Enhancing current density of perovskite solar cells using TiO2-ZrO2 composite scaffold layer

A novel scaffold layer composed of TiO₂-ZrO₂ composite was fabricated for perovskite solar cell. Compared with pure TiO₂ nanoparticles (NPs), the relatively larger ZrO₂ NPs could increase film roughness and enhance light-scattering effect in TiO₂-ZrO₂ composite films. The device exhibited outstanding power conversion efficiency (PCE) of 11.41%. The morphology and aggregation of particles, three-dimensional roughness, as well as the ingredient and micro-structure of FTO/compact TiO₂/TiO₂-ZrO₂ was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD), respectively. Moreover, the optical property of TiO₂-ZrO₂ films for visible light was characterized by UV–visible absorption spectroscopy (UV–vis), and its influence on quantum yield of the device was further demonstrated by incident photon-to-electron conversion efficiency (IPCE). Owing to the inert oxide, the short-circuit current density of perovskite solar cell using TiO₂-ZrO₂ composition as scaffold layer increased by 21% compared to the one employing pure TiO₂ mesoporous film.     

High performance dye-sensitized solar cells (DSSCs) achieved via electrophoretic technique by optimizing of photoelectrode properties

This paper describes a simple method utilizing electrophoretic deposition (EPD) of commercial P25 nanoparticles (NPs) films on fluoride-doped tin oxide (FTO) substrate. In this process, voltage and the number of deposition cycles are well controlled to achieve TiO₂ film thickness of around 1.5–26 μm, without any mechanical compression processing. The experimental results indicate that the TiO₂ film thickness plays an important role as the photoelectrode in DSSCs because it adsorbs a large number of dye molecules which are responsible for electrons supply. Furthermore, it was found that effects of the bulk traps and surface states within the TiO₂ films on the recombination of the photo-injected electrons (electron–hole pairs) strongly depend on the TiO₂ electrode annealing temperature. Finally, a DSSC with a 24 μm thick TiO₂ film and annealed at 500 °C produced the highest conversion efficiency (η=6.56%, I_SC=16.4, V_OC=0.72, FF=0.55) with an incident solar energy of 100 mW/cm².     

Enhanced gas barrier properties of graphene-TiO2 nanocomposites on plastic substrates assisted by UV photoreduction of graphene oxide

Reduced graphene oxide (rGO) sheets have received great attention as a key element for thin barrier films that block the permeation of water vapor and other gases. However, it remains a challenge to prepare the rGO-based barrier films on plastic substrates through a chemically benign and low temperature fabrication route. Toxic chemicals or high temperature thermal treatments that are widely used for preparing rGO need to be avoided because they can damage the underlying plastic substrates. In this study, we report the fabrication of rGO/TiO₂ composite films via an eco-friendly and low temperature ultraviolet (UV) photoreduction process and demonstrate their enhanced gas barrier properties by measuring water vapor transmission rates (WVTRs). When photocatalytic TiO₂ nanoparticles are employed, UV exposure reduces the GO/TiO₂ composite solution to form rGO/TiO₂, which is subsequently deposited on plastic substrates. The rGO/TiO₂ composites become resistant to water absorption because the UV photoreduction of GO/TiO₂ effectively removes most polar groups on the GO sheets. We confirmed that rGO/TiO₂ composites were successfully deposited onto the plastic substrate through a solution process and the barrier films led to a substantial reduction in WVTRs of the substrate. Our strategy for preparing graphene-based thin barrier films by using a UV photoreduction process enables the fabrication of solution-processed graphene-based encapsulation layers on plastic substrates with an eco-friendly and low temperature fabrication method.     

