Combined photoelectrochemical cell and capacitor

A nanophotocapacitive device wherein: a photovoltaic element ( 1 ) extends over substantially the whole area of the device, a charge storage element ( 3 ) also extends over substantially the whole area of the device, connection mechanism ( 14 ) are provided for interconnecting the photovoltaic and charge storage elements, the photovoltaic element comprises a nanoparticulate dye sensitized layer ( 11 ) of wide band gap semiconductor, a catalytic layer ( 13 ) and an electrolyte ( 12 ) placed between the semiconductor and the catalytic layers. The photovoltaic (photoelectrochemical) element and charge storage element (capacitor) are formed on opposite sides of a titanium foil substrate ( 8 ). Light ( 16 ) is incident on the transparent electrode ( 15 ). A diode ( 2 ) may be integral with the device to prevent the charge storage element discharging when there is no solar energy input to the photovoltaic element.