Impact of preparation method of TiO 2 -RGO nanocomposite photoanodes on the performance of dye-sensitized solar cells

Reduced Graphene Oxide-Laminated One-Dimensional TiO2-Bronze Nanowire Composite: An Efficient Photoanode Material for Dye-Sensitized Solar Cells

A facile one-step hydrothermal method was developed to prepare reduced graphene oxide-laminated TiO₂-bronze (TiO₂-B) nanowire composites (TNWG), which contain two-dimensional graphene oxide nanosheets and TiO₂-B nanowires. In the hydrothermal process, the functional groups of graphene oxide were reduced significantly. Dye-sensitized solar cells (DSSCs) were fabricated using TNWG as the photoanode material. The effects of different reduced graphene oxide contents in TNWG on the energy conversion efficiency of the dye-sensitized solar cells were investigated using J-V and incident photon-to-current conversion efficiency characteristics. DSSCs based on a TNWG hybrid photoanode with a reduced graphene oxide content of 8 wt % demonstrated an overall light-to-electricity conversion efficiency of 4.95%, accompanied by a short-circuit current density of 10.41 mA cm^-2, an open-circuit voltage of 0.71 V, and a fill factor of 67%, which were much higher than those of DSSC made with a pure TiO₂-B NW-based photoanode. The overall improvement in photovoltaic performance could be associated to the intense visible light absorption and enhanced dye adsorption because of the increased surface area of the composite, together with faster electron transport due to reduced carrier recombination.

Recent Advances in Synthesis and Applications of Carbon-Doped TiO2 Nanomaterials

TiO2 has been widely used as a photocatalyst and an electrode material toward the photodegradation of organic pollutants and electrochemical applications, respectively. However, the properties of TiO2 are not enough up to meet practical needs because of its intrinsic disadvantages such as a wide bandgap and low conductivity. Incorporation of carbon into the TiO2 lattice is a promising tool to overcome these limitations because carbon has metal-like conductivity, high separation efficiency of photogenerated electron/hole pairs, and strong visible-light absorption. This review would describe and discuss a variety of strategies to develop carbon-doped TiO2 with enhanced photoelectrochemical performances in environmental, energy, and catalytic fields. Emphasis is given to highlight current techniques and recent progress in C-doped TiO2-based materials. Meanwhile, how to tackle the challenges we are currently facing is also discussed. This understanding will allow the process to continue to evolve and provide facile and feasible techniques for the design and development of carbon-doped TiO2 materials.

Influence of Sputtering Temperature of TiO2 Deposited onto Reduced Graphene Oxide Nanosheet as Efficient Photoanodes in Dye-Sensitized Solar Cells

Renewable solar energy is the key target to reduce fossil fuel consumption, minimize global warming issues, and indirectly minimizes erratic weather patterns. Herein, the authors synthesized an ultrathin reduced graphene oxide (rGO) nanosheet with ~47 nm via an improved Hummer's method. The TiO2 was deposited by RF sputtering onto an rGO nanosheet with a variation of temperature to enhance the photogenerated electron or charge carrier mobility transport for the photoanode component. The morphology, topologies, element composition, crystallinity as well as dye-sensitized solar cells' (DSSCs) performance were determined accordingly. Based on the results, FTIR spectra revealed presence of Ti-O-C bonds in every rGO-TiO2 nanocomposite samples at 800 cm-1. Besides, XRD revealed that a broad peak of anatase TiO2 was detected at ~25.4° after incorporation with the rGO. Furthermore, it was discovered that sputtering temperature of 120 °C created a desired power conversion energy (PCE) of 7.27% based on the J-V plot. Further increase of the sputtering temperature to 160 °C and 200 °C led to excessive TiO2 growth on the rGO nanosheet, thus resulting in undesirable charge recombination formed at the photoanode in the DSSC device.

AgInS2 and graphene co-sensitized TiO2 photoanodes for photocathodic protection of Q235 carbon steel under visible light

AgInS₂ nanoparticle and graphene nanosheet co-sensitized anatase TiO₂ nanotube array films were fabricated by a combination of hydrothermal reaction and electrochemical anodization on titanium sheets. The results showed that the co-sensitization of AgInS₂ nanoparticles and graphene nanosheets extended the photoresponse of TiO₂ nanotubes into the visible-light region, and improved the photogenerated charge separation and transfer capability. The photocurrent density of the AgInS₂/graphene/TiO₂ composites (about 4.0 mA cm^-2) was 20 times that of bare TiO₂ (only 0.2 mA cm^-2) under visible-light illumination. The potential negative shift value of AgInS₂/graphene/TiO₂ composites was up to 0.68 V versus saturated calomel electrode. The AgInS₂/graphene/TiO₂ composites can provide Q235 carbon steel with highly efficient photocathodic protection under visible-light illumination.

