Photoelectron Conversion Efficiency Research Articles

Heterostructured nanorod array with piezophototronic and plasmonic effect for photodynamic bacteria killing and wound healing

Bacteria induced infectious diseases have threated the lives and health of millions people each year. Nanosized titanium dioxide (TiO2) have been developed for photodynamic bacterial killing with minimal drug resistance, but the efficiency was restricted by their large band gap, limited light-absorption region, and rapid electron-hole recombination. In this work, we rationally fabricated a TiO2/BTO/Au multilayered coaxial heterostructured nanorod array by inserting a ferroelectric semiconductor barium titanate (BaTiO3) nanolayer between TiO2 nanorod and gold nanoparticles (AuNPs). The TiO2/BTO/Au heterostructure showed greatly enhanced reactive oxygen species (ROS) (superoxide (O2•-) and hydroxyl radicals (•OH)) generation, and incident photo-electron conversion efficiency (IPCE) in UV/visible light region. On the basis of experimental observations, the detailed photodynamic mechanism of the enhanced ROS generation was proposed, mainly ascribed to the piezophototronic effect and plasmonic property of the nanorod array. The nanorod array was used as an antibacterial coating to kill gram-negative bacterium E. coli and gram-positive bacterium S. Aureus with an antibacterial efficiency up to 99.9% under simulated sunlight. It also showed an efficient promotion of infectious wound regeneration in mice with S. aureus infected dermal wounds.

Bandgap engineering of a lead-free defect perovskite Cs3Bi2I9 through trivalent doping of Ru3.

Inorganic defect halide compounds such as Cs3Bi2I9 have been regarded as promising alternatives to overcome the instability and toxicity issues of conventional perovskite solar cells. However, their wide indirect bandgaps and deep defect states severely limit their photoelectronic conversion efficiency when implemented in devices. Trivalent cation substitution has been proposed by previous calculations allowing the engineering of their band structures, but experimental evidences are still lacking. Herein we use the trivalent cation Ru3+ to partially replace Bi3+ in Cs3Bi2I9, and reveal their structural and optoelectronic properties, as well as the environmental stability. The Ru-doped Cs3Bi2I9 shows a decreasing bandgap with the increasing doping levels and an overall up-shift of band structure, owing to the dopant-induced defect states and thus enhanced phonon–electron coupling. As a result, upon Ru3+ doping, the narrowed bandgap and the upward shift of the band structures might facilitate and broaden their applications in optoelectronic devices.

Size dependence of nanosheet BiVO4 with oxygen vacancies and exposed {0 0 1} facets on the photodegradation of oxytetracycline

A new type of promising nanosheet BiVO4 with reduced dimension, sufficient oxygen vacancies (OVs) concentration, and exposed {0 0 1} crystal facets for oxytetracycline removal were synthesized via hydrothermal method. The prepared samples were fully characterized. SEM, HR-TEM, XRD, and BET analyses determined the existence, proportion, and intensity of the exposed {0 0 1} facets on BiVO4 nanosheet. DRS and LSV were used to investigate the photoelectric properties of the samples. In addition, the XPS, solid EPR, and PL characteristics were examined to explore the change in OVs concentration of the as-synthesized BiVO4 nanosheet when compared with reported BiVO4 layer. In particular, BiVO4 lamella within the thickness of ten nanometer (tBV200) had notable relative intensity of dominant {0 0 1} facets in XRD results, thereby enhancing the internal electric field to facilitate the formation and separation of photogenerated electrons in the PL test. Nevertheless, tBV200 had a greater OVs density and a relatively larger percentage of dominant {0 0 1} facets, which could be ascribed to its remarkably enlarged BET surface area and significantly reduced size compared with the reported BiVO4 layer within the thickness of a hundred nanometer (hBV200). tBV200 showed enhanced photocurrent (1.083 mA/cm2) in the LSV test, and this value was 1.33 times higher than the larger counterpart. This finding demonstrated outstanding photoelectron conversion efficiency. The best oxytetracycline degradation ratio (95.83%) and TOC removal ratio (89.55%) were obtained with the tBV200, which involved the active species O2− and h+. The excellent photoelectric capability, photocatalytic properties, and stability of tBV200 novel catalyst could be attributed to the high number of active sites, as well as the improved formation, transportation, and collection of photogenerated charges. These advantages are related to the characteristics of reduced thickness, well-crystallized and enlarged dominant {0 0 1} facets, and enhanced OVs intensity in tBV200.

