adsorption. The photocatalysts were tested in the reaction of hydrogen production from Na2S/Na2SO3 solution under visible light irradiation. The photocurrents were measured in aqueous solution of Na2Sn and NaCl. It was shown that the target properties in the hydrogen evolution and photocurrent production are changed differently dependent on the composition of the mixed solid solutions. The highest photocatalytic hydrogen production rate was observed over Cd0.3Zn0.7S while the most effective photoelectrode was Cd0.8Zn0.2S/FTO. The Cd1-xZnxS/FTO samples were studied by the electrochemical methods in details. The factors affecting the photocatalytic activity and the photocurrent generation were found and listed for the first time. Conduction band potential (or flat band potential) and electron lifetime play a crucial role for effective photocatalytic hydrogen production over Cd1-xZnxS. Optimal photoelectrochemical characteristics were obtained in case of high values of electron lifetime. If the electron lifetimes of the tested samples have similar values, the high concentration of charge carriers is required for high photocurrent generation over Cd1-xZnxS/FTO photoelectrodes.

Summary For state-of-the-art organic solar cells (OSCs) consisting of a large-bandgap polymer donor and a near-infrared (NIR) molecular acceptor, the control of the HOMO offset is the key to simultaneously achieve small energy loss (Eloss) and high photocurrent. However, the relationship between HOMO offsets and the efficiency for hole separation is quite elusive so far, which requires a comprehensive understanding on how small the driving force can effectively perform the charge separation while obtaining a high photovoltage to ensure high OSC performance. By designing a new family of ZITI-X NIR acceptors (X = S, C, N) with a high structural similarity and matching them with polymer donor J71 forming reduced HOMO offsets, we systematically investigated and established the relationship among the photovoltaic performance, energy loss, and hole-transfer kinetics. We achieved the highest PCEavgs of 14.05 ± 0.21% in a ternary system (J71:ZITI-C:ZITI-N) that best optimize the balance between driving force and energy loss., Graphical Abstract, Highlights • NIR acceptors with high structural similarity and variable HOMO levels were designed • We achieved the highest PCE of 14.36% by combining J71, ZITI-C, and ZITI-N acceptors • We revealed the importance of the optimized driving force on the device performance, Energy Storage; Materials Characterization; Solid State Physics

Photovoltaic (PV) panel has been widely used in many spectrum splitting systems. However the spectrum splitting normally discussed only with photocurrent. In this paper, the relationship between the current-voltage (I-V) curve and the irradiation spectrum is discussed by combining the single diode model. An explicit elementary analytical model with two defined shape parameters is improved with three approximations and second order Taylor expansion. The relationship between the physical parameters and the condition parameters is applied to extract the shape parameters at different scenarios. Considering the aging effect, the process of calculation to predict I-V curve is simplified as follow: (1) two shape parameters are gotten from I-V data at measurement reference conditions (MRC); (2) short circuit current, open circuit voltage and shape parameters under any splitting spectrum can be calculated based on the relationship provided in article; (3) the performance of PV panel can be predicted with parameters. The validation of this model was experimentally proven leveraging monocrystalline silicon photovoltaic module with different splitting films. Moreover, the presented model performs superior compared to other investigated models when looking at accuracy and simplicity. Keywords: Photovoltaic panel, Explicit model, Spectrum splitting, I-V characteristic prediction, Shape parameter

Environmentally friendly synthesis and scalable photoelectrode fabrication are important for the photoelectric conversion in photocurrent generation. We find that 28% ethanol in 72% deionized water are the best mixed solvent for efficient exfoliation of layered ReS2 by absorption spectra and the enthalpy of mixing theory. Electrophoretic deposition method is used to fabricate photoelectrodes with different thicknesses by controlling the deposition time. These photoelectrodes demonstrate fast and stable photoelectric response and enhanced photocurrent with the thickness of the nanosheet films controlled by the deposition time. We also discuss the photoelectric mechanism as well as the influence of the effective mass of the monolayer, two-layer, and bulk ReS2 via Vienna ab initio Simulation Package (VASP). This work paves the way for the solvent selection in exfoliation of ReS2 nanosheets as well as the scalable fabrications for the photodetectors, photoelectrodes, and other solar energy conversion devices. Keywords: Mixed-solvent, ReS2, Electrophoretic deposition, Photoelectric response, First-principle calculations

