Photoanodes For Dye-sensitized Solar Cells Research Articles

Synthesis and Characterization of Cerium Oxide Impregnated Titanium Oxide Photoanodes for Efficient Dye-Sensitized Solar Cells

Cerium oxide (CeO2) nanoparticles (NPs) were mixed with titanium dioxide (TiO2) in different wt.% to obtain an improved composite photoanode with better electron-injection property. Using these composite photoanode materials, dye-sensitized solar cells were fabricated, and photovoltaic performances were evaluated. For performance comparison, a cell with pure TiO2 as a photoanode was also prepared. Devices fabricated using composite photoanodes with 1%, 3%, 5%, and 7% of CeO2 showed power conversion efficiency (PCE) of 7.0%, 5.68%, 5.64%, and 3.97%, respectively. Whereas, the cell with pure TiO2 as photoanode showed an efficiency of 3.35%. This enhanced PCE was attributed to the presence of CeO2 within the photoanode, which helps to reduce the charge recombination loss and improve photo-absorption. Eventually improved the open-circuit voltage and short-circuit current. Pure and composite photoanode samples were characterized for their optical and morphological properties. Homogeneous distribution of CeO2 NPs within the composites were confirmed by TEM analysis.

Effect of precipitating agents on the performance of ZnO nanoparticles based photo-anodes in dye-sensitized solar cells

Dye-Sensitized Solar Cell (DSSC), as a unique non-conventional energy system, is rapidly gaining more attention from researchers. Efforts to fabricate photovoltaic devices with high conversion efficiencies at low cost with a simple fabrication process have prompted researchers to continuously work on different components of DSSC. This research focuses on the effect of precipitating agents, sodium hydroxide, and ammonium hydroxide on the fabrication of ZnO-based DSSCs. ZnO nanoparticles were prepared and characterized based on structural and microstructural analyses, UV-absorption and reflectance spectroscopy, and FTIR analysis, as one of the potential semiconductor photo-anodes for DSSCs. The uniformly prepared films using the doctor blade technique were soaked in Ruthenizer 535-bisTBA dye solutions for sensitization. The films were assembled and current-density characteristics measurements were taken using a solar simulator at 100 mW/cm2 and 25 °C. The effect of precipitating agents on the performance of the fabricated DSSC was studied. Photovoltaic performance evaluation of DSSCs using N719 dye as a sensitizer revealed that the open-circuit voltage (VOC) ranged between 0.535 and 0.719 V, and the short-circuit photocurrent density (JSC) was in the range of 3.621 to 5.875 mAcm−2. The highest conversion efficiency of 2.43 % was recorded for the synthesized ZnO semiconductor photo-anode using NaOH as the precipitating agent.

Efficiency enhancement in dye-sensitized solar cells through the decoration of electro-spun TiO2 nanofibers with Ag nanoparticles

Dye-sensitized solar cells (DSSCs) are low cost and eco-friendly photovoltaic devices which require new ideas for further development. In this paper, we use electro-spun TiO2 nanofibers to prepare the DSSCs photoanode. In order to isolate the FTO and electrolyte species, we deposit a spin-coated TiO2 blocking layer at their interface. The performance of this cell is further improved by introducing surface plasmon resonances (SPRs) at the surface of the nanofibers. It is shown that SPRs increase the generated current in the cells by providing a higher light absorption and lower recombination. Our best cell showed an efficiency of 6.19%, which is a 28% improvement in comparison to the bare DSSC with 4.84% efficiency. The results of this paper are acquired and confirmed by XRD, FESEM, TEM, EDS, dye-loading, IPCE, J–V, and EIS measurements.

Titanium Dioxide-Coated Zinc Oxide Nanorods as an Efficient Photoelectrode in Dye-Sensitized Solar Cells.

