High thermoelectric performance of the undoped and Tl-doped hexagonal SiP₃ monolayers

A theoretical investigation into the thermoelectric (TE) properties of the undoped and Tl-doped SiP₃ monolayers has been performed based on the first-principles calculations. The Seebeck coefficient peak and valley, the electronic conductance valley, and the thermal conductance valley of the SiP₃ can be moved to the positions close to the Fermi level by the Tl doping. In addition, the two peaks of figures of merit ZTs are also shifted with enhanced ZT peak values. Furthermore, different dependences of ZTs on temperature are observed for the undoped and Tl-doped SiP₃ monolayers. At low temperatures both the undoped and Tl-doped SiP₃ can show high ZTs, while at high temperatures the Tl-doped SiP₃ shows much higher ZT than the undoped one especially along the zigzag direction. This work demonstrates that the SiP₃ and Tl-doped SiP₃ monolayers can be used as high-performance TE materials.