Development of a new self-powered electrochromic device for light modulation without external power supply

Despite considerable improvements within the last decades, electrochromic (EC) window coatings are still too expensive to be applied in buildings on a large scale. Beside the manufacturing costs, wiring costs have to be added which may exceed the fabrication expenses of the electrochromic window. Therefore, self-powered electrochromic windows have been considered, where a semi-transparent photovoltaic (PV) cell provides the power to activate an electrochromic system deposited on top of the solar cell. The whole PVEC device consists of up to eight layers which must be deposited on large scales without short circuits or other failures. Recently, we came up with a much simpler idea where power generation and electrochromic properties are combined rather than just added as in the case of the PVEC cell. The whole device now is obtained by the deposition of only three layers and is highly transparent in the bleached state. Exposing it to sunlight and completing an external circuit the device can be colored within a few minutes, reducing the transmission by about 40%. Bleaching occurs either spontaneously by blocking the sunlight or is induced by a small rechargeable battery which can be incorporated in the external circuit and is charged from the device when exposed to sunlight. (C) 1998 Elsevier Science B.V. All rights reserved.