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Solar cells that operate efficiently under indoor lighting are of great practical interest as they can serve as electric power sources for portable electronics and devices for wireless sensor networks or the Internet of Things. Here, we demonstrate a dye-sensitized solar cell (DSC) that achieves very high power-conversion efficiencies (PCEs) under ambient light conditions. Our photosystem combines two judiciously designed sensitizers, coded D35 and XY1, with the copper complex Cu(II/I)(tmby) as a redox shuttle (tmby, 4,4′,6,6′-tetramethyl-2,2′-bipyridine), and features a high open-circuit photovoltage of 1.1 V. The DSC achieves an external quantum efficiency for photocurrent generation that exceeds 90% across the whole visible domain from 400 to 650 nm, and achieves power outputs of 15.6 and 88.5 μW cm–2 at 200 and 1,000 lux, respectively, under illumination from a model Osram 930 warm-white fluorescent light tube. This translates into a PCE of 28.9%. A dye-sensitized solar cell that has been designed for efficient operation under indoor lighting could offer a convenient means for powering the Internet of Things.

Propionitrile electrolyte solutions mixed with sulfolane or with 1-ethyl 3-methyl imidazolium tetracyanoborate (ionic liquid) are optimized for Co(bpy)(3)(3+)/Co(bpy)(3)(2+)-tmediated DSCs working at low illumination intensity. Highly-active cathode catalysts based on graphene oxide, either pure or mixed with graphene nanoplatelets or with stacked graphene fibers, can be prepared at temperatures

The dependence of the electron density and electron lifetime in nanocrystalline-TiO2 electrode on the electron back reaction with I3− in a dye-sensitized solar cell, based on a mesoporous titania (TiO2) matrix immersed in an iodine-based electrolyte, has been presented by analyzing the results of voltage decay and charge extraction measurements without modelling, without interpretation of mechanism, and without complicating calculations. This new analysis approach utilizes simple equations and basic definition of kinetics, concluding in absolute electron-density and charge-lifetime measurements. The relation of electron lifetime to open-circuit voltage indicates a peak of the long-lifetime charge at 5.5 V, which is consistent with the information of middle band suggested by Bisquert et al. (2004).

Stacked multijunction (tandem) solar cells have been prepared by mechanically stacking dye-sensitised solar cells (DSCs) and a GaAs/AlXGa(1−X)As graded solar cell (GGC) as the top and bottom cells, respectively. Three organic dyes with different absorption spectra (D131, D102 and D205) were used in the DSCs, in order to match the photocurrent density between the DSC and the GGC. Tuning the absorption range of the DSC by choosing an appropriate dye, increased the overall photovoltaic conversion efficiency due to the optimal utilisation of the solar spectrum in the individual cells. The open circuit photovoltages (VOC) of the GGC and the DSC with D131 were 1.11 V and 0.76 V, respectively, resulting in a VOC of 1.85 V and a photovoltaic conversion efficiency of 7.63% for the tandem cell. Although the overall conversion efficiency has not exceeded that of the GGC (7.66%), these tandem cells provide adequate VOC values for water splitting applications.

The high molar extinction coefficient heteroleptic ruthenium dye, NaRu(4,4'-bis(5-(hexylthio)thiophen-2-yl)-2,2'-bipyridine) (4-carboxylic acid-4'-carboxylate-2,2'-bipyridine) (NCS)(z), exhibits certified 5% electric power conversion efficiency at AM 1.5 solar irradiation (100 mWcm(-2)) in a solid-state dye-sensitized solar cell using 2,2',7,7'-tetrakis-(N,N-dipmethoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD) as the organic hole-transporting material. This demonstration elucidates a class of photovoltaic devices with potential for low-cost power generation. (C) 2010 Elsevier Ltd. All rights reserved.

Solar energy is a promising solution to global energy-related problems because it is clean, inexhaustible and readily available. However, the deployment of conventional photovoltaic cells based on silicon is still limited by cost, so alternative, more cost-effective approaches are sought. Here we report a bifacial dye-sensitized solar cell structure that provides high photo-energy conversion efficiency (∼6%) for incident light striking its front or rear surfaces. The design comprises a highly stable ruthenium dye (Z907Na) in combination with an ionic-liquid electrolyte and a porous TiO2 layer. The inclusion of a SiO2 layer between the electrodes to prevent generation of unwanted back current and optimization of the thickness of the TiO2 layer are responsible for the enhanced performance. Low-cost, efficient solar cells are sought as an alternative to silicon photovoltaics. Here a dye-based bifacial solar cell that is capable of efficient generation of electricity for light incident on either its front or rear face is demonstrated.

