FTO Glass Research Articles

First Steps Towards a Joint Measurement System for Light-Addressable Potentiometric Sensors and Light-Addressable Electrodes

Introduction A rapid diagnostic of the patients’ disease is essential for the success of the therapy. To support the doctor, lab-on-a-chip devices could be used. These devices contain different components, which one would primarily find in an analytical laboratory. Typically, sensors, liquid-handling devices or actuators are integrated in a microfluidic channel to allow a medical analysis on a single chip. Through the miniaturization of the single components, only a small volume e.g., of the patients’ blood, is needed and a first diagnosis can be done on-site.In the past research, mostly rigid sensor and actuator structures such as electrodes are integrated in lab-on-a-chip devices. For their implementation, photolithographic fabrication processes are necessary. On the contrary, devices based on semiconductor structures can be spatially and temporally resolved by light, whereby the sophisticated structuring process is no longer required. For sensing, light-addressable potentiometric sensors (LAPS) can detect different target species in the analyte [1,2], while with light-addressable electrodes (LAE), photoelectrochemical reactions can be triggered [3,4].In this work, the joint implementation of these two technologies integrated in a microfluidic channel will be presented for the first time, as depicted in figure 1. Methods and Materials LAPS are based on a semiconductor-insulator-transducer sandwich structure. An applied d.c. bias voltage will induce a space-charge region at the semiconductor-insulator interface. By illumination with an intensity-modulated light source from the rear-side, electron-hole pairs are generated leading to a detectable a.c. photocurrent. Local variations of the analyte concentration at the transducer surface will influence the width of the space-charge region and therewith the photocurrent. Therefore, moving the light source in a scanning like-manner, a spatially resolved mapping of the photocurrent, which is proportional to the analyte concentration, can be recorded.To fabricate the Al/p-Si/SiO2/Ta2O5 field-effect structure of the LAPS chip, SiO2 was grown by a thermal dry oxidation step on a p-doped silicon wafer. Subsequently, Ta was deposited by electron-beam evaporation followed by an oxidation step to achieve the Ta2O5 layer. In a final step, an Al ohmic rear-side contact was prepared and an illumination window was etched inside the Al layer for rear-side illumination.The LAE can be used for the spatially resolved manipulation inside the microfluidic channel. Semiconductors can be applied as electrode materials where charge carriers are generated upon illumination. In contrast to LAPS, LAEs have no insulating layer, which enables a direct charge transfer with the analyte and triggering of surface reactions. By spatially resolved illumination, a localized photocurrent will occur at the illuminated spot, while the remaining electrode is still isolated.A titanium dioxide layer was fabricated by means of pulsed laser deposition on a SnO2:F (FTO) glass substrate. The TiO2 target was vaporized by a KrF excimer laser (wavelength = 248 nm) with a repetition rate of 10 Hz at a pressure of 2x102 hPa O2. During deposition, the FTO glass substrate has been heated up to 400 °C. Results and Conclusions A possible strategy for the implementation of both technologies into a microfluidic channel was introduced. Furthermore, as a proof-of-concept, by local illumination, the pH value inside a microchannel was changed photoelectrocatalytically by the LAE. Simultaneously, a chemical image of the localized pH shift has been recorded by the LAPS. Since both systems can be addressed by light, dynamic manipulation and sensing is possible, which enables an easy adjustment of both technologies at run time. A detailed description of the experiment and the obtained results will be presented and discussed.Figure 1: Schematic illustration of the combination of a light-addressable electrode and a light-addressable potentiometric sensor. The pH gradient, generated by the LAE can be measured by the LAPS. Acknowledgements This work was supported by the German Federal Ministry of Education and Research (BMBF) within “NanoMatFutur“ (13N12585).