Well-arrayed zinc oxide nanorods applied as photoelectrodes for dye-sensitized solar cells were synthesized on an aluminum-doped zinc oxide substrate by the multi-annealing method. In order to improve the chemical stability and surface-to-volume ratio of photoanodes in dye-sensitized solar cells, the synthesized zinc oxide nanorods were coated with pure anatase phase titanium dioxide film using a novel mist chemical vapor deposition method. The effects of the titanium dioxide film on the morphological, structural, optical, and photovoltaic properties of zinc oxide–titanium dioxide core–shell nanorods were investigated. It was found that the diameter and surface-to-volume ratio of zinc oxide nanorods were significantly increased by coating them with titanium dioxide thin film. The power conversion efficiency of dye-sensitized solar cells was improved from 1.31% to 2.68% by coating titanium dioxide film onto the surface of zinc oxide nanorods.

Correction to: Synthesis of nanosized TiO2 using different molecular weight polyethylene glycol (PEG) as capping agent and their performance as photoanode in dye-sensitized solar cells

Correction to: Synthesis of nanosized TiO2 using different molecular weight polyethylene glycol (PEG) as capping agent and their performance as photoanode in dye-sensitized solar cells

Hydrothermal synthesized Nd-doped TiO2 with Anatase and Brookite phases as highly improved photoanode for dye-sensitized solar cell

In this study, the effects of Nd doping on the performance of TiO2 photoanode based dye-sensitized solar cells (DSSC) are reported. Nd-doped TiO2 (Nd-TiO2) was synthesized using hydrothermal method. Un-doped TiO2 (TiO2) was also synthesized for reference. XRD, IR, Raman and electron microscopy characterisation of the obtained material were performed and the subsequent electrochemical tests, CV and EIS studies were made to explore their application. The XRD and Raman analysis’s results indicated that the Nd-TiO2 and TiO2 have both the Anatase and Brookite phases. TEM, EDX and EIS studies were used to obtain particle size, morphology, the presence of the element, electron lifetime and recombination characteristics respectively. The Nd-TiO2 nanoparticles have uniform particle size, a strong red shift of their absorption into the visible region and greater dye-loading as compared with TiO2 nanoparticles. It is proved that higher efficiency was achieved when the TiO2 Anatase and Brookite structure were mixed. Further, Nd had a positive effect on the performance of photoelectrode and DSSC fabricated with Nd-TiO2 photoanode revealed an appreciable current conversion efficiency of 5.23% with a short-circuit current (Jsc) of 12.8 mA/cm2, open-circuit voltage (Voc) of 0.62 V and fill factor (FF) of 0.66. The increased current conversion efficiency was attributed to the greater dye loading, reduced charge recombination and facile charge transport with Nd-doped TiO2.

Performance of TiO2 nanoparticles synthesized by microwave and solvothermal methods as photoanode in dye-sensitized solar cells (DSSC)

In this work, a direct comparison of the properties of the TiO2 nanoparticles prepared by microwave and solvothermal methods were carried out and its performance as photoanode in dye-sensitized solar cells (DSSC) was analyzed. Though previously some works exist on the preparation of TiO2 nanoparticles by solvothermal or microwave methods, they could not be compared directly as the experiment conditions such as choice of solvent, precursors and reaction temperatures were not virtually same. Herein, TiO2 nanoparticles were synthesized by microwave and solvothermal methods using the same initial precursors and properties of the prepared nanoparticles were compared. From the X-ray diffraction pattern and Raman analysis, the prepared nanoparticles in both the cases were found to be of anatase phase. Optical properties and its carrier lifetime were studied using UV–Vis absorption, photoluminescence (PL) analysis and PL lifetime studies, respectively. Further, its morphology analyzed using scanning electron microscope (SEM) and transmission electron microscope (TEM) images, and SAED (selected area electron diffraction) patterns reveals the polycrystalline nature of the prepared nanoparticles. The surface area and the pore size distribution were studied using BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda) analysis, which revealed its mesoporous nature and uniform pore distribution. The chemical states of the prepared nanoparticles were further characterized using X-ray photoelectron spectroscopy. The DSSC was fabricated using the prepared TiO2 nanoparticles as photoanodes. Further, the power conversion efficiency and the electron transport properties were analyzed.

