Enhanced efficiency and improved photocatalytic activity of 1 : 1 composite mixture of TiO<Subscript>2</Subscript> nanoparticles and nanotubes in dye-sensitized solar cell

TiO₂-based nanotubes (NTs), nanoparticles (NPs) and composite structural film (50% NP + 50% NT film) were synthesized by sol-gel hydrothermal process. Synthetic indigo dye was used as a sensitizer with the unique combination of electrolyte (EMII + BMII + PMII) and with cobalt sulphide as counter electrode. The structure and morphology of the three films, namely, NP, NT and NPNT is studied through X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The absorption spectra and incident photon-to-current conversion efficiency (IPCE) of the three films were compared and found to be higher for NPNT film. The efficiency and photocatalytic activity of three films were evaluated. The composite structure showed improved efficiency (1.72%) than NP (1%) and NT films (0.78%). The photocatalytic activity of the three films were measured using organic dye, methylene blue under UV light radiation. The composite structure showed higher dye absorption and higher rate of reaction with time. This paper certainly proves that there are many rooms to focus on the photoanode configuration, which plays a key role to improve the efficiency of dye-sensitized solar cell (DSSC).     

TiO(2) fibers enhance film integrity and photovoltaic performance for electrophoretically deposited dye solar cell photoanodes

Nanoparticulated TiO(2) fibers as one-dimensional long structures were introduced into TiO(2) P25 nanoparticle films using coelectrophoretic deposition. This prevented the usual crack formation occurring in wet coatings, and resulted in less porosity and higher roughness factor of the films that provided more favorable conditions for electron transport. The films used as the photoanode of a dye solar cell (DSC) produced 65% higher photovoltaic efficiency. TiO(2) fibers can be excellent binders in single-step, organic-free electrophoretic deposition of TiO(2) for DSC photoanode.     

Direct Growth of Polymeric Carbon Nitride Nanosheet Photoanode for Greatly Efficient Photoelectrochemical Water-Splitting

A general method for the direct synthesis of highly homogeneous and dense polymerized carbon nitride (PCN) nanosheet films on F: SnO₂ (FTO) is developed. Detailed photoelectrochemical (PEC) water-splitting studies reveal that the as-synthesized PCN films exhibit outstanding performance as photoanode for PEC water-splitting. The optimal PCN photoanode exhibits excellent photocurrent density of 650 µA cm⁻², and monochromatic incident photon-to-electron conversion efficiency ( IPCE) value up to 30.55% (λ = 400 nm) and 25.97% (λ = 420 nm) at 1.23 V_RHE in 0.1 m KOH electrolyte. More importantly, the PCN photoanode has an excellent hole extraction efficiency of up to 70 ± 3% due to the abundance of active sites provided by the PCN photoanode nanosheet, which promotes the transport rates of OER-relevant species. These PCN films provide a new benchmark for PCN photoanode materials.     

Different hierarchical nanostructured carbons as counter electrodes for CdS quantum dot solar cells

CdS quantum dot sensitized solar cells based on TiO(2) photoanode and nanostructured carbon as well as Pt as counter electrodes using iodide/triiodide and polysulfide electrolytes were fabricated to improve the efficiency and reduce the cost of solar cells. Compared with conventional Pt (η = 1.05%) and CMK-3 (η = 0.67%) counter electrodes, hollow core-mesoporous shell carbon (HCMSC) counter electrode using polysulfide electrolyte exhibits much larger incident photon to current conversion efficiency (IPCE = 27%), photocurrent density (J(sc) = 4.31 mA.cm(-2)) and power conversion efficiency (η = 1.08%), which is basically due to superb structural characters of HCMSC such as large specific surface area, high mesoporous volume, and 3D interconnected well-developed hierarchical porosity network, which facilitate fast mass transfer with less resistance and enable HCMSC to have highly enhanced catalytic activity toward the reduction of electrolyte shuttle.     

Expanding the spectral response of a dye-sensitized solar cell by applying a selective positioning method

We have developed a facile method to position different dyes (N719 and N749) sequentially in a mesoporous TiO(2) layer through selective desorption and adsorption processes. From the selective removal of the only upper part of the first adsorbed dye, double-layered dye-sensitized solar cells have been successfully achieved without any damage to the dye. From the incident photon-to-current conversion efficiency (IPCE) measurement, the multi-layered dye-sensitized solar cell (MDSSC) was found to exhibit an expanded spectral response for the solar spectrum while maintaining the maximum IPCE value of each single-layered cell. The highest photocurrent density, 19.3 mA cm( - 2), was obtained from the MDSSC utilizing an N719/N749 bi-layered mesoporous TiO(2) film. The power conversion efficiency of 9.8% was achieved from the MDSSC, which is higher than that of single N719-or N749-based cells and cocktail-dyed (a mixture of N719 and N749) cells.     

