Improvement in thermoelectric figure of merit of Bi2Se3 crystal with Sulfur substitution

•Sulfur substituted Bi2Se3 crystals were grown by using vertical Bridgman method.•Enhancement in Seebeck coefficient is observed with Sulfur concentration.•Thermal conductivity reduced with Sulfur in Bi2Se3.•Peak ZT of 0.72 at 543 K is obtained for Bi2Se2.7S0.3 crystal. Bismuth Selenide has gained a great deal of attention as a thermoelectric material owing to its lower toxicity compared to Bi2Te3 based materials. In this work, Sulfur substitution in Bi2Se3 is carried out by the vertical Bridgman method and the influence of Sulfur on the structural, electrical and thermal properties of Bi2Se3 was studied. The thermoelectric figure of merit (ZT) was calculated from electrical conductivity, Seebeck coefficient and thermal conductivity, which were measured from 303 K to 773 K. Sulfur incorporation did not improve the electrical conductivity of Bi2Se3 but proved to be beneficial in improving the Seebeck coefficient and reducing thermal conductivity. Hence, the calculated figure of merit of Bi2Se2.7S0.3 crystal comes out to be 0.72 at 543 K, which is higher than that of pure Bi2Se3 crystal, which is 0.31 at 533 K.