The Addition of Reduced Graphene Oxide Layer to TiO<sub>2 </sub>Photoanode of DSSC Using UV Oven Spraying Method

The third generation of photovoltaic, called as dye-sensitized solar cells (DSSC) have attracted much attention and currently become an interesting research topics. One important part of DSSC that determines its performance is photoanodes. Recently, graphene has been used to enhance the efficiency of DSSC through the increasing of electronic transportation. Introduction of graphene into DSSC is realized by changing the form of graphene oxide (GO) into reduced graphene oxide (rGO) through the reduction process. In this work, DSSC based on TiO2 photoanodes modified by rGO were fabricated. rGO layer was deposited on TiO2 mesoporous layer using UV-oven spraying method. We found that parameters of DSSC such as open circuit voltage, short circuit current and fill factor increase with the incorporation of rGO layer in TiO2photoanodes. DSSC with TiO2/rGO photoanodes has the highest power conversion efficiency of 11.01% which contributed from the enhancement of short circuit current. The rGO layer found to be an effective layer to block charge recombination in photoanode.

Role of Metal Ion-Linked Multilayer Thickness and Substrate Porosity in Surface Loading, Diffusion, and Solar Energy Conversion.

Metal ion-linked multilayers offer an easily prepared and modular architecture for controlling energy and electron transfer events on nanoparticle, metal oxide films. However, unlike with planar electrodes, the mesoporous nature of the films inherently limits both the thickness of the multilayer and subsequent diffusion through the pores. Here, we systematically investigated the role of TiO2 nanoparticle film porosity and metal ion-linked multilayer thickness in surface loading, through-pore diffusion, and overall device performance. The TiO2 porosity was controlled by varying TiO2 sintering times. Molecular multilayer thickness was controlled through assembling ZnII-linked bridging molecules (B = p-terphenyl diphosphonic acid) between the metal oxide and the Ru(bpy)2((4,4'-PO3H2)2bpy)]Cl2 dye (RuP), thus producing TiO2-(Bn)-RuP films. Using attenuated total reflectance infrared absorption and UV-vis spectroscopy, we observed that at least two molecular layers (i.e., TiO2-B2 or TiO2-B1-RuP) could be formed on all films but subsequent loading was dependent on the porosity of the TiO2. Rough estimates indicate that in a film with 34 nm average pore diameter, the maximum multilayer film thickness is on the order of 4.6-6 nm, which decreases with decreasing pore size. These films were then incorporated as the photoanodes in dye-sensitized solar cells with cobalt(II/III)tris(4,4'-di-tert-butyl-2,2'-bipyridine) as a redox mediator. In agreement with the surface-loading studies, electrochemical impedance spectroscopy measurements indicate that mediator diffusion is significantly hindered in films with thicker multilayers and less porous TiO2. Collectively, these results show that care must be taken to balance multilayer thickness, substrate porosity, and size of the mediator in designing and maximizing the performance of new multilayer energy and electron management architectures.

Optimization of titanium dioxide decorated by graphene quantum dot as a light scatterer for enhanced dye-sensitized solar cell performance

Titanium dioxide (TiO 2 ) as a photoanode in dye-sensitized solar cells (DSSCs) has some drawbacks that reduce its photovoltaic performances i.e. low dye loading capacity and low light-harvesting efficiency. Therefore, TiO 2 decorated by graphene quantum dot (GQD) as a light scatterer has been successfully fabricated via electrodeposition and drop-casting. The response surface methodology/central composite design was successfully utilized to optimize the preparation of photoanode with TiO 2 -GQD as a light scattering layer (LSL). A reduced quadratic model was successfully designed to predict the power conversion efficiency (PCE) accurately up to 97% with a 3% residual standard error. The TiO 2 -GQD LSL depicted a cluster of spherical nanoparticles on top of the photoanode that not only enhanced the light scattering effect but also improved the light-harvesting range from visible light to ultraviolet and near-infrared range. The resultant TiO 2 nanoparticles with TiO 2 -GQD LSL showed vast enhancement of PCE up to 66% from 3.06% to 5.01% due to a good synergistic effect. • TiO 2 -GQD as light scattering layer (LSL) was optimized using response surface methodology • The reduced quadratic model displays a low residual standard error. • TiO 2 nanoparticles with TiO 2 -GQD LSL displays enhanced efficiency up to 66%.