CSA-doped PANI/TiO2 hybrid BHJ solar cells – Material synthesize and device fabrication

In this study, camphorsulfonic acid (CSA) doped polyaniline (PANI) synthesized by oxidative polymerization and titanium-di-oxide (TiO₂) nanoparticles synthesized by sol-gel were solution blend in a mixed solvent of 1:1 m-cresol and chloroform to fabricate hybrid bulk heterojunction (BHJ) solar cells of structure ITO/PEDOT:PSS/CSA-doped PANI-TiO₂/Al. The effect of TiO₂ weight ratio on the cell performance was investigated by analyzing the structural and optical properties of CSA-doped PANI/TiO₂ hybrid thin films with different TiO₂ ratio. Crystalline structure of TiO₂ nanoparticles, polymer and hybrid thin films were identified by XRD studies and root-like structure of both polymer and hybrid thin films by SEM image. CSA-doped PANI was confirmed as p-type semiconductor through Hall-effect analysis. High absorption coefficient along with PL quenching in hybrid thin film confirms its application in solar cells as photoactive layer. For optimal fabrication conditions, maximum photo conversion efficiency (PCE) of 0.21% was obtained for a device with lower TiO₂ weight ratio. The results show that optimization of absorption intensity of CSA-doped PANI in the visible region of spectrum and morphology of hybrid films will effectively enhance the performance of hybrid solar cells. Error analysis of PCE for all the fabricated solar cells has been reported.     

Dependence of energy conversion efficiency of dye-sensitized solar cells on the annealing temperature of TiO2 nanoparticles

Dye-sensitized solar cells (DSSCs) were fabricated from porous electrodes derived from sol–gel-synthesized (SGS) nanoparticles (NPs) of TiO₂. Current–voltage measurements were performed to investigate performance characteristics of electrodes derived from SGS-NPs of TiO₂ annealed at different temperatures. Experimental results indicate that the effects of bulk traps and surface states within TiO₂ films on recombination of photo-injected electrons in DSSCs depend upon annealing temperature of SGS-TiO₂ NPs. Moreover, electrodes fabricated from SGS-TiO₂ showed higher photoelectric conversion efficiency than nonporous commercial (P25) TiO₂ NPs. Porous structures within SGS-TiO₂ NPs are of great benefit to sensitizer dye adsorption, and consequently to improvement of photo-electrochemical properties of DSSCs.     

Efficient organic photovoltaics using solution-processed,annealing-free TiO2 nanocrystalline particles as an interface modification layer

A solution-processed, annealing-free TiO₂ nanocrystalline particles (TiO₂ NPs) as an interface modification layer was inserted in organic photovoltaics (OPVs), in which the widely used polymer poly (3-hexyl thiophene) (P3HT), a low band gap alkoxylphenyl substituted [1,2-b:4,5-b′] dithiophene-based polymer (PBDTPO-DTBO), and a soluble small molecule benzodithiophene derivative (TIBDT) were used as the donor material, respectively. The annealing-free TiO₂ NPs could be easily spin-coated upon the surface of organic active layers, and showed comparable properties to thermal-annealed ones. The power conversion efficiencies (PCEs) of OPV devices could be enhanced dramatically with inserting an annealing-free TiO₂ NPs layer. The PCEs of OPV devices based on P3HT:PC₆₁BM, PBDTPO-DTBO:PC₇₁BM and TIBDT:PC₆₁BM bulk heterojunctions were improved by 28%, 15% and 27%, respectively, with an annealing-free TiO₂ NPs layer, in which the highest PCE of 5.76% was achieved in PBDTPO-DTBO:PC₇₁BM OPVs. The solution-processed, annealing-free TiO₂ NPs thin films show great potential applications in the fabrication of large-area OPVs by printing or coating techniques on flexible polymer substrates. In particularly, it would promote to fabricate solution-processed, annealing-free OPV devices with suitable hole transport layer and organic/polymer active materials.     

The optical properties of monolayer amorphous Al2O3–TiO2 composite films used as HT-APSM blanks for ArF immersion lithography

Amorphous (Al₂O₃)_x–(TiO₂)_1−x composite films are prepared using r.f. unbalanced magnetron sputtering in an atmosphere of argon and oxygen at room temperature. The optical constants of (Al₂O₃)_x–(TiO₂)_1−x composite films are linearly dependent on the Al₂O₃ mole fraction in the Al₂O₃–TiO₂ composite film. The optical constants of these Al₂O₃–TiO₂ composite films can be made to meet the optical requirements for a high transmittance attenuated phase shift mask (HT-APSM) blank by tuning the Al₂O₃ mole fraction. The Al₂O₃ mole fraction range that would allow the films to meet the optical requirements of an HT-APSM blank for ArF immersion lithography is calculated to be between 76% and 84%. One π-phase-shifted Al₂O₃–TiO₂ composite thin film to be used as an HT-APSM blank for ArF immersion lithography is fabricated and is shown to satisfy the optical requirements.     

