Patent ID: 8679445

Claim:
A process of forming CsSnI 3 in a high temperature resistant tube, comprising the steps of: (1) providing a 3 zone high temperature heating unit having first and second end or opposing zones and a third intermediate portion or zone; (2) providing CsI powder; (3) providing SnI 2 powder; (4) mixing said CsI and SnI 2 powders to provide a mixture wherein the molar ratio of the SnI 2 and CsI in the mixture is selected to be in the range from about 1/1 to 5/1; (5) creating a vacuum within said heating unit and sealing the mixed powder in said first zone of said heating unit; (6) placing said heating unit into a heating chamber of a furnace and heating said first zone of said heating unit at a temperature maintained above 450° C. to form black CsSnI 3 ; and (7) collecting evaporated SnI 2 in said second zone of said heating unit.