Blocking layer and transfer skeleton of the electron transfer layer are found to play a crucial role in devices efficiency improvement. We develop a homogeneous and isomorphic electron transfer structure of rutile TiO2 by preferred orientation growth in a facile two-step hydrothermal synthesis. The aligned TiO2 nanowire array skeleton (TS) about 2.47 μm long grew neatly over the isomorphic ultra-thin blocking layer (BL). Those homogeneous and isomorphic structures promote the charge injection and transfer capability by means of increased driving force by higher Fermi-level and decreased resistance, in which the cell photocurrent and PCE improve significantly. Of the cells with isomorphic transfer structure, the PCE is 2.87%, the short-circuit current (Jsc) is 6.74 mA/cm2, open-circuit voltage (Voc) is 0.91 V and fill factor (FF) is 38.4% under one sun illumination (100 mW/cm2). Keywords: Electron transfer capability, Homogeneous and isomorphic structure, Fermi level, Device equivalent resistance

We report photocurrent enhancement through ligand exchange in cadmium selenide (CdSe) photoelectrochemical (PEC) cells. CdSe quantum dot (QD) layers were used as a light absorption layer in combination with titanium dioxide (TiO2) layers. For a shorter ligand exchange, pristine CdSe QDs with oleic acid (OA) ligands were treated with 1,2-ethanedithiol (EDT) and CdSe QD PEC cells exhibited enhanced photocatalytic properties in comparison with pristine CdSe PEC cells. To articulate the origin of enhanced photocurrent, ligand dependent energy band bending at the CdSe/TiO2 interface was probed from thickness dependent highest occupied molecular orbital level measurements using photoelectron spectroscopy in air. Increase in the photocurrent also originates from enhancement in charge transport through ligand exchange to shorter EDT ligands in the bulk CdSe film with OA ligands suppressing back diffusion of carriers from TiO2 to CdSe.

Summary The use of biomacromolecules is a nascent development in clean alternative energies. In applications of biosensors and biophotovoltaic devices, the bacterial photosynthetic reaction center (RC) is a protein-pigment complex that has been commonly interfaced with electrodes, in large part to take advantage of the long-lived and high efficiency of charge separation. We investigated assemblies of RCs on an electrode that range from monolayer to multilayers by measuring the photocurrent produced when illuminated by an intensity-modulated excitation light source. In addition, atomic force microscopy and modeling of the photocurrent with the Marcus-Hush-Chidsey theory detailed the reorganization energy for the electron transfer process, which also revealed changes in the RC local environment due to the adsorbed conformations. The local environment in which the RCs are embedded significantly influenced photocurrent generation, which has implications for electron transfer of other biomacromolecules deposited on a surface in sensor and photovoltaic applications employing a redox electrolyte., Graphical abstract, Highlights • Controlled the formation of monolayer or multilayers of RCs on a gold electrode • Correlated electrochemical and photocurrent responses to the RC adsorbed conformations measured using AFM • Adsorbed RC conformations affect photocurrent generation • Photocurrent-potential response influenced by local redox mediator concentration and pH environment experienced by the adsorbed RCs, Chemistry; Electrochemistry; Surface chemistry; Surface science

The electrical response of dye-based photovoltaic cells upon a sudden illumination is explained in terms of a theoretical approach based on a time-hierarchical emergence of several physical processes. Our approach ensures the coupling the four main processes that take place, namely, the photochemical activation of the cell, the electrical current associated with electron transport, the relaxation of the polarization due to the motion of ions and, finally, the elastic–osmotic effect that produces rapid oscillations in the output photocurrent of the cell when is suddenly illuminated. The model shows that mordants control/modify three relaxation times: the characteristic time of the photochemical activation due to a partial light-blocking, the characteristic time for the electrical current associated with the electron transport due to mordant adsorption into the mesoporous surface, and the polarization relaxation due to a change in the ions transported to the electrodes. The model fits with high-precision the experimental data of the photo-induced current showing highly non-linear time-dependent oscillations.

