Impact of Four-Phonon Scattering on Thermal Transport and Thermoelectric Performance of Penta-XP2 (X = Pd, Pt) Monolayers

Accurately understanding and modulating thermal and thermoelectric transport in penta-XP2 (X = Pd, Pt) monolayers is crucial for their applications in nanoelectronics and energy conversion. We systematically investigate the thermal conductivity and thermoelectric properties of penta-XP2 monolayers through first-principles calculations, incorporating four-phonon (4ph) scattering and electron–phonon interaction (EPI) effects. The 4ph scattering, particularly Umklapp and redistribution processes, markedly suppresses lattice thermal conductivity by generating substantial thermal resistance and disrupting phonon population distributions. At 300 K, the lattice thermal conductivity is reduced to 0.87 W/mK (80% reduction) for penta-PdP2 and 1.64 W/mK (79% reduction) for penta-PtP2 compared to three-phonon-only scattering. Combining this with EPI-optimized electronic transport yields enhanced thermoelectric figures of merit (ZT), increasing from 0.21 to 0.86 for penta-PdP2 and from 0.11 to 0.34 for penta-PtP2, alongside a broadened optimal carrier concentration range. These findings highlight momentum-conserving 4ph scattering as a key mechanism for phonon transport modulation and thermoelectric efficiency improvement in penta-XP2 materials, providing theoretical guidance for designing high-performance nanoscale thermal management and energy conversion devices.