We now report metal-free organic dyes having a new type of indoline structure, which exhibits high efficiencies in dye-sensitized solar cells. The solar energy to current conversion efficiencies with the new indoline dye was 6.51%. Under the same conditions, the N3 dye was 7.89% and the N719 dye was 8.26%. The new indoline dye was optimized for the amount of 4-tert-butyl pyridine in the electrolyte and cholic acid as a coadsorbent. Subsequently, the solar energy to current conversion efficiencies reached 8.00%. This value was the highest obtained efficiency for dye-sensitized solar cells based on metal-free organic dyes without an antireflection layer.

The dye-sensitized solar cell (DSC) [1,2] is an attractive candidate for a new renewable energy source because of the low-cost materials and the facile manufacturing used in its production. [3] This cell has been intensively studied in the last decade. The photovoltaic effect in a DSC originates at the interface between a redox electrolyte containing iodide and triiodide (I -/I 3 -) ions and a dye-derivatized mesoscopic TiO 2 electrode. For outdoor applications, ionic liquids containing I -and I 3 -ions are the medium of choice because of their high thermal stability, non-flammability, negligible vapor pressure, and low toxicity. [4] Since the diffusion of I -and I 3 -ions in ionic liquids is slow owing to their high viscosity, [5] a thin nanocrystalline TiO 2 film is required to reach a high conversion efficiency. In order to compensate for the lower optical depth of such thin, porous electrodes, a high-extinction-coefficient dye should be used. A similar strategy is applied to other types of viscous electrolytes [6] and organic hole conductors. [7] The present study reports, for the first time, on a DSC combining a high-extinction-coefficient organic sensitizer with an ionic-liquid electrolyte. An indoline dye was employed (referred to as D149 below, Fig. 1), [8] which has an extinction coefficient (68 700 mol -1 cm -1 at 526 nm) that is five times higher than that of the conventional high-efficiency Ru dye (N719, 13 900 mol -1 cm -1 at 541 nm) [9] and reaches 8 % conversion efficiency with a volatile organic electrolyte. A screen-printed double layer, consisting of a nanocrystalline TiO 2 film and a scattering layer, constitute the mesoporous working electrode that supports the organic sensitizer (Fig. 1b). Below, we scrutinize the effect of the film thickness of nanocrystalline TiO 2 films on the photovoltaic performance of ionic-liquid-and acetonitrile (AcCN)-based electrolytes.Results obtained under 100 % sun irradiation are shown in Figure 2. The open-circuit photovoltage (V OC , Fig. 2a) decreases for both the AcCN-and ionic-liquid-based electrolytes with increasing film thickness, due to augmentation of the surface area, which provides additional charge-recombination sites [10][11][12] and enhances the dark current. [13] Moreover, for thick films the outer TiO 2 particle layers do not contribute significantly to the photogeneration of conduction-band electrons, owing to the filtering of light by the dyed particles located close to the fluorinated tin oxide (FTO) glass. The sharing of photoinjected conduction-band electrons by these particles lowers their quasi-Fermi level and hence the V OC . In contrast to the V oc , the short-circuit photocurrent density (J SC ), fill factor (FF), and overall solar-energy-conversion efficiency (g) obtained with the two electrolytes are affected in a different way by the film thickness. For the AcCN solvent (Fig. 2b), J SC increases continuously with film thickness, reaching a plateau value of close to 20 mA cm -2 at 14 lm, while g reaches a maximum of 9 % at a thicknes...

An indoline dye (D205), the synthesis method of which is disclosed in this report, gave high-efficiency organic dye-sensitized solar cells (9.52%) using an anti-aggregation reagent (chenodeoxycholic acid).

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TiO(2) nanotube arrays prepared by electrochemical anodization of Ti foils show impressive light to electricity conversion efficiency in the dye-sensitized solar cells (DSCs). The length of the TiO(2) nanotube arrays (5-14 microm) was controlled by varying the anodization time from 2 to 20 h. The influence of nanotube lengths on the photovoltaic performance of DSCs was investigated by impedance. A flexible DSC using TiO(2) nanotube arrays on a Ti foil as a working electrode and polyethylene naphthalate (ITO/PEN) as counterelectrode in combination with solvent-free ionic liquid electrolyte achieved 3.6% photovoltaic conversion efficiency under simulated AM 1.5 sunlight.