Graphical abstract, Highlights • Ultrasonication-assisted synthesis of MoS2 nanosheets improved PEC performance. • Liquid phase exfoliation was used for MoS2 nanosheets with 6 nm thickness. • Photocurrent of α-Fe2O3 photoanode significantly increased by MoS2 heterojunction. • α-Fe2O3/8-MoS2 showed a thinner space charge layer and reduced flat band potential. • p-n junction decreased resistance due to the reduced recombination rate of charge carriers., This study successfully manufactured a p-n heterojunction hematite (α-Fe2O3) structure with molybdenum disulfide (MoS2) to address the electron–hole transfer problems of conventional hematite to enhance photoelectrochemical (PEC) performance. The two-dimensional MoS2 nanosheets were prepared through ultrasonication-assisted liquid-phase exfoliation, after which the concentration, number of layers, and thickness parameters of the MoS2 nanosheets were respectively estimated by UV–vis, HRTEM and AFM analysis to be 0.37 mg/ml, 10–12 layers and around 6 nm. The effect of heterojunction α-Fe2O3/MoS2 and the role of the ultrasonication process were investigated by the optimized concentration of MoS2 in the forms of bulk and nanosheet on the surface of the α-Fe2O3 electrode while measuring the PEC performance. The best photocurrent density of the α-Fe2O3/MoS2 photoanode was obtained at 1.52 and 0.86 mA.cm−2 with good stability at 0.6 V vs. Ag/AgCl under 100 mW/cm2 (AM 1.5) illumination from the back- and front-sides of α-Fe2O3/MoS2; these values are 13.82 and 7.85-times higher than those of pure α-Fe2O3, respectively. The results of electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis showed increased donor concentration (2.6-fold) and decreased flat band potential (by 20%). Moreover, the results of IPCE, ABPE, and OCP analyses also supported the enhanced PEC performance of α-Fe2O3/MoS2 through the formation of a p–n heterojunction, leading to a facile electron–hole transfer.

In the present work, we compare the photoresponse of vertically erected (VE) single crystal anatase layers with that of widely used TiO2 nanotube layers. These VE-anatase layers were grown hydrothermally, directly on fluorine-doped tin oxide (FTO) glass, and consist of an array of anatase single crystal flakes with preferred (0 0 1) facets. As formed, these single crystal layers are fluorine terminated – this termination can be removed by a thermal treatment in air. We compare the photocurrent magnitude and photocurrent transients using intensity-modulated photocurrent spectroscopy (IMPS). We find that the “de-fluorinated” VE-anatase layers show significantly higher photocurrents than the comparable nanotube layers. This high efficiency of the VE-anatase layers is due to the electron transport being 100 times faster in these single crystal electrodes, provided that the blocking fluorine termination is removed.

The use of sunlight for photoelectrochemically splitting water into hydrogen and oxygen has aroused great interest in the last decades. Photocathode materials based on cupric oxide (CuO) are promising for large-scale, widespread photoelectrochemical water splitting due to the high Earth-abundance of copper, suitable band gap, and favorable band alignment for hydrogen generation. The main challenge for the development of practical CuO photocathodes is to enhance stability against photocorrosion, together with increasing the efficiency of solar hydrogen evolution. In this work, stable CuO nanowire photocathodes are synthetized in a straightforward and scalable way by electrodeposition followed by chemical oxidation and thermal treatment. Subsequently, the electrodes are modified with aluminum following two different strategies: (i) adsorption of aluminum from an Al acetylacetonate solution or (ii) drop-casting of a solution containing Al nitrate. In both cases, a thermal treatment is applied after Al addition. The stability of CuO nanowires (measured as the percent of the initial photocurrent retained after 20 min of continuous illumination at −0.4 V vs. Ag/AgCl) is enhanced from 2% up to 80%. The amount of aluminum needed to modify cupric oxide is very low in both strategies, indicating that Al operates at the surface level. Admittedly, these modifications improve stability at the expense of photocurrent. To palliate this, the addition of co-catalysts should be addressed in the future. This work has been developed in the context of project RTI2018- 102061-B-I00 financed by FEDER/Ministerio de Ciencia e Innovación- Agencia Estatal de Investigación. The Generalitat Valenciana through project PROMETEO/2020/089 is also gratefully acknowledged. A.C. acknowledges the University of Alicante for a predoctoral grant (FPU-UA).

A simple method for obtaining the charge carrier density of two-dimensional (2D) materials is proposed herein. A formula is suggested for the extraction of the 2D charge carrier density using the horizontal depletion width, which is visually represented by photocurrent mapping methods. An example of this method is demonstrated using a MoS2 Schottky diode. The results suggest that this method can be useful for a basic analysis of the physical properties of 2D devices.