Preparation of Zr-doped mesoporous TiO2 particles and their applications in the novel working electrode of a dye-sensitized solar cell

This paper presents an implementation of our recent theory on the suspension of electron-hole recombination via electronic- and micro-structure optimization to study the influence of Zr-doping on the efficiency (η) of TiO2-based dye-sensitized solar cells (DSSCs). We developed a four-layered working electrode, in which the size of particles increased from the bottom layer of TiO2 (P-25) through three successive layers of Zr-doped TiO2, which were calcined at 450, 600, and 850°C respectively. The enhancement in open-circuit photovoltage (Voc) and short-circuit photocurrent density (Jsc) can be attributed to the electronic- and micro-structures in the working electrode. The former is related to band bending, whereas the latter is related to light-scattering within multiple layers. Simulation results (FactSage) demonstrate that Zr doping in TiO2 can suspend or delay the formation of oxygen vacancies and thereby reduce the number of electron scattering centers, which helps to suspend electron-hole recombination by strengthening Ti-O bonds. The proposed four-layered working electrode produced an 80.2% increase in η, compared with DSSCs using a TiO2 (P-25) electrode. This study demonstrated a novel metal doping strategy for the manipulation of electronic structure and photoelectron conversion efficiency. The proposed methodology could also be used to guide the design of photo-catalysts in general.

Bamboo-like nitrogen-doped carbon nanotubes formed by direct pyrolysis of Prussian blue analogue as a counter electrode material for dye-sensitized solar cells

Nitrogen-doped carbon materials were prepared by direct pyrolysis of nanostructured Prussian blue analogue (metal hexacyanoferrates) without additional carbon sources and metal catalysts. The pyrolysis temperature played a crucial role in determining the structure of resultant carbon materials. Bamboo-like nitrogen-doped carbon nanotubes (NCNTs) could be formed at a pyrolysis temperature of 700°C, while only the nitrogen-doped carbon spheres (NCNSs) were obtained at 500°C. After removal of metal catalysts, the bamboo-like NCNTs exhibited superior electrocatalytic behavior towards I−/I3− than the hollow NCNSs, primarily due to their higher surface area and electrical conductivity in comparison with NCNSs. The photoelectron conversion efficiency of dye-sensitized solar cell (DSC) using NCNT counter electrode reached 7.48%, which was even better than that using Pt counter (7.12%) and much higher than that using NCNS counter (5.53%). The improved photovoltaic performance of DSC employing metal-free NCNT counter electrode was primarily attributed to the significantly reduced diffusion and charge-transfer resistances in porous NCNT catalyst layer in comparison with the compact NCNS electrode.

Surface plasmon resonance enhanced multi-shell-modified upconversion NaYF4:Yb3+, Er3+@SiO2@Au@TiO2 crystallites for dye-sensitized solar cells

Both upconversion of near-infrared light and surface plasmon resonance (SPR) of nobel metal nanoparticles (NPs) show potential application in dye-sensitized solar cells(DSSCs). For the first time, the novel multi-shell-coated and Au-NPs decorated hexagonal submicron β-NaYF4:Yb3+, Er3+(NFYE)@SiO2@Au@TiO2(NSAT) prisms were prepared and incorporated into the photoanodes of DSSCs. The influences of different coating layers and decorated Au-NPs on the upconversion of NFYE and the performance of DSSCs were comparatively investigated. Studies indicated that the coated multi-shells have great influences on the upconversion and the properties of DSSCs. The Au-NPs can remarkably enhance the intensity of upconversion luminous emission and thus the short-circuit current density (Jsc) and photoelectron conversion efficiency (η) of the DSSCs. The TiO2 shell is beneficial for absorbing more dye and lowering the interface transport resistance. The optimal Jsc and η obtained in a typical DSSC containing NSAT are 18.62 mA/cm2 and 7.79%, respectively, corresponding 38.2% and 28.1% higher than that of the DSSC with a pure TiO2 photoanode. This significant improvement can be mainly attributed to the enhanced upconversion emission of the NSAT prisms arising from the SPR effect of the embeded Au-NPs and to the possible enhanced scattering from the submicron prisms.

