Band Structure Engineering of Bi₄O₄SeCl₂ for Thermoelectric Applications

The mixed anion material Bi₄O₄SeCl₂ has an ultralow thermal conductivity of 0.1 W m^-1 K^-1 along its stacking axis (c axis) at room temperature, which makes it an ideal candidate for electronic band structure optimization via doping to improve its thermoelectric performance. Here, we design and realize an optimal doping strategy for Bi₄O₄SeCl₂ from first principles and predict an enhancement in the density of states at the Fermi level of the material upon Sn and Ge doping. Experimental work realizes the as-predicted behavior in Bi_4- Sn O₄SeCl₂ (x = 0.01) through the precise control of composition. Careful consideration of multiple accessible dopant sites and charge states allows for the effective computational screening of dopants for thermoelectric properties in Bi₄O₄SeCl₂ and may be a suitable route for assessing other candidate materials.