This chapter introduces recent research on intermediate band solar cells (IBSCs) using quantum dots (QDs). A detailed discussion is given of the numerical analysis of device characteristics based on a self-consistent drift-diffusion model, for which the carrier dynamics, with a particular emphasis on the two-step inter-sub-band photo-absorption (TSPA), and recombination processes are taken into consideration. The current status of the fabrication and performance of high-density In(Ga)As QD solar cells grown using self-organised epitaxy is discussed. Further, maximising TSPA processes via QDs is of paramount importance in a successful implementation of high-efficiency IBSCs and Fourier transform infrared photocurrent spectroscopy provides a powerful tool to study the IR photocurrent response via TSPA in In(Ga)As QDSCs.

[EN] Hybrid TiO2-WO3 nanostructures has been synthesized by electrochemical anodization under controlled hydrodynamic conditions followed by electrodeposition in the presence of different contents of Na2WO4 (5, 15 and 25 mM) and H2O2 (20, 30 and 40 mM). The influence of the electrolyte used for electrodeposition on the morphology, crystalline structure and photoelectrochemical response for water splitting has been evaluated through Field Emission Electronic Microscopy, High-Resolution Transmission Electron Microscopy, Confocal Raman Spectroscopy, Grazing Incidence X Ray Diffraction, X-Ray Photoelectron Spectroscopy, Atomic Force microscopy and photocurrent versus potential measurements. Additionally, a statistical multi-factor categorical analysis was performed to determine the most significant influential parameters. Results show that hybrid TiO2-WO3 nanostructures formed by simple anodization and subsequent electrodeposition with 30 mM H2O2 and 25 mM Na2WO4 present the highest photocurrent response, 60% higher if compared to TiO2 anodized nanotubes, solving the main problems presented during the usual fabrication of heterostructures, i.e. high temperatures, pressures, number of chemicals and time., Authors thank for the financial support to the Generalitat Valenciana (Project Code: GV/2020/044) as well as to the project co-funded by FEDER operational programme 2014-2020 of Comunitat Valenciana (IDIFEDER/18/044). Authors also thank the Ministerio de Ciencia e Innovacion (Project Code: PID2019-105844RB-I00), for its help in the Laser Raman Microscope acquisition (UPOV08-3E-012) and for the cofinance by the European Social Fund. Authors also thank Alicia Mestre and Said Agouram from the SCSIE (Universitat de Val`encia) for their help with the XRD and HR-TEM measurements.

Photoelectrochemistry has been one of the most frequently studied branches of chemistry for the past 2 decades and its principle is based on monitoring a photocurrent generated by the irradiation of photosensitive material on an electrode surface with a light source. Photoelectrochemical (PEC) analysis has found wide applications in various fields such as water splitting, hydrogen or oxygen production, pollutant degradation, CO2 reduction, and construction of sensors and biosensors. In PEC studies, various photosensitive materials such as organic redox mediators (ORMs), semiconductors, heterostructures, and composite nanomaterials have been used. Among these, quantum dots (QDs) are of great interest to researchers because of their unique and superior optical and electronic properties. In this chapter the principles and mechanisms of PEC-sensing strategies using ORMs, QDs or their hybrid nanostructures are described and applications of PEC-sensing platforms such as in small analyte detection, immunoassays, nucleic acids, and enzyme-based biosensors.

The effect of pH, concentration, and membrane thickness on the performance of a photoelectrochemical (PEC) cell using kraft lignin as a reactant was studied at 25 °C. Kraft lignin served as an electron donor which consumed photogenerated holes on the TiO2 anode, while photogenerated electrons reduced protons to hydrogen gas at the Pt cathode. Saturated photocurrent increased linearly with UV intensity. High concentrations of kraft lignin reduced the photo-current of the cell. A high pH differential across the membrane could degrade a thin perfluorosulfonic acid (PFSA) membrane. This study demonstrated the potential of kraft lignin as an electron donor.

