Large area high-current photocells have been made using sensitive photoconductive CdS powder, the CdS particles being held together with plastic on a supporting surface. The electrodes may either be in the form of an interdigital pattern on the insulating surface which supports the layer, or they may consist of conducting surfaces on opposite sides of the layer. In the latter case the transparent conductive coating of the glass plate on which the layer is supported serves as one electrode. In practice, the CdS powder can be applied to a surface by conventional techniques such as spraying or silk screening, or by mechanically spreading.
Since such photoconductive cells can be fabricated in almost any size and since the powder is capable of a photosensitivity of approximately one ampere per lumen, cells can readily be made capable of carrying photocurrents of an ampere or more in room light. Cells made with present powders have time constants of buildup and decay of the order of 0.1 second. Devices of this type are thus ideally suited for operating relays or directly controlling, over a continuous range, high-current devices such as incandescent light bulbs or motors.
© 1955 Optical Society of AmericaFull Article | PDF Article
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