High‐Sensitivity Photoconductor Layers

High‐sensitivity photoconductor ``powder'' layers and ``sintered'' layers have been prepared in large‐area form, with most of the desirable characteristics of single crystals. The methods involved in the preparation of these layers are simple and avoid the difficulties involved in growing large‐area single crystals, or in producing large‐area photoconductors by evaporation in vacuum. Both types of layers can be made into photocells of any desired area, by providing suitable electrodes. At an illumination of 1 ft‐c, ratios of photo‐current to dark current as large as 106 may be obtained for both types of layers. A two‐inch square cell made from either a powder or a sintered layer can pass an ampere for an illumination of a few foot candles. In addition to their ease of fabrication, the new layers also have advantages in the large increase in red sensitivity obtainable with cadmium sulfide, and in the ohmic character of sintered layers with silver‐paste electrodes.