Photoconductive cells

A method of forming a photosensitive layer of lead sulfide crystals which comprises precipitating the crystals onto a seeded glass support by adding a concentrated aqueous solution of allyl-thiourea to an alkaline solution of copper nitrate and lead nitrate having a concentration of copper between 5 .times. 10.sup.-.sup.5 and 5 .times. 10.sup.-.sup.4 molar, a concentration of lead between 0.05 and 0.06 molar, and a concentration of hydroxide between 0.55 and 0.75 molar and immersing said seeded glass support in the resulting mixture.

The method of forming a photosensitive layer on a clean glass surface which comprises seeding the surface slowly in a stabilized colloidal solution of lead sulfide, preparing a second solution by adding a lead nitrate solution to a copper nitrate solution containing a concentration of copper between 5 .times. 10.sup.-.sup.5 and 5 .times. 10.sup.-.sup.4 molar, a concentration of lead between 0.05 and 0.06 molar and a concentration of hydroxide between 0.55 and 0.75 molar, pouring a solution of allyl-thiourea into said second solution, then immersing therein the seeded surface to receive precipitated crystals of lead sulfide with a trace of copper sulfide and then drying the surface.

The method of forming a uniform highly sensitive layer of lead sulfide crystals which comprises adding a concentrated aqueous solution of allyl-thiourea to a solution of lead nitrate at a temperature between 5.degree.C and 40.degree.C, allowing the mixture to stand from 5 minutes to three hours which is beyond the period of normal automatic seeding and then immersing a preseeded glass plate in the mixture for a period of time between 10 and 100 minutes, then washing and drying the crystal coated plate.

The method of forming a uniform highly sensitive layer of lead sulfide crystals which comprises adding a concentrated aqueous solution of allyl-thiourea containing sodium sulfite to a solution of lead nitrate at a temperature between 5.degree.C and 40.degree.C, allowing the mixture to pass through the period of normal automatic seeding and to darken due to gross precipitated lead sulfide crystals until the mixture appears black and then immersing a preseeded glass plate in the mixture for a period of time between 10 and 100 minutes, then washing and drying the crystal coated plate.