Silver-loaded anatase nanotubes dispersed plasmonic composite photoanode for dye-sensitized solar cells

In this article, a typical silver-loaded anatase TiO₂ nanotube (Ag-TNTs) was developed and assembled in DSSCs. By blending the Ag-TNTs and TiO₂ nanoparticles as the composite photoanode, this hybrid nanostructure exhibits a promising architecture for accelerating electron transport as well as enhancing dye adsorption. These nanotubes could provide direct charge transfer pathways and increase electrolyte penetration in comparison with the TiO₂ nanoparticles alone network. Moreover, the presence of the Ag nanoparticles could enhance the light harvesting efficiency and promote the charge separation, which further improves the performance of the DSSCs. The DSSC with metal-modified hybrid nanostructures has achieved an efficiency of 8.19% which is about 56% higher than DSSCs based on TiO₂ nanoparticles photoanode with 5.26%.     

Trifunctional TiO2 Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

In this study, highly mesoporous TiO₂ composite photoanodes composed of functional {001}‐faceted TiO₂ nanoparticles (NPs) and commercially available 20 nm TiO₂ NPs are employed in efficient porphyrin‐sensitized solar cells together with cobalt polypyridyl‐based mediators. Large TiO₂ NPs (approximately 50 nm) with exposed {001} facets are prepared using a fast microwave‐assisted hydrothermal (FMAH) method. These unique composite photoanodes favorably mitigate the aggregation of porphyrin on the surface of TiO₂ NPs and strongly facilitate the mass transport of cobalt‐polypyridyl‐based electrolytes in the mesoporous structure. Linear sweep voltammetry reveals that the transportation of Co(polypyridyl) redox is a diffusion‐controlled process, which is highly dependent on the porosity of TiO₂ films. Electrochemical impedance spectroscopy confirms that the FMAH TiO₂ NPs effectively suppress the interfacial charge recombination toward [Co(bpy)₃]³⁺ because of their oxidative {001} facets. In an optimal condition of 40 wt% addition of FMAH TiO₂ NPs in the final formula, the power conversion efficiency of the dye‐sensitized cells improves from 8.28% to 9.53% under AM1.5 (1 sun) conditions.     

Charge transport mechanisms in anisotype n-TiO2/p-Si heterostructures

Anisotype n-TiO₂/p-Si heterojunctions are fabricated by the deposition of a TiO₂ film on a polished poly-Si substrate using magnetron sputtering. The electrical properties of the heterojunctions are investigated and the dominant charge transport mechanisms are established; these are multi-step tunneling recombination via surface states at the metallurgical TiO₂/Si interface at low forward biases V and tunneling at V > 0.6 V. The reverse current through the heterojunctions under study is analyzed within the tunneling mechanism.     

Facile fabrication and enhanced photoresponse of hybrid heterojunction films of ZnOEP nanowire network/ZnO nanoparticles

Hybrid heterojunction films of zinc octaethylporphyrin/zinc oxide (ZnOEP/ZnO) were fabricated by a facile solution process, in which ZnO nanoparticles were directly added to ZnOEP nanowire networks. The devices based on the as-fabricated films displayed high sensitivity and stable photoswitching. The largest I_on/I_off switching ratio of the phototransistor devices was over 10³. Moreover, the ZnOEP/ZnO heterojunctions could effectively prevent the photogenerated charge carrier recombination and prolong the photocarrier lifetime. Therefore, higher photocurrent or photoresponsivity of hybrid photodetectors were obtained. The excellent performance associated with facile, large-scale, and cost-effective fabrication process of ZnOEP/ZnO heterojunctions is promising for photodetector and photoswitch application.     