Ag2Se量子点共敏化固态染料敏化太阳能电池光电性能研究

采用水相共沉积法制备Ag₂Se量子点(QDs), 并与染料共敏化制备固态染料敏化太阳能电池(DSSCs)。考察了Ag₂Se量子点不同敏化方式(TiO₂/N719/QDs, TiO₂/QDs/N719)及敏化时间(0~5 h)对DSSCs性能的影响。通过透射电子显微镜(TEM)和紫外-可见光谱图(UV-Vis)对Ag₂Se量子点结构及光学性质进行了表征; 采用光调制光电流/电压谱(IMPS/VS)以及交流阻抗谱(EIS)对器件中载流子传输过程进行了研究。TiO₂/QDs/N719的电池器件比TiO₂/ N719/QDs具有更高的单色光量子转化效率(IPCE)及光电转化效率, 这是由于TiO₂/QDs/N719可以吸附更多的量子点和染料。随着Ag₂Se量子点敏化时间的延长, 光电转化效率先提高后降低, 最高达到3.97%。Ag₂Se量子点在器件中起到了阻挡层作用, 可以促进电子传输, 抑制电子-空穴复合。而随着量子点敏化时间超过2 h, 电子陷入陷阱的几率增加, 导致器件的光伏性能下降。     

Vapor deposited sculptured nano-porous titania films by glancing angle deposition for efficiency enhancement in dye-sensitized solar cells

Sculptured porous titania films as photoanode in dye-sensitized solar cell (DSSC) were prepared using an electron-beam evaporation system with glancing angle deposition (GLAD) method. By controlling the substrate rotation rate and the incident angle of evaporant, titania films of various thicknesses were prepared on ITO glasses. The as-deposited nano-porous films are comprised of helical nano-columns and assembled in an orderly manner with gaps or pores in between, which offer large internal surface area for dye adsorption and direct electron transfer path. There is a positive correlation between the film thickness, film effective surface area, amount of absorbed dye and cell efficiency. The nano-porous films provide a synergistic effect of high surface area, effective route for electron transfer, tight interfaces, and enhanced light trapping, which are all beneficial for higher cell efficiency. The DSSC consisting of a 6 μm titania film, deposited at substrate rotating rate 0.17 rpm and incident angle 73°, gave a cell efficiency of 6.1%.     

Synthesis of Fe alloyed PbS thin films and investigation of their photovoltaic properties

Lead sulfide (PbS) and iron (Fe)-alloyed PbS thin films with different Fe concentrations were synthesized by chemical bath deposition (CBD) technique, which is suitable for cost on glass substrates at room temperature. The structural, elemental and optical properties of the synthesized thin films were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX) and optical absorption measurements, respectively. It was observed that Fe dopant alters crystal size and energy band gap of PbS although it does not change the structure of PbS. PbS and Fe-alloyed PbS thin films with different Fe concentrations were grown on zinc tin oxide (Zn₂SnO₄) substrates coated on fluorine-alloyed tin oxide conductive glasses to investigate their photovoltaic properties. Incident photon-to-current efficiency (IPCE) and current density (J)–voltage (V) measurements were carried out to determine IPCE (%) and power conversion efficiency (η%) values of thin films. As a result, it was observed that as the concentration of Fe dopant is increased in Fe-alloyed PbS thin films, there is an increase in η%.     

基于介孔TiO2/石墨烯修饰的TiO2纳米线光阳极的染料敏化太阳能电池

本工作制作了基于介孔TiO₂/石墨烯修饰的TiO₂纳米线光阳极的染料敏化太阳能电池,并进行表征。光阳极结合了介孔TiO₂的高染料吸附率,TiO₂纳米线的高载流子传导率和石墨烯的高电子收获能力等优点,使器件光电转换效率有了很大的提高。制作出的染料敏化太阳能电池光电转换效率高达7.58%,比纯纳米线制作的电池约提高了1.5倍,在拥有相似一维结构的染料敏化太阳能电池中具有较大优势。     

Opaline backreflector coating in dye-sensitized solar cell

Photonic crystals are ordered nanostructures that are designed to manipulate the propagation of light. The periodicity of a photonic crystal can be engineered to be highly reflective at selected wavelengths. In this work, a mono-layer and double-layer colloidal photonic crystal film were self-assembled on a glass substrate to be used as backreflectors in a dye-sensitized solar cell (DSSC). The colloidal photonic crystal film consists of different polystyrene monodispersed particles with sizes between 200 nm and 290 nm. Making use of flow controlled vertical deposition (FCVD) method, opaline films of Bragg's reflection wavelength between 450 nm to 750 nm were achieved. These wavelengths were designed to match the absorption spectrum of the Ruthenium-complex dye used in DSSC. An enhancement in incident photon-to-current conversion efficiency (IPCE) of the opaline backreflector DSSC of about 30% at Bragg's peak wavelength has been achieved.     

