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Dye-sensitized solar cells (DSCs) have attracted widespread attention in recent years, attributed to their low production costs, facile fabrication and tunable optical properties. In order to achieve competitive conversion efficiencies, the sunlight harvesting capacities of DSCs should be improved over a broad range of wavelengths and incidence angle. Here, we demonstrate a facile strategy to enhance the light absorptions of the devices via employing self-organized cholesteric liquid crystal (CLC) polymer films as transparent and flexible back-reflectors for DSCs. The photonic band gap of these CLC films can be precisely tailored by modulating the helical pitch and twist sense. The selective light reflection of these CLC films gives rise to the possibility for increasing the optical path length of the light in particular wavelength region while retaining the cell transparency. The enhancement of photocurrent and power conversion efficiency (PCE) reveals strong wavelength dependence owing to the selective reflection of these CLC polymer films. The DSCs with proper combination of CLC back-reflectors yield the maximum enhancement over 21% in photocurrent and 17% in PCE. The work presented here provides new insights into the design of cell geometry for achieving extra absorption enhancement, which can also be compatible with other photovoltaic concepts. [ABSTRACT FROM AUTHOR]

We synthesized highly uniform Au-decorated core-shell β -NaYF 4 :Er/Yb@SiO 2 microprisms and investigated its coupling effects on the performance of dye-sensitized solar cells (DSCs). The incorporation of upconversion phosphors (UCPs) and localized surface plasmon resonance (LSPR) arising from Au nanoparticles (AuNPs) was beneficial to achieve a higher photocurrent and power conversion efficiency of the devices. Furthermore, the contribution and interaction between upconversion and LSPR on the performance of DSCs were identified by UV–vis spectroscopy, upconversion fluorescence spectroscopy, and J - V characterization under different simulated illuminations. The presence of AuNPs increased the optical absorption of dye molecules in the visible region, but decreased the emission of UCPs. Thorough analysis showed that the energy of upconversion emission was transferred to the upconversion induced LSPR of AuNPs, that resulted from the incorporation between the SPR band of AuNPs and a matched emission bands of UCPs. These results validated the advantages of incorporation between upconversion and LSPR for DSC applications and revealed the underlying enhancement mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between ZnO compact layer and TiCl4 post-treatment on TiO2 photoelectrode for dye sensitized solar cell (DSSC) is investigated. Photoelectrode combined the two modifications is designated as ZnO+2l+TiCl4. It is found that after the TiCl4 treatment the ZnO compact layer transforms to a bi-functional layer, which suppresses back electrons transfer from FTO to electrolyte and reduces the FTO/TiO2 interfacial resistance. In addition, the newly formed TiO2 coating generated by TiCl4 post-treatment contains abundant and well dispersed Zn element, which further facilitates electron transfer at TiO2 layer. Meanwhile, the electron lifetime in ZnO+2l+TiCl4 is the longest. Consequently, the overall energy conversion efficiency of the cell with ZnO+2l+TiCl4 is significantly enhanced to 8.9%, which is 8.8% higher than that with pure TiCl4 post-treatment and 17.7% higher than that without any treatment. These results are verified by material characterization and corresponding opto-electrical properties measurements. Experimental results demonstrate this facile method is a more promising alternative to the conventional interface and surface modification in high efficient DSSCs. [Copyright &y& Elsevier]

Abstract: Arrays of TiO2 nanotubes were fabricated by the anodization of Ti foils and then used in assembling dye-sensitized solar cells (DSSCs). The role of the morphologies of the TiO2 nanotubes in the photovoltaic performances of the DSSCs was studied in terms of the surface topography and the tube length. The necessity of removing the nanoporous films from the surface of the nanotube arrays for good DSSC performance has been demonstrated. Also, it has been shown that appropriately increasing the tube length was an effective measure for enhancing both the short-circuit current density and the conversion efficiency of the DSSCs. [Copyright &y& Elsevier]