Improved photovoltaic performance of dye-sensitized solar cells by Au-ion implantation of titania film electrodes

Plasmonic metal nanoparticles are known to work as light-harvesting antennae and to enhance photocurrents of photovoltaic cells. Therefore, in this work, the effect of gold (Au) ions distribution on the efficiency of dye sensitized solar cells (DSSCs) has been investigated. Thin films of TiO2 have been deposited on FTO glass substrates by the doctor tape method. Au ions were then implanted on these films with different fluence rates (i.e., 2 × 1014, 4 × 1014 and 6 × 1014 ions/cm2). XRD results confirmed that TiO2 is present in the anatase phase up to a 4 × 104 ions/cm2 fluence rate. At a 6 × 1014 ions/cm2 fluence rate, one peak of rutile is obtained which confirmed that the film has mixed phases of TiO2. UV results show that dye is adsorbed into all photoanodes. Maximum dye absorption is seen at a fluence rate of 4 × 1014 ions/cm2. The energy conversion efficiency of DSSC is highly dependent on the fluence rate of Au. At a fluence rate of 4 × 1014 ions/cm2, the cell has a high short circuit current density (JSC) of 7.21 mA/cm2, resulting in a high efficiency (×) of 2.92%. Impedance spectroscopy shows that the cell formed by Au ions fluence rate of 4 × 1014 ions/cm2 has a low recombination rate of electron/hole pairs.

Fabrication and performance analysis of a low cost, Pt free counter electrode using carbon coated ZnAl layered double hydroxide (C/ZnAl-LDH) for dye sensitized solar cells

Carbon based material represents an effective substitute for Pt counter electrodes (CEs) in Dye Sensitized Solar Cells (DSSCs). This study introduces a novel carbon coated ZnAl layered double hydroxides (C/ZnAl-LDH) can be utilised as an effective CE in DSSCs. C/ZnAl-LDH was synthesised by the pyrolysis of ZnAl-LDH using glucose solution. The synthesised C/ZnAl-LDH was characterised using TEM, SEM, XRD and BET analysis. The surface roughness of both Pt and C/ZnAl-LDH films were analysed using AFM spectroscopy. C/ZnAl-LDH slurry was pasted uniformly using doctor blade technique onto FTO glass substrate. The electrochemical measurements such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Tafel polarization recommends that C/ZnAl-LDH can be used as a CE due to its good reduction rate of I3- comparable with Pt CEs. The photovoltaic parameters were observed to be 0.66 V and 11.97 mA/cm2 for open circuit voltage (Voc) and short circuit current density (Jsc) respectively for C/ZnAl-LDH CE. The assembled cell with C/ZnAl LDH CE having power conversion efficiency (PCE) of 3.18% is comparable to Pt CE having 4.62% which is measured under the similar testing conditions.

Photochemiresistor Sensor Development Based on a Bismuth Vanadate Type Semiconductor for Determination of Chemical Oxygen Demand.

The present paper describes the development of a novel photochemiresistor sensor for the determination of chemical oxygen demand (COD). A chemiresistive device was produced by a thin film of the monoclinic phase of bismuth vanadate deposited on an FTO glass surface. The resistive properties of the photosensor were carried out by electrochemical impedance spectroscopy (EIS). The electrical resistance of the platform was dependent on the presence of organic material in aqueous solution and the incidence of light. The decrease in resistance can be explained by considering that by increasing the amount of organic material, the amount of charge transferred to BiVO4 increases, as does the amount of the photogenerated conduction band on the film. This behavior is not observed when carrying out the same measurements in the absence of light. Under the optimal experimental conditions, the linear response of the chemiresistor sensor is between 0.20 and 19.9 mg L-1 COD at a fixed AC frequency of 0.1 Hz. There is a good correlation between the charge transfer resistance and COD concentration in the electrolyte solution. Quantification of COD in waste and lake waters was successfully performed using the novel photochemiresistor sensor. The results achieved in the analysis with the sensor are in accordance with the conventional method.

300 keV cobalt ions irradiations effect on the structural, morphological, optical and photovolatic properties of Zn doped TiO2 thin films based dye sensitized solar cells