Hydrogen-treated TiO2 nanowire arrays for photoelectrochemical water splitting

We report the first demonstration of hydrogen treatment as a simple and effective strategy to fundamentally improve the performance of TiO(2) nanowires for photoelectrochemical (PEC) water splitting. Hydrogen-treated rutile TiO(2) (H:TiO(2)) nanowires were prepared by annealing the pristine TiO(2) nanowires in hydrogen atmosphere at various temperatures in a range of 200-550 °C. In comparison to pristine TiO(2) nanowires, H:TiO(2) samples show substantially enhanced photocurrent in the entire potential window. More importantly, H:TiO(2) samples have exceptionally low photocurrent saturation potentials of -0.6 V vs Ag/AgCl (0.4 V vs RHE), indicating very efficient charge separation and transportation. The optimized H:TiO(2) nanowire sample yields a photocurrent density of ～1.97 mA/cm(2) at -0.6 V vs Ag/AgCl, in 1 M NaOH solution under the illumination of simulated solar light (100 mW/cm(2) from 150 W xenon lamp coupled with an AM 1.5G filter). This photocurrent density corresponds to a solar-to-hydrogen (STH) efficiency of ～1.63%. After eliminating the discrepancy between the irradiance of the xenon lamp and solar light, by integrating the incident-photon-to-current-conversion efficiency (IPCE) spectrum of the H:TiO(2) nanowire sample with a standard AM 1.5G solar spectrum, the STH efficiency is calculated to be ～1.1%, which is the best value for a TiO(2) photoanode. IPCE analyses confirm the photocurrent enhancement is mainly due to the improved photoactivity of TiO(2) in the UV region. Hydrogen treatment increases the donor density of TiO(2) nanowires by 3 orders of magnitudes, via creating a high density of oxygen vacancies that serve as electron donors. Similar enhancements in photocurrent were also observed in anatase H:TiO(2) nanotubes. The capability of making highly photoactive H:TiO(2) nanowires and nanotubes opens up new opportunities in various areas, including PEC water splitting, dye-sensitized solar cells, and photocatalysis.     

Organized mesoporous TiO2 films exhibiting greatly enhanced performance in dye-sensitized solar cells

The Pluronic P123 templated mesoporous TiO2 film was grown via layer-by-layer deposition and characterized by a novel methodology based on the adsorption of n-pentane. Multiple-layer depositions did not perturb the mesoporous structure significantly. Our TiO2 film was sensitized by a newly developed Ru-bipyridine dye (N945) and was applied as a photoanode in dye-sensitized solar cell. The 1-microm-thick mesoporous film, made by the superposition of three layers, showed enhanced solar conversion efficiency by about 50% compared to that of traditional films of the same thickness made from randomly oriented anatase nanocrystals.     

Preparation and characterization of TiO2 anode film with spinodal phase separation structure in dye-sensitized solar cells

Low electronic transmission efficiency and high charge recombination are the existing problems of photoanode film in traditional dye sensitized solar cells (DSSCs). This paper put forward the photoanode TiO₂ films with spinodal phase separation structure (SPSS) and continuous TiO₂ skeleton which were triggered by the photopolymerization of organic monomers in a photomonomer-inorganic precursor system. The photoanode TiO₂ films fabricated by different precursor solution compositions and different coating layers were characterized mainly by scanning electron microscopy (SEM), photocatalysis and photoelectric performance test. The results indicated that, the as-prepared TiO₂ anode film with seven coating layers and heat treated at 500 °C showed higher photoelectric conversion efficiency at about 2% than that of other samples with less coating layers and lower heat treatment temperature. The film also showed excellent photocatalytic activity by using methylene blue (MB) dye as a model organic substrate under fluorescent lamp irradiation. It is suggested that the film with SPSS structure has the potential to improve the electronic transmission efficiency and reduce the carrier recombination due to its particular structure, higher surface area, and lack of bottleneck in electronic transmission. It is worth noting that the SPSS structure provides new ideas to develop new photoanode films and further improve the photoelectric conversion performance of the DSSC in future.     