Abstract: An effective ZnO compact film (ZCF) has been introduced at the interface of fluorine doped tin oxide (FTO) substrate and mesoporous TiO2 layer, and its effect on dye-sensitized solar cells (DSSCs) has been compared to that of conventional TiO2 compact film (TCF). The ZCF and TCF prepared by spin-coating method on FTO are characterized by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and UV–vis spectrophotometer. The existence of TiO2 can suppress the recombination occurring at the interface of FTO/electrolyte, resulting in a higher J sc and V oc than bare FTO. The ZCF creates an energy barrier between FTO substrate and mesoporous TiO2 layer, which not only reduces the electron back transfer from FTO to I3 − in the electrolyte, but also leads to the accumulation of photogenerated electrons, and increases the electron density in the conduction band of TiO2. The device based on FTO/ZCF substrate remarkably improves V oc and FF, finally increases energy conversion efficiency by 13.1% compared to the device based on bare FTO and 4.7% compared to the counterpart based on FTO/TCF. [Copyright &y& Elsevier]

Abstract: A novel and thin ZnO compact blocking film is employed at the interface of fluorine-doped tin oxide (FTO) substrate and mesoporous TiO2, and its influence on dye-sensitized solar cells (DSSCs) is investigated. The ZnO film prepared by spin-coating method on FTO is characterized by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and UV–vis spectrophotometer. The ZnO film is firstly employed as an energy barrier between FTO and mesoporous TiO2 film in DSSCs, which improves open-circuit photovoltage (V oc) and fill factor (FF) with compensation of J sc decrease, finally increasing energy conversion efficiency from 5.85% to 6.70%. Electrochemical impedance spectra (EIS) analysis and open-circuit voltage decay (OCVD) technique reveal that the existence of the energy barrier not only resulted in the effect of suppressing back electrons transfer from FTO to electrolyte but also blocking the electrons injection from the conductive band of TiO2 to FTO. The former effect effectively reduces the recombination which occurs in the region of FTO substrate, and the latter leads to remarkable increment of electron density in the TiO2, thus resulting in enhanced V oc and FF. These results suggest that the methodology of introducing the semiconductor with a more negative conduction band edge than TiO2 as the compact blocking film in DSSCs may be feasible. [ABSTRACT FROM AUTHOR]

We demonstrate a method for incorporating plasmon metallic nanoparticles in hierarchical rutile TiO 2 clusters (RTC) assembled from single-crystal nanospindles. The RTC could efficiently improve the diffusion of the photoelectrons, which can be ascribed to the improvement of the connectivity by bridging the neighbouring microflowers through the single-crystal nanospindles. But not all the nanospindles are tightly interconnected, hence organic colloid has been prepared for post-treatment of the device based on RTC by the generation of TiO 2 nanoparticles. When added into Au nanoparticles, localized electric fields can be produced, because Au can excite dye molecules more intensively than incident far-field light. The surface plasmon synergistic effect had been investigated by Uv-vis absorption spectrum of Au@ organic colloid and the relative change of the IPCE. As a result, the cell based on RTC exhibits an overall conversion efficiency of 7.68%, indicating a 17% promotion compared with that derived from commercial P25 (6.58%) which could be ascribed to faster electron transfer of single-crystal nanospindles. With the Au nanoparticles incorporation in RTC, the device achieves a conversion efficiency of 9.15%, resulting in a 11% increase compared to the RTC device post-treated by organic colloid without Au nanoparticles (8.24%), which is attributed to the surface plasmon synergistic of Au nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: In-doped TiO2 thin film was introduced at the interface of fluorine-doped tin oxide (FTO) substrate and mesoporous TiO2 film by spin-coating method, and its application as a new compact layer material for dye-sensitized solar cells (DSSCs) was investigated. The scanning electron microscopy (SEM), UV-visible spectroscopy, current-voltage characteristics, Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS) analysis and open-circuit voltage decay (OCVD) technique are used to characterize the morphology, optical transmittance and flat-band potentials (V fb ) of In-doped titania compact film and its effect to the photoelectron conversion process. It was found that In-doping increased the transmittance of TiO2 compact layer, the interfacial resistance between FTO substrate and porous TiO2 film and the flat-band potential of TiO2 film. The In-doped TiO2 compact layer effectively suppressed the charge recombination from FTO to the electrolyte, increased the optical absorption of dye and then increased the short-circuit photocurrent density (J sc ). Furthermore, In-doped TiO2 compact layer acted as a weak energy barrier, which increased the electron density in the mesoporous TiO2 film, thus improved open-circuit photovoltage (V oc ). As a result, the overall energy conversion efficiency of the DSSC with In-doped TiO2 compact layer was enhanced by 11.9% and 6.9% compared to the DSSC without compact layer and with pure TiO2 compact layer, respectively. It indicated that In-doped TiO2 is a promising compact layer material for dye-sensitized solar cells. [Copyright &y& Elsevier]