Dye Sensitized Solar Cell (DSSC) is a potential too to convert solar energy into electrical energy due to its low cost, ease in synthesis and higher photo electron conversion efficiency (PEC) in contrast with conventional silicon solar cell. The photo-electrode of DSSC is a key component which is responsible for collection and transportation of electrons through the circuit. Sol-gel route was adopted to manufacture photo anodes of 1% Zinc doped titanium dioxide (Zn–TiO2) where FTO glass was used as substrate. These photo anodes were irradiated by 300 keV Cobalt (Co) ions with different fluence rates as 2 × 104 atomscm-2s-1 and 4 × 104 atoms cm-2s-1. We investigated the anatase phase of TiO2 using the Raman spectra which also showed that Zn and Co are completely doped in TiO2. UV–visible spectroscopy showed that band gap of films was decreased by doping and ions implantation. Maximum reduction in band gap is observed at the fluence rate of 4 × 104 atoms cm-2s-1 i.e. 2.77 eV. SEM micrographs showed that the film irradiated with Co ions with fluence rate of 2 × 104 atoms cm-2s-1 have maximum porosity which supports the maximum dye loading on the surface due to which the efficiency of DSSC is enhanced. In all cells, N719 dye is used as sensitizer. The solar simulator results indicated the higher efficiency up to 3.78% is achieved by 300 keV cobalt ions irradiation with fluence rate of 2 × 104 atoms cm-2s-1. The present work shows that the appropriate percentage of Co ions in Zn–TiO2 layer plays a significant role to escalate the effectiveness of DSSC.

Towards visible light driven photoelectrocatalysis for water treatment: Application of a FTO/BiVO4/Ag2S heterojunction anode for the removal of emerging pharmaceutical pollutants

Pharmaceuticals have been classified as emerging water pollutants which are recalcitrant in nature. In the quest to find a suitable technique in removing them from contaminated water, photoelectrocatalytic oxidation method has attracted much attention in recent years. This report examined the feasibility of degrading ciprofloxacin and sulfamethoxazole through photoelectrocatalytic oxidation using FTO-BiVO4/Ag2S with p-n heterojunction as anode. BiVO4/Ag2S was prepared through electrodeposition and successive ionic layer adsorption/reaction on FTO glass. Structural and morphological studies using XRD, SEM, EDS and diffusive reflectance UV-Vis confirmed the successful construction of p-n heterojunction of BiVO4/Ag2S. Electrochemical techniques were used to investigate enhanced charge separation in the binary electrode. The FTO-BiVO4/Ag2S electrode exhibited the highest photocurrent response (1.194 mA/cm−2) and longest electron lifetime (0.40 ms) than both pristine BiVO4 and Ag2S electrodes which confirmed the reduction in recombination of charge carriers in the electrode. Upon application of the prepared FTO-BiVO4/Ag2S in photoelectrocatalytic removal of ciprofloxacin and sulfamethoxazole, percentage removal of 80% and 86% were achieved respectively with a low bias potential of 1.2 V (vs Ag/AgCl) within 120 min. The electrode possesses good stability and reusability. The results obtained revealed BiVO4/Ag2S as a suitable photoanode for removing recalcitrant pharmaceutical molecules in water.

Preparation and characterization of tin sulfide films with or without sodium chloride

The successive ionic adsorption and reaction (SILAR) method was used to obtain tin sulfide film on FTO glass. In this work tin sulfide films were prepared with or without the immersion stage in distilled water. As-deposited tin sulfide films consisted of orthorhombic structures SnS and Sn2S3. This multiphase composition of obtained thin films was confirmed by X-ray diffraction and Raman spectroscopy. The estimated average crystallite size was in the range of 14–31 nm and was dependent on the conditions of the film preparation. Energy-dispersive X-ray analysis showed that tin sulfides films prepared without the immersion stage in distilled water formed with sodium chloride. The percentage incorporation of sodium and chlorine in those films was 5.29–8.10 and 8.71–11.22 at. %, respectively. The addition of sodium and chlorine atoms exhibited better crystallinity and effected on the optical properties of tin sulfides films.

Unstable cell efficiency in CdS quantum dot sensitized solar cell using low cost lugols iodine aqueous electrolyte

We have designed and synthesis rutile TiO2 rod like nanoflower on the FTO glass by one step hydrothermal method operating at 150 °C for 15 h. The lower concentration of CdS Quantum dots was deposited on the surface of TiO2 through chemical bath deposition (CBD) method. The samples were characterized x-ray diffraction pattern (XRD), Scanning electron microscopy (SEM) and UV–Vis absorption studies. In this work lugols iodine was used as an aqueous electrolyte between FTO/TiO2/CdS photoanode and Cu2S as counter electrode respectively. The result of photo conversion efficiency (PCE) is decreased from 0.13 to 0.033%, this may be the reason photo degradation and corrosion were happened in CdS.