Rose bengal-sensitized nanocrystalline ceria photoanode for dye-sensitized solar cell application

For efficient charge injection and transportation, wide bandgap nanostructured metal oxide semiconductors with dye adsorption surface and higher electron mobility are essential properties for photoanode in dye-sensitized solar cells (DSSCs). TiO₂-based DSSCs are well established and so far have demonstrated maximum power conversion efficiency when sensitized with ruthenium-based dyes. Quest for new materials and/or methods is continuous process in scientific investigation, for getting desired comparative results. The conduction band (CB) position of CeO₂ photoanode lies below lowest unoccupied molecular orbital level (LUMO) of rose bengal (RB) dye. Due to this, faster electron transfer from LUMO level of RB dye to CB of CeO₂ is facilitated. Recombination rate of electrons is less in CeO₂ photoanode than that of TiO₂ photoanode. Hence, the lifetime of electrons is more in CeO₂ photoanode. Therefore, we have replaced TiO₂ by ceria (CeO₂) and expensive ruthenium-based dye by a low cost RB dye. In this study, we have synthesized CeO₂ nanoparticles. X-ray diffraction (XRD) analysis confirms the formation of CeO₂ with particle size ～7 nm by Scherrer formula. The bandgap of 2.93 eV is calculated using UV–visible absorption data. The scanning electron microscopy (SEM) images show formation of porous structure of photoanode, which is useful for dye adsorption. The energy dispersive spectroscopy is in confirmation with XRD results, confirming the presence of Ce and O in the ratio of 1:2. UV–visible absorption under diffused reflectance spectra of dye-loaded photoanode confirms the successful dye loading. UV–visible transmission spectrum of CeO₂ photoanode confirms the transparency of photoanode in visible region. The electrochemical impedance spectroscopy analysis confirms less recombination rate and more electron lifetime in RB-sensitized CeO₂ than TiO₂ photoanode. We found that CeO₂ also showed with considerable difference between dark and light DSSCs performance, when loaded with RB dye. The working mechanism of solar cells with fluorine-doped tin oxide (FTO)/CeO₂/RB dye/carbon-coated FTO is discussed. These solar cells show V _OC ～360 mV, J _SC ～0.25 mA cm ^?2 and fill factor ～63% with efficiency of 0.23%. These results are better as compared to costly ruthenium dye-sensitized CeO₂ photoanode.     

Photoelectrochemical properties of SnO2/TiO2 coupled electrode sensitized by a mercurochrome dye

The photoelectrochemical properties of the mercurochrome-sensitized SnO₂/TiO₂ coupled cell were studied with TiO₂ film thickness at a constant SnO₂ thickness. The optimal film thickness in the coupled cell is 3.5-μm-thick SnO₂ and 6–7-μm-thick TiO₂ and the maximum incident photon-to-current conversion efficiency (IPCE) value reached about 30.5% at 520 nm. The higher IPCE value in the 3.5 μm SnO₂/6–7 μm TiO₂ coupled cell is attributed to a better charge separation by fast electron transfer process from excited dye to TiO₂ to SnO₂.     

Hierarchical structured TiO2 photoanodes for dye-sensitized solar cells

A novel approach has been developed to fabricate hills-like hierarchical structured TiO2 photoanodes for dye-sensitized solar cells (DSSCs). The appropriately aggregated TiO2 clusters in the photoanode layer could cause stronger light scattering and higher dye loading that increases the efficiency of photovoltaic device. For detailed light-harvesting study, different molecular weights of polyvinyl alcohol (PVA) were used as binders for TiO2 nanoparticles (P-25 Degussa) aggregation. A series of TiO2 films with dissimilar morphology, the reflection of TiO2 films, absorbance of attached dye, amount of dye loading, and performance of fabricated DSSC devices, were measured and investigated. An optimized device had energy conversion efficiency of 4.47% having a higher dye loading and good light harvesting, achieving a 23% increase of short-circuit current J(sc) in DSSCs.     