Techniques of TiO2 film fabrication for dye-sensitized solar cells having a conversion efficiency of global air mass 1.5 (AM 1.5, 1000 W/m(2)) solar light to electric power over 10% are reported. Newly implemented fabrication technologies consist of pre-treatment of the working photoelectrode by TiCl4, variations in layer thickness of the transparent nanocrystalline-TiO2 and applying a topcoat light-scattering layer as well as the adhesion of an anti-reflecting film to the electrode's surface. TiCl4 treatments induce improvements in the adhesion and mechanical strength of the nanocrystalline TiO2 layer. Optimization of the thickness of the TiO2 layer, acting as the working electrode, affects both the photocurrent and the photovoltage of the devices. Covering of the TiO2 photoanode by an anti-reflecting film results in enhancement of the photocurrent. Each of these components of film fabrication exerts a significant influence on the overall photovoltaic parameters of the devices resulting in improvements in the net energy conversion performance. (C) 2007 Elsevier B.V. All rights reserved.

FTIR spectra of [Ru(dcbpyH2)2(NCS)2] (N3), (Bu4N)2[Ru(dcbpyH)2(NCS)2] (N719), and (Bu4N)4[Ru(dcbpy)2(NCS)2] (N712) complexes measured as solid samples in photoacoustic mode display fine resolution of IR bands and exhibit differences between the cis and the trans carboxylic acid groups. The interaction between N3, N719, and N712 sensitizers with nanocrystalline TiO2 film was investigated by ATR-FTIR spectroscopy. The data show that these complexes are being anchored onto the TiO2 surface in bridging coordination mode using two out of their four carboxylic acid groups, which are trans to the NCS ligand. The effect of protons on both the short circuit photocurrent and the open circuit photovoltage of dye-sensitized nanocrystalline solar cells was scrutinized. For the standard electrolyte formulation employed and TiCl4 treated mesoporous TiO2 films, the monoprotonated form of the N3 dye exhibited superior power conversion efficiency under AM 1.5 sun compared to the four, two, and zero proton sensitizers.

The woven fabric containing electrochemically platinized tungsten wire is an affordable flexible cathode for liquid-junction dye-sensitized solar cells with the I3(-)/I(-) redox mediator and electrolyte solution consisting of ionic liquids and propionitrile. The fabric-based electrode outperforms the thermally platinized FTO in serial ohmic resistance and charge-transfer resistance for triiodide reduction, and it offers comparable or better optical transparency in the visible and particularly in the near-IR spectral region. The electrode exhibits good stability during electrochemical loading and storage at open circuit. The dye-sensitized solar cells with a C101-sensitized titania photoanode and either Pt-W/PEN or Pt-FTO cathodes show a comparable performance.

A nanocrystalline TiO2 (anatase) nanosheet ex- posing mainly the (001) crystal faces was tested as photo- anode material in dye-sensitized solar cells. The nanosheets were prepared by hydrothermal growth in HF medium. Good-quality thin films were deposited on F-doped SnO2 support from the TiO2 suspension in ethanolic or aqueous media. The anatase (001) face adsorbs a smaller amount of the used dye sensitizer (C101) per unit area than the (101) face which was tested as a reference. The corresponding solar cell with sensitized (001)-nanosheet photoanode exhibits a larger open-circuit voltage than the reference cell with (101)-terminated anatase nanocrystals. The voltage enhancement is attributed to the negative shift of flatband potential for the (001) face. This conclusion rationalizes earlier works on similar systems, and it indicates that careful control of experimental conditions is needed to extract the effect of band energetic on the current/voltage character- istics of dye-sensitized solar cell.

A round robin for the performance of roll-to-roll coated flexible large-area polymer solar-cell modules involving 18 different laboratories in Northern America, Europe and Middle East is presented. The study involved the performance measurement of the devices at one location (Risø DTU) followed by transportation to a participating laboratory for performance measurement and return to the starting location (Risø DTU) for re-measurement of the performance. It was found possible to package polymer solar-cell modules using a flexible plastic barrier material in such a manner that degradation of the devices played a relatively small role in the experiment that has taken place over 4 months. The method of transportation followed both air-mail and surface-mail paths.