This chapter aims to provide an overview of the photoelectrochemical characterization of semiconducting photocatalysts and, in particular, present Photocurrent Spectroscopy (PCS) as a useful tool in determining the band structure of semiconducting/insulating materials. Some fundamentals on PCS will be provided looking at the experimental setup and underlying its advantages and disadvantages. Then, the photoelectrochemical behavior of a semiconductor/electrolyte junction under irradiation will be presented, also taking into account its crystalline or amorphous nature, highlighting how it is possible to get information on the energetics of the junction. This will be exploited to show how to depict the band structure of the semiconducting photocatalysts using the data gathered by PCS.

Reducing the metal particle size on semiconductor-based materials from a few nanometers down to well-dispersed clusters or single atoms has been demonstrated to be an effective strategy to enhance the photocatalytic performance. However, designing a simple and fast synthesis procedure has consistently been a challenge. In this work, gold clusters have been easily synthesized and dispersed onto TiO2 surface by one-step ball milling from TiO2 and gold acetate. The Au clusters strongly interact with TiO2 and the resulting material exhibits outstanding photocatalytic performances on the generation of hydrogen under UV and visible light, which double those obtained on conventional Au/TiO2 photocatalysts containing Au nanoparticles. We have studied the effect of various preparation parameters and characterized the samples by a variety of microscopic and spectroscopic techniques. The particular architecture accomplished by ball milling results in efficient charge separation, low charge transfer resistance and high photocurrent response. This mechanochemical method not only provides a facile and cost-effective alternative to the conventional methods of fabricating Au/TiO2 catalysts, but also opens a promising avenue for developing other ultrasmall metal clusters onto different supports.

Summary Ferroelectric synapses using polarization switching (a purely electronic switching process) to induce analog conductance change have attracted considerable interest. Here, we propose ferroelectric photovoltaic (FePV) synapses that use polarization-controlled photocurrent as the readout and thus have no limitations on the forms and thicknesses of the constituent ferroelectric and electrode materials. This not only makes FePV synapses easy to fabricate but also reduces the depolarization effect and hence enhances the polarization controllability. As a proof-of-concept implementation, a Pt/Pb(Zr0.2Ti0.8)O3/LaNiO3 FePV synapse is facilely grown on a silicon substrate, which demonstrates continuous photovoltaic response modulation with good controllability (small nonlinearity and write noise) enabled by gradual polarization switching. Using photovoltaic response as synaptic weight, this device exhibits versatile synaptic functions including long-term potentiation/depression and spike-timing-dependent plasticity. A simulated FePV synapse-based neural network achieves high accuracies (>93%) for image recognition. This study paves a new way toward highly controllable and silicon-compatible synapses for neuromorphic computing., Graphical Abstract, Highlights • Switchable ferroelectric photovoltaic (FePV) effect is used for synaptic application • Tunable photovoltaic response is enabled by gradual polarization switching • Versatile synaptic functions and high image recognition accuracy are achieved • The FePV synapses are facilely grown on silicon substrates, Circuit Systems; Electrical Engineering; Semiconductor Manufacturing; Materials Science; Devices

Photoanode based CO2 reduction has two major advantages- water oxidation provides required electron-hole pairs and photogenerated anode current compensates the negative cathodic potential required for CO2 reduction. Generally, silver dendrites in combination with copper based substrates have been reported as electrocathodes for electrochemical CO2 reduction. Whereas, in this work, silver nanodendrites decorated titania nanotubes array (Ag-TNT) was used as a photoanode and prepared via simple sodium citrate assisted electrodeposition. Silver dendrites have influenced in light absorption, charge separation efficiency. Ag-TNT employed in photoanode for photoelectrocatalytic reduction of CO2 into CO under the optimized condition with a photocurrent density of 0.29 mA cm−2 at 1.23 V (vs. RHE). This system yielded CO of 61 μmol cm2/h and the design paves the way to facilitate photoelectrocatalytic CO2 reduction through water oxidation.