Metal Oxide Semiconductors for Dye‐ and Quantum‐Dot‐Sensitized Solar Cells

This Review provides a brief summary of the most recent research developments in the synthesis and application of nanostructured metal oxide semiconductors for dye sensitized and quantum dot sensitized solar cells. In these devices, the wide bandgap semiconducting oxide acts as the photoanode, which provides the scaffold for light harvesters (either dye molecules or quantum dots) and electron collection. For this reason, proper tailoring of the optical and electronic properties of the photoanode can significantly boost the functionalities of the operating device. Optimization of the functional properties relies with modulation of the shape and structure of the photoanode, as well as on application of different materials (TiO₂, ZnO, SnO₂) and/or composite systems, which allow fine tuning of electronic band structure. This aspect is critical because it determines exciton and charge dynamics in the photoelectrochemical system and is strictly connected to the photoconversion efficiency of the solar cell. The different strategies for increasing light harvesting and charge collection, inhibiting charge losses due to recombination phenomena, are reviewed thoroughly, highlighting the benefits of proper photoanode preparation, and its crucial role in the development of high efficiency dye sensitized and quantum dot sensitized solar cells.     

Enhancing the performance of dye-sensitized solar cells by ZnO nanorods/ZnO nanoparticles composite photoanode

In this paper, ZnO nanorods (NRs) were prepared by a two-step solution phase reaction. A composite photoanode architecture is fabricated by adding 0–0.20 at.% ZnO NRs into ZnO nanoparticles (NPs). The scanning electron microscopy image shows that the average diameter and length of the ZnO NRs are about 50 nm and 2–5 µm, respectively, and the ZnO NRs are uniformly embedded into the ZnO NPs photoanode. The UV–vis spectrum analysis reveals that the amount of dye adsorption of the composite photoanode decreases with increasing ZnO NRs content. Meanwhile, the influence of ZnO NRs contents on the dye-sensitized solar cells (DSSCs) performance is systematically investigated. The photocurrent density–voltage (J–V) characteristics reveal that the device performance of DSSCs can be significantly enhanced by the composite photoanode. Typically, the DSSC with 0.15 at.% ZnO NRs obtains the optimal energy conversion efficiency of 3.8%, which is 28.4% higher than that of the pristine ZnO DSSCs. The electrochemical impedance spectroscopy (EIS) analysis shows that ZnO NRs can provide a direct pathway for accelerating electron transport, extending the electron lifetime, suppressing electron recombination and improving electron collection efficiency. These results indicate that the incorporation of ZnO NRs in the photoanode is an effective way to improve the performance of DSSCs.     

Influence of Cu nanoparticle size on the photo-electrochemical response from Cu-multiwall carbon nanotube composites

We show that Cu metal nanoparticle-multiwall carbon nanotube (MWCNT) assemblies can act as a new hybrid photoactive layer in photo-electrochemical devices. The carbon nanotube (CNT) composites were formed by a controlled thermal deposition of copper which produced crystalline metal nanoparticles localized on the carbon tube outer walls. The photoresponse evaluated in terms of IPCE (incident photon-to-charge carrier generation efficiency) varied for different sized-Cu-MWCNT samples across all the visible and near ultraviolet photon energy range with respect to the response of bare MWCNTs. In the case of 0.2 nm Cu nominal thickness, the IPCE increased, reaching 15%, a value 2.5 times higher than that measured for bare MWCNTs. As the Cu nominal coverage thickened, the IPCE started to decrease and become totally ineffective after 1 nm deposited Cu. The IPCE increase found was interpreted as being the result of a remarkable charge transfer between the Cu metal nanoparticles and the CNTs due to the formation of a strong ionic bond at their interface. The results obtained prove that the metal nanoparticle-CNT composites have optical, electrical and structural properties that can be applied in a variety of nanoscale architectures for novel photo-electrochemical devices.     

Photocatalytic degradation of Basic Red 46 and Basic Yellow 28 in single and binary mixture by UV/TiO2/periodate system

The present study deals with the investigation of photocatalytic degradation and mineralization of C.I. Basic Red 46 (BR46) and C.I. Basic Yellow 28 (BY28) dyes in single and binary solutions as a function of periodate ion concentration (IO(4)(-)), irradiation time, initial pH and initial dye concentrations. First order derivative spectrophotometric method was used for to simultaneous analysis of BY28 and BR46 in binary mixtures. Langmuir-Hinshelwood kinetic model was applied to experimental data and apparent reaction rate constant values were calculated. The apparent degradation rate constant values of BR46 were higher than those of BY28 for all experiments in single dye solutions. On the other hand, the significant reductions were observed for the apparent degradation rate constant values of the BR46 in the presence of BY28 in binary solutions whereas TOC removal efficiency slightly enhanced in binary system. The highest TOC removal efficiency was obtained at pH 3.0 by adding 5mM periodate ion in to the solution in the presence of 1g/L TiO(2) for both dye solutions. After 3h illumination, 68, 76 and 75% mineralization were found for 100mg/L BY28, 100mg/L BR46 and 50+50mg/L mixed solutions, respectively.