Effect of guest concentration on carrier transportation in blends of conjugated polymers

In this paper, the charge transport in pure poly (9,9-dioctylfluorene-2, 7-diyl) (PFO) and its blend with poly (5-methoxy-2-2-ethyl-hexylthio)-p-phenylenevinylene (MEH-PPV) is studied. The mobility (μ_eff) and diffusivity (D) of the pure and blend thin films have been calculated using electroluminescence transient (ELT) technique. MEH-PPV concentration was varied from 0.8 to 15 wt%. It is found that at relatively low concentration of MEH-PPV, less than 1.2 wt%, the mobility of PFO:MEH-PPV blend increases with the concentration of MEH-PPV, and after that, it starts decreasing. The field dependence of effective hole mobility follows the Poole–Frenkel (P–F) plot of mobility (μ) as a function applied electric field with positive slope (β_PF > 0) up to 5.0 wt% concentration of MEH-PPV. A negative P-F type dependence is then observed for 8.0–15 wt% MEH-PPV concentration. Diffusivity (D) of blends is following the same trends as mobility i.e. blend with 1.2 wt% MEH-PPV shows the highest diffusivity. These results have been correlated with the morphology of pure and blend thin films. Gaussian Disorder Model (GDM) alone is not able to explain the change in β_PF with the MEH-PPV concentration, guest induced crystallization of PFO plays an important role at low concentrations of MEH-PPV. At higher concentrations of MEH-PPV (≥8 wt%), crystallization is suppressed, and position disorder induced behavior of polymer determines the charge transport in the blends.     

Template free titiania photoanodes modified with carbon black or multi-wall carbon nanotubes: Thermal treatment at low and high temperature for the fabrication of quasi-solid state dye sensitized solar cells

A simple procedure was developed to prepare modified titiania (TiO₂) photoanodes for dye sensitized solar cells at low and high temperature in order to improve overall cell efficiency. Modification of TiO₂ films achieved by the incorporation of either carbon black powder (CBP) or multi-wall carbon nanotubes (MWCNTs). A small quantity of titanium alkoxide was added in a dispersion of titiania (TiO₂) powder consisting of nanoparticles at room temperature, which after alkoxide׳s hydrolysis helps to the connection between titiania (TiO₂) particles and to the formation of mechanically stable relatively thick films on conductive glass substrates. The absence of surfactant allowed us to prepare films at relatively low temperature (~100 °C), while the effect of sintering at a higher temperature (500 °C) was also studied. The structural properties of the films were examined with porosimetry method and microscopy analysis. Better electrical results were obtained for the MWCNT (0.1 wt%) modified TiO₂ films, with 3.14% and 4.68% conversion efficiencies under 1 sun illumination after treatment at 100 °C and 500 °C, respectively. The enhancement in photocurrent for MWCNT-TiO₂ films compared to pure TiO₂ films is attributed to the improved interconnectivity between TiO₂ nanoparticles, which further improved the electron transport through the film. For carbon doped CBP-TiO₂ cells, lower efficiencies were observed compared to pure TiO₂.     

Effect of TiO2 nanoparticle content in sol–gel derived TiO2 paste on the photovoltaic properties of TiO2 photoanode of dye-sensitized solar cells

In the present work, the effect of the amount of TiO₂ nanoparticles, added to the sol–gel derived paste, on the photovoltaic properties of fabricated dye-sensitized solar cells (DSSCs) was investigated. A titanium sol (Ti-sol) was synthesized using a Pechini type sol–gel method, and different pastes were prepared by adding various amounts of TiO₂ nanoparticles to the obtained Ti-sol. The pastes were used to fabricate the mesoporous TiO₂ semiconducting layers for DSSCs. It was observed that by increasing the mass ratio (MR) of TiO₂ nanoparticles to Ti-sol the thickness of TiO₂ layer increases. This led to the more adsorption of dye molecules per unit area of active TiO₂ layer, which were determined by UV–vis spectrophotometry. Also, micro-cracks were observed in TiO₂ layers obtained from pastes with low MR values. But their amount and size decreased with increasing MR, which was due to the decrease of paste surface tension (σ). As a result, short circuit current density (I_sc) showed continuous increase with increasing MR, which was due to the more dye adsorption. Open circuit voltage (V_oc) first increased and then decreased by enhancing MR, which was explained by considering the electron–hole recombination rate. Finally, the DSSC fabricated from the paste with MR=0.65 showed the maximum conversion efficiency (η).     