First-Principles Theory Investigation on Structural and Photoelectronic Properties of Formamidinium Lead Halide Perovskites

Formamidinium lead halide perovskites have attracted wide attention as photoelectronic conversion materials due to the high photoelectronic conversion efficiency (PCE), low cost and simple synthetic process. The structural, electronic and optical properties of mixed formamidinium lead halide perovskites FAPbIxCl3-x (FA= 22 NH CH NH + = , x=0~3) have been investigated by the first-principles theory. Our results show that FA cations lie along (001) direction in the trigonal FAPbX3 (X=Cl, Br, I). However, the direction is slightly shifted owing to the distortion of PbX6 (X=Cl, I) octahedrons in the mixed FAPbI xCl3-x. The Pb—I bond distances (0.315~0.334 nm) are larger than Pb—Cl bond distances (0.282~0.302 nm). With the increase of I/Cl ratio, the lattice parameters and volumes of FAPbIxCl3-x increase. The FA cations play a crucial role in balancing the crystal structure, but they do not participate into the process of frontier orbital transition directly. They just play the role of charge donors to contribute ca. 0.76 e to PbI3 framework. FAPbIxCl3-x are direct band-gap semiconductors, with the direct bandgap nature at Z (0, 0, 0.5) symmetry point. The valence band maximum (VBM) is composed of antibonding orbitals of I 5p (Cl 3p) and a few Pb 6s orbitals, and the conduction band minimum (CBM) is composed of Pb 6p orbital. There exists a combined covalent and ionic bonding mechanism between Pb and I (Cl) ions. As the I/Cl ratio increases, the band gaps decrease and the absorption spectra are red shifted. FAPbI3 has an ideal band gap of 1.53 eV. It exhibits the superi- or absorption spectrum especially in the range of 300 nm to 500 nm, which elucidates that FAPbI3 has great potential as the photoelectronic conversion material. Our results could provide theoretical guidance for the experimental design and synthesis of perovskite solar cells. Keywords perovskite; first-principles theory; photoelectronic property; band structure; absorption spectrum

Crystallization Behavior of Solution-Processed CIGSe Thin Film Semiconductor by Stepwise Annealing Process.

CuIn(x)Ga1-xSe2 (CIGS) thin films were prepared by a solution-based CuInGa (CIG) precursor- selenization process. First, we investigated the effect of selenization temperature on the formation of polycrystalline CIGS and grain growth. The CIG precursor films were selenized using a two-step process to investigate the reaction of Se and CIG precursors during the formation of CIGS thin films. Depending on the temperature in the 1st step of the selenization process, the CIG precursor forms a different intermediate phase between the single phase to ternary phase such as Cu, Se, CuSe, InSe, and CuInSe2. In addition, the intermediate phase exerts a significant influence on the final phase obtained after the 2nd step of the selenization process, particularly with regard to characteristics such as polycrystalline structure and grain growth in the CIGS films. The photoelectron conversion efficiency of devices prepared using CIGS thin films was approximately 1.59-2.75%.

Experimental study of ultrafast carrier dynamics in polycrystalline ZnTe nanofilm

Zinc telluride, due to its direct band gap and broadband light absorption, has the good application prospects in terahertz devices, solar cells, waveguide devices, and green light emitting diodes. In the photovoltaic field, it is possible to further improve the photoelectron conversion efficiency of multi-junction tandem solar cells by combining zinc telluride with III-V semiconductors. Ultrafast photo-excited carrier dynamics is fundamental to understand photoelectron conversion process of nanofilm solar cells. In this study, the ultrafast energy carrier dynamics of N-doped polycrystalline zinc telluride is investigated by using the femtosecond laser two-color pump-probe method at room temperature. The polycrystalline zinc telluride nanofilm is grown on a 500 μm GaAs (001) substrate via molecular beam epitaxy and doped by using a nitrogen ratio frequency plasma cell. The laser pulses with a central wavelength of 800 nm are divided into pump beam and probe beam by a beam splitter, after which the pump beam passes through a bismuth triborate crystal and its frequency is doubled to 400 nm. The 400 nm pump beam and 800 nm probe beam are focused on the sample collinearly through the same objective lens. Photo-excited carriers will be generated since the excitation photon energy of 400 nm pump beam (3.1 eV) is higher than the band gap of zinc telluride (～ 2.39 eV). The experimental data are analyzed by using the theoretical fitting model which includes energy relaxation processes of electrons and lattice, and the theoretical curves are consistent well with the experimental data. The fitted results show that the three dominated relaxation processes which affect the initial reflectivity recovery are in sub-picosecond time regime. The positive amplitude electron relaxation process is attributed to inter-band carrier cooling and carrier diffusion through electron-photon interactions, and the deduced decay time of this positive amplitude electron relaxation process is about 0.75 ps. The negative amplitude electron relaxation process is characterized as a photo-generated carrier trapping process induced by defects, and the decay time of this process is about 0.61 ps. The lattice heating process is realized through electron-phonon coupling process, and the calculated time constant of the lattice heating is about 0.86 ps.