Preparation of Multicycle GO/TiO2 Composite Photocatalyst and Study on Degradation of Methylene Blue Synthetic Wastewater

A series of composite photocatalysts were prepared by using graphene oxide (GO) prepared by modified Hummers method and TiO2 hydrogel prepared by using butyl titanate as raw materials. The composite photocatalyst was characterized through scanning electron microscope（SEM）, x ray diffraction （XRD）, and Raman spectroscopy, and the degradation effect of pure TiO2 and composite photocatalyst on methylene blue (MB) dye wastewater under different experimental conditions was studied. The results showed that TiO2 in composite photocatalyst was mainly anatase phase and its photocatalytic activity was better than pure TiO2. When the addition of GO reached 15 wt%, the photocatalytic activity was the highest. When 200 mg composite photocatalyst was added to 200 mL synthetic wastewater with a concentration of 10 mg/L and an initial pH of about 8, the degradation rate could reach 95.8% after 2.5 h. It is presumed that the photogenerated charges of GO/TiO2 composite photocatalyst may directly destroy the luminescent groups in the MB molecule and thus decolorize the wastewater, and no other new luminescent groups are generated during the treatment.

On the assessment of incorporation of CNT-TiO2 core-shell structures into nanoparticle TiO2 photoanodes in dye-sensitized solar cells

Herein, we report dye-sensitized solar cells (DSCs) based on conventional nanocrystalline TiO2 photoanodes decorated with one-dimensional (1D) CNT-TiO2 core-shell structures (CTH). The core-shell nanotubes are synthesized by a simple sol-gel template-assisted method via in situ deposition of TiO2 on the surface of non-covalently functionalized CNTs. The core-shell nanotubes are well characterized by various techniques. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images show that formation of the TiO2 shell on the surface of the CNT core follows a layer or Frank-van der Merwe growth mode, resulting in a highly uniform interface with excellent charge transfer from the TiO2 conduction band into the CNTs. The thickness and crystal structure of the TiO2 shell can be tailored by controlling the processing parameters. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy verify that CNTs have no surface defects and are well preserved using the employed method and the subsequent heat treatment in air, respectively. UV-vis spectroscopy and photoluminescence spectroscopy reveal an extension to visible regions with an increase in overall intensity and a significant reduction in charge recombination due to a shift of the Fermi level toward positive potentials. We find an increase by up to 37% in the DSC device's power conversion efficiency by incorporating the CNT-TiO2 core-shell nanotubes into the nanoparticle TiO2 photoanode due to the charge recombination reduction and electron injection enhancement.

SnO2-rGO nanocomposite as an efficient electron transport layer for stable perovskite solar cells on AZO substrate

Electron transport layer (ETL) plays an important role in realizing efficient and stable perovskite solar cells (PSCs). There are continuous efforts in developing new types of low cost ETLs with improved conductivity and compatibility with perovskite and the conducting electrode. Here, in order to obtain high efficient and stable PSCs on ZnO:Al (AZO) substrate, reduced graphene oxide (rGO) is incorporated into SnO₂ nanoparticles to form composite ETL. For planar PSC on AZO substrates, SnO₂-rGO with a low incorporation ratio of 3 wt% rGO significantly enhances the device short circuit current density (J _sc) and the fill factor when compared to the device with pristine SnO₂ ETL, leading to an overall power conversion efficiency of 16.8% with negligible hysteresis. The effectiveness of the excited charge transfer process of SnO₂-rGO ETL is revealed by time-resolved photoluminescence decay, and by electrochemical impedance spectrum measurements. Furthermore, the solar cell stability is also enhanced due to the incorporation of rGO in the ETL. This work provides a low cost and effective ETL modification strategy for achieving high performance planar PSCs.

Construction of Perovskite Solar Cells Using Inorganic Hole-Extracting Components

A NiO _x -graphene oxide (NiO _x -GO) hybrid has been prepared by a simple solution-processed method and was used as hole-extraction material in perovskite solar cells with either gold or carbon as back contact electrode. The impact of GO content on the optoelectronic behavior of NiO _x and the photovoltaic performance of the fabricated devices has been studied. Thus, GO incorporation showed a significant improvement in the performance of NiO _x -based devices. The best attained efficiency was 13.3%, and it was 45% higher than that with pure NiO _x . This is attributed to a significant improvement in the hole extraction, recombination resistance, and energy-level matching in comparison to pure NiO _x . In addition, NiO _x -GO/Au-based perovskite solar cell devices showed a negligible hysteresis effect and high reliability and repeatability. When carbon was used as back contact electrode, the obtained efficiencies were lower, but it leaves space for improvement. Devices based on inorganic hole transporters NiO _x or NiO _x -GO demonstrated higher stability in ambient air compared to a standard cell based on spiro-OMeTAD.

Long-term stability of dye-sensitized solar cells using a facile gel polymer electrolyte

Hydroxypropyl cellulose as a polymeric gelator agent was incorporated in the liquid electrolyte of dye-sensitized solar cells, showing long-term stability and efficient performance.

Improvement of the photovoltaic parameters of perovskite solar cells using a reduced-graphene-oxide-modified titania layer and soluble copper phthalocyanine as a hole transporter

Graphene modified mesoporous titania for perovskite solar cells.

Inverted perovskite solar cells based on lithium-functionalized graphene oxide as an electron-transporting layer

A perovskite solar cell with an inverted p–i–n architecture employing GO and GO-Li as functional charge transport components.