This paper presents an overview of the research carried out by a European consortium with the aim to develop and test new and improved ways to realise dye-sensitized solar cells (DSC) with enhanced efficiencies and stabilities. Several new areas have been explored in the field of new concepts and materials, fabrication protocols for TiO2 and scatterlayers, metal oxide blocking layers, strategies for co-sensitization and low temperature processes of platinum deposition. Fundamental understanding of the working principles has been gained by means of electrical and optical modelling and advanced characterization techniques. Cost analyses have been made to demonstrate the potential of DSC as a low cost thin film PV technology. The combined efforts have led to maximum non-certified power conversion efficiencies under full sunlight of 11% for areas < 0 center dot 2 cm(2) and 10 center dot 1% for a cell with an active area of 1 center dot 3 cm(2). Lifetime studies revealed negligible device degradation after 1000hrs of accelerated tests under thermal stress at 80 degrees C in the dark and visible light soaking at 60 degrees C. An outlook summarizing future directions in the research and large-scale production of DSC is presented.

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.

Multijunction stacked (tandem) solar cells can increase the overall photovoltaic conversion efficiency by optimal utilization of the solar spectrum in individual cells. We demonstrate that a photovoltaic tandem cell comprising a nanocrystalline dye-sensitized solar cell as a top cell for high-energy photons and a copper indium gallium selenide thin-film bottom cell for lower-energy photons produces AM 1.5 solar to electric conversion efficiencies greater than 15%.

The energy conversion efficiency of photoelectrochemical solar cells using those oxide semiconductor electrodes which are stable in contact with aqueous electrolytes is low because their wide band gaps do not permit a photoresponse to the visible spectrum. By adsorption of a sufficient quantity of a charge-transfer dye with intimate contact to the semiconductor, the electrode can be sensitised to visible radiation. Titanium dioxide electrodes were derivatised by attached ruthenium bis- and tris- bipyridyl and zinc porphyrin dyes and their efficiency as photoelectrochemical solar cell electrodes is reported.

Ruthenium(II) complexes [Ru(L2)(NCS)2] (K8) and [Ru(L)(L9)(NCS)2] (K9) (where L = 4,4′-bis(carboxyvinyl)-2,2′-bipyridine and L9 = 4,4′-dinonyl-2,2′-bipyridine) were synthesized and characterized by spectroscopic and electrochemical techniques. The performance of K8 and K9 complexes as charge transfer photosensitizers in nanocrystalline TiO2-based solar cells was investigated. These complexes when anchored onto TiO2 films exhibit very efficient sensitization yielding 75 ± 5% incident photon-to-current efficiencies (IPCE) in the visible region using an electrolyte consisting of 0.6 M methyl-N-butyl imidazolium iodide, 0.05 M iodine, 0.1 M LiI and 0.5 M tert-butylpyridine in 50/50 (v/v) mixture of valeronitrile and acetonitrile. At one sun, the K8 complex gave a short circuit photocurrent density of 18 ± 0.5 mA/cm2, the open circuit voltage 640 ± 50 mV and fill factor of 0.75 ± 0.05, corresponding to an overall conversion efficiency of 8.64 ± 0.5%. Under similar conditions, the K9-sensitized solar cell gave a photocurrent density of 16.5 ± 0.5 mA/cm2, 666 ± 50 mV open circuit potential and 0.71 ± 0.05 fill factor yielding 7.81% ± 0.6% efficiency.

Reference LPI-ARTICLE-1999-019doi:10.1149/1.1391698View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

The concept of a tandem hybrid concentrator solar module was demonstrated from a dye-sensitized TiO2 solar cell (DSSCs) and a silicon p-n junction solar cell. The test system employed DSSC and Si cells with indoor AM1.5G efficiencies of 9.1 and 18.1%, respectively. Two different optical filters were used to selectively reflect and concentrate near-infrared light from the DSSC onto the Si cell. On the basis of outdoor testing in a 2 x concentrator reflector arrangement, the tandem system generated 93 and 96% of the output power of directly illuminated Si cells under altostratus/cirrostratus and clear sky irradiances, respectively, despite a DSSC-to-Si active area ratio of only 0.92. Similar performance is expected at higher (5-10 x) concentration ratios. The hybrid arrangement of visible- and IR-absorbing solar cells addresses the problem of lower performance of conventional concentrators under diffuse irradiance conditions. These proof-of-concept results suggest that system level efficiencies approaching 20% should be achievable.