Low temperature efficient interconnecting layer for tandem polymer solar cells

Tandem solar cells are found to be promising in organic photovoltaic research because they can double open-circuit voltage (Voc) and utilize photon energy efficiently, as compared to single junction solar cells. In a typical tandem polymer solar cell, two single subcells are staked and connected by an interconnecting layer, which is a prerequisite to achieving high photo-electron conversion efficiency. In this work, a low temperature solution processed and chemically stable PEDOT:PSS/AZO/PEIE interconnecting layer is reported. Tandem polymer solar cells based on this efficient layer can realize a high Voc, which can sum the Voc׳s of subcells. Furthermore, the operation mechanism of the interconnecting layer is discussed to help better understand the electron recombination process in the interconnecting layer.

Toward Tandem Photovoltaic Devices Employing Nanoarray Graphene-Based Sheets

Graphene quantum dots (GQDs) are promising photonic materials for light harvesting. However, only low photoelectron conversion efficiency can be generated in single-junction graphene-based solar cells when isolated GQDs with the edge bonding defects are used as semiconductors. To address this issue, a four-junction GQD-based tandem solar cell with high theoretical conversion efficiency was proposed in this paper. Instead of isolated GQDs, nanoarray GQDs embedded in hexagonal host materials, such as graphane or boron nitride, was adopted as the photoactive layer. Utilizing our universal thermodynamic approach to the gap openings in low-dimensional graphene, nanoarray armchair-interfaced GQDs embedded in graphane to achieve the maximal diameter of confined GQDs are found preferential for fabricating tandem solar cell devices. Besides these, the separation between GQDs and the thickness of GQD-based sheets were determined. This contribution is of benefit to the application of graphene for solar cell devices.

ZnTe Semiconductor‐Polymer Gel Composited Electrolyte for Conversion of Solar Energy

Nanostructured cubic p‐type ZnTe for dye sensitized solar cells (DSSCs) was synthesized from 1 : 1 molar ratio of Zn : Te by 600 W and 900 W microwave plasma for 30 min. In this research, their green emissions were detected at the same wavelengths of 563 nm, the energy gap (Eg) at 2.24 eV, and three Raman shifts at 205, 410, and 620 cm−1. The nanocomposited electrolyte of quasisolid state ZnO‐DSSCs was in correlation with the increase in the JSC, VOC, fill factor (ff), and efficiency (η) by increasing the wt% of ZnTe‐GPE (gel polymer electrolyte) to an optimum value and decreased afterwards. The optimal ZnO‐DSSC performance was achieved for 0.20 wt% ZnTe‐GPE with the highest photoelectronic energy conversion efficiency at 174.7% with respect to that of the GPE without doping of p‐type ZnTe.

SrTiO3/TiO2 Hybridstructure as Photoanode in Dye‐Sensitized Solar Cell

AbstractIn dye‐sensitized solar cells (DSSCs), the charge recombination at the TiO2/dye/electrolyte interface greatly influences the photoelectron conversion efficiency. Hybrid semiconductor materials with matched band potentials are designed to reduce the charge recombination. In this study, SrTiO3/TiO2 hybridstructure was synthesized by using TiO2 nanoparticles as template in a hydrothermal, showing a negative shift in the flat band potential. The DSSC with the SrTiO3/TiO2 anode exhibits an increased photovoltage and a reduced photocurrent. The suppression of charge recombination at the TiO2/dye/electrolyte interface was observed in the electrochemical impedance spectroscopy, causing an improvement in the photovoltage. However, the SrTiO3/TiO2 system shows an obstructed electrons injection from the dye to SrTiO3/TiO2, limiting the photocurrent performance. The photoelectrochemical properties of the SrTiO3/TiO2 system are discussed in detail herein.

