First-principles insights into biphenylene-based graphynes: promising novel two-dimensional carbon allotropes for thermoelectric applications

Graphene is not an ideal candidate for thermoelectric applications due to its inherent high electrical and thermal conductivity. Graphynes are another class of carbon-based materials that exhibit a unique combination of sp² and sp hybridization in the carbon network. Certain graphynes are promising candidates for thermoelectric applications owing to their semiconducting nature and the presence of acetylenic linkers, i.e. γ-graphyne. In this work, we designed novel forms of biphenylene-based graphynes (BPNYnes) for potential use in thermoelectric applications. Density functional theory (DFT) has been employed to examine the electronic, structural and mechanical properties of various BPNYne nanosheets. The incorporation of the acetylenic π-conjugations altered the metallic nature of the pristine biphenylene monolayer. Boltzmann transport theory-based calculations reveal that the induced band gap in the carbon nanosheets significantly enhances the thermoelectric performance. Notably, 6,8,16-BPNYne nanosheet exhibits promising thermoelectric efficiency, with a figure of merit (ZT) significantly surpassing that of conventional carbon materials such as graphene and graphynes. This study suggests that these novel carbon allotropes could be viable candidates for future thermoelectric devices, offering a combination of high electrical conductivity and optimized Seebeck coefficients.