Hybrid Solar Cells from a Blend of Poly(3‐hexylthiophene) and Ligand‐Capped TiO2 Nanorods

Hybrid bulk heterojunction solar cells based on nanocrystalline TiO₂ (nc‐TiO₂) nanorods capped with trioctylphosphine oxide (TOPO) and regioregular poly(3‐hexylthiophene) (P3HT) are processed from solution and characterized in order to relate the device function (optical absorption, charge separation, and transport and photovoltaic properties) to active‐layer properties and device parameters. Annealing the blend films is found to greatly improve the polymer–metal oxide interaction at the nc‐TiO₂/P3HT interface, resulting in a six‐fold increase of the charge separation yield and improved photovoltaic device performance under simulated solar illumination. In addition, the influence of the organic ligand at the nc‐TiO₂ particle surface is found to be crucial for charge separation. Ligand‐exchange procedures applied on the TOPO‐capped nc‐TiO₂ nanorods with an amphiphilic ruthenium‐based dye are found to further improve the charge‐separation yield at the polymer–nanocrystal interface. However, the poor photocurrents generated in the hybrid blend devices, before and after ligand exchange, suggest that transport within or between nanoparticles limits performance. By comparison with other donor–acceptor bulk heterojunction systems, we conclude that charge transport in the nc‐TiO₂:P3HT blend films is limited by the presence of an intrinsic trap distribution mainly associated with the nc‐TiO₂ particles.     

Composites of Core/Shell-Structured Copper-Phthalocyanine-Decorated TiO2 Particles Embedded in Poly(Arylene Ether Nitrile) Matrix with Enhanced Dielectric Properties

Polymer-based composite films were prepared by employing core/shell-structured tetranitrophthalocyanine copper/titanium dioxide (TNCuPc–TiO₂) hybrid particles as fillers and poly(arylene ether nitrile)s (PEN) as polymer matrix. Core/shell-structured TNCuPc–TiO₂ hybrid particles were successfully synthesized through a facile solvothermal synthesis route. Compared with raw TiO₂, the dispersibility and interfacial compatibility between TNCuPc–TiO₂ hybrid particles and PEN matrix were observably improved because the TNCuPc decorated on the TiO₂ can interact with nitrile groups in PEN. Consequently, core/shell-structured TNCuPc–TiO₂ had a more significant enhancement effect on the properties of PEN. Although the mechanical strength was reduced to 41 MPa, all of the composite films exhibited excellent thermal stability. Their initial decomposition temperatures were up to 510°C, and the glass-transition temperatures were over 191°C. More importantly, the permittivity of the composite film was as high as 19.8 at 100 Hz when the weight fraction of TNCuPc–TiO₂ hybrid particle loading reached 40.0 wt.%. Compared with the permittivity of PEN/TiO₂ composite films with 40.0 wt.% raw TiO₂ particle loading, the dielectric constant was increased by 161%.     

Molecular orientation anisotropy and hole transport properties of diluted semiconducting films of poly(p-phenylenevinylene) derivative

The electrical and optical properties of certain semiconducting polymers are improved in blend films with inert host materials. The improvements have been attributed to the dilution effect of electron traps and interchain species in semiconductor materials. In this paper, we report on anisotropy in the blend films of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and its strong dependence on an inert host material, such as polystyrene (PS) or polyvinylcarbazole (PVK). We found that the orientation of the MEH-PPV backbone in the blend film changed from horizontal to random on dilution with PS. Moreover, the in-plane hole conductivity was enhanced in the MEH-PPV:PVK blend film, although the out-of-plane conductivity reduced owing to excessive dilution. Mott–Schottky analysis of the capacitance–voltage characteristics revealed opposite trends for dilution with PS and PVK; i.e., PS increased the accumulated charge density in the bulk of the blend film, whereas PVK reduced it. These results demonstrate that isotropy was induced in the PS blend films, whereas anisotropy was induced in the PVK blend films. Anisotropy is an important factor for understanding the hole transport characteristics in the diluted films.     