Synthesis of nanosized TiO2 using different molecular weight polyethylene glycol (PEG) as capping agent and their performance as photoanode in dye-sensitized solar cells

In this study, synthesis of nanosized TiO2 in which hydrolysis and polycondensation of precursor, Ti(OC4H9)4, has been performed in presence of different molecular weight polyethylene glycol (PEG) polymer as a capping agent is reported. Three different capped materials (TN-P400, TN-P4000, and TN-P8000) were synthesized along with un-capped TiO2 (TiO2 synthesized without using PEG, TN) for the sake of comparison. The structure and morphology of the synthesized TiO2 were characterized by XRD, FTIR, SEM, and DLS analyses. The X-ray diffraction spectrums show the presence of anatase phase TiO2. The as-synthesized PEG-capped TiO2 were used as photoanode material for dye-sensitized solar cells (DSSC) after coating with sensitizer dye N719, and photoelectric conversion efficiency (PCE) of 2.52%, under the illumination of 100 mW cm−2, has been achieved with TN-P8000, which was much improved compared with DSSC performance with un-capped TiO2 (PCE = 1.02%). EIS analyses revealed that TN-P8000 photoanode–based cell exhibited facile charge transfer, enhanced electron lifetime, and greater charge collection efficiency that contributed better photovoltaic performance. The results demonstrated that using PEG as a capping agent is a potential approach for improving the efficiency of DSSC and current conversion efficiency was increased as the molecular weight of PEG was increased.

Study of Novel Dye-Sensitized Solar Cells With Modified Photoelectrode by ZrO2 and rGO Doped TiO2 Composite Nanofibers

Titanium dioxide (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is an excellent photoanode material in dye-sensitized solar cells (DSSCs). However, the surface morphology of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticle has some disadvantages such as weak dye adsorption capacity and low electron mobility leading to low performance of DSSCs. In this study, TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanofibers (NFs) were prepared by electrospinning technology and doped with reduced grapheme oxide (rGO) and zirconium dioxide (ZrO2) to modify the photoanode of DSSCs. For exploring its properties and the impact of photovoltaic performance, NF can not only improve the particle arrangement but also increase its specific surface area to facilitate the adsorption of dye in DSSCs. rGO is characterized by good electrochemical property and excellent electron conduction. The doped ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> improves the photovoltaic performance of the DSSCs in order to reduce charge recombination. The composite NF is employed to increase the surface area to promote the adsorption of dyes in DSSCs and improve the power conversion efficiency. The power conversion efficiency (η) of the DSSCs with modified photoelectrode by ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and rGO doped TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> composite NF is 5.44% and η increases 75% compared with the DSSCs without modified photoelectrode.

Design and fabrication of carbon dots decorated WO3 nanosheets hybrid photoanodes for sunlight-driven dye-sensitized solar cell applications

This work demonstrates the selection of the substrates to be used for photoanode and counter electrode for dye-sensitized solar cells (DSSC). A novel carbon dots (CDs) decorated WO3 nanosheets hybrid structure was synthesized by facile hydrothermal route, which acts as a photoanode materials: counter electrode (Pt) and iodide/triiodide (I−/I3−). Sun stimulator (AM 1.5G, 100 mW/cm2) is used as source of light to evaluate the photovoltaic characteristics. The samples using various mass ratios (1:1, 1:2, 1:3) of CDs and WO3 were prepared under the same conditions. The monoclinic structure with sheet-like morphology of WO3 was identified by XRD, Raman and TEM measurements. The optimized CDs/WO3 (1:3) photoanode exhibits a huge surface area (102.4 m2/g) and porous size (12 nm) since the CDs are rapidly anchored on the WO3 nanosheets. Due to the high absorption ability that prevents the recombination rate of the electron–hole pair, the optimized CDs/WO3 (1:3) photoanode delivers a high photoconversion efficiency of 11.7%, which is 3.35 times better than that of bare WO3 (3.5%). The improved photoconversion efficiency of WO3 by carbon was also discussed in detail.