Colloidal semiconductor quantum dots (QDs) are considered as promising building blocks to fabricate efficient and stable optoelectronic devices, thanks to their size/shape/composition-dependent electronic and optical properties based on the quantum confinement effect. However, inadequate light absorption and undesirable charge recombination events still limit the efficiency and long-term stability of solar energy to fuel conversion in QD-based photoelectrochemical (PEC) cells. In this work, we engineer the optoelectronic properties and band alignment in colloidal heterostructured CdS/CdSe core/shell QDs by tuning the shell thickness. Starting with a 3.0 nm CdS QD core (in diameter), we investigate the changes in structural and optical properties as a function of CdSe shell thickness (0.6–1.9 nm). We show that the optimization of the shell thickness can significantly broaden the light absorption range towards longer wavelengths and enhance the rate of photoelectron separation and transport in photoanodes made of QDs sensitized TiO2 mesoporous film. Complemented by theoretical modeling, we find that the band alignment in this heterostructured system can be engineered from quasi type-II (electrons are localized over the entire QDs but holes are mostly delocalized in shell) to inverted type-I (both electrons and holes are largely delocalized in shell) by changing the shell thickness. As a proof-of-concept, employing QDs with optimal shell thickness of 1.6 nm together with carbon nanotube doped TiO2 as photoanode in PEC cells, we obtained a very high photocurrent density of ~ 16.0 mA/cm2 (at 0.9 V vs. the reversible hydrogen electrode, RHE), which is the highest value ever reported for PEC cells based on CdS/CdSe QDs. We also observed an excellent long-term stability (maintaining 83% of its initial value after four hours) under one sun illumination (AM 1.5G, 100 mW/cm2). These results indicate that optimizing the design and band engineering of heterostructured core/shell QDs is a facile and efficient approach to enhance the performance of QDs-based PEC cells and other optoelectronic devices.

To improve the photocatalytic performance of TiO2-based heterostructures, Z-scheme/Ⅱ-type rutile TiO2 (R)/anatase TiO2 (A)/ZrTiO4 ternary heterojunction photocatalyst was designed and prepared via a facile one-step calcining strategy. Phase interface and band structure of the materials were controlled and optimized by regulating R–TiO2/A–TiO2 mass ratio in the TiO2 (A, R)/ZrTiO4 structures using boron doping. The highest photocatalytic performance and excellent catalytic stability of Rhodamine B removal was observed from the heterojunction with a low R–TiO2/A–TiO2 mass ratio of 0.066, even after five testing cycles, accompanying with low photoluminescence intensity and electrochemical impedance, high photocurrent and charge carrier density (5.12 × 1022 cm−3), and a positive shift of valence band position (from +2.06 to + 2.16 eV). The increased photodegradation behaviour was due to the remarkably enhanced separation efficiency and improved redox ability of the photo-induced charge carriers as a result of the high content of oxygen vacancies and the formed anatase TiO2/rutile TiO2 Z-scheme heterojunction.

HfO2 thin film is deposited on p-Si substrates by RF magnetron sputtering apparatus and annealed at 750 °C for 10 min with O2 atmosphere. Spectral analysis shows that HfO2 thin films have good transmittance to light, especially ultraviolet band. The HfO2 layers belong monoclinic phase and its thickness is about 50 nm. In the Au/HfO2/p-Si structure, photodiode characteristics were studied at room temperature and compared with the light current generated under white light, the response current generated under ultraviolet light is more prominent. The photocurrent reaches 80 μA and the repeatable response of device under 23.5 mW/cm2 ultraviolet illuminating is stable. It's found that the working mechanism of this photodiode could have three different states: the majority carrier stacking state of reverse bias, the majority carrier depletion state of forward bias with dark condition and the minority carrier inversion state of forward bias with ultraviolet illumination. The device also has a high damage threshold and its photocurrent is still not saturated at bias 8 V, indicating that it can be applied as a new type of UV detector. Keywords: HfO2 thin films, MOS device, Photodiode, Photocurrent, Free carriers

Photonic structures allow reducing the thickness of photovoltaic (PV) devices while improving their photocurrent, thereby enabling high-efficient, low-cost, and mechanically flexible solar cells. Wave-optical front structures have shown to be promising for integration in various thin-film PV technologies, as those based on silicon or perovskite semiconductors, due to a combination of: (1) Broadband absorption amplification—wavelength-sized structures provide geometrical index-matching for the impinging light, strongly reducing reflection while boosting the photons' path length within the absorber via scattering. (2) Improved electrical performance—their incorporation in the transparent contact can enable higher electrode volume, thereby improving the cells' voltage and fill factor. Such a location can also prevent increasing the cells' roughness, therefore not contributing to recombination. (3) Enhanced stability—particularly in perovskite cells, the front photonic structures block most of the harmful UV radiation that degrades such devices. Colloidal lithography methods have revealed to be highly cost-effective for the nanopatterning of such structures, allowing compatibility with industrial scalability and low-cost requirements.