Improved electrochemical performance of dye-sensitized solar cell via surface modifications of the working electrode by electrodeposition

Modifications of the working electrode with TiO2 blocking or coating layers are carried by electrodeposi- tion in TiCl3 precursor solution. The results suggest that the electrodeposited TiO2 blocking layer provides excellent agglutination between the FTO substrate and the active TiO2 layer. In addition, the electrodeposited TiO2 coating layer enhances the interconnections between the TiO2 nanoparticles and the FTO substrate, and therefore it increases the electron transport efficiency. The morphology and crystalline structure of the electrodeposited TiO2 layers are char- acterized by SEM, TEM, and XRD. The electrochemical impedance spectroscopy measurements show that the improved DSSC performance with the electrodeposited coating layer is mainly due to the increase in the lifetime of the conduction band electron in the TiO2 film. The photoelectron conversion efficiency of DSSC is increased from 3.47% to 5.38% by employing the TiO2 electrodeposited working electrode. � /I3 � ) redox electrolyte, and a platinum-coated transparent conducting oxide (TCO) glass as a counter electrode. The electrons excited from the dye are transferred step by step through the conducting band of TiO2 nanoc- rystallites and FTO electrode. The dye is regenerated by electron donation from the redox system of the electrolyte. The iodide is re- covered by the reduction of triiodide on the platinum layer of the counter electrode. In practice, the FTO surface might not be fully covered with the mesoporous TiO2 film due to the porous nature of the TiO2 film. The exposed surface area of the FTO to the electro- lyte may lead to charge recombination between the TiO2 and the FTO interfaces. Electron transfer to the FTO is possibly intercepted by the reduction of the electrolyte interacting with the electrode. Another weakness of mesoporous TiO2 films is the inadequate con- nection between TiO2 nanoparticles, leading to an increase in elec- tron transfer resistance (6-8). To solve this recombination and elec- tron transfer resistance problem, previous studies have demonstrated that it is effective to introduce a compact and thin TiO2 blocking layer onto the transparent conducting glass substrate (9-11) using a range of preparation methods such as sputtering (11,12), sol-gel (13, 14), and spray-coating (15,16) techniques. A TiCl4 post-treatment of the TiO2 photoanode is a common modification method for ob- taining a reliable thin TiO2 coating layer to improve the cell perfor- mance such as current density, fill factor, and conversion efficiency (17-19). In this study, an electrodeposition strategy was used to modify the mesoporous TiO2 photoanode in two schemes: i) a blocking layer prepared first by the electrodeposition on the FTO substrate and then TiO2 photoanode fabricated, and ii) a TiO2 photoanode fabri- cated first and then the electrodeposition performed for covering the interfaces on the FTO substrate and mesopores between TiO2 nanoparticles. Experimental parameters for TiO2 electrodeposition were applied voltage and electrodeposition time. The blocking layer can reduce the electron recombination phenomena from FTO to electrolyte by separating effectively at a specific layer thickness (20). In addition, a thin TiO2 coating layer formed by the electrodeposi- tion can not only reduce electron recombination from FTO to elec- trolyte, but also increase electron transport between TiO2 nanoparticles because the TiCl3 precursor solution can penetrate deep into the ex- posed FTO surface and the mesoporous TiO2 nanoparticles. The photovoltaic properties of the DSSCs with the TiO2 modified photo anode by electrodeposition were characterized and compared with those of the unmodified photo anode case.

Pulse-reverse electrodeposition of transparent nickel phosphide film with porous nanospheres as a cost-effective counter electrode for dye-sensitized solar cells

A Ni2P nanolayer with porous nanospheres was directly coated on fluorine-doped tin oxide glass by pulse-reverse deposition as a low-cost counter electrode catalyst for dye-sensitized solar cells, and the photoelectron conversion efficiency of the cell was increased to 7.32% by using a porous nanosphere catalyst due to the significantly improved ion transport.

