Unravelling the thermoelectric properties and suppression of bipolar effect under strain engineering for the asymmetric Janus SnSSe and PbSSe monolayers

• Published in: Applied surface science 2022-10, Vol.599, p.153962, Article 153962
• Main Authors: Bai, Shulin, Tang, Shuwei, Wu, Mengxiu, Luo, Dongming, Zhang, Jingyi, Wan, Da, Yang, Shaobin
• Format: Article
• Language: English
• Subjects: Bipolar effect; Janus SnSSe and PbSSe monolayers; Power factor; Strain engineering; Thermoelectric properties; Two-dimensional (2D) materials
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2022.153962

The asymmetrical Janus SnSSe and PbSSe monolayers under strain engineering are potential thermoelectric materials. [Display omitted] •The calculated optimal ZT of the SnSSe monolayer is ∼ 1.20 at 900 K on account of excellent electronic transport properties.•The calculated optimal ZT of the PbSSe monolayer with ultralow thermal conductivity is ∼ 2.99 at 900 K.•The bipolar effect in the PbSSe monolayer could be well suppressed by tuning band gap under strain engineering.•Strain engineering can reduce the thermal transport by softening the lattice, and thus greatly improve the thermoelectric properties of the PbSSe monolayer (ZT ∼ 3.77 @ 900 K). Inspired by the groundbreaking discovery of the two-dimensional (2D) MoSSe materials, the electronic, thermal, and thermoelectric properties of asymmetric Janus SnSSe and PbSSe monolayers are theoretically evaluated by the first-principles calculations. The SnSSe and PbSSe monolayers are indirect semiconductors with bandgaps of ∼ 1.39 and ∼ 0.44 eV by the HSE06 functional in combination with spin-orbital coupling (SOC) calculation. The further analysis of phonon dispersion curves and mechanical stabilities indicate that the SnSSe and PbSSe monolayers are thermodynamically and mechanically stable in the absence of negative frequency and elastic constant. The optimal dimensionless figure-of-merit (ZT) values of the SnSSe and PbSSe monolayers are ∼ 1.20 and ∼ 2.99 at 900 K, respectively. Furthermore, the strong bipolar effect is observed in the PbSSe monolayer at high temperature, which is detrimental for thermoelectric applications. Nevertheless, the strain engineering could modulate the bandgap of the PbSSe monolayer, which is benifical to improving the thermoelectric performance of the PbSSe monolayer (ZT ∼ 3.77 @ 900 K). Our present work would not only provide a fundamental understanding of electrical and thermal transport properties of asymmetric Janus SnSSe and PbSSe monolayers but also shed some light on the theoretical design of low-dimensional nanomaterials under strain engineering in thermoelectric applications.