Abstract: Light harvesting in dye-sensitized solar cells (DSSCs) mediated by plasmonic metallic nanoparticles and sub-micron light-scattering metal oxides is a facile and cost-effective approach to achieving high device performance. Ag nanoparticles, protected by thin shells of TiO2, were incorporated in TiO2 photoanode. The large plasmonic near-field intensity generated by these nanoparticles caused an 18.3% rise in photocurrent, which resulted in an enhanced efficiency of 6.23% as compared to 5.29% efficiency of DSSC based on unmodified TiO2 photoanode. In addition, DSSC with TiO2 nanofibers (NFs) embedded in TiO2 photoanode was also constructed, which because of the efficient light scattering ability of the nanofibers, attained an efficiency of 7.14% as a result of a current rise of 36.9%. Another DSSC was assembled with Ag NPs added to the photoanode of the NFs-based DSSC to further boost cell performance. The addition of Ag NPs, however, did not produce an appreciable change in the cell performance. The reason for this unexpected outcome was probably due to the low internal resistance associated with charge recombination and large resistance to electron transport in the cell as determined by electrochemical impedance analysis computed in this work. [Copyright &y& Elsevier]

Abstract: TiO2 doping has been widely used to improve the performance of dye-sensitized solar cells. In this paper, we study the use of N as a dopant of TiO2 in dye-sensitized solar cells (DSSCs), analyzing the effect on the photovoltaic properties of the cells based on different amounts of N doping. Results indicate that the dye absorption is increased, which would enhance the amount of photoelectron; moreover, the resistance (R 3) of the electron transport within photoelectrode and electron lifetime of it are improved by N doping. The above two reasons would lead the high short circuit current density (J sc). However, owing to the sites of recombination and severe defects introduced, the trend of dye absorption, R 3 and electron lifetime is opposite when the amount of N doping is more than 3%. Finally, we find that the optimal amount of N doing is 3%, which outstandingly increase the performance of DSSCs. The conversion efficiency of the DSSCs can be reached to 6.25% when using the 3% N-doped TiO2 photoelectrode, and this efficiency is 23.03% higher than that of the pure TiO2. [Copyright &y& Elsevier]

Abstract: A novel transparent and stable polypyrrole (PPy) electrode that can properly serve as a counter electrode for the bifacial dye-sensitized solar cell (DSSC) has been prepared by in situ polymerization of pyrrole monomer on FTO glass. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurement show the considerable catalytic activity of PPy counter electrode. The photovoltaic parameters of bifacial DSSCs are strongly dependent on the initial monomer concentration of pyrrole. The optimized PPy counter electrode has been fabricated under the initial monomer concentration of 0.3 M, a bifacial DSSC based on this PPy electrode shows conversion efficiencies of 5.74% and 3.06% corresponding to front- and rear-side illumination, respectively. Compared to the conventional Pt-based DSSCs, the design of bifacial DSSC with transparent PPy counter electrode improves the utilization ratio of incident light. Moreover, the considerable conversion efficiency and the good long-term stability of PPy-based device demonstrated by the stability test highlight the potential large-scale commercial application of this transparent PPy counter electrode. [Copyright &y& Elsevier]