Characteristics of Electron Transport Study of Composited Graphene-Zinc Oxide Thin Film Photoanode for Dye-Sensitized Solar Cells

Graphene-Zinc Oxide (Gr-ZnO) nanocomposites films were successfully synthesized via facile electrodeposition method in an aqueous solution under Gr concentration conditions. Gr, as a highly conductive carbon, acts as an anchor for ZnO nanosheets and plays a substantial role in controlling the degree of dispersion of ZnO nanosheets onto indium-doped tin oxide (ITO) substrate to form Gr-ZnO nanocomposite. Atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM) analysis of Gr-ZnO nanocomposite samples confirmed that the presence of ZnO nanosheets with a high degree of dispersity and crystallinity which is well linked to the thin layer of Gr nanoparticle on ITO substrate. The surface roughness of the films found increased to ~270 nm on Gr-ZnO as compared to Gr ~44 nm and ZnO ~3 nm. Further, the x-ray diffraction spectroscopy (XRD) analysis showed the result is in good agreement with Raman spectroscopy study. The cyclic voltammetry (CV) of Gr-ZnO nanocomposite revealed that the effect of electron-hole recombination process was increased and the presence of Gr in ZnO photoanode provides the fastest redox reaction and hence offers the fastest electron transfer in photoanode.

Synthesis and Characterization of TiO2 Semiconductor Doped by AgNO3 and Their Application as Photoanode in Dye-sensitized Solar Cells

The use of Titanium dioxide (TiO2) semiconductors in Dye-Sensitized Solar Cells (DSSC) devices have been extensively studied and synthesized with various techniques to obtain optimal performance. The TiO2 semiconductors with optimal performance are influenced by the growth method, the time of growth, the shape of the microstructure, and the optical properties. In this study, it was reported about the effect of silver nanoparticles (AgNO3) doping onto TiO2 semiconductors on their microstructure, reflectance, and efficiency of the DSSC device. The synthesis of TiO2 was carried out using liquid phase deposition (LPD) and immersed into an AgNO3 solution with a variation of time namely 0.5 h, 1 h, 2 h, 4 h, and 6 h. The entire TiO2 + AgNO3 sample, then used as a photoanode on DSSC with plastisol as a counter electrode. Characterization of microstructure, reflectance, and DSSC performance was carried out by using field emission scanning electron microscopy (FESEM), Uv-Vis Spectrophotometer, and Gamry Instrument, respectively. The FESEM results show that AgNO3 has successfully grown on the ITO substrate in a spherical shape with an average particle diameter ranging from 1.52-2.29 μm. From observations using the Uv-Vis Spectrophotometer, obtained the energy band gap values ranged from 0.22 to 2.27 eV. The best results of DSSC device efficiency, with TiO2+AgNO3/Dye/Plastisol structure, have resulted in the Voc of 0.694 V, current density (Jsc) of 0,943 mA/cm2and fill factor (FF) of 43,50% which is obtained at sample 1.

Low-cost and novel preparation of porous NiS2/graphene heterojunctions photoanodes for high-efficiency dye-sensitized solar cells

It's critical and challenging to investigate cost-effective and strong electrocatalyst within the advancement of large scaled dye-sensitized solar cells (DSSCs). In this work, we develop a novel strategy to prepare NiS2 microspheres interface with 2D graphene nanosheets constructed through a facile hydrothermal technique. Na2S2O3·5H2O plays an important role as the reducing agent for GO as well as the sulfur source for NiS2. The microstructures, morphologies and optical properties of the NiS2/graphene hybrid composite samples were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption isotherm, UV–Vis diffuse reflectance spectra and photoluminescence spectra analysis. A significant narrowing the band gap (2.69 eV–2.44 eV) and control the prevention of electron-hole pair recombination process was examined through UV and PL studies. The J-V characteristics of the fabricated sandwich type DSSC device was monitored and the results demonstrate that NiS2/graphene hybrid photoanode displayed an excellent electrocatalytic activity in the reduction of I3− showing a power conversion efficiency of 12.56%, which is 2.5 times better than bare NiS2 photoanode (5.02%). This is ascribed to the low resistance to diffusion and transfer of electrolyte ions. These results suggest that the NiS2/graphene prepared through a facile process is a promising substitute to Pt electrode.

