Method of making thermoelectric materials

A method of making a CsSnI3 perovskite thermoelectric material having a figure of merit (FoM ZT) from 1 to 1.5, comprising:

• mixing a fatty acid, a fatty amine, a C8-C30 hydrocarbon, and Cs2CO3 in a vessel to form a cesium mixture;
• heating the cesium mixture to a temperature of 400-450 K to form a heated mixture;
• dissolving SnI2 in an organophosphine to form a tin solution;
• mixing the tin solution and the heated mixture to form a reaction mixture in an enclosed chamber;
• pressurizing the chamber containing the reaction mixture to a hydrostatic pressure of 1.7 GPa;
• heating the chamber and the reaction mixture to a temperature of 500 to 600 K;
• then cooling the reaction mixture to form a precipitate comprising the CsSnI3 perovskite thermoelectric material having a FoM ZT from 1 to 1.5,
• wherein the bandgap of the CsSnI3 perovskite thermoelectric material is 0 eV,
• wherein the bandgap of the CsSnI3 perovskite thermoelectric material is inverted at a pressure of 1.7 GPa, and
• wherein FoM ZT represents an efficiency of the CsSnI3 perovskite thermoelectric material's energy conversion process.