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For many low-power applications, solar cells are used as an environmentally friendly power supply. In order to provide electrical power also in the absence of solar radiation, we invented a device which unifies both a solar cell and a rechargeable battery in one unit. The main components are a photoactive layer on a charge-storage layer. Thus, this new device represents a flat battery, which charges itself on illumination. In principle it can be produced cheaply, e.g., by screen printing. The characteristics of charging and discharging are presented with special consideration of the variation of light intensity and ion concentration in the electrolyte. A relatively high reverse reaction at the WO 3 electrode still takes place. After charging for 1 h under an illumination of 1000 W/m 2 , the first samples yielded 1.8 C/cm 2 when discharged in the dark.The dye-sensitized solar cell represents an electrochemical solar cell in which an organic dye is excited by illumination with light and transfers an electron from a redox couple in an electrolyte ͑I Ϫ /I 3 Ϫ in an organic solvent͒ to a highly porous TiO 2 layer. 1 By this, the energy of the electron is increased and this energy can be used to supply an external load. The electrons are re-injected into the I Ϫ /I 3 Ϫ couple in the electrolyte via a catalyst like Pt. This dye sensitized solar cell already contains most of the components of a battery, one redox couple (I Ϫ /I 3 Ϫ ), an electrolyte ͑mostly an organic solvent͒, and two electrodes ͑TiO 2 and Pt͒. To complete the battery, only a second redox couple is needed. TiO 2 is usually not sufficient, because its reduction potential for Li ϩ intercalation is too high, as can be concluded from Ref. 2. The charge capacity of a typical dyesensitized solar cell is measured in Ref. 3 to be about 20 C/ cm 2 , which is due to surface adsorption phenomena. In this paper, we present the idea to add a second redox couple in the form of an additional layer (WO 3 ), which is able to store the energy generated by the solar cell. The reduction potential for Li ϩ -intercalation of WO 3 is close to 0 V vs. standard hydrogen electrode, 4 and therefore it is suitable for the potentials in a dye-sensitized solar cell, where the reodox potential of the I Ϫ /I 3 Ϫ couple is about 0.53 V vs.hydrogen, 5 and the open-circuit potentials of the dye-sensitized TiO 2 layer vs. the I Ϫ /I 3 Ϫ couple on the Pt electrode are about 0.7 V. 6The design of the photovoltaically self-charging battery ͑PSB͒ is shown in Fig. 1. It consists of a photoactive layer ͑dye-coated nanocrystalline TiO 2 ͒ which is situated on a charge-storage layer ͑e.g., nanocrystalline WO 3 ͒ on a glass substrate coated with a transparent conductive oxide ͑TCO͒. The opposing electrode is a platinized, TCO-coated glass substrate. The Pt layer is so thin that it is still transparent. The pores of the WO 3 and TiO 2 layers and the space between the two electrodes are filled with an electrolyte which contains Li ϩ and a redox couple ͑I Ϫ and I 3 Ϫ ͒ in an organic solvent ͑e.g.,pro...

ExperimentalPreparation of Polymers 3 and 4: 3 and 4 were prepared by transition metal catalyzed ROP of [1]silaferrocenophane monomers according to wellknown procedures [5]. Molecular weights were estimated by gel permeation chromatography (GPC) calibrated to polystyrene standards. For 3: M w = 4.3´10 5 , Polydispersity Index (PDI) = 1.9. For 4: M w = 2.9´10 5 , PDI = 1.6.Preparation of Devices: Devices based on 3 and 4 were prepared by coating a 50 mm thick Mylar film with 1.5 mL of a 15 wt.-% solution of 3 or 4 in toluene. Film applications were accomplished with the use of a motor-driven blade applicator (designed and built in-house) using a stainless steel blade (Paul N. Gardiner Company) with a 0.25 mm slit opening driven at a constant linear velocity of 1 cm s ±1 . Mylar films (type A Mylar, Dupont) were purchased from Cadillac Plastics.Arc Discharge Simulations: Films of 3 and 4 supported on Mylar were placed underneath a copper mask possessing a 4.5 cm diameter circular aperture. The electron beam was generated using a modified SEM operating at variable filament currents. Discharge images were captured with a Tektronix model C1002 CCD video camera, which is fed into a Sony model EVO-9800 Hi8 videocassette recorder. Discharge current pulses were measured using a Tektronix model 72 500 transient digitizing oscilloscope.

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