Template-assisted synthesis of porous TiO2 photoanode for efficient dye-sensitized solar cells

Abstract

Highly porous Ba3Ti4Nb4O21 perovskite nanofibers as photoanodes for quasi-solid state dye-sensitized solar cells

Ternary oxides are considered promising electrode materials for light harvesting devices due to their optical and electronic properties that can be tuned by controlling their composition and doping ratio. Herein, a facile approach is demonstrated to fabricate ternary oxide perovskite nanofibers (NFs) and their investigation investigated as efficient electrode materials in dye-sensitized solar cells (DSSCs). The fabricated electrospun hexagonal perovskite-like (A3B8O21) nanofibers are made of several small single crystals that are connected together to several micrometers in length. Upon sintering to 650 ⁰C, highly porous perovskite nanofibers were obtained, which increased the dye adsorption capacity of the nanofibers and in turn resulted in higher photoconversion efficiency than the traditional nanotubes counterparts. The crystallinity, chemical, and thermal characteristics of the fabricated NFs were investigated using XRD, SEM, TEM, and TGA analyses. Moreover, Brunauer–Emmett–Teller (BET) measurements were used to evaluate the effect of annealing temperature on the pore size and the overall surface area of the NFs. The fabricated nanofibers were used to construct full solar cell devices, revealing enhancement in the overall performance as indicated via the photocurrent-voltage curves. This enhancement is mainly related to the higher adsorption rate of the dye on the nanofibers surface. Highly porous electrospun nanofibers are good platforms that should be useful for the future development of solar cell devices.

Preparation of MoS2/graphene nanocomposite-based photoanode for dye-sensitized solar cells (DSSCs)

We reported on the preparation of different composition of molybdenum sulfide (MoS2)/graphene nanocomposites by facile hydrothermal route and its further application in the dye-sensitized solar cells (DSSCs). The structural, morphological, optical and textural properties of the samples were systematically investigated by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Raman, UV–Vis diffuse reflectance spectra (DRS), Photoluminescence and N2 adsorption-desorption analysis, respectively. XRD and TEM results suggest that hexagonal crystalline structure with uniform spherical shaped nanoparticles are uniformly wrapped on the graphene nanosheets. The incorporated graphene could effectively reducing the band gap (2.38–1.92 eV) and recombination of electron-hole pair. The fabricated DSSCs shows outstanding photo-conversion efficiency (PCE) of 8.92% for MoS2/graphene, which is higher than that of bare MoS2 (3.36%). The enhancement is assigned to less recombination of photo-generated electrons and higher incident photon to current conversion yield as a result of rapid charge collection and higher dye sensitization. Moreover, the synergic effect between the MoS2 and graphene could provide large active path owing to their huge surface area (89.25 m2/g) and porous nature (12.23 nm). The mechanism improved by graphene was also explained based on the obtained results.

Solvothermal synthesis of g-C3N4 and ZnO nanoparticles on TiO2 nanotube as photoanode in DSSC

In this research, the dye-sensitized solar cells (DSSCs) were fabricated by using g-C3N4 and ZnO modified TiO2nanotube (TNT) arrays as photoanodes. The TNT arrays were synthesized by the anodizing method. G-C3N4 and ZnO modified TNTs were synthesized via a solvothermal method in which ethylene glycol served as a solvent. The short circuit current (ISC) and open-circuit voltage (VOC) of DSSCs based on ZnO + g-C3N4modified TNTs photoanode considerably increased from 9.25 mA/cm−2to 14.68 mA/cm−2, and from 0.707 mV to 0.695 mV, respectively, resulting in a135% increase in the efficiency compared with the pure TNT arrays photoanode. However, the DSSC fabricated with g-C3N4 TNT did not show much improvement in the conversion efficiency compared with the pure TNT arrays photoanode, implying more effective processes of the carrier production and transport between ZnO, g-C3N4 and TNTs. Also, the electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) analyses showed that ZnO + g-C3N4 can promote the electron collecting rate, suppress he electron recombination and extend the electron lifetime.