Effect of annealing temperature of MoO3 layer in MoO3/Au/MoO3 (MAM) coated PbS QDs sensitized ZnO nanorods/FTO glass solar cell

This research reports fabrication of MoO3/Au/MoO3 (MAM) coated PbS sensitized quantum dot solar cell. ZnO nanorod grown FTO glass substrates were sensitized by PbS quantum dots (PbS QDs/ZnO nanorods/FTO Glass), followed by (MoO3/Au/MoO3) coating. Hydrothermal process was used to grow ZnO nanorods, followed by the deposition of PbS QDs using Successive Ionic Layer Adsorption and Reaction (SILAR). Finally, (MoO3/Au/MoO3) layers were deposited for the back contact. Spin coating was used to deposit MoO3 layers while middle layer of Au was deposited by sputter coating. Three such devices were fabricated with three different annealing temperatures i.e. 100 °C, 150 °C and 200 °C for first MoO3 layer. Scanning Electron Microscopy (SEM) was used for surface morphology of the devices; Energy Dispersive Spectroscopy Analysis (EDS) and X-Ray Diffraction (XRD) techniques were used for elemental and structural analysis, Optical properties of the devices were determined using UV–Visible analysis. Power conversion efficiency (PCE) of all three devices was obtained to observe devices performance. Improved PCE of 4.617% was obtained by the device with the thermal treatment of 150 °C.

Growth of ZnO nanorods on FTO glass substrate

A simple and direct method has been developed to grow zinc oxide (ZnO) nanorods (NRs) on a fluorine-doped tin oxide-coated glass (FTO) substrate. Firstly, spray pyrolysis deposition method is applied followed by dipping the substrate in a solution of ZnO growth reagents. The morphology, structure, and optical properties of the obtained thin film are investigated. The results demonstrate the successful synthesis of the ZnO NRs on FTO substrate. The NRs have a hexagonal rod like structure with diameter and length of 240 nm and 670 nm, respectively. FTO/ZnO NRs exhibited absorption of UV wavelengths and high transmittance in visible light region, with energy bandgap (Eg) of 3.2 eV. The characteristics of the FTO/ZnO NRs film can be explored in photovoltaic applications such as dye-sensitized solar cells.

Fabrication of WO3 nanorod/graphene/BiV1−xMoxO4 heterojunction photoelectrode for efficient photoelectrochemical water splitting

We report the fabrication of a novel WO3 nanorod/graphene/BiV1−xMoxO4 heterojunction photoelectrode for photoelectrochemical (PEC) water splitting. The heterojunction arrays were fabricated via a hydrothermal deposition of WO3 nanorods on FTO glass, with subsequent depositing of graphene nanosheets and BiV1−xMoxO4 by spin-coating method, respectively. The structure of materials and PEC water splitting properties of the photoelectrodes were systemically investigated. The heterojunction exhibits an enhanced photocurrent density (2.27 mA/cm2 at 0.9 V vs. Ag/AgCl), which leads to a significant improvement in photoconversion efficiency (1.00% at about 0.7 V vs. Ag/AgCl). This remarkable PEC performance is mainly due to the constructive effect of the graphene (RGO) in expediting electron transfer and reducing charge recombination to realize enhanced use ratio of photo-generated carriers for the water splitting reaction. This result demonstrates the superiorities of the new graphene-mediated composites photoelectrode and provides a promising route for high-performance photoelectrochemical systems.

A novel photoelectrochemical sensor based on tailoring printable mesoscopic chip for fast and real-time phospholipids oxidation detection

The detection of phospholipids oxidation is important for meat control and disease prevention. In this paper, a photoelectrochemical sensor based on printable mesoscopic chip (PMC) for fast and real-time monitoring phospholipids oxidation was designed and fabricated. TiO2, ZrO2 and carbon films of PMC were screen-printed onto the FTO glass layer by layer. The PMC and the feasibility for determination of phospholipids oxidation were investigated by scanning electron microscope (SEM), UV–vis spectroscopy, cyclic voltammograms (CVs) and electrochemical impedance spectroscopy (EIS), etc. The short circuit current (Jsc) was used as a signal current, which would decrease if phospholipids in PMC were undergoing oxidation for the change of electrical properties. Compared with other methods, phospholipids in PMC did not require pretreatment, and the process was nondestructive and real-time. Meanwhile, this method showed high sensitivity and good selectivity. The fabricating process of PMC is simple, and the costs are low, relatively.

