High In-Plane Thermoelectric Performance of Layered Bi 4 O 4 SeCl 2 .

The van der Waals semiconductor Bi 4 O 4 SeCl 2 has recently attracted great interest due to its extremely small lattice thermal conductivity, which may find possible application in the field of energy conversion. Herein, we accurately predict the thermoelectric transport properties of Bi 4 O 4 SeCl 2 using first-principles calculations and Boltzmann transport theory, where the carrier relaxation time is obtained by fully considering the electron-phonon coupling. It is found that a maximum p -type ZT value of 3.1 can be reached at 1100 K along the in-plane direction, which originates from increased Seebeck coefficient induced by multivalley band structure, as well as enhanced electrical conductivity caused by relatively stronger intralayer bonding. Besides, it is interesting to note that comparable p - and n -type ZT values can be realized in certain temperature regions, which is very desirable in the fabrication of thermoelectric modules.