Abstract: The concentration of tetrabutyl titanate (TBT) and H2O influence on the reaction kinetics of TBT and acetic acid (AcOH) solvothermal system are systematically studied. It is found that TBT and H2O have greatly accelerated the hydrolysis–condensation process of the TBT–AcOH system. By adjusting those concentrations with reaction time, we prepare five kinds of sub-micron/micron precursors, which are hierarchical structures consisting of different primary building blocks. The morphology of these precursors varies from noninterlaced structures composed of flower-like microsphere and ellipsoid sphere to interlaced structures composed of flower-like microsphere interlaced nanofibers, ellipsoid spheres interlaced flower-like microsphere and nanoparticles interlaced flower-like microsphere. These interlaced structures are synthesized for the first time and are not ordinary mixtures of the noninterlaced structures. After heat treatment, these precursors are transformed to anatase TiO2. Shape-dependent photovoltaic performances of dye-sensitized solar cells (DSSCs) are also discussed. DSSCs based on these hierarchical sub-micron/micron TiO2 show 7.3%–7.9% energy conversion efficiencies, and the devices based on interlaced structures have higher efficiencies (7.4%–7.9%) than those of the devices based on noninterlaced structures (7.3%–7.6%). [Copyright &y& Elsevier]

Abstract: A facile and reliable method is applied to prepare the electrolyte based on hydroquinone (HQ)/benzoquinone (BQ) redox couple for dye-sensitized solar cells (DSSCs) in open environment by adding moderate amount of acetic acid (HAc), and the best conversion efficiency (η) of 5.82% is achieved under 100mWcm−2 (AM 1.5G) illumination. Electrochemistry properties of DSSCs using such redox couple are measured and the results show a higher current and better charge transfer in contrast to I −/I 3 −. And a slightly higher efficiency of 5.88% is obtained when HQ and BQ are symmetrically substituted by two methyls. With advantages of high efficiency, compatible with the most common dye N719 and easily tuned by facile structural modification, the redox shuttle employing HQ/BQ via HAc treatment is very promising to be employed in efficient DSSCs. [Copyright &y& Elsevier]

Abstract: Trace amount chromium-doped (Cr-doped) TiO2 is prepared by hydrothermal method for dye-sensitized solar cells (DSSCs). The effect on photovoltaic performance of the cells is investigated via control of the concentrations of Cr doped in TiO2. Rutile phase increases when Cr is incorporated into TiO2 while the property of electron transport in photoelectrodes is improved by doping Cr which results in a reduced resistance (R ct) of the electron transport within mesoporous layer and an improved electron lifetime. The regularity of R ct and electron lifetime is reversed when the level of doped Cr exceeds 50 ppm. On the other hand, owing to the doping effect of Cr, the short-circuit photocurrent density (J sc) of DSSCs is remarkably enhanced and reaches maximum. Consequently, the overall energy conversion efficiency enhances to 6.35% with Cr-doped TiO2 of 50 ppm, which is 14.62% higher than that with undoped TiO2. In general, compared with undoped TiO2, Cr-doped TiO2 is a better photoanode material and a more promising alternative for high efficient DSSCs. [Copyright &y& Elsevier]

Abstract: Highly porous carbon/SnO2/TiO2 nanocomposite films that can be used as counter electrodes in dye-sensitized solar cells (DSSCs) are fabricated by coating a homogeneous and viscous carbon paste on F-doped tin oxide conducting glass. The carbon paste is prepared by ball-milling a mixture of carbon, SnO2 powder and TiO2 hydrosol in an organic solution. The composite films are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, Brunauer–Emmett–Teller and Form Talysruf Profiler. The results indicate that the photovoltaic performances of the composite DSSCs are influenced by the content of SnO2. When the content is increased to 30%, SnO2 not only acts as “framework” to strengthen the mechanical stability of the composite film but also increases the specific surface area and root-mean-square roughness, which improve fill factor and short-circuit current, finally increasing power conversion efficiency from 5.12% to 6.15%. Cyclic voltammetry analysis and electronic impedance spectroscopy of the optimum composite film display higher catalytic activity for I3 −/I− redox reactions and much lower charge-transfer resistance compared with Pt, respectively. Dye-sensitized solar cells based on this nanocomposite counter electrode achieve efficiency as high as 6.15% which is comparable to that of the cells using sputtering Pt as counter electrode at similar conditions. [Copyright &y& Elsevier]