Rectifying resistance switching behaviors of SnO2 microsphere films modulated by top electrodes

Based on the bipolar resistive switching (RS) characteristics of SnO2 films, we have fabricated a new prototypical device with sandwiched structure of Metal/SnO2/fluorine-doped tin oxide (FTO). The SnO2 microspheres film was grown on FTO glass by template-free hydrothermal synthesis, which was evaporated with various commonly used electrodes such as aluminium (Al), silver (Ag), and gold (Au), respectively. Typical self-rectifying resistance switching behaviors were observed for the RS devices with Al and Au electrodes. However, no obvious rectifying resistance switching behavior was observed for the RS device with Ag electrode. Above results were interpreted by considering the different interface barriers between SnO2 and top metal electrodes. Our current studies pave the ways for modulating the self-rectifying resistance switching properties of resistive memory devices by choosing suitable metal electrodes.

Impact of TiO2 layer formed on CuxS Films on the Photoelectrochemical Water Reduction Process

Solar radiation is the main source of renewable energy capable of satisfying the increasing energy demand without contributing to climate changes using fossil fuels. Energy harvesting from solar radiation requires innovation in materials with appropriate functional properties to produce chemical energy. This study aims to contribute in that sense. It reports the synthesis and characterization of photocathodes for hydrogen evolution based on TiO2/CuxS films formed on FTO glass. CuxS is prepared by electrodeposition of copper, followed by chalcogenide formation through immersion in a sulfide source solution and then modified by heat treatment. A TiO2 layer is deposited on CuxS film to favor its stability and charge carrier separation process. The calcination of bare CuxS film causes the formation of a mixture of copper oxides. TiO2 film acts as an effective protector, preserving a larger proportion of Cu chalcogenide species by preventing the complete oxidation, without considerably varying the reducing power of photogenerated electrons in the films. TiO2 layer favors the absorption of low energy photons and increases the photocurrent, diminishing electron-hole recombination probability.

A pseudo-metal-free strategy for constructing high performance photoelectrodes

By in situ growth of g-CN film on FTO glass with sulfur-rich poly thiourea formaldehyde resin as precursor, a pseudo-metal-free strategy for constructing photoelectrode with high PEC performance based on g-CN/SnS2 composite film is proposed.

Scanning atmospheric-pressure plasma jet treatment of nickel oxide with peak temperature of ∼500 °C for fabricating p-i-n structure perovskite solar cells.

Scanning atmospheric-pressure plasma jet (APPJ) treatment of nickel oxide with a peak temperature of 500 °C was performed for fabricating p–i–n structure perovskite solar cells (PSCs). APPJ post-treatment increases the haze of NiO on FTO glass, leading to enhanced light scattering in PSCs that in turn improves the cell efficiency. APPJ treatment on NiO also improves the wettability to facilitate the follow-up deposition of CH3NH3PbI3. This also leads to better PSC performance. X-ray photoelectron spectroscopy indicates that APPJ treatment results in fewer C–N bonds and reduced NiAc2 content, suggesting more complete conversion of the liquid precursor into NiO. With three APPJ scans, the average PCE improves from 11.91% to 13.47%, with the best-performing PSC achieving an efficiency of 15.67%.

Optimization of electrical and photovoltaic properties of Au-BiFeO<sub>3</sub> nanocomposite films