Electrophoresis of randomly and vertically embedded graphenenanosheets in activated carbon film as a counter electrode for dye-sensitized solar cells

A new approach has been developed to randomly and vertically embed the graphene nanosheets (GNs) in the activated carbon (AC) film in an applied electric field. The activated carbon (AC) nanoparticles in suspension during electrophoresis play an important role in supporting the GNs perpendicular to the FTO (fluorine-doped tin oxide) glass. Insufficient amount of AC nanoparticles might result in a deposition of GNs parallel to the FTO glass, leading to incomplete utilization of the surface area accessible to electrolyte ions. An AC cathode with randomly and vertically embedded GNs facilitated electrolyte penetration and electron conduction. The photoelectron conversion efficiency of the cell was increased to 7.50% by employing the AC cathode with randomly and vertically embedded GNs.

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by Förster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of Förster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells.

Improve photo-electron conversion efficiency of ZnO/CdS coaxial nanorods by p-type CdTe coating

Coaxial nanorods with a single-crystalline core and nanocrystal sensitizer shell are a promising nanostructure to enhance the performance of semiconductor sensitized solar cells. Herein, we report the fabrication of coaxial nanorods by depositing n-type CdS and p-type CdTe nanocrystals sequentially on ZnO nanorods. We find that p-type CdTe nanocrystals can work jointly with n-type CdS nanocrystals to enhance the photocurrent and voltage, achieving a conversion efficiency more than three times that of pure ZnO/CdS nanorods. Electrochemical impedance spectroscopy characterization suggests that the stepwise band structure of ZnO/CdS/CdTe is conducive to improving charge separation and extending the electron diffusion length, finally contributing to a high conversion efficiency.

Improved performance of dye-sensitized solar cells: An TiO2–nano-SiO2 hybrid photoanode with post-treatment of TiCl4 aqueous solution

A TiO2–nano-SiO2 hybrid film was prepared on a conductive F-doped tin oxide (FTO) substrate by depositing a mixture paste of TiO2 (P25) and nano-sized SiO2 particles. The hybrid film was further treated by a titanium tetrachloride (TiCl4) aqueous solution with different concentrations before it was assembled as a photoanode in dye sensitized solar cells (DSSCs). We studied the performance of DSSCs by using the dye molecule of cis-bis(isothiocy-anato)-bis-(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) bis-tetrabutylammonium (N719) as sensitizer. Results suggested that the post-treatment using TiCl4 could enhance the dye adsorption. The thin TiO2 layer hydrolyzed from TiCl4 could fill gaps between nanoparticles in the composite film, leading to a better electron transport than non-treated films, and improve the light harvesting efficiency. The optimal concentration was found to be 75mM for the post-treatment of TiO2–SiO2 hybrid film by TiCl4 solution. A photoelectron conversion efficiency of 6.39% was achieved in the back-side illuminated dye-sensitized solar cells, which is ∼105% higher than the basic efficiency of the bare TiO2 sensitized sample. TiO2–nano-SiO2 hybrid photoanode was prepared by incorporation of nano-sized SiO2 in the TiO2 film. The introduced SiO2 as a wide band-gap material gives a significant improvement of the performance of corresponding DSSCs in terms of photocurrent densities and energy conversion efficiency.

Anatase TiO2 sol as a low reactive precursor to form the photoanodes with compact films of dye-sensitized solar cells

An anatase TiO2 sol containing ultrafine TiO2 crystallites (ca. 5nm) was used to fabricate the dye-sensitized solar cells (DSSCs) with a compact layer, which was prepared by the peptization–hydrothermal method using the CF3COOH as peptizing agent. The dried sol was calcined at 300°C for 1h to eliminate the organics over the surface of TiO2 and increase the crystallite size of the TiO2 nanocrystals (the special surface area of the calcined TiO2 decreased from 224.7 to 94.9m2/g); and then it was used to prepare the paste for the porous layer of DSSCs. The compact layer was prepared by the diluted sol through the layer-by-layer (LBL) self assembly technique to control its thickness. The compact films derived from LBL self assembly method not only prevented the charge recombination at the conductor substrate/electrolyte interface but also improved the adhesion between the porous layer and the conductive layer on the substrate, which increased the number of the effective electron pathways with the short distance of the porous layer and consequently resulted in a better electrical contact. The photoelectron conversion efficiency of the DSSCs with the LBL films had increased apparently. In particular, a 12-layer TiO2/PSS LBL film of the DSSC led to a 24.5% increase in the photoelectron conversion efficiency from 5.93 to 7.38%.