Visible light active TiO2–ZnO composite films by cerium and fluorine codoping for photocatalytic decontamination

The visible light active Ce/F codoped TiO₂–ZnO composite films with a bad gap of 1.82 eV were successfully prepared though a simple sol–gel method. Experimental results indicated that the composite films showed excellent photocatalytic performance towards photocatalytic oxidation of organic pollutants including formaldehyde, acid naphthol red (ANR) and methyl green (MG). The catalysts were characterized by photoluminescence (PL) spectra, UV–vis diffraction reflectance absorption spectra (DRS), X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy (EDS), and N₂ adsorption/desorption isotherms. The DRS and PL spectra results showed that multi-modification not only induced strong visible light absorption but also reduced the recombination rate of electron–hole pairs. The DTA-TG and XRD results indicated that the crystal type of the TiO₂-based catalyst was mostly stabilized in anatase. The FE-SEM and BET surface area results revealed that the nanocrystalline Ce/F codoped TiO₂–ZnO composite samples with the larger specific surface area were composed of smaller nanoparticles compared to pure TiO₂. The mechanism of the enhanced photocatalytic activity was discussed in this study.     

Rapid Fabrication of an Inverse Opal TiO2 Photoelectrode for DSSC Using a Binary Mixture of TiO2 Nanoparticles and Polymer Microspheres

A rapid fabrication method of highly reflective TiO₂ inverse opal (IO) film exhibiting controllable thickness, high TiO₂ content, and excellent interfacial contact with glass substrate is presented. By inducing accelerated solvent evaporation during the colloidal self‐assembly process, a composite film of polystyrene (PS)/TiO₂ has been directly fabricated on a fluorine doped tin oxide (FTO) glass substrate, which exhibits the highly ordered opaline structure of PS embedded into the TiO₂ matrix. This hybrid fabrication path leads to the formation of layers with the preferred {111} face‐centered cubic (FCC) orientation parallel to the substrate and to produce a 1 cm²‐wide well‐ordered composite colloidal crystal film in less than 30 min. The film showed highly ordered FCC structure, particularly at the upper region, due to the induced solvent evaporation and exhibited a reliable light modulation at a reflectance mode. Regardless of the size of sacrificial PS microspheres, TiO₂ IO films of controllable thickness were successfully formed by varying the moving speed of the fabrication cell. The binary aqueous dispersion of tailor‐made anatase TiO₂ nanoparticles and monodisperse PS microspheres showed a high degree of dispersion stability under basic conditions. Hydrothermal treatment of the TiO₂ dispersion favored the crystallinity of the coated film and provided small volume contraction after thermal calcinations. The high degree of dispersion stability enabled to increase TiO₂ content in a binary mixture, which is more favorable toward the robust and large‐area IO film. The calcined films exhibited excellent mechanical robustness and intimate interfacial contact with the glass substrate. which in turn resulted in higher TiO₂ content near the glass substrate. The TiO₂ IO film was tested as a dye‐sensitized solar cell (DSSC) photoelectrode, and a single cell showed a relatively high photon‐to‐current conversion efficiency of 4.2%. The high TiO₂ content of IO film and its good adhesion to the FTO subratrate remarkably improved in the performance of the solar cell compared to the previous investigations where post‐infiltration of TiO₂ had been employed.     

Functional Free‐Standing Graphene Honeycomb Films

Fabricating free‐standing, three‐dimensional (3D) ordered porous graphene structure can service a wide range of functional materials such as environmentally friendly materials for antibacterial medical applications and efficient solar harvesting devices. A scalable solution processable strategy is developed to create such free‐standing hierarchical porous structures composed of functionalized graphene sheets via an “on water spreading” method. The free‐standing film shows a large area uniform honeycomb structure and can be transferred onto any substrate of interest. The graphene‐based free‐standing honeycomb films exhibit superior broad spectrum antibacterial activity as confirmed using green fluorescent protein labeled Pseudomonas aeruginosa PAO1 and Escherichia coli as model pathogens. Functional nanoparticles such as titanium dioxide (TiO₂) nanoparticles can be easily introduced into conductive graphene‐based scaffolds by premixing. The formed composite honeycomb film electrode shows a fast, stable, and completely reversible photocurrent response accompanying each switch‐on and switch‐off event. The graphene‐based honeycomb scaffold enhances the light‐harvesting efficiency and improves the photoelectric conversion behavior; the photocurrent of the composite film is about two times as high as that of the pure TiO₂ film electrode. Such composite porous films combining remarkably good electrochemical performance of graphene, a large electrode/electrolyte contact area, and excellent stability during the photo‐conversion process hold promise for further applications in water treatment and solar energy conversion.