Ferroelectric films, are an important class of photoelectric functional material, which possess the following characteristics: the breaking of their symmetry can lead to self-polarization and this polarization state can be regulated by external stimuli. The photovoltaic properties of ferroelectric films have been extensively investigated due to their potential applications in the field of photodetection, energy conversion harvesting and nonvolatile storage. In view of the small photocurrent density and the degradation of photovoltaic property caused by the depolarization effect in ferroelectric films, it is necessary to explore an approach to improving the self-polarization phenomenon and regulating the conduction mechanism to further optimize their photovoltaic properties. Here in this work, BiFeO<sub>3</sub> (BFO) films dispersed with Au nanoparticles are deposited on FTO glass substrates by the sol-gel method to obtain the Au-BFO nanocomposite films. Moreover, the relationships between Au content (0 mol%, 0.25 mol%, 0.5 mol%, 1 mol% and 3 mol%) and microstructure, electrical and photovoltaic properties of Au-BFO nanocomposite films are investigated to determine the optimal Au content. Piezoresponse force microscopy studies show that the Au-BFO nanocomposite film with 0.5 mol% Au has the strong self-polarization phenomenon. With the increase of Au content, the conduction mechanism of the Au-BFO nanocomposite films is described by the space-charge limited current theory but not the Schottky emission model any more. The photovoltaic properties of the Au-BFO nanocomposite films first increase and then decrease. When Au content is 0.5 mol%, the Au-BFO nanocomposite film has the best photovoltaic property. The open-circuit voltage and short-circuit photocurrent density of the Au-BFO nanocomposite film with 0.5 mol% Au increase nearly 3 and 5 times counterparts of the BFO film, respectively. The photovoltaic effects of Au-BFO nanocomposite films are improved mainly by regulating the self-polarization phenomenon and conduction mechanism. This study demonstrates the merits of BFO films dispersed with Au nanoparticles, specifically, the photovoltaic properties of Au-BFO nanocomposite films are further optimized. In this work, we propose a simple and effective method to regulate the electrical and photovoltaic properties of ferroelectric films, which provides a new perspective for further understanding the photovoltaic effects of ferroelectric films.

Production and characterization of TiO2 nanoparticle thin films for its application in DSSCs

In this research, TiO2 nanoparticle thin films were successfully prepared on FTO glass substrates through a doctor blade technique, and its application was tested in dye-sensitized solar cells (DSSCs) with different sensitizing dyes such as methylene blue (MB) and methyl orange (MO). The physicochemical properties of intended thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and UV-vis diffuse reflectance spectra (UV-vis DRS) techniques. The experimental results revealed that dipped TiO2 nanoparticle thin films into MB dye solution showed a higher photovoltaic efficiency (1.45%) when compared with the MO dye solution. A reasonable mechanism of DSSCs was also proposed.

Exploration of the antibacterial capacity and ethanol sensing ability of Cu-TiO2 nanoparticles

Titanium oxide (TiO2) is one of the most scrutinized material because of its in-built fundamental properties and has been developed as an outstanding photo-catalytic material intended for many different industrial applications. In order to further explore the properties of TiO2, we prepared Copper-loaded TiO2 (Cu-TiO2) nanoparticles (NPs) for inhibiting the growth of bacterial cells and also to serve as a chemical sensor. The physico-chemical characteristics of the synthesized Cu-TiO2 NPs were characterized by many different techniques for the crystallinity, bonding and functionality, morphology, elemental composition, and absorption characteristics. From the results, we confirm for the formation of anatase phase of TiO2 having a tetragonal crystal system, while the morphology studies indicated that the Cu dope TiO2 has spherical morphology. The elemental analysis confirmed for the inclusion of Cu into TiO2 crystal lattice and the absorption spectroscopic analysis helped for the bandgap calculation and visible light absorption property of Cu-TiO2 NPs. The metal nanoclusters of Cu are observed to be deposited on different phases and sites of TiO2 resulting in the inter-band transitions. Further, the sensitivity of Cu-TiO2 as a chemical sensor is determined by fabricating the electrode at the FTO glass substrate where the ethanol sensitivity was found to be little increased/enhanced with Cu loading. Finally, the antibacterial activity of Cu-TiO2 NPs was confirmed by its activity against various bacterial cultures and are found to be efficient.

WO3/Cu2O heterojunction for the efficient photoelectrochemical property without external bias

Photoelectrochemical (PEC) splitting of water to produce hydrogen without external bias is an important approach to resolve the serious energy crisis. Herein, we prepared a PEC cell system based on the WO3/Cu2O heterojunction in situ grown on the FTO glass substrates by a seed-mediated hydrothermal followed by electrodeposition method. Under visible light illumination, the pure WO3 exhibited no photocurrent at 0 V vs. RHR in aqueous Na2SO4 and the pure Cu2O struggled with serious photo-corrosion. By contrast, the obtained Z-scheme WO3/Cu2O-30 min heterojunction can not only effectively suppress the corrosion of Cu2O but also obtained a photocurrent density of 12 μA cm−2 without external bias or adding sacrificial agent. Additionally, the possible mechanism of a Z-scheme system was also proposed based on the XPS analysis and the experimental results. Thus, this study reveals that the as-obtained Z-scheme WO3/Cu2O-30 min heterojunction has a